linux/net/ipv4/tcp_input.c
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   1/*
   2 * INET         An implementation of the TCP/IP protocol suite for the LINUX
   3 *              operating system.  INET is implemented using the  BSD Socket
   4 *              interface as the means of communication with the user level.
   5 *
   6 *              Implementation of the Transmission Control Protocol(TCP).
   7 *
   8 * Authors:     Ross Biro
   9 *              Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>
  10 *              Mark Evans, <evansmp@uhura.aston.ac.uk>
  11 *              Corey Minyard <wf-rch!minyard@relay.EU.net>
  12 *              Florian La Roche, <flla@stud.uni-sb.de>
  13 *              Charles Hedrick, <hedrick@klinzhai.rutgers.edu>
  14 *              Linus Torvalds, <torvalds@cs.helsinki.fi>
  15 *              Alan Cox, <gw4pts@gw4pts.ampr.org>
  16 *              Matthew Dillon, <dillon@apollo.west.oic.com>
  17 *              Arnt Gulbrandsen, <agulbra@nvg.unit.no>
  18 *              Jorge Cwik, <jorge@laser.satlink.net>
  19 */
  20
  21/*
  22 * Changes:
  23 *              Pedro Roque     :       Fast Retransmit/Recovery.
  24 *                                      Two receive queues.
  25 *                                      Retransmit queue handled by TCP.
  26 *                                      Better retransmit timer handling.
  27 *                                      New congestion avoidance.
  28 *                                      Header prediction.
  29 *                                      Variable renaming.
  30 *
  31 *              Eric            :       Fast Retransmit.
  32 *              Randy Scott     :       MSS option defines.
  33 *              Eric Schenk     :       Fixes to slow start algorithm.
  34 *              Eric Schenk     :       Yet another double ACK bug.
  35 *              Eric Schenk     :       Delayed ACK bug fixes.
  36 *              Eric Schenk     :       Floyd style fast retrans war avoidance.
  37 *              David S. Miller :       Don't allow zero congestion window.
  38 *              Eric Schenk     :       Fix retransmitter so that it sends
  39 *                                      next packet on ack of previous packet.
  40 *              Andi Kleen      :       Moved open_request checking here
  41 *                                      and process RSTs for open_requests.
  42 *              Andi Kleen      :       Better prune_queue, and other fixes.
  43 *              Andrey Savochkin:       Fix RTT measurements in the presence of
  44 *                                      timestamps.
  45 *              Andrey Savochkin:       Check sequence numbers correctly when
  46 *                                      removing SACKs due to in sequence incoming
  47 *                                      data segments.
  48 *              Andi Kleen:             Make sure we never ack data there is not
  49 *                                      enough room for. Also make this condition
  50 *                                      a fatal error if it might still happen.
  51 *              Andi Kleen:             Add tcp_measure_rcv_mss to make
  52 *                                      connections with MSS<min(MTU,ann. MSS)
  53 *                                      work without delayed acks.
  54 *              Andi Kleen:             Process packets with PSH set in the
  55 *                                      fast path.
  56 *              J Hadi Salim:           ECN support
  57 *              Andrei Gurtov,
  58 *              Pasi Sarolahti,
  59 *              Panu Kuhlberg:          Experimental audit of TCP (re)transmission
  60 *                                      engine. Lots of bugs are found.
  61 *              Pasi Sarolahti:         F-RTO for dealing with spurious RTOs
  62 */
  63
  64#include <linux/mm.h>
  65#include <linux/slab.h>
  66#include <linux/module.h>
  67#include <linux/sysctl.h>
  68#include <linux/kernel.h>
  69#include <net/dst.h>
  70#include <net/tcp.h>
  71#include <net/inet_common.h>
  72#include <linux/ipsec.h>
  73#include <asm/unaligned.h>
  74#include <net/netdma.h>
  75
  76int sysctl_tcp_timestamps __read_mostly = 1;
  77int sysctl_tcp_window_scaling __read_mostly = 1;
  78int sysctl_tcp_sack __read_mostly = 1;
  79int sysctl_tcp_fack __read_mostly = 1;
  80int sysctl_tcp_reordering __read_mostly = TCP_FASTRETRANS_THRESH;
  81EXPORT_SYMBOL(sysctl_tcp_reordering);
  82int sysctl_tcp_ecn __read_mostly = 2;
  83EXPORT_SYMBOL(sysctl_tcp_ecn);
  84int sysctl_tcp_dsack __read_mostly = 1;
  85int sysctl_tcp_app_win __read_mostly = 31;
  86int sysctl_tcp_adv_win_scale __read_mostly = 2;
  87EXPORT_SYMBOL(sysctl_tcp_adv_win_scale);
  88
  89int sysctl_tcp_stdurg __read_mostly;
  90int sysctl_tcp_rfc1337 __read_mostly;
  91int sysctl_tcp_max_orphans __read_mostly = NR_FILE;
  92int sysctl_tcp_frto __read_mostly = 2;
  93int sysctl_tcp_frto_response __read_mostly;
  94int sysctl_tcp_nometrics_save __read_mostly;
  95
  96int sysctl_tcp_thin_dupack __read_mostly;
  97
  98int sysctl_tcp_moderate_rcvbuf __read_mostly = 1;
  99int sysctl_tcp_abc __read_mostly;
 100
 101#define FLAG_DATA               0x01 /* Incoming frame contained data.          */
 102#define FLAG_WIN_UPDATE         0x02 /* Incoming ACK was a window update.       */
 103#define FLAG_DATA_ACKED         0x04 /* This ACK acknowledged new data.         */
 104#define FLAG_RETRANS_DATA_ACKED 0x08 /* "" "" some of which was retransmitted.  */
 105#define FLAG_SYN_ACKED          0x10 /* This ACK acknowledged SYN.              */
 106#define FLAG_DATA_SACKED        0x20 /* New SACK.                               */
 107#define FLAG_ECE                0x40 /* ECE in this ACK                         */
 108#define FLAG_DATA_LOST          0x80 /* SACK detected data lossage.             */
 109#define FLAG_SLOWPATH           0x100 /* Do not skip RFC checks for window update.*/
 110#define FLAG_ONLY_ORIG_SACKED   0x200 /* SACKs only non-rexmit sent before RTO */
 111#define FLAG_SND_UNA_ADVANCED   0x400 /* Snd_una was changed (!= FLAG_DATA_ACKED) */
 112#define FLAG_DSACKING_ACK       0x800 /* SACK blocks contained D-SACK info */
 113#define FLAG_NONHEAD_RETRANS_ACKED      0x1000 /* Non-head rexmitted data was ACKed */
 114#define FLAG_SACK_RENEGING      0x2000 /* snd_una advanced to a sacked seq */
 115
 116#define FLAG_ACKED              (FLAG_DATA_ACKED|FLAG_SYN_ACKED)
 117#define FLAG_NOT_DUP            (FLAG_DATA|FLAG_WIN_UPDATE|FLAG_ACKED)
 118#define FLAG_CA_ALERT           (FLAG_DATA_SACKED|FLAG_ECE)
 119#define FLAG_FORWARD_PROGRESS   (FLAG_ACKED|FLAG_DATA_SACKED)
 120#define FLAG_ANY_PROGRESS       (FLAG_FORWARD_PROGRESS|FLAG_SND_UNA_ADVANCED)
 121
 122#define TCP_REMNANT (TCP_FLAG_FIN|TCP_FLAG_URG|TCP_FLAG_SYN|TCP_FLAG_PSH)
 123#define TCP_HP_BITS (~(TCP_RESERVED_BITS|TCP_FLAG_PSH))
 124
 125/* Adapt the MSS value used to make delayed ack decision to the
 126 * real world.
 127 */
 128static void tcp_measure_rcv_mss(struct sock *sk, const struct sk_buff *skb)
 129{
 130        struct inet_connection_sock *icsk = inet_csk(sk);
 131        const unsigned int lss = icsk->icsk_ack.last_seg_size;
 132        unsigned int len;
 133
 134        icsk->icsk_ack.last_seg_size = 0;
 135
 136        /* skb->len may jitter because of SACKs, even if peer
 137         * sends good full-sized frames.
 138         */
 139        len = skb_shinfo(skb)->gso_size ? : skb->len;
 140        if (len >= icsk->icsk_ack.rcv_mss) {
 141                icsk->icsk_ack.rcv_mss = len;
 142        } else {
 143                /* Otherwise, we make more careful check taking into account,
 144                 * that SACKs block is variable.
 145                 *
 146                 * "len" is invariant segment length, including TCP header.
 147                 */
 148                len += skb->data - skb_transport_header(skb);
 149                if (len >= TCP_MSS_DEFAULT + sizeof(struct tcphdr) ||
 150                    /* If PSH is not set, packet should be
 151                     * full sized, provided peer TCP is not badly broken.
 152                     * This observation (if it is correct 8)) allows
 153                     * to handle super-low mtu links fairly.
 154                     */
 155                    (len >= TCP_MIN_MSS + sizeof(struct tcphdr) &&
 156                     !(tcp_flag_word(tcp_hdr(skb)) & TCP_REMNANT))) {
 157                        /* Subtract also invariant (if peer is RFC compliant),
 158                         * tcp header plus fixed timestamp option length.
 159                         * Resulting "len" is MSS free of SACK jitter.
 160                         */
 161                        len -= tcp_sk(sk)->tcp_header_len;
 162                        icsk->icsk_ack.last_seg_size = len;
 163                        if (len == lss) {
 164                                icsk->icsk_ack.rcv_mss = len;
 165                                return;
 166                        }
 167                }
 168                if (icsk->icsk_ack.pending & ICSK_ACK_PUSHED)
 169                        icsk->icsk_ack.pending |= ICSK_ACK_PUSHED2;
 170                icsk->icsk_ack.pending |= ICSK_ACK_PUSHED;
 171        }
 172}
 173
 174static void tcp_incr_quickack(struct sock *sk)
 175{
 176        struct inet_connection_sock *icsk = inet_csk(sk);
 177        unsigned quickacks = tcp_sk(sk)->rcv_wnd / (2 * icsk->icsk_ack.rcv_mss);
 178
 179        if (quickacks == 0)
 180                quickacks = 2;
 181        if (quickacks > icsk->icsk_ack.quick)
 182                icsk->icsk_ack.quick = min(quickacks, TCP_MAX_QUICKACKS);
 183}
 184
 185static void tcp_enter_quickack_mode(struct sock *sk)
 186{
 187        struct inet_connection_sock *icsk = inet_csk(sk);
 188        tcp_incr_quickack(sk);
 189        icsk->icsk_ack.pingpong = 0;
 190        icsk->icsk_ack.ato = TCP_ATO_MIN;
 191}
 192
 193/* Send ACKs quickly, if "quick" count is not exhausted
 194 * and the session is not interactive.
 195 */
 196
 197static inline int tcp_in_quickack_mode(const struct sock *sk)
 198{
 199        const struct inet_connection_sock *icsk = inet_csk(sk);
 200        return icsk->icsk_ack.quick && !icsk->icsk_ack.pingpong;
 201}
 202
 203static inline void TCP_ECN_queue_cwr(struct tcp_sock *tp)
 204{
 205        if (tp->ecn_flags & TCP_ECN_OK)
 206                tp->ecn_flags |= TCP_ECN_QUEUE_CWR;
 207}
 208
 209static inline void TCP_ECN_accept_cwr(struct tcp_sock *tp, const struct sk_buff *skb)
 210{
 211        if (tcp_hdr(skb)->cwr)
 212                tp->ecn_flags &= ~TCP_ECN_DEMAND_CWR;
 213}
 214
 215static inline void TCP_ECN_withdraw_cwr(struct tcp_sock *tp)
 216{
 217        tp->ecn_flags &= ~TCP_ECN_DEMAND_CWR;
 218}
 219
 220static inline void TCP_ECN_check_ce(struct tcp_sock *tp, const struct sk_buff *skb)
 221{
 222        if (!(tp->ecn_flags & TCP_ECN_OK))
 223                return;
 224
 225        switch (TCP_SKB_CB(skb)->ip_dsfield & INET_ECN_MASK) {
 226        case INET_ECN_NOT_ECT:
 227                /* Funny extension: if ECT is not set on a segment,
 228                 * and we already seen ECT on a previous segment,
 229                 * it is probably a retransmit.
 230                 */
 231                if (tp->ecn_flags & TCP_ECN_SEEN)
 232                        tcp_enter_quickack_mode((struct sock *)tp);
 233                break;
 234        case INET_ECN_CE:
 235                tp->ecn_flags |= TCP_ECN_DEMAND_CWR;
 236                /* fallinto */
 237        default:
 238                tp->ecn_flags |= TCP_ECN_SEEN;
 239        }
 240}
 241
 242static inline void TCP_ECN_rcv_synack(struct tcp_sock *tp, const struct tcphdr *th)
 243{
 244        if ((tp->ecn_flags & TCP_ECN_OK) && (!th->ece || th->cwr))
 245                tp->ecn_flags &= ~TCP_ECN_OK;
 246}
 247
 248static inline void TCP_ECN_rcv_syn(struct tcp_sock *tp, const struct tcphdr *th)
 249{
 250        if ((tp->ecn_flags & TCP_ECN_OK) && (!th->ece || !th->cwr))
 251                tp->ecn_flags &= ~TCP_ECN_OK;
 252}
 253
 254static inline int TCP_ECN_rcv_ecn_echo(const struct tcp_sock *tp, const struct tcphdr *th)
 255{
 256        if (th->ece && !th->syn && (tp->ecn_flags & TCP_ECN_OK))
 257                return 1;
 258        return 0;
 259}
 260
 261/* Buffer size and advertised window tuning.
 262 *
 263 * 1. Tuning sk->sk_sndbuf, when connection enters established state.
 264 */
 265
 266static void tcp_fixup_sndbuf(struct sock *sk)
 267{
 268        int sndmem = SKB_TRUESIZE(tcp_sk(sk)->rx_opt.mss_clamp + MAX_TCP_HEADER);
 269
 270        sndmem *= TCP_INIT_CWND;
 271        if (sk->sk_sndbuf < sndmem)
 272                sk->sk_sndbuf = min(sndmem, sysctl_tcp_wmem[2]);
 273}
 274
 275/* 2. Tuning advertised window (window_clamp, rcv_ssthresh)
 276 *
 277 * All tcp_full_space() is split to two parts: "network" buffer, allocated
 278 * forward and advertised in receiver window (tp->rcv_wnd) and
 279 * "application buffer", required to isolate scheduling/application
 280 * latencies from network.
 281 * window_clamp is maximal advertised window. It can be less than
 282 * tcp_full_space(), in this case tcp_full_space() - window_clamp
 283 * is reserved for "application" buffer. The less window_clamp is
 284 * the smoother our behaviour from viewpoint of network, but the lower
 285 * throughput and the higher sensitivity of the connection to losses. 8)
 286 *
 287 * rcv_ssthresh is more strict window_clamp used at "slow start"
 288 * phase to predict further behaviour of this connection.
 289 * It is used for two goals:
 290 * - to enforce header prediction at sender, even when application
 291 *   requires some significant "application buffer". It is check #1.
 292 * - to prevent pruning of receive queue because of misprediction
 293 *   of receiver window. Check #2.
 294 *
 295 * The scheme does not work when sender sends good segments opening
 296 * window and then starts to feed us spaghetti. But it should work
 297 * in common situations. Otherwise, we have to rely on queue collapsing.
 298 */
 299
 300/* Slow part of check#2. */
 301static int __tcp_grow_window(const struct sock *sk, const struct sk_buff *skb)
 302{
 303        struct tcp_sock *tp = tcp_sk(sk);
 304        /* Optimize this! */
 305        int truesize = tcp_win_from_space(skb->truesize) >> 1;
 306        int window = tcp_win_from_space(sysctl_tcp_rmem[2]) >> 1;
 307
 308        while (tp->rcv_ssthresh <= window) {
 309                if (truesize <= skb->len)
 310                        return 2 * inet_csk(sk)->icsk_ack.rcv_mss;
 311
 312                truesize >>= 1;
 313                window >>= 1;
 314        }
 315        return 0;
 316}
 317
 318static void tcp_grow_window(struct sock *sk, const struct sk_buff *skb)
 319{
 320        struct tcp_sock *tp = tcp_sk(sk);
 321
 322        /* Check #1 */
 323        if (tp->rcv_ssthresh < tp->window_clamp &&
 324            (int)tp->rcv_ssthresh < tcp_space(sk) &&
 325            !tcp_memory_pressure) {
 326                int incr;
 327
 328                /* Check #2. Increase window, if skb with such overhead
 329                 * will fit to rcvbuf in future.
 330                 */
 331                if (tcp_win_from_space(skb->truesize) <= skb->len)
 332                        incr = 2 * tp->advmss;
 333                else
 334                        incr = __tcp_grow_window(sk, skb);
 335
 336                if (incr) {
 337                        tp->rcv_ssthresh = min(tp->rcv_ssthresh + incr,
 338                                               tp->window_clamp);
 339                        inet_csk(sk)->icsk_ack.quick |= 1;
 340                }
 341        }
 342}
 343
 344/* 3. Tuning rcvbuf, when connection enters established state. */
 345
 346static void tcp_fixup_rcvbuf(struct sock *sk)
 347{
 348        u32 mss = tcp_sk(sk)->advmss;
 349        u32 icwnd = TCP_DEFAULT_INIT_RCVWND;
 350        int rcvmem;
 351
 352        /* Limit to 10 segments if mss <= 1460,
 353         * or 14600/mss segments, with a minimum of two segments.
 354         */
 355        if (mss > 1460)
 356                icwnd = max_t(u32, (1460 * TCP_DEFAULT_INIT_RCVWND) / mss, 2);
 357
 358        rcvmem = SKB_TRUESIZE(mss + MAX_TCP_HEADER);
 359        while (tcp_win_from_space(rcvmem) < mss)
 360                rcvmem += 128;
 361
 362        rcvmem *= icwnd;
 363
 364        if (sk->sk_rcvbuf < rcvmem)
 365                sk->sk_rcvbuf = min(rcvmem, sysctl_tcp_rmem[2]);
 366}
 367
 368/* 4. Try to fixup all. It is made immediately after connection enters
 369 *    established state.
 370 */
 371static void tcp_init_buffer_space(struct sock *sk)
 372{
 373        struct tcp_sock *tp = tcp_sk(sk);
 374        int maxwin;
 375
 376        if (!(sk->sk_userlocks & SOCK_RCVBUF_LOCK))
 377                tcp_fixup_rcvbuf(sk);
 378        if (!(sk->sk_userlocks & SOCK_SNDBUF_LOCK))
 379                tcp_fixup_sndbuf(sk);
 380
 381        tp->rcvq_space.space = tp->rcv_wnd;
 382
 383        maxwin = tcp_full_space(sk);
 384
 385        if (tp->window_clamp >= maxwin) {
 386                tp->window_clamp = maxwin;
 387
 388                if (sysctl_tcp_app_win && maxwin > 4 * tp->advmss)
 389                        tp->window_clamp = max(maxwin -
 390                                               (maxwin >> sysctl_tcp_app_win),
 391                                               4 * tp->advmss);
 392        }
 393
 394        /* Force reservation of one segment. */
 395        if (sysctl_tcp_app_win &&
 396            tp->window_clamp > 2 * tp->advmss &&
 397            tp->window_clamp + tp->advmss > maxwin)
 398                tp->window_clamp = max(2 * tp->advmss, maxwin - tp->advmss);
 399
 400        tp->rcv_ssthresh = min(tp->rcv_ssthresh, tp->window_clamp);
 401        tp->snd_cwnd_stamp = tcp_time_stamp;
 402}
 403
 404/* 5. Recalculate window clamp after socket hit its memory bounds. */
 405static void tcp_clamp_window(struct sock *sk)
 406{
 407        struct tcp_sock *tp = tcp_sk(sk);
 408        struct inet_connection_sock *icsk = inet_csk(sk);
 409
 410        icsk->icsk_ack.quick = 0;
 411
 412        if (sk->sk_rcvbuf < sysctl_tcp_rmem[2] &&
 413            !(sk->sk_userlocks & SOCK_RCVBUF_LOCK) &&
 414            !tcp_memory_pressure &&
 415            atomic_long_read(&tcp_memory_allocated) < sysctl_tcp_mem[0]) {
 416                sk->sk_rcvbuf = min(atomic_read(&sk->sk_rmem_alloc),
 417                                    sysctl_tcp_rmem[2]);
 418        }
 419        if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf)
 420                tp->rcv_ssthresh = min(tp->window_clamp, 2U * tp->advmss);
 421}
 422
 423/* Initialize RCV_MSS value.
 424 * RCV_MSS is an our guess about MSS used by the peer.
 425 * We haven't any direct information about the MSS.
 426 * It's better to underestimate the RCV_MSS rather than overestimate.
 427 * Overestimations make us ACKing less frequently than needed.
 428 * Underestimations are more easy to detect and fix by tcp_measure_rcv_mss().
 429 */
 430void tcp_initialize_rcv_mss(struct sock *sk)
 431{
 432        const struct tcp_sock *tp = tcp_sk(sk);
 433        unsigned int hint = min_t(unsigned int, tp->advmss, tp->mss_cache);
 434
 435        hint = min(hint, tp->rcv_wnd / 2);
 436        hint = min(hint, TCP_MSS_DEFAULT);
 437        hint = max(hint, TCP_MIN_MSS);
 438
 439        inet_csk(sk)->icsk_ack.rcv_mss = hint;
 440}
 441EXPORT_SYMBOL(tcp_initialize_rcv_mss);
 442
 443/* Receiver "autotuning" code.
 444 *
 445 * The algorithm for RTT estimation w/o timestamps is based on
 446 * Dynamic Right-Sizing (DRS) by Wu Feng and Mike Fisk of LANL.
 447 * <http://public.lanl.gov/radiant/pubs.html#DRS>
 448 *
 449 * More detail on this code can be found at
 450 * <http://staff.psc.edu/jheffner/>,
 451 * though this reference is out of date.  A new paper
 452 * is pending.
 453 */
 454static void tcp_rcv_rtt_update(struct tcp_sock *tp, u32 sample, int win_dep)
 455{
 456        u32 new_sample = tp->rcv_rtt_est.rtt;
 457        long m = sample;
 458
 459        if (m == 0)
 460                m = 1;
 461
 462        if (new_sample != 0) {
 463                /* If we sample in larger samples in the non-timestamp
 464                 * case, we could grossly overestimate the RTT especially
 465                 * with chatty applications or bulk transfer apps which
 466                 * are stalled on filesystem I/O.
 467                 *
 468                 * Also, since we are only going for a minimum in the
 469                 * non-timestamp case, we do not smooth things out
 470                 * else with timestamps disabled convergence takes too
 471                 * long.
 472                 */
 473                if (!win_dep) {
 474                        m -= (new_sample >> 3);
 475                        new_sample += m;
 476                } else if (m < new_sample)
 477                        new_sample = m << 3;
 478        } else {
 479                /* No previous measure. */
 480                new_sample = m << 3;
 481        }
 482
 483        if (tp->rcv_rtt_est.rtt != new_sample)
 484                tp->rcv_rtt_est.rtt = new_sample;
 485}
 486
 487static inline void tcp_rcv_rtt_measure(struct tcp_sock *tp)
 488{
 489        if (tp->rcv_rtt_est.time == 0)
 490                goto new_measure;
 491        if (before(tp->rcv_nxt, tp->rcv_rtt_est.seq))
 492                return;
 493        tcp_rcv_rtt_update(tp, jiffies - tp->rcv_rtt_est.time, 1);
 494
 495new_measure:
 496        tp->rcv_rtt_est.seq = tp->rcv_nxt + tp->rcv_wnd;
 497        tp->rcv_rtt_est.time = tcp_time_stamp;
 498}
 499
 500static inline void tcp_rcv_rtt_measure_ts(struct sock *sk,
 501                                          const struct sk_buff *skb)
 502{
 503        struct tcp_sock *tp = tcp_sk(sk);
 504        if (tp->rx_opt.rcv_tsecr &&
 505            (TCP_SKB_CB(skb)->end_seq -
 506             TCP_SKB_CB(skb)->seq >= inet_csk(sk)->icsk_ack.rcv_mss))
 507                tcp_rcv_rtt_update(tp, tcp_time_stamp - tp->rx_opt.rcv_tsecr, 0);
 508}
 509
 510/*
 511 * This function should be called every time data is copied to user space.
 512 * It calculates the appropriate TCP receive buffer space.
 513 */
 514void tcp_rcv_space_adjust(struct sock *sk)
 515{
 516        struct tcp_sock *tp = tcp_sk(sk);
 517        int time;
 518        int space;
 519
 520        if (tp->rcvq_space.time == 0)
 521                goto new_measure;
 522
 523        time = tcp_time_stamp - tp->rcvq_space.time;
 524        if (time < (tp->rcv_rtt_est.rtt >> 3) || tp->rcv_rtt_est.rtt == 0)
 525                return;
 526
 527        space = 2 * (tp->copied_seq - tp->rcvq_space.seq);
 528
 529        space = max(tp->rcvq_space.space, space);
 530
 531        if (tp->rcvq_space.space != space) {
 532                int rcvmem;
 533
 534                tp->rcvq_space.space = space;
 535
 536                if (sysctl_tcp_moderate_rcvbuf &&
 537                    !(sk->sk_userlocks & SOCK_RCVBUF_LOCK)) {
 538                        int new_clamp = space;
 539
 540                        /* Receive space grows, normalize in order to
 541                         * take into account packet headers and sk_buff
 542                         * structure overhead.
 543                         */
 544                        space /= tp->advmss;
 545                        if (!space)
 546                                space = 1;
 547                        rcvmem = SKB_TRUESIZE(tp->advmss + MAX_TCP_HEADER);
 548                        while (tcp_win_from_space(rcvmem) < tp->advmss)
 549                                rcvmem += 128;
 550                        space *= rcvmem;
 551                        space = min(space, sysctl_tcp_rmem[2]);
 552                        if (space > sk->sk_rcvbuf) {
 553                                sk->sk_rcvbuf = space;
 554
 555                                /* Make the window clamp follow along.  */
 556                                tp->window_clamp = new_clamp;
 557                        }
 558                }
 559        }
 560
 561new_measure:
 562        tp->rcvq_space.seq = tp->copied_seq;
 563        tp->rcvq_space.time = tcp_time_stamp;
 564}
 565
 566/* There is something which you must keep in mind when you analyze the
 567 * behavior of the tp->ato delayed ack timeout interval.  When a
 568 * connection starts up, we want to ack as quickly as possible.  The
 569 * problem is that "good" TCP's do slow start at the beginning of data
 570 * transmission.  The means that until we send the first few ACK's the
 571 * sender will sit on his end and only queue most of his data, because
 572 * he can only send snd_cwnd unacked packets at any given time.  For
 573 * each ACK we send, he increments snd_cwnd and transmits more of his
 574 * queue.  -DaveM
 575 */
 576static void tcp_event_data_recv(struct sock *sk, struct sk_buff *skb)
 577{
 578        struct tcp_sock *tp = tcp_sk(sk);
 579        struct inet_connection_sock *icsk = inet_csk(sk);
 580        u32 now;
 581
 582        inet_csk_schedule_ack(sk);
 583
 584        tcp_measure_rcv_mss(sk, skb);
 585
 586        tcp_rcv_rtt_measure(tp);
 587
 588        now = tcp_time_stamp;
 589
 590        if (!icsk->icsk_ack.ato) {
 591                /* The _first_ data packet received, initialize
 592                 * delayed ACK engine.
 593                 */
 594                tcp_incr_quickack(sk);
 595                icsk->icsk_ack.ato = TCP_ATO_MIN;
 596        } else {
 597                int m = now - icsk->icsk_ack.lrcvtime;
 598
 599                if (m <= TCP_ATO_MIN / 2) {
 600                        /* The fastest case is the first. */
 601                        icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + TCP_ATO_MIN / 2;
 602                } else if (m < icsk->icsk_ack.ato) {
 603                        icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + m;
 604                        if (icsk->icsk_ack.ato > icsk->icsk_rto)
 605                                icsk->icsk_ack.ato = icsk->icsk_rto;
 606                } else if (m > icsk->icsk_rto) {
 607                        /* Too long gap. Apparently sender failed to
 608                         * restart window, so that we send ACKs quickly.
 609                         */
 610                        tcp_incr_quickack(sk);
 611                        sk_mem_reclaim(sk);
 612                }
 613        }
 614        icsk->icsk_ack.lrcvtime = now;
 615
 616        TCP_ECN_check_ce(tp, skb);
 617
 618        if (skb->len >= 128)
 619                tcp_grow_window(sk, skb);
 620}
 621
 622/* Called to compute a smoothed rtt estimate. The data fed to this
 623 * routine either comes from timestamps, or from segments that were
 624 * known _not_ to have been retransmitted [see Karn/Partridge
 625 * Proceedings SIGCOMM 87]. The algorithm is from the SIGCOMM 88
 626 * piece by Van Jacobson.
 627 * NOTE: the next three routines used to be one big routine.
 628 * To save cycles in the RFC 1323 implementation it was better to break
 629 * it up into three procedures. -- erics
 630 */
 631static void tcp_rtt_estimator(struct sock *sk, const __u32 mrtt)
 632{
 633        struct tcp_sock *tp = tcp_sk(sk);
 634        long m = mrtt; /* RTT */
 635
 636        /*      The following amusing code comes from Jacobson's
 637         *      article in SIGCOMM '88.  Note that rtt and mdev
 638         *      are scaled versions of rtt and mean deviation.
 639         *      This is designed to be as fast as possible
 640         *      m stands for "measurement".
 641         *
 642         *      On a 1990 paper the rto value is changed to:
 643         *      RTO = rtt + 4 * mdev
 644         *
 645         * Funny. This algorithm seems to be very broken.
 646         * These formulae increase RTO, when it should be decreased, increase
 647         * too slowly, when it should be increased quickly, decrease too quickly
 648         * etc. I guess in BSD RTO takes ONE value, so that it is absolutely
 649         * does not matter how to _calculate_ it. Seems, it was trap
 650         * that VJ failed to avoid. 8)
 651         */
 652        if (m == 0)
 653                m = 1;
 654        if (tp->srtt != 0) {
 655                m -= (tp->srtt >> 3);   /* m is now error in rtt est */
 656                tp->srtt += m;          /* rtt = 7/8 rtt + 1/8 new */
 657                if (m < 0) {
 658                        m = -m;         /* m is now abs(error) */
 659                        m -= (tp->mdev >> 2);   /* similar update on mdev */
 660                        /* This is similar to one of Eifel findings.
 661                         * Eifel blocks mdev updates when rtt decreases.
 662                         * This solution is a bit different: we use finer gain
 663                         * for mdev in this case (alpha*beta).
 664                         * Like Eifel it also prevents growth of rto,
 665                         * but also it limits too fast rto decreases,
 666                         * happening in pure Eifel.
 667                         */
 668                        if (m > 0)
 669                                m >>= 3;
 670                } else {
 671                        m -= (tp->mdev >> 2);   /* similar update on mdev */
 672                }
 673                tp->mdev += m;          /* mdev = 3/4 mdev + 1/4 new */
 674                if (tp->mdev > tp->mdev_max) {
 675                        tp->mdev_max = tp->mdev;
 676                        if (tp->mdev_max > tp->rttvar)
 677                                tp->rttvar = tp->mdev_max;
 678                }
 679                if (after(tp->snd_una, tp->rtt_seq)) {
 680                        if (tp->mdev_max < tp->rttvar)
 681                                tp->rttvar -= (tp->rttvar - tp->mdev_max) >> 2;
 682                        tp->rtt_seq = tp->snd_nxt;
 683                        tp->mdev_max = tcp_rto_min(sk);
 684                }
 685        } else {
 686                /* no previous measure. */
 687                tp->srtt = m << 3;      /* take the measured time to be rtt */
 688                tp->mdev = m << 1;      /* make sure rto = 3*rtt */
 689                tp->mdev_max = tp->rttvar = max(tp->mdev, tcp_rto_min(sk));
 690                tp->rtt_seq = tp->snd_nxt;
 691        }
 692}
 693
 694/* Calculate rto without backoff.  This is the second half of Van Jacobson's
 695 * routine referred to above.
 696 */
 697static inline void tcp_set_rto(struct sock *sk)
 698{
 699        const struct tcp_sock *tp = tcp_sk(sk);
 700        /* Old crap is replaced with new one. 8)
 701         *
 702         * More seriously:
 703         * 1. If rtt variance happened to be less 50msec, it is hallucination.
 704         *    It cannot be less due to utterly erratic ACK generation made
 705         *    at least by solaris and freebsd. "Erratic ACKs" has _nothing_
 706         *    to do with delayed acks, because at cwnd>2 true delack timeout
 707         *    is invisible. Actually, Linux-2.4 also generates erratic
 708         *    ACKs in some circumstances.
 709         */
 710        inet_csk(sk)->icsk_rto = __tcp_set_rto(tp);
 711
 712        /* 2. Fixups made earlier cannot be right.
 713         *    If we do not estimate RTO correctly without them,
 714         *    all the algo is pure shit and should be replaced
 715         *    with correct one. It is exactly, which we pretend to do.
 716         */
 717
 718        /* NOTE: clamping at TCP_RTO_MIN is not required, current algo
 719         * guarantees that rto is higher.
 720         */
 721        tcp_bound_rto(sk);
 722}
 723
 724/* Save metrics learned by this TCP session.
 725   This function is called only, when TCP finishes successfully
 726   i.e. when it enters TIME-WAIT or goes from LAST-ACK to CLOSE.
 727 */
 728void tcp_update_metrics(struct sock *sk)
 729{
 730        struct tcp_sock *tp = tcp_sk(sk);
 731        struct dst_entry *dst = __sk_dst_get(sk);
 732
 733        if (sysctl_tcp_nometrics_save)
 734                return;
 735
 736        dst_confirm(dst);
 737
 738        if (dst && (dst->flags & DST_HOST)) {
 739                const struct inet_connection_sock *icsk = inet_csk(sk);
 740                int m;
 741                unsigned long rtt;
 742
 743                if (icsk->icsk_backoff || !tp->srtt) {
 744                        /* This session failed to estimate rtt. Why?
 745                         * Probably, no packets returned in time.
 746                         * Reset our results.
 747                         */
 748                        if (!(dst_metric_locked(dst, RTAX_RTT)))
 749                                dst_metric_set(dst, RTAX_RTT, 0);
 750                        return;
 751                }
 752
 753                rtt = dst_metric_rtt(dst, RTAX_RTT);
 754                m = rtt - tp->srtt;
 755
 756                /* If newly calculated rtt larger than stored one,
 757                 * store new one. Otherwise, use EWMA. Remember,
 758                 * rtt overestimation is always better than underestimation.
 759                 */
 760                if (!(dst_metric_locked(dst, RTAX_RTT))) {
 761                        if (m <= 0)
 762                                set_dst_metric_rtt(dst, RTAX_RTT, tp->srtt);
 763                        else
 764                                set_dst_metric_rtt(dst, RTAX_RTT, rtt - (m >> 3));
 765                }
 766
 767                if (!(dst_metric_locked(dst, RTAX_RTTVAR))) {
 768                        unsigned long var;
 769                        if (m < 0)
 770                                m = -m;
 771
 772                        /* Scale deviation to rttvar fixed point */
 773                        m >>= 1;
 774                        if (m < tp->mdev)
 775                                m = tp->mdev;
 776
 777                        var = dst_metric_rtt(dst, RTAX_RTTVAR);
 778                        if (m >= var)
 779                                var = m;
 780                        else
 781                                var -= (var - m) >> 2;
 782
 783                        set_dst_metric_rtt(dst, RTAX_RTTVAR, var);
 784                }
 785
 786                if (tcp_in_initial_slowstart(tp)) {
 787                        /* Slow start still did not finish. */
 788                        if (dst_metric(dst, RTAX_SSTHRESH) &&
 789                            !dst_metric_locked(dst, RTAX_SSTHRESH) &&
 790                            (tp->snd_cwnd >> 1) > dst_metric(dst, RTAX_SSTHRESH))
 791                                dst_metric_set(dst, RTAX_SSTHRESH, tp->snd_cwnd >> 1);
 792                        if (!dst_metric_locked(dst, RTAX_CWND) &&
 793                            tp->snd_cwnd > dst_metric(dst, RTAX_CWND))
 794                                dst_metric_set(dst, RTAX_CWND, tp->snd_cwnd);
 795                } else if (tp->snd_cwnd > tp->snd_ssthresh &&
 796                           icsk->icsk_ca_state == TCP_CA_Open) {
 797                        /* Cong. avoidance phase, cwnd is reliable. */
 798                        if (!dst_metric_locked(dst, RTAX_SSTHRESH))
 799                                dst_metric_set(dst, RTAX_SSTHRESH,
 800                                               max(tp->snd_cwnd >> 1, tp->snd_ssthresh));
 801                        if (!dst_metric_locked(dst, RTAX_CWND))
 802                                dst_metric_set(dst, RTAX_CWND,
 803                                               (dst_metric(dst, RTAX_CWND) +
 804                                                tp->snd_cwnd) >> 1);
 805                } else {
 806                        /* Else slow start did not finish, cwnd is non-sense,
 807                           ssthresh may be also invalid.
 808                         */
 809                        if (!dst_metric_locked(dst, RTAX_CWND))
 810                                dst_metric_set(dst, RTAX_CWND,
 811                                               (dst_metric(dst, RTAX_CWND) +
 812                                                tp->snd_ssthresh) >> 1);
 813                        if (dst_metric(dst, RTAX_SSTHRESH) &&
 814                            !dst_metric_locked(dst, RTAX_SSTHRESH) &&
 815                            tp->snd_ssthresh > dst_metric(dst, RTAX_SSTHRESH))
 816                                dst_metric_set(dst, RTAX_SSTHRESH, tp->snd_ssthresh);
 817                }
 818
 819                if (!dst_metric_locked(dst, RTAX_REORDERING)) {
 820                        if (dst_metric(dst, RTAX_REORDERING) < tp->reordering &&
 821                            tp->reordering != sysctl_tcp_reordering)
 822                                dst_metric_set(dst, RTAX_REORDERING, tp->reordering);
 823                }
 824        }
 825}
 826
 827__u32 tcp_init_cwnd(const struct tcp_sock *tp, const struct dst_entry *dst)
 828{
 829        __u32 cwnd = (dst ? dst_metric(dst, RTAX_INITCWND) : 0);
 830
 831        if (!cwnd)
 832                cwnd = TCP_INIT_CWND;
 833        return min_t(__u32, cwnd, tp->snd_cwnd_clamp);
 834}
 835
 836/* Set slow start threshold and cwnd not falling to slow start */
 837void tcp_enter_cwr(struct sock *sk, const int set_ssthresh)
 838{
 839        struct tcp_sock *tp = tcp_sk(sk);
 840        const struct inet_connection_sock *icsk = inet_csk(sk);
 841
 842        tp->prior_ssthresh = 0;
 843        tp->bytes_acked = 0;
 844        if (icsk->icsk_ca_state < TCP_CA_CWR) {
 845                tp->undo_marker = 0;
 846                if (set_ssthresh)
 847                        tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
 848                tp->snd_cwnd = min(tp->snd_cwnd,
 849                                   tcp_packets_in_flight(tp) + 1U);
 850                tp->snd_cwnd_cnt = 0;
 851                tp->high_seq = tp->snd_nxt;
 852                tp->snd_cwnd_stamp = tcp_time_stamp;
 853                TCP_ECN_queue_cwr(tp);
 854
 855                tcp_set_ca_state(sk, TCP_CA_CWR);
 856        }
 857}
 858
 859/*
 860 * Packet counting of FACK is based on in-order assumptions, therefore TCP
 861 * disables it when reordering is detected
 862 */
 863static void tcp_disable_fack(struct tcp_sock *tp)
 864{
 865        /* RFC3517 uses different metric in lost marker => reset on change */
 866        if (tcp_is_fack(tp))
 867                tp->lost_skb_hint = NULL;
 868        tp->rx_opt.sack_ok &= ~2;
 869}
 870
 871/* Take a notice that peer is sending D-SACKs */
 872static void tcp_dsack_seen(struct tcp_sock *tp)
 873{
 874        tp->rx_opt.sack_ok |= 4;
 875}
 876
 877/* Initialize metrics on socket. */
 878
 879static void tcp_init_metrics(struct sock *sk)
 880{
 881        struct tcp_sock *tp = tcp_sk(sk);
 882        struct dst_entry *dst = __sk_dst_get(sk);
 883
 884        if (dst == NULL)
 885                goto reset;
 886
 887        dst_confirm(dst);
 888
 889        if (dst_metric_locked(dst, RTAX_CWND))
 890                tp->snd_cwnd_clamp = dst_metric(dst, RTAX_CWND);
 891        if (dst_metric(dst, RTAX_SSTHRESH)) {
 892                tp->snd_ssthresh = dst_metric(dst, RTAX_SSTHRESH);
 893                if (tp->snd_ssthresh > tp->snd_cwnd_clamp)
 894                        tp->snd_ssthresh = tp->snd_cwnd_clamp;
 895        } else {
 896                /* ssthresh may have been reduced unnecessarily during.
 897                 * 3WHS. Restore it back to its initial default.
 898                 */
 899                tp->snd_ssthresh = TCP_INFINITE_SSTHRESH;
 900        }
 901        if (dst_metric(dst, RTAX_REORDERING) &&
 902            tp->reordering != dst_metric(dst, RTAX_REORDERING)) {
 903                tcp_disable_fack(tp);
 904                tp->reordering = dst_metric(dst, RTAX_REORDERING);
 905        }
 906
 907        if (dst_metric(dst, RTAX_RTT) == 0 || tp->srtt == 0)
 908                goto reset;
 909
 910        /* Initial rtt is determined from SYN,SYN-ACK.
 911         * The segment is small and rtt may appear much
 912         * less than real one. Use per-dst memory
 913         * to make it more realistic.
 914         *
 915         * A bit of theory. RTT is time passed after "normal" sized packet
 916         * is sent until it is ACKed. In normal circumstances sending small
 917         * packets force peer to delay ACKs and calculation is correct too.
 918         * The algorithm is adaptive and, provided we follow specs, it
 919         * NEVER underestimate RTT. BUT! If peer tries to make some clever
 920         * tricks sort of "quick acks" for time long enough to decrease RTT
 921         * to low value, and then abruptly stops to do it and starts to delay
 922         * ACKs, wait for troubles.
 923         */
 924        if (dst_metric_rtt(dst, RTAX_RTT) > tp->srtt) {
 925                tp->srtt = dst_metric_rtt(dst, RTAX_RTT);
 926                tp->rtt_seq = tp->snd_nxt;
 927        }
 928        if (dst_metric_rtt(dst, RTAX_RTTVAR) > tp->mdev) {
 929                tp->mdev = dst_metric_rtt(dst, RTAX_RTTVAR);
 930                tp->mdev_max = tp->rttvar = max(tp->mdev, tcp_rto_min(sk));
 931        }
 932        tcp_set_rto(sk);
 933reset:
 934        if (tp->srtt == 0) {
 935                /* RFC2988bis: We've failed to get a valid RTT sample from
 936                 * 3WHS. This is most likely due to retransmission,
 937                 * including spurious one. Reset the RTO back to 3secs
 938                 * from the more aggressive 1sec to avoid more spurious
 939                 * retransmission.
 940                 */
 941                tp->mdev = tp->mdev_max = tp->rttvar = TCP_TIMEOUT_FALLBACK;
 942                inet_csk(sk)->icsk_rto = TCP_TIMEOUT_FALLBACK;
 943        }
 944        /* Cut cwnd down to 1 per RFC5681 if SYN or SYN-ACK has been
 945         * retransmitted. In light of RFC2988bis' more aggressive 1sec
 946         * initRTO, we only reset cwnd when more than 1 SYN/SYN-ACK
 947         * retransmission has occurred.
 948         */
 949        if (tp->total_retrans > 1)
 950                tp->snd_cwnd = 1;
 951        else
 952                tp->snd_cwnd = tcp_init_cwnd(tp, dst);
 953        tp->snd_cwnd_stamp = tcp_time_stamp;
 954}
 955
 956static void tcp_update_reordering(struct sock *sk, const int metric,
 957                                  const int ts)
 958{
 959        struct tcp_sock *tp = tcp_sk(sk);
 960        if (metric > tp->reordering) {
 961                int mib_idx;
 962
 963                tp->reordering = min(TCP_MAX_REORDERING, metric);
 964
 965                /* This exciting event is worth to be remembered. 8) */
 966                if (ts)
 967                        mib_idx = LINUX_MIB_TCPTSREORDER;
 968                else if (tcp_is_reno(tp))
 969                        mib_idx = LINUX_MIB_TCPRENOREORDER;
 970                else if (tcp_is_fack(tp))
 971                        mib_idx = LINUX_MIB_TCPFACKREORDER;
 972                else
 973                        mib_idx = LINUX_MIB_TCPSACKREORDER;
 974
 975                NET_INC_STATS_BH(sock_net(sk), mib_idx);
 976#if FASTRETRANS_DEBUG > 1
 977                printk(KERN_DEBUG "Disorder%d %d %u f%u s%u rr%d\n",
 978                       tp->rx_opt.sack_ok, inet_csk(sk)->icsk_ca_state,
 979                       tp->reordering,
 980                       tp->fackets_out,
 981                       tp->sacked_out,
 982                       tp->undo_marker ? tp->undo_retrans : 0);
 983#endif
 984                tcp_disable_fack(tp);
 985        }
 986}
 987
 988/* This must be called before lost_out is incremented */
 989static void tcp_verify_retransmit_hint(struct tcp_sock *tp, struct sk_buff *skb)
 990{
 991        if ((tp->retransmit_skb_hint == NULL) ||
 992            before(TCP_SKB_CB(skb)->seq,
 993                   TCP_SKB_CB(tp->retransmit_skb_hint)->seq))
 994                tp->retransmit_skb_hint = skb;
 995
 996        if (!tp->lost_out ||
 997            after(TCP_SKB_CB(skb)->end_seq, tp->retransmit_high))
 998                tp->retransmit_high = TCP_SKB_CB(skb)->end_seq;
 999}
1000
1001static void tcp_skb_mark_lost(struct tcp_sock *tp, struct sk_buff *skb)
1002{
1003        if (!(TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_ACKED))) {
1004                tcp_verify_retransmit_hint(tp, skb);
1005
1006                tp->lost_out += tcp_skb_pcount(skb);
1007                TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
1008        }
1009}
1010
1011static void tcp_skb_mark_lost_uncond_verify(struct tcp_sock *tp,
1012                                            struct sk_buff *skb)
1013{
1014        tcp_verify_retransmit_hint(tp, skb);
1015
1016        if (!(TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_ACKED))) {
1017                tp->lost_out += tcp_skb_pcount(skb);
1018                TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
1019        }
1020}
1021
1022/* This procedure tags the retransmission queue when SACKs arrive.
1023 *
1024 * We have three tag bits: SACKED(S), RETRANS(R) and LOST(L).
1025 * Packets in queue with these bits set are counted in variables
1026 * sacked_out, retrans_out and lost_out, correspondingly.
1027 *
1028 * Valid combinations are:
1029 * Tag  InFlight        Description
1030 * 0    1               - orig segment is in flight.
1031 * S    0               - nothing flies, orig reached receiver.
1032 * L    0               - nothing flies, orig lost by net.
1033 * R    2               - both orig and retransmit are in flight.
1034 * L|R  1               - orig is lost, retransmit is in flight.
1035 * S|R  1               - orig reached receiver, retrans is still in flight.
1036 * (L|S|R is logically valid, it could occur when L|R is sacked,
1037 *  but it is equivalent to plain S and code short-curcuits it to S.
1038 *  L|S is logically invalid, it would mean -1 packet in flight 8))
1039 *
1040 * These 6 states form finite state machine, controlled by the following events:
1041 * 1. New ACK (+SACK) arrives. (tcp_sacktag_write_queue())
1042 * 2. Retransmission. (tcp_retransmit_skb(), tcp_xmit_retransmit_queue())
1043 * 3. Loss detection event of one of three flavors:
1044 *      A. Scoreboard estimator decided the packet is lost.
1045 *         A'. Reno "three dupacks" marks head of queue lost.
1046 *         A''. Its FACK modfication, head until snd.fack is lost.
1047 *      B. SACK arrives sacking data transmitted after never retransmitted
1048 *         hole was sent out.
1049 *      C. SACK arrives sacking SND.NXT at the moment, when the
1050 *         segment was retransmitted.
1051 * 4. D-SACK added new rule: D-SACK changes any tag to S.
1052 *
1053 * It is pleasant to note, that state diagram turns out to be commutative,
1054 * so that we are allowed not to be bothered by order of our actions,
1055 * when multiple events arrive simultaneously. (see the function below).
1056 *
1057 * Reordering detection.
1058 * --------------------
1059 * Reordering metric is maximal distance, which a packet can be displaced
1060 * in packet stream. With SACKs we can estimate it:
1061 *
1062 * 1. SACK fills old hole and the corresponding segment was not
1063 *    ever retransmitted -> reordering. Alas, we cannot use it
1064 *    when segment was retransmitted.
1065 * 2. The last flaw is solved with D-SACK. D-SACK arrives
1066 *    for retransmitted and already SACKed segment -> reordering..
1067 * Both of these heuristics are not used in Loss state, when we cannot
1068 * account for retransmits accurately.
1069 *
1070 * SACK block validation.
1071 * ----------------------
1072 *
1073 * SACK block range validation checks that the received SACK block fits to
1074 * the expected sequence limits, i.e., it is between SND.UNA and SND.NXT.
1075 * Note that SND.UNA is not included to the range though being valid because
1076 * it means that the receiver is rather inconsistent with itself reporting
1077 * SACK reneging when it should advance SND.UNA. Such SACK block this is
1078 * perfectly valid, however, in light of RFC2018 which explicitly states
1079 * that "SACK block MUST reflect the newest segment.  Even if the newest
1080 * segment is going to be discarded ...", not that it looks very clever
1081 * in case of head skb. Due to potentional receiver driven attacks, we
1082 * choose to avoid immediate execution of a walk in write queue due to
1083 * reneging and defer head skb's loss recovery to standard loss recovery
1084 * procedure that will eventually trigger (nothing forbids us doing this).
1085 *
1086 * Implements also blockage to start_seq wrap-around. Problem lies in the
1087 * fact that though start_seq (s) is before end_seq (i.e., not reversed),
1088 * there's no guarantee that it will be before snd_nxt (n). The problem
1089 * happens when start_seq resides between end_seq wrap (e_w) and snd_nxt
1090 * wrap (s_w):
1091 *
1092 *         <- outs wnd ->                          <- wrapzone ->
1093 *         u     e      n                         u_w   e_w  s n_w
1094 *         |     |      |                          |     |   |  |
1095 * |<------------+------+----- TCP seqno space --------------+---------->|
1096 * ...-- <2^31 ->|                                           |<--------...
1097 * ...---- >2^31 ------>|                                    |<--------...
1098 *
1099 * Current code wouldn't be vulnerable but it's better still to discard such
1100 * crazy SACK blocks. Doing this check for start_seq alone closes somewhat
1101 * similar case (end_seq after snd_nxt wrap) as earlier reversed check in
1102 * snd_nxt wrap -> snd_una region will then become "well defined", i.e.,
1103 * equal to the ideal case (infinite seqno space without wrap caused issues).
1104 *
1105 * With D-SACK the lower bound is extended to cover sequence space below
1106 * SND.UNA down to undo_marker, which is the last point of interest. Yet
1107 * again, D-SACK block must not to go across snd_una (for the same reason as
1108 * for the normal SACK blocks, explained above). But there all simplicity
1109 * ends, TCP might receive valid D-SACKs below that. As long as they reside
1110 * fully below undo_marker they do not affect behavior in anyway and can
1111 * therefore be safely ignored. In rare cases (which are more or less
1112 * theoretical ones), the D-SACK will nicely cross that boundary due to skb
1113 * fragmentation and packet reordering past skb's retransmission. To consider
1114 * them correctly, the acceptable range must be extended even more though
1115 * the exact amount is rather hard to quantify. However, tp->max_window can
1116 * be used as an exaggerated estimate.
1117 */
1118static int tcp_is_sackblock_valid(struct tcp_sock *tp, int is_dsack,
1119                                  u32 start_seq, u32 end_seq)
1120{
1121        /* Too far in future, or reversed (interpretation is ambiguous) */
1122        if (after(end_seq, tp->snd_nxt) || !before(start_seq, end_seq))
1123                return 0;
1124
1125        /* Nasty start_seq wrap-around check (see comments above) */
1126        if (!before(start_seq, tp->snd_nxt))
1127                return 0;
1128
1129        /* In outstanding window? ...This is valid exit for D-SACKs too.
1130         * start_seq == snd_una is non-sensical (see comments above)
1131         */
1132        if (after(start_seq, tp->snd_una))
1133                return 1;
1134
1135        if (!is_dsack || !tp->undo_marker)
1136                return 0;
1137
1138        /* ...Then it's D-SACK, and must reside below snd_una completely */
1139        if (after(end_seq, tp->snd_una))
1140                return 0;
1141
1142        if (!before(start_seq, tp->undo_marker))
1143                return 1;
1144
1145        /* Too old */
1146        if (!after(end_seq, tp->undo_marker))
1147                return 0;
1148
1149        /* Undo_marker boundary crossing (overestimates a lot). Known already:
1150         *   start_seq < undo_marker and end_seq >= undo_marker.
1151         */
1152        return !before(start_seq, end_seq - tp->max_window);
1153}
1154
1155/* Check for lost retransmit. This superb idea is borrowed from "ratehalving".
1156 * Event "C". Later note: FACK people cheated me again 8), we have to account
1157 * for reordering! Ugly, but should help.
1158 *
1159 * Search retransmitted skbs from write_queue that were sent when snd_nxt was
1160 * less than what is now known to be received by the other end (derived from
1161 * highest SACK block). Also calculate the lowest snd_nxt among the remaining
1162 * retransmitted skbs to avoid some costly processing per ACKs.
1163 */
1164static void tcp_mark_lost_retrans(struct sock *sk)
1165{
1166        const struct inet_connection_sock *icsk = inet_csk(sk);
1167        struct tcp_sock *tp = tcp_sk(sk);
1168        struct sk_buff *skb;
1169        int cnt = 0;
1170        u32 new_low_seq = tp->snd_nxt;
1171        u32 received_upto = tcp_highest_sack_seq(tp);
1172
1173        if (!tcp_is_fack(tp) || !tp->retrans_out ||
1174            !after(received_upto, tp->lost_retrans_low) ||
1175            icsk->icsk_ca_state != TCP_CA_Recovery)
1176                return;
1177
1178        tcp_for_write_queue(skb, sk) {
1179                u32 ack_seq = TCP_SKB_CB(skb)->ack_seq;
1180
1181                if (skb == tcp_send_head(sk))
1182                        break;
1183                if (cnt == tp->retrans_out)
1184                        break;
1185                if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
1186                        continue;
1187
1188                if (!(TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS))
1189                        continue;
1190
1191                /* TODO: We would like to get rid of tcp_is_fack(tp) only
1192                 * constraint here (see above) but figuring out that at
1193                 * least tp->reordering SACK blocks reside between ack_seq
1194                 * and received_upto is not easy task to do cheaply with
1195                 * the available datastructures.
1196                 *
1197                 * Whether FACK should check here for tp->reordering segs
1198                 * in-between one could argue for either way (it would be
1199                 * rather simple to implement as we could count fack_count
1200                 * during the walk and do tp->fackets_out - fack_count).
1201                 */
1202                if (after(received_upto, ack_seq)) {
1203                        TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
1204                        tp->retrans_out -= tcp_skb_pcount(skb);
1205
1206                        tcp_skb_mark_lost_uncond_verify(tp, skb);
1207                        NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPLOSTRETRANSMIT);
1208                } else {
1209                        if (before(ack_seq, new_low_seq))
1210                                new_low_seq = ack_seq;
1211                        cnt += tcp_skb_pcount(skb);
1212                }
1213        }
1214
1215        if (tp->retrans_out)
1216                tp->lost_retrans_low = new_low_seq;
1217}
1218
1219static int tcp_check_dsack(struct sock *sk, const struct sk_buff *ack_skb,
1220                           struct tcp_sack_block_wire *sp, int num_sacks,
1221                           u32 prior_snd_una)
1222{
1223        struct tcp_sock *tp = tcp_sk(sk);
1224        u32 start_seq_0 = get_unaligned_be32(&sp[0].start_seq);
1225        u32 end_seq_0 = get_unaligned_be32(&sp[0].end_seq);
1226        int dup_sack = 0;
1227
1228        if (before(start_seq_0, TCP_SKB_CB(ack_skb)->ack_seq)) {
1229                dup_sack = 1;
1230                tcp_dsack_seen(tp);
1231                NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPDSACKRECV);
1232        } else if (num_sacks > 1) {
1233                u32 end_seq_1 = get_unaligned_be32(&sp[1].end_seq);
1234                u32 start_seq_1 = get_unaligned_be32(&sp[1].start_seq);
1235
1236                if (!after(end_seq_0, end_seq_1) &&
1237                    !before(start_seq_0, start_seq_1)) {
1238                        dup_sack = 1;
1239                        tcp_dsack_seen(tp);
1240                        NET_INC_STATS_BH(sock_net(sk),
1241                                        LINUX_MIB_TCPDSACKOFORECV);
1242                }
1243        }
1244
1245        /* D-SACK for already forgotten data... Do dumb counting. */
1246        if (dup_sack && tp->undo_marker && tp->undo_retrans &&
1247            !after(end_seq_0, prior_snd_una) &&
1248            after(end_seq_0, tp->undo_marker))
1249                tp->undo_retrans--;
1250
1251        return dup_sack;
1252}
1253
1254struct tcp_sacktag_state {
1255        int reord;
1256        int fack_count;
1257        int flag;
1258};
1259
1260/* Check if skb is fully within the SACK block. In presence of GSO skbs,
1261 * the incoming SACK may not exactly match but we can find smaller MSS
1262 * aligned portion of it that matches. Therefore we might need to fragment
1263 * which may fail and creates some hassle (caller must handle error case
1264 * returns).
1265 *
1266 * FIXME: this could be merged to shift decision code
1267 */
1268static int tcp_match_skb_to_sack(struct sock *sk, struct sk_buff *skb,
1269                                 u32 start_seq, u32 end_seq)
1270{
1271        int in_sack, err;
1272        unsigned int pkt_len;
1273        unsigned int mss;
1274
1275        in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) &&
1276                  !before(end_seq, TCP_SKB_CB(skb)->end_seq);
1277
1278        if (tcp_skb_pcount(skb) > 1 && !in_sack &&
1279            after(TCP_SKB_CB(skb)->end_seq, start_seq)) {
1280                mss = tcp_skb_mss(skb);
1281                in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq);
1282
1283                if (!in_sack) {
1284                        pkt_len = start_seq - TCP_SKB_CB(skb)->seq;
1285                        if (pkt_len < mss)
1286                                pkt_len = mss;
1287                } else {
1288                        pkt_len = end_seq - TCP_SKB_CB(skb)->seq;
1289                        if (pkt_len < mss)
1290                                return -EINVAL;
1291                }
1292
1293                /* Round if necessary so that SACKs cover only full MSSes
1294                 * and/or the remaining small portion (if present)
1295                 */
1296                if (pkt_len > mss) {
1297                        unsigned int new_len = (pkt_len / mss) * mss;
1298                        if (!in_sack && new_len < pkt_len) {
1299                                new_len += mss;
1300                                if (new_len > skb->len)
1301                                        return 0;
1302                        }
1303                        pkt_len = new_len;
1304                }
1305                err = tcp_fragment(sk, skb, pkt_len, mss);
1306                if (err < 0)
1307                        return err;
1308        }
1309
1310        return in_sack;
1311}
1312
1313static u8 tcp_sacktag_one(const struct sk_buff *skb, struct sock *sk,
1314                          struct tcp_sacktag_state *state,
1315                          int dup_sack, int pcount)
1316{
1317        struct tcp_sock *tp = tcp_sk(sk);
1318        u8 sacked = TCP_SKB_CB(skb)->sacked;
1319        int fack_count = state->fack_count;
1320
1321        /* Account D-SACK for retransmitted packet. */
1322        if (dup_sack && (sacked & TCPCB_RETRANS)) {
1323                if (tp->undo_marker && tp->undo_retrans &&
1324                    after(TCP_SKB_CB(skb)->end_seq, tp->undo_marker))
1325                        tp->undo_retrans--;
1326                if (sacked & TCPCB_SACKED_ACKED)
1327                        state->reord = min(fack_count, state->reord);
1328        }
1329
1330        /* Nothing to do; acked frame is about to be dropped (was ACKed). */
1331        if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
1332                return sacked;
1333
1334        if (!(sacked & TCPCB_SACKED_ACKED)) {
1335                if (sacked & TCPCB_SACKED_RETRANS) {
1336                        /* If the segment is not tagged as lost,
1337                         * we do not clear RETRANS, believing
1338                         * that retransmission is still in flight.
1339                         */
1340                        if (sacked & TCPCB_LOST) {
1341                                sacked &= ~(TCPCB_LOST|TCPCB_SACKED_RETRANS);
1342                                tp->lost_out -= pcount;
1343                                tp->retrans_out -= pcount;
1344                        }
1345                } else {
1346                        if (!(sacked & TCPCB_RETRANS)) {
1347                                /* New sack for not retransmitted frame,
1348                                 * which was in hole. It is reordering.
1349                                 */
1350                                if (before(TCP_SKB_CB(skb)->seq,
1351                                           tcp_highest_sack_seq(tp)))
1352                                        state->reord = min(fack_count,
1353                                                           state->reord);
1354
1355                                /* SACK enhanced F-RTO (RFC4138; Appendix B) */
1356                                if (!after(TCP_SKB_CB(skb)->end_seq, tp->frto_highmark))
1357                                        state->flag |= FLAG_ONLY_ORIG_SACKED;
1358                        }
1359
1360                        if (sacked & TCPCB_LOST) {
1361                                sacked &= ~TCPCB_LOST;
1362                                tp->lost_out -= pcount;
1363                        }
1364                }
1365
1366                sacked |= TCPCB_SACKED_ACKED;
1367                state->flag |= FLAG_DATA_SACKED;
1368                tp->sacked_out += pcount;
1369
1370                fack_count += pcount;
1371
1372                /* Lost marker hint past SACKed? Tweak RFC3517 cnt */
1373                if (!tcp_is_fack(tp) && (tp->lost_skb_hint != NULL) &&
1374                    before(TCP_SKB_CB(skb)->seq,
1375                           TCP_SKB_CB(tp->lost_skb_hint)->seq))
1376                        tp->lost_cnt_hint += pcount;
1377
1378                if (fack_count > tp->fackets_out)
1379                        tp->fackets_out = fack_count;
1380        }
1381
1382        /* D-SACK. We can detect redundant retransmission in S|R and plain R
1383         * frames and clear it. undo_retrans is decreased above, L|R frames
1384         * are accounted above as well.
1385         */
1386        if (dup_sack && (sacked & TCPCB_SACKED_RETRANS)) {
1387                sacked &= ~TCPCB_SACKED_RETRANS;
1388                tp->retrans_out -= pcount;
1389        }
1390
1391        return sacked;
1392}
1393
1394static int tcp_shifted_skb(struct sock *sk, struct sk_buff *skb,
1395                           struct tcp_sacktag_state *state,
1396                           unsigned int pcount, int shifted, int mss,
1397                           int dup_sack)
1398{
1399        struct tcp_sock *tp = tcp_sk(sk);
1400        struct sk_buff *prev = tcp_write_queue_prev(sk, skb);
1401
1402        BUG_ON(!pcount);
1403
1404        if (skb == tp->lost_skb_hint)
1405                tp->lost_cnt_hint += pcount;
1406
1407        TCP_SKB_CB(prev)->end_seq += shifted;
1408        TCP_SKB_CB(skb)->seq += shifted;
1409
1410        skb_shinfo(prev)->gso_segs += pcount;
1411        BUG_ON(skb_shinfo(skb)->gso_segs < pcount);
1412        skb_shinfo(skb)->gso_segs -= pcount;
1413
1414        /* When we're adding to gso_segs == 1, gso_size will be zero,
1415         * in theory this shouldn't be necessary but as long as DSACK
1416         * code can come after this skb later on it's better to keep
1417         * setting gso_size to something.
1418         */
1419        if (!skb_shinfo(prev)->gso_size) {
1420                skb_shinfo(prev)->gso_size = mss;
1421                skb_shinfo(prev)->gso_type = sk->sk_gso_type;
1422        }
1423
1424        /* CHECKME: To clear or not to clear? Mimics normal skb currently */
1425        if (skb_shinfo(skb)->gso_segs <= 1) {
1426                skb_shinfo(skb)->gso_size = 0;
1427                skb_shinfo(skb)->gso_type = 0;
1428        }
1429
1430        /* We discard results */
1431        tcp_sacktag_one(skb, sk, state, dup_sack, pcount);
1432
1433        /* Difference in this won't matter, both ACKed by the same cumul. ACK */
1434        TCP_SKB_CB(prev)->sacked |= (TCP_SKB_CB(skb)->sacked & TCPCB_EVER_RETRANS);
1435
1436        if (skb->len > 0) {
1437                BUG_ON(!tcp_skb_pcount(skb));
1438                NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SACKSHIFTED);
1439                return 0;
1440        }
1441
1442        /* Whole SKB was eaten :-) */
1443
1444        if (skb == tp->retransmit_skb_hint)
1445                tp->retransmit_skb_hint = prev;
1446        if (skb == tp->scoreboard_skb_hint)
1447                tp->scoreboard_skb_hint = prev;
1448        if (skb == tp->lost_skb_hint) {
1449                tp->lost_skb_hint = prev;
1450                tp->lost_cnt_hint -= tcp_skb_pcount(prev);
1451        }
1452
1453        TCP_SKB_CB(skb)->tcp_flags |= TCP_SKB_CB(prev)->tcp_flags;
1454        if (skb == tcp_highest_sack(sk))
1455                tcp_advance_highest_sack(sk, skb);
1456
1457        tcp_unlink_write_queue(skb, sk);
1458        sk_wmem_free_skb(sk, skb);
1459
1460        NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SACKMERGED);
1461
1462        return 1;
1463}
1464
1465/* I wish gso_size would have a bit more sane initialization than
1466 * something-or-zero which complicates things
1467 */
1468static int tcp_skb_seglen(const struct sk_buff *skb)
1469{
1470        return tcp_skb_pcount(skb) == 1 ? skb->len : tcp_skb_mss(skb);
1471}
1472
1473/* Shifting pages past head area doesn't work */
1474static int skb_can_shift(const struct sk_buff *skb)
1475{
1476        return !skb_headlen(skb) && skb_is_nonlinear(skb);
1477}
1478
1479/* Try collapsing SACK blocks spanning across multiple skbs to a single
1480 * skb.
1481 */
1482static struct sk_buff *tcp_shift_skb_data(struct sock *sk, struct sk_buff *skb,
1483                                          struct tcp_sacktag_state *state,
1484                                          u32 start_seq, u32 end_seq,
1485                                          int dup_sack)
1486{
1487        struct tcp_sock *tp = tcp_sk(sk);
1488        struct sk_buff *prev;
1489        int mss;
1490        int pcount = 0;
1491        int len;
1492        int in_sack;
1493
1494        if (!sk_can_gso(sk))
1495                goto fallback;
1496
1497        /* Normally R but no L won't result in plain S */
1498        if (!dup_sack &&
1499            (TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_RETRANS)) == TCPCB_SACKED_RETRANS)
1500                goto fallback;
1501        if (!skb_can_shift(skb))
1502                goto fallback;
1503        /* This frame is about to be dropped (was ACKed). */
1504        if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
1505                goto fallback;
1506
1507        /* Can only happen with delayed DSACK + discard craziness */
1508        if (unlikely(skb == tcp_write_queue_head(sk)))
1509                goto fallback;
1510        prev = tcp_write_queue_prev(sk, skb);
1511
1512        if ((TCP_SKB_CB(prev)->sacked & TCPCB_TAGBITS) != TCPCB_SACKED_ACKED)
1513                goto fallback;
1514
1515        in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) &&
1516                  !before(end_seq, TCP_SKB_CB(skb)->end_seq);
1517
1518        if (in_sack) {
1519                len = skb->len;
1520                pcount = tcp_skb_pcount(skb);
1521                mss = tcp_skb_seglen(skb);
1522
1523                /* TODO: Fix DSACKs to not fragment already SACKed and we can
1524                 * drop this restriction as unnecessary
1525                 */
1526                if (mss != tcp_skb_seglen(prev))
1527                        goto fallback;
1528        } else {
1529                if (!after(TCP_SKB_CB(skb)->end_seq, start_seq))
1530                        goto noop;
1531                /* CHECKME: This is non-MSS split case only?, this will
1532                 * cause skipped skbs due to advancing loop btw, original
1533                 * has that feature too
1534                 */
1535                if (tcp_skb_pcount(skb) <= 1)
1536                        goto noop;
1537
1538                in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq);
1539                if (!in_sack) {
1540                        /* TODO: head merge to next could be attempted here
1541                         * if (!after(TCP_SKB_CB(skb)->end_seq, end_seq)),
1542                         * though it might not be worth of the additional hassle
1543                         *
1544                         * ...we can probably just fallback to what was done
1545                         * previously. We could try merging non-SACKed ones
1546                         * as well but it probably isn't going to buy off
1547                         * because later SACKs might again split them, and
1548                         * it would make skb timestamp tracking considerably
1549                         * harder problem.
1550                         */
1551                        goto fallback;
1552                }
1553
1554                len = end_seq - TCP_SKB_CB(skb)->seq;
1555                BUG_ON(len < 0);
1556                BUG_ON(len > skb->len);
1557
1558                /* MSS boundaries should be honoured or else pcount will
1559                 * severely break even though it makes things bit trickier.
1560                 * Optimize common case to avoid most of the divides
1561                 */
1562                mss = tcp_skb_mss(skb);
1563
1564                /* TODO: Fix DSACKs to not fragment already SACKed and we can
1565                 * drop this restriction as unnecessary
1566                 */
1567                if (mss != tcp_skb_seglen(prev))
1568                        goto fallback;
1569
1570                if (len == mss) {
1571                        pcount = 1;
1572                } else if (len < mss) {
1573                        goto noop;
1574                } else {
1575                        pcount = len / mss;
1576                        len = pcount * mss;
1577                }
1578        }
1579
1580        if (!skb_shift(prev, skb, len))
1581                goto fallback;
1582        if (!tcp_shifted_skb(sk, skb, state, pcount, len, mss, dup_sack))
1583                goto out;
1584
1585        /* Hole filled allows collapsing with the next as well, this is very
1586         * useful when hole on every nth skb pattern happens
1587         */
1588        if (prev == tcp_write_queue_tail(sk))
1589                goto out;
1590        skb = tcp_write_queue_next(sk, prev);
1591
1592        if (!skb_can_shift(skb) ||
1593            (skb == tcp_send_head(sk)) ||
1594            ((TCP_SKB_CB(skb)->sacked & TCPCB_TAGBITS) != TCPCB_SACKED_ACKED) ||
1595            (mss != tcp_skb_seglen(skb)))
1596                goto out;
1597
1598        len = skb->len;
1599        if (skb_shift(prev, skb, len)) {
1600                pcount += tcp_skb_pcount(skb);
1601                tcp_shifted_skb(sk, skb, state, tcp_skb_pcount(skb), len, mss, 0);
1602        }
1603
1604out:
1605        state->fack_count += pcount;
1606        return prev;
1607
1608noop:
1609        return skb;
1610
1611fallback:
1612        NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SACKSHIFTFALLBACK);
1613        return NULL;
1614}
1615
1616static struct sk_buff *tcp_sacktag_walk(struct sk_buff *skb, struct sock *sk,
1617                                        struct tcp_sack_block *next_dup,
1618                                        struct tcp_sacktag_state *state,
1619                                        u32 start_seq, u32 end_seq,
1620                                        int dup_sack_in)
1621{
1622        struct tcp_sock *tp = tcp_sk(sk);
1623        struct sk_buff *tmp;
1624
1625        tcp_for_write_queue_from(skb, sk) {
1626                int in_sack = 0;
1627                int dup_sack = dup_sack_in;
1628
1629                if (skb == tcp_send_head(sk))
1630                        break;
1631
1632                /* queue is in-order => we can short-circuit the walk early */
1633                if (!before(TCP_SKB_CB(skb)->seq, end_seq))
1634                        break;
1635
1636                if ((next_dup != NULL) &&
1637                    before(TCP_SKB_CB(skb)->seq, next_dup->end_seq)) {
1638                        in_sack = tcp_match_skb_to_sack(sk, skb,
1639                                                        next_dup->start_seq,
1640                                                        next_dup->end_seq);
1641                        if (in_sack > 0)
1642                                dup_sack = 1;
1643                }
1644
1645                /* skb reference here is a bit tricky to get right, since
1646                 * shifting can eat and free both this skb and the next,
1647                 * so not even _safe variant of the loop is enough.
1648                 */
1649                if (in_sack <= 0) {
1650                        tmp = tcp_shift_skb_data(sk, skb, state,
1651                                                 start_seq, end_seq, dup_sack);
1652                        if (tmp != NULL) {
1653                                if (tmp != skb) {
1654                                        skb = tmp;
1655                                        continue;
1656                                }
1657
1658                                in_sack = 0;
1659                        } else {
1660                                in_sack = tcp_match_skb_to_sack(sk, skb,
1661                                                                start_seq,
1662                                                                end_seq);
1663                        }
1664                }
1665
1666                if (unlikely(in_sack < 0))
1667                        break;
1668
1669                if (in_sack) {
1670                        TCP_SKB_CB(skb)->sacked = tcp_sacktag_one(skb, sk,
1671                                                                  state,
1672                                                                  dup_sack,
1673                                                                  tcp_skb_pcount(skb));
1674
1675                        if (!before(TCP_SKB_CB(skb)->seq,
1676                                    tcp_highest_sack_seq(tp)))
1677                                tcp_advance_highest_sack(sk, skb);
1678                }
1679
1680                state->fack_count += tcp_skb_pcount(skb);
1681        }
1682        return skb;
1683}
1684
1685/* Avoid all extra work that is being done by sacktag while walking in
1686 * a normal way
1687 */
1688static struct sk_buff *tcp_sacktag_skip(struct sk_buff *skb, struct sock *sk,
1689                                        struct tcp_sacktag_state *state,
1690                                        u32 skip_to_seq)
1691{
1692        tcp_for_write_queue_from(skb, sk) {
1693                if (skb == tcp_send_head(sk))
1694                        break;
1695
1696                if (after(TCP_SKB_CB(skb)->end_seq, skip_to_seq))
1697                        break;
1698
1699                state->fack_count += tcp_skb_pcount(skb);
1700        }
1701        return skb;
1702}
1703
1704static struct sk_buff *tcp_maybe_skipping_dsack(struct sk_buff *skb,
1705                                                struct sock *sk,
1706                                                struct tcp_sack_block *next_dup,
1707                                                struct tcp_sacktag_state *state,
1708                                                u32 skip_to_seq)
1709{
1710        if (next_dup == NULL)
1711                return skb;
1712
1713        if (before(next_dup->start_seq, skip_to_seq)) {
1714                skb = tcp_sacktag_skip(skb, sk, state, next_dup->start_seq);
1715                skb = tcp_sacktag_walk(skb, sk, NULL, state,
1716                                       next_dup->start_seq, next_dup->end_seq,
1717                                       1);
1718        }
1719
1720        return skb;
1721}
1722
1723static int tcp_sack_cache_ok(const struct tcp_sock *tp, const struct tcp_sack_block *cache)
1724{
1725        return cache < tp->recv_sack_cache + ARRAY_SIZE(tp->recv_sack_cache);
1726}
1727
1728static int
1729tcp_sacktag_write_queue(struct sock *sk, const struct sk_buff *ack_skb,
1730                        u32 prior_snd_una)
1731{
1732        const struct inet_connection_sock *icsk = inet_csk(sk);
1733        struct tcp_sock *tp = tcp_sk(sk);
1734        const unsigned char *ptr = (skb_transport_header(ack_skb) +
1735                                    TCP_SKB_CB(ack_skb)->sacked);
1736        struct tcp_sack_block_wire *sp_wire = (struct tcp_sack_block_wire *)(ptr+2);
1737        struct tcp_sack_block sp[TCP_NUM_SACKS];
1738        struct tcp_sack_block *cache;
1739        struct tcp_sacktag_state state;
1740        struct sk_buff *skb;
1741        int num_sacks = min(TCP_NUM_SACKS, (ptr[1] - TCPOLEN_SACK_BASE) >> 3);
1742        int used_sacks;
1743        int found_dup_sack = 0;
1744        int i, j;
1745        int first_sack_index;
1746
1747        state.flag = 0;
1748        state.reord = tp->packets_out;
1749
1750        if (!tp->sacked_out) {
1751                if (WARN_ON(tp->fackets_out))
1752                        tp->fackets_out = 0;
1753                tcp_highest_sack_reset(sk);
1754        }
1755
1756        found_dup_sack = tcp_check_dsack(sk, ack_skb, sp_wire,
1757                                         num_sacks, prior_snd_una);
1758        if (found_dup_sack)
1759                state.flag |= FLAG_DSACKING_ACK;
1760
1761        /* Eliminate too old ACKs, but take into
1762         * account more or less fresh ones, they can
1763         * contain valid SACK info.
1764         */
1765        if (before(TCP_SKB_CB(ack_skb)->ack_seq, prior_snd_una - tp->max_window))
1766                return 0;
1767
1768        if (!tp->packets_out)
1769                goto out;
1770
1771        used_sacks = 0;
1772        first_sack_index = 0;
1773        for (i = 0; i < num_sacks; i++) {
1774                int dup_sack = !i && found_dup_sack;
1775
1776                sp[used_sacks].start_seq = get_unaligned_be32(&sp_wire[i].start_seq);
1777                sp[used_sacks].end_seq = get_unaligned_be32(&sp_wire[i].end_seq);
1778
1779                if (!tcp_is_sackblock_valid(tp, dup_sack,
1780                                            sp[used_sacks].start_seq,
1781                                            sp[used_sacks].end_seq)) {
1782                        int mib_idx;
1783
1784                        if (dup_sack) {
1785                                if (!tp->undo_marker)
1786                                        mib_idx = LINUX_MIB_TCPDSACKIGNOREDNOUNDO;
1787                                else
1788                                        mib_idx = LINUX_MIB_TCPDSACKIGNOREDOLD;
1789                        } else {
1790                                /* Don't count olds caused by ACK reordering */
1791                                if ((TCP_SKB_CB(ack_skb)->ack_seq != tp->snd_una) &&
1792                                    !after(sp[used_sacks].end_seq, tp->snd_una))
1793                                        continue;
1794                                mib_idx = LINUX_MIB_TCPSACKDISCARD;
1795                        }
1796
1797                        NET_INC_STATS_BH(sock_net(sk), mib_idx);
1798                        if (i == 0)
1799                                first_sack_index = -1;
1800                        continue;
1801                }
1802
1803                /* Ignore very old stuff early */
1804                if (!after(sp[used_sacks].end_seq, prior_snd_una))
1805                        continue;
1806
1807                used_sacks++;
1808        }
1809
1810        /* order SACK blocks to allow in order walk of the retrans queue */
1811        for (i = used_sacks - 1; i > 0; i--) {
1812                for (j = 0; j < i; j++) {
1813                        if (after(sp[j].start_seq, sp[j + 1].start_seq)) {
1814                                swap(sp[j], sp[j + 1]);
1815
1816                                /* Track where the first SACK block goes to */
1817                                if (j == first_sack_index)
1818                                        first_sack_index = j + 1;
1819                        }
1820                }
1821        }
1822
1823        skb = tcp_write_queue_head(sk);
1824        state.fack_count = 0;
1825        i = 0;
1826
1827        if (!tp->sacked_out) {
1828                /* It's already past, so skip checking against it */
1829                cache = tp->recv_sack_cache + ARRAY_SIZE(tp->recv_sack_cache);
1830        } else {
1831                cache = tp->recv_sack_cache;
1832                /* Skip empty blocks in at head of the cache */
1833                while (tcp_sack_cache_ok(tp, cache) && !cache->start_seq &&
1834                       !cache->end_seq)
1835                        cache++;
1836        }
1837
1838        while (i < used_sacks) {
1839                u32 start_seq = sp[i].start_seq;
1840                u32 end_seq = sp[i].end_seq;
1841                int dup_sack = (found_dup_sack && (i == first_sack_index));
1842                struct tcp_sack_block *next_dup = NULL;
1843
1844                if (found_dup_sack && ((i + 1) == first_sack_index))
1845                        next_dup = &sp[i + 1];
1846
1847                /* Event "B" in the comment above. */
1848                if (after(end_seq, tp->high_seq))
1849                        state.flag |= FLAG_DATA_LOST;
1850
1851                /* Skip too early cached blocks */
1852                while (tcp_sack_cache_ok(tp, cache) &&
1853                       !before(start_seq, cache->end_seq))
1854                        cache++;
1855
1856                /* Can skip some work by looking recv_sack_cache? */
1857                if (tcp_sack_cache_ok(tp, cache) && !dup_sack &&
1858                    after(end_seq, cache->start_seq)) {
1859
1860                        /* Head todo? */
1861                        if (before(start_seq, cache->start_seq)) {
1862                                skb = tcp_sacktag_skip(skb, sk, &state,
1863                                                       start_seq);
1864                                skb = tcp_sacktag_walk(skb, sk, next_dup,
1865                                                       &state,
1866                                                       start_seq,
1867                                                       cache->start_seq,
1868                                                       dup_sack);
1869                        }
1870
1871                        /* Rest of the block already fully processed? */
1872                        if (!after(end_seq, cache->end_seq))
1873                                goto advance_sp;
1874
1875                        skb = tcp_maybe_skipping_dsack(skb, sk, next_dup,
1876                                                       &state,
1877                                                       cache->end_seq);
1878
1879                        /* ...tail remains todo... */
1880                        if (tcp_highest_sack_seq(tp) == cache->end_seq) {
1881                                /* ...but better entrypoint exists! */
1882                                skb = tcp_highest_sack(sk);
1883                                if (skb == NULL)
1884                                        break;
1885                                state.fack_count = tp->fackets_out;
1886                                cache++;
1887                                goto walk;
1888                        }
1889
1890                        skb = tcp_sacktag_skip(skb, sk, &state, cache->end_seq);
1891                        /* Check overlap against next cached too (past this one already) */
1892                        cache++;
1893                        continue;
1894                }
1895
1896                if (!before(start_seq, tcp_highest_sack_seq(tp))) {
1897                        skb = tcp_highest_sack(sk);
1898                        if (skb == NULL)
1899                                break;
1900                        state.fack_count = tp->fackets_out;
1901                }
1902                skb = tcp_sacktag_skip(skb, sk, &state, start_seq);
1903
1904walk:
1905                skb = tcp_sacktag_walk(skb, sk, next_dup, &state,
1906                                       start_seq, end_seq, dup_sack);
1907
1908advance_sp:
1909                /* SACK enhanced FRTO (RFC4138, Appendix B): Clearing correct
1910                 * due to in-order walk
1911                 */
1912                if (after(end_seq, tp->frto_highmark))
1913                        state.flag &= ~FLAG_ONLY_ORIG_SACKED;
1914
1915                i++;
1916        }
1917
1918        /* Clear the head of the cache sack blocks so we can skip it next time */
1919        for (i = 0; i < ARRAY_SIZE(tp->recv_sack_cache) - used_sacks; i++) {
1920                tp->recv_sack_cache[i].start_seq = 0;
1921                tp->recv_sack_cache[i].end_seq = 0;
1922        }
1923        for (j = 0; j < used_sacks; j++)
1924                tp->recv_sack_cache[i++] = sp[j];
1925
1926        tcp_mark_lost_retrans(sk);
1927
1928        tcp_verify_left_out(tp);
1929
1930        if ((state.reord < tp->fackets_out) &&
1931            ((icsk->icsk_ca_state != TCP_CA_Loss) || tp->undo_marker) &&
1932            (!tp->frto_highmark || after(tp->snd_una, tp->frto_highmark)))
1933                tcp_update_reordering(sk, tp->fackets_out - state.reord, 0);
1934
1935out:
1936
1937#if FASTRETRANS_DEBUG > 0
1938        WARN_ON((int)tp->sacked_out < 0);
1939        WARN_ON((int)tp->lost_out < 0);
1940        WARN_ON((int)tp->retrans_out < 0);
1941        WARN_ON((int)tcp_packets_in_flight(tp) < 0);
1942#endif
1943        return state.flag;
1944}
1945
1946/* Limits sacked_out so that sum with lost_out isn't ever larger than
1947 * packets_out. Returns zero if sacked_out adjustement wasn't necessary.
1948 */
1949static int tcp_limit_reno_sacked(struct tcp_sock *tp)
1950{
1951        u32 holes;
1952
1953        holes = max(tp->lost_out, 1U);
1954        holes = min(holes, tp->packets_out);
1955
1956        if ((tp->sacked_out + holes) > tp->packets_out) {
1957                tp->sacked_out = tp->packets_out - holes;
1958                return 1;
1959        }
1960        return 0;
1961}
1962
1963/* If we receive more dupacks than we expected counting segments
1964 * in assumption of absent reordering, interpret this as reordering.
1965 * The only another reason could be bug in receiver TCP.
1966 */
1967static void tcp_check_reno_reordering(struct sock *sk, const int addend)
1968{
1969        struct tcp_sock *tp = tcp_sk(sk);
1970        if (tcp_limit_reno_sacked(tp))
1971                tcp_update_reordering(sk, tp->packets_out + addend, 0);
1972}
1973
1974/* Emulate SACKs for SACKless connection: account for a new dupack. */
1975
1976static void tcp_add_reno_sack(struct sock *sk)
1977{
1978        struct tcp_sock *tp = tcp_sk(sk);
1979        tp->sacked_out++;
1980        tcp_check_reno_reordering(sk, 0);
1981        tcp_verify_left_out(tp);
1982}
1983
1984/* Account for ACK, ACKing some data in Reno Recovery phase. */
1985
1986static void tcp_remove_reno_sacks(struct sock *sk, int acked)
1987{
1988        struct tcp_sock *tp = tcp_sk(sk);
1989
1990        if (acked > 0) {
1991                /* One ACK acked hole. The rest eat duplicate ACKs. */
1992                if (acked - 1 >= tp->sacked_out)
1993                        tp->sacked_out = 0;
1994                else
1995                        tp->sacked_out -= acked - 1;
1996        }
1997        tcp_check_reno_reordering(sk, acked);
1998        tcp_verify_left_out(tp);
1999}
2000
2001static inline void tcp_reset_reno_sack(struct tcp_sock *tp)
2002{
2003        tp->sacked_out = 0;
2004}
2005
2006static int tcp_is_sackfrto(const struct tcp_sock *tp)
2007{
2008        return (sysctl_tcp_frto == 0x2) && !tcp_is_reno(tp);
2009}
2010
2011/* F-RTO can only be used if TCP has never retransmitted anything other than
2012 * head (SACK enhanced variant from Appendix B of RFC4138 is more robust here)
2013 */
2014int tcp_use_frto(struct sock *sk)
2015{
2016        const struct tcp_sock *tp = tcp_sk(sk);
2017        const struct inet_connection_sock *icsk = inet_csk(sk);
2018        struct sk_buff *skb;
2019
2020        if (!sysctl_tcp_frto)
2021                return 0;
2022
2023        /* MTU probe and F-RTO won't really play nicely along currently */
2024        if (icsk->icsk_mtup.probe_size)
2025                return 0;
2026
2027        if (tcp_is_sackfrto(tp))
2028                return 1;
2029
2030        /* Avoid expensive walking of rexmit queue if possible */
2031        if (tp->retrans_out > 1)
2032                return 0;
2033
2034        skb = tcp_write_queue_head(sk);
2035        if (tcp_skb_is_last(sk, skb))
2036                return 1;
2037        skb = tcp_write_queue_next(sk, skb);    /* Skips head */
2038        tcp_for_write_queue_from(skb, sk) {
2039                if (skb == tcp_send_head(sk))
2040                        break;
2041                if (TCP_SKB_CB(skb)->sacked & TCPCB_RETRANS)
2042                        return 0;
2043                /* Short-circuit when first non-SACKed skb has been checked */
2044                if (!(TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED))
2045                        break;
2046        }
2047        return 1;
2048}
2049
2050/* RTO occurred, but do not yet enter Loss state. Instead, defer RTO
2051 * recovery a bit and use heuristics in tcp_process_frto() to detect if
2052 * the RTO was spurious. Only clear SACKED_RETRANS of the head here to
2053 * keep retrans_out counting accurate (with SACK F-RTO, other than head
2054 * may still have that bit set); TCPCB_LOST and remaining SACKED_RETRANS
2055 * bits are handled if the Loss state is really to be entered (in
2056 * tcp_enter_frto_loss).
2057 *
2058 * Do like tcp_enter_loss() would; when RTO expires the second time it
2059 * does:
2060 *  "Reduce ssthresh if it has not yet been made inside this window."
2061 */
2062void tcp_enter_frto(struct sock *sk)
2063{
2064        const struct inet_connection_sock *icsk = inet_csk(sk);
2065        struct tcp_sock *tp = tcp_sk(sk);
2066        struct sk_buff *skb;
2067
2068        if ((!tp->frto_counter && icsk->icsk_ca_state <= TCP_CA_Disorder) ||
2069            tp->snd_una == tp->high_seq ||
2070            ((icsk->icsk_ca_state == TCP_CA_Loss || tp->frto_counter) &&
2071             !icsk->icsk_retransmits)) {
2072                tp->prior_ssthresh = tcp_current_ssthresh(sk);
2073                /* Our state is too optimistic in ssthresh() call because cwnd
2074                 * is not reduced until tcp_enter_frto_loss() when previous F-RTO
2075                 * recovery has not yet completed. Pattern would be this: RTO,
2076                 * Cumulative ACK, RTO (2xRTO for the same segment does not end
2077                 * up here twice).
2078                 * RFC4138 should be more specific on what to do, even though
2079                 * RTO is quite unlikely to occur after the first Cumulative ACK
2080                 * due to back-off and complexity of triggering events ...
2081                 */
2082                if (tp->frto_counter) {
2083                        u32 stored_cwnd;
2084                        stored_cwnd = tp->snd_cwnd;
2085                        tp->snd_cwnd = 2;
2086                        tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
2087                        tp->snd_cwnd = stored_cwnd;
2088                } else {
2089                        tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
2090                }
2091                /* ... in theory, cong.control module could do "any tricks" in
2092                 * ssthresh(), which means that ca_state, lost bits and lost_out
2093                 * counter would have to be faked before the call occurs. We
2094                 * consider that too expensive, unlikely and hacky, so modules
2095                 * using these in ssthresh() must deal these incompatibility
2096                 * issues if they receives CA_EVENT_FRTO and frto_counter != 0
2097                 */
2098                tcp_ca_event(sk, CA_EVENT_FRTO);
2099        }
2100
2101        tp->undo_marker = tp->snd_una;
2102        tp->undo_retrans = 0;
2103
2104        skb = tcp_write_queue_head(sk);
2105        if (TCP_SKB_CB(skb)->sacked & TCPCB_RETRANS)
2106                tp->undo_marker = 0;
2107        if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) {
2108                TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
2109                tp->retrans_out -= tcp_skb_pcount(skb);
2110        }
2111        tcp_verify_left_out(tp);
2112
2113        /* Too bad if TCP was application limited */
2114        tp->snd_cwnd = min(tp->snd_cwnd, tcp_packets_in_flight(tp) + 1);
2115
2116        /* Earlier loss recovery underway (see RFC4138; Appendix B).
2117         * The last condition is necessary at least in tp->frto_counter case.
2118         */
2119        if (tcp_is_sackfrto(tp) && (tp->frto_counter ||
2120            ((1 << icsk->icsk_ca_state) & (TCPF_CA_Recovery|TCPF_CA_Loss))) &&
2121            after(tp->high_seq, tp->snd_una)) {
2122                tp->frto_highmark = tp->high_seq;
2123        } else {
2124                tp->frto_highmark = tp->snd_nxt;
2125        }
2126        tcp_set_ca_state(sk, TCP_CA_Disorder);
2127        tp->high_seq = tp->snd_nxt;
2128        tp->frto_counter = 1;
2129}
2130
2131/* Enter Loss state after F-RTO was applied. Dupack arrived after RTO,
2132 * which indicates that we should follow the traditional RTO recovery,
2133 * i.e. mark everything lost and do go-back-N retransmission.
2134 */
2135static void tcp_enter_frto_loss(struct sock *sk, int allowed_segments, int flag)
2136{
2137        struct tcp_sock *tp = tcp_sk(sk);
2138        struct sk_buff *skb;
2139
2140        tp->lost_out = 0;
2141        tp->retrans_out = 0;
2142        if (tcp_is_reno(tp))
2143                tcp_reset_reno_sack(tp);
2144
2145        tcp_for_write_queue(skb, sk) {
2146                if (skb == tcp_send_head(sk))
2147                        break;
2148
2149                TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST;
2150                /*
2151                 * Count the retransmission made on RTO correctly (only when
2152                 * waiting for the first ACK and did not get it)...
2153                 */
2154                if ((tp->frto_counter == 1) && !(flag & FLAG_DATA_ACKED)) {
2155                        /* For some reason this R-bit might get cleared? */
2156                        if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS)
2157                                tp->retrans_out += tcp_skb_pcount(skb);
2158                        /* ...enter this if branch just for the first segment */
2159                        flag |= FLAG_DATA_ACKED;
2160                } else {
2161                        if (TCP_SKB_CB(skb)->sacked & TCPCB_RETRANS)
2162                                tp->undo_marker = 0;
2163                        TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
2164                }
2165
2166                /* Marking forward transmissions that were made after RTO lost
2167                 * can cause unnecessary retransmissions in some scenarios,
2168                 * SACK blocks will mitigate that in some but not in all cases.
2169                 * We used to not mark them but it was causing break-ups with
2170                 * receivers that do only in-order receival.
2171                 *
2172                 * TODO: we could detect presence of such receiver and select
2173                 * different behavior per flow.
2174                 */
2175                if (!(TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)) {
2176                        TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
2177                        tp->lost_out += tcp_skb_pcount(skb);
2178                        tp->retransmit_high = TCP_SKB_CB(skb)->end_seq;
2179                }
2180        }
2181        tcp_verify_left_out(tp);
2182
2183        tp->snd_cwnd = tcp_packets_in_flight(tp) + allowed_segments;
2184        tp->snd_cwnd_cnt = 0;
2185        tp->snd_cwnd_stamp = tcp_time_stamp;
2186        tp->frto_counter = 0;
2187        tp->bytes_acked = 0;
2188
2189        tp->reordering = min_t(unsigned int, tp->reordering,
2190                               sysctl_tcp_reordering);
2191        tcp_set_ca_state(sk, TCP_CA_Loss);
2192        tp->high_seq = tp->snd_nxt;
2193        TCP_ECN_queue_cwr(tp);
2194
2195        tcp_clear_all_retrans_hints(tp);
2196}
2197
2198static void tcp_clear_retrans_partial(struct tcp_sock *tp)
2199{
2200        tp->retrans_out = 0;
2201        tp->lost_out = 0;
2202
2203        tp->undo_marker = 0;
2204        tp->undo_retrans = 0;
2205}
2206
2207void tcp_clear_retrans(struct tcp_sock *tp)
2208{
2209        tcp_clear_retrans_partial(tp);
2210
2211        tp->fackets_out = 0;
2212        tp->sacked_out = 0;
2213}
2214
2215/* Enter Loss state. If "how" is not zero, forget all SACK information
2216 * and reset tags completely, otherwise preserve SACKs. If receiver
2217 * dropped its ofo queue, we will know this due to reneging detection.
2218 */
2219void tcp_enter_loss(struct sock *sk, int how)
2220{
2221        const struct inet_connection_sock *icsk = inet_csk(sk);
2222        struct tcp_sock *tp = tcp_sk(sk);
2223        struct sk_buff *skb;
2224
2225        /* Reduce ssthresh if it has not yet been made inside this window. */
2226        if (icsk->icsk_ca_state <= TCP_CA_Disorder || tp->snd_una == tp->high_seq ||
2227            (icsk->icsk_ca_state == TCP_CA_Loss && !icsk->icsk_retransmits)) {
2228                tp->prior_ssthresh = tcp_current_ssthresh(sk);
2229                tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
2230                tcp_ca_event(sk, CA_EVENT_LOSS);
2231        }
2232        tp->snd_cwnd       = 1;
2233        tp->snd_cwnd_cnt   = 0;
2234        tp->snd_cwnd_stamp = tcp_time_stamp;
2235
2236        tp->bytes_acked = 0;
2237        tcp_clear_retrans_partial(tp);
2238
2239        if (tcp_is_reno(tp))
2240                tcp_reset_reno_sack(tp);
2241
2242        if (!how) {
2243                /* Push undo marker, if it was plain RTO and nothing
2244                 * was retransmitted. */
2245                tp->undo_marker = tp->snd_una;
2246        } else {
2247                tp->sacked_out = 0;
2248                tp->fackets_out = 0;
2249        }
2250        tcp_clear_all_retrans_hints(tp);
2251
2252        tcp_for_write_queue(skb, sk) {
2253                if (skb == tcp_send_head(sk))
2254                        break;
2255
2256                if (TCP_SKB_CB(skb)->sacked & TCPCB_RETRANS)
2257                        tp->undo_marker = 0;
2258                TCP_SKB_CB(skb)->sacked &= (~TCPCB_TAGBITS)|TCPCB_SACKED_ACKED;
2259                if (!(TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_ACKED) || how) {
2260                        TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_ACKED;
2261                        TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
2262                        tp->lost_out += tcp_skb_pcount(skb);
2263                        tp->retransmit_high = TCP_SKB_CB(skb)->end_seq;
2264                }
2265        }
2266        tcp_verify_left_out(tp);
2267
2268        tp->reordering = min_t(unsigned int, tp->reordering,
2269                               sysctl_tcp_reordering);
2270        tcp_set_ca_state(sk, TCP_CA_Loss);
2271        tp->high_seq = tp->snd_nxt;
2272        TCP_ECN_queue_cwr(tp);
2273        /* Abort F-RTO algorithm if one is in progress */
2274        tp->frto_counter = 0;
2275}
2276
2277/* If ACK arrived pointing to a remembered SACK, it means that our
2278 * remembered SACKs do not reflect real state of receiver i.e.
2279 * receiver _host_ is heavily congested (or buggy).
2280 *
2281 * Do processing similar to RTO timeout.
2282 */
2283static int tcp_check_sack_reneging(struct sock *sk, int flag)
2284{
2285        if (flag & FLAG_SACK_RENEGING) {
2286                struct inet_connection_sock *icsk = inet_csk(sk);
2287                NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSACKRENEGING);
2288
2289                tcp_enter_loss(sk, 1);
2290                icsk->icsk_retransmits++;
2291                tcp_retransmit_skb(sk, tcp_write_queue_head(sk));
2292                inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
2293                                          icsk->icsk_rto, TCP_RTO_MAX);
2294                return 1;
2295        }
2296        return 0;
2297}
2298
2299static inline int tcp_fackets_out(const struct tcp_sock *tp)
2300{
2301        return tcp_is_reno(tp) ? tp->sacked_out + 1 : tp->fackets_out;
2302}
2303
2304/* Heurestics to calculate number of duplicate ACKs. There's no dupACKs
2305 * counter when SACK is enabled (without SACK, sacked_out is used for
2306 * that purpose).
2307 *
2308 * Instead, with FACK TCP uses fackets_out that includes both SACKed
2309 * segments up to the highest received SACK block so far and holes in
2310 * between them.
2311 *
2312 * With reordering, holes may still be in flight, so RFC3517 recovery
2313 * uses pure sacked_out (total number of SACKed segments) even though
2314 * it violates the RFC that uses duplicate ACKs, often these are equal
2315 * but when e.g. out-of-window ACKs or packet duplication occurs,
2316 * they differ. Since neither occurs due to loss, TCP should really
2317 * ignore them.
2318 */
2319static inline int tcp_dupack_heuristics(const struct tcp_sock *tp)
2320{
2321        return tcp_is_fack(tp) ? tp->fackets_out : tp->sacked_out + 1;
2322}
2323
2324static inline int tcp_skb_timedout(const struct sock *sk,
2325                                   const struct sk_buff *skb)
2326{
2327        return tcp_time_stamp - TCP_SKB_CB(skb)->when > inet_csk(sk)->icsk_rto;
2328}
2329
2330static inline int tcp_head_timedout(const struct sock *sk)
2331{
2332        const struct tcp_sock *tp = tcp_sk(sk);
2333
2334        return tp->packets_out &&
2335               tcp_skb_timedout(sk, tcp_write_queue_head(sk));
2336}
2337
2338/* Linux NewReno/SACK/FACK/ECN state machine.
2339 * --------------------------------------
2340 *
2341 * "Open"       Normal state, no dubious events, fast path.
2342 * "Disorder"   In all the respects it is "Open",
2343 *              but requires a bit more attention. It is entered when
2344 *              we see some SACKs or dupacks. It is split of "Open"
2345 *              mainly to move some processing from fast path to slow one.
2346 * "CWR"        CWND was reduced due to some Congestion Notification event.
2347 *              It can be ECN, ICMP source quench, local device congestion.
2348 * "Recovery"   CWND was reduced, we are fast-retransmitting.
2349 * "Loss"       CWND was reduced due to RTO timeout or SACK reneging.
2350 *
2351 * tcp_fastretrans_alert() is entered:
2352 * - each incoming ACK, if state is not "Open"
2353 * - when arrived ACK is unusual, namely:
2354 *      * SACK
2355 *      * Duplicate ACK.
2356 *      * ECN ECE.
2357 *
2358 * Counting packets in flight is pretty simple.
2359 *
2360 *      in_flight = packets_out - left_out + retrans_out
2361 *
2362 *      packets_out is SND.NXT-SND.UNA counted in packets.
2363 *
2364 *      retrans_out is number of retransmitted segments.
2365 *
2366 *      left_out is number of segments left network, but not ACKed yet.
2367 *
2368 *              left_out = sacked_out + lost_out
2369 *
2370 *     sacked_out: Packets, which arrived to receiver out of order
2371 *                 and hence not ACKed. With SACKs this number is simply
2372 *                 amount of SACKed data. Even without SACKs
2373 *                 it is easy to give pretty reliable estimate of this number,
2374 *                 counting duplicate ACKs.
2375 *
2376 *       lost_out: Packets lost by network. TCP has no explicit
2377 *                 "loss notification" feedback from network (for now).
2378 *                 It means that this number can be only _guessed_.
2379 *                 Actually, it is the heuristics to predict lossage that
2380 *                 distinguishes different algorithms.
2381 *
2382 *      F.e. after RTO, when all the queue is considered as lost,
2383 *      lost_out = packets_out and in_flight = retrans_out.
2384 *
2385 *              Essentially, we have now two algorithms counting
2386 *              lost packets.
2387 *
2388 *              FACK: It is the simplest heuristics. As soon as we decided
2389 *              that something is lost, we decide that _all_ not SACKed
2390 *              packets until the most forward SACK are lost. I.e.
2391 *              lost_out = fackets_out - sacked_out and left_out = fackets_out.
2392 *              It is absolutely correct estimate, if network does not reorder
2393 *              packets. And it loses any connection to reality when reordering
2394 *              takes place. We use FACK by default until reordering
2395 *              is suspected on the path to this destination.
2396 *
2397 *              NewReno: when Recovery is entered, we assume that one segment
2398 *              is lost (classic Reno). While we are in Recovery and
2399 *              a partial ACK arrives, we assume that one more packet
2400 *              is lost (NewReno). This heuristics are the same in NewReno
2401 *              and SACK.
2402 *
2403 *  Imagine, that's all! Forget about all this shamanism about CWND inflation
2404 *  deflation etc. CWND is real congestion window, never inflated, changes
2405 *  only according to classic VJ rules.
2406 *
2407 * Really tricky (and requiring careful tuning) part of algorithm
2408 * is hidden in functions tcp_time_to_recover() and tcp_xmit_retransmit_queue().
2409 * The first determines the moment _when_ we should reduce CWND and,
2410 * hence, slow down forward transmission. In fact, it determines the moment
2411 * when we decide that hole is caused by loss, rather than by a reorder.
2412 *
2413 * tcp_xmit_retransmit_queue() decides, _what_ we should retransmit to fill
2414 * holes, caused by lost packets.
2415 *
2416 * And the most logically complicated part of algorithm is undo
2417 * heuristics. We detect false retransmits due to both too early
2418 * fast retransmit (reordering) and underestimated RTO, analyzing
2419 * timestamps and D-SACKs. When we detect that some segments were
2420 * retransmitted by mistake and CWND reduction was wrong, we undo
2421 * window reduction and abort recovery phase. This logic is hidden
2422 * inside several functions named tcp_try_undo_<something>.
2423 */
2424
2425/* This function decides, when we should leave Disordered state
2426 * and enter Recovery phase, reducing congestion window.
2427 *
2428 * Main question: may we further continue forward transmission
2429 * with the same cwnd?
2430 */
2431static int tcp_time_to_recover(struct sock *sk)
2432{
2433        struct tcp_sock *tp = tcp_sk(sk);
2434        __u32 packets_out;
2435
2436        /* Do not perform any recovery during F-RTO algorithm */
2437        if (tp->frto_counter)
2438                return 0;
2439
2440        /* Trick#1: The loss is proven. */
2441        if (tp->lost_out)
2442                return 1;
2443
2444        /* Not-A-Trick#2 : Classic rule... */
2445        if (tcp_dupack_heuristics(tp) > tp->reordering)
2446                return 1;
2447
2448        /* Trick#3 : when we use RFC2988 timer restart, fast
2449         * retransmit can be triggered by timeout of queue head.
2450         */
2451        if (tcp_is_fack(tp) && tcp_head_timedout(sk))
2452                return 1;
2453
2454        /* Trick#4: It is still not OK... But will it be useful to delay
2455         * recovery more?
2456         */
2457        packets_out = tp->packets_out;
2458        if (packets_out <= tp->reordering &&
2459            tp->sacked_out >= max_t(__u32, packets_out/2, sysctl_tcp_reordering) &&
2460            !tcp_may_send_now(sk)) {
2461                /* We have nothing to send. This connection is limited
2462                 * either by receiver window or by application.
2463                 */
2464                return 1;
2465        }
2466
2467        /* If a thin stream is detected, retransmit after first
2468         * received dupack. Employ only if SACK is supported in order
2469         * to avoid possible corner-case series of spurious retransmissions
2470         * Use only if there are no unsent data.
2471         */
2472        if ((tp->thin_dupack || sysctl_tcp_thin_dupack) &&
2473            tcp_stream_is_thin(tp) && tcp_dupack_heuristics(tp) > 1 &&
2474            tcp_is_sack(tp) && !tcp_send_head(sk))
2475                return 1;
2476
2477        return 0;
2478}
2479
2480/* New heuristics: it is possible only after we switched to restart timer
2481 * each time when something is ACKed. Hence, we can detect timed out packets
2482 * during fast retransmit without falling to slow start.
2483 *
2484 * Usefulness of this as is very questionable, since we should know which of
2485 * the segments is the next to timeout which is relatively expensive to find
2486 * in general case unless we add some data structure just for that. The
2487 * current approach certainly won't find the right one too often and when it
2488 * finally does find _something_ it usually marks large part of the window
2489 * right away (because a retransmission with a larger timestamp blocks the
2490 * loop from advancing). -ij
2491 */
2492static void tcp_timeout_skbs(struct sock *sk)
2493{
2494        struct tcp_sock *tp = tcp_sk(sk);
2495        struct sk_buff *skb;
2496
2497        if (!tcp_is_fack(tp) || !tcp_head_timedout(sk))
2498                return;
2499
2500        skb = tp->scoreboard_skb_hint;
2501        if (tp->scoreboard_skb_hint == NULL)
2502                skb = tcp_write_queue_head(sk);
2503
2504        tcp_for_write_queue_from(skb, sk) {
2505                if (skb == tcp_send_head(sk))
2506                        break;
2507                if (!tcp_skb_timedout(sk, skb))
2508                        break;
2509
2510                tcp_skb_mark_lost(tp, skb);
2511        }
2512
2513        tp->scoreboard_skb_hint = skb;
2514
2515        tcp_verify_left_out(tp);
2516}
2517
2518/* Mark head of queue up as lost. With RFC3517 SACK, the packets is
2519 * is against sacked "cnt", otherwise it's against facked "cnt"
2520 */
2521static void tcp_mark_head_lost(struct sock *sk, int packets, int mark_head)
2522{
2523        struct tcp_sock *tp = tcp_sk(sk);
2524        struct sk_buff *skb;
2525        int cnt, oldcnt;
2526        int err;
2527        unsigned int mss;
2528
2529        WARN_ON(packets > tp->packets_out);
2530        if (tp->lost_skb_hint) {
2531                skb = tp->lost_skb_hint;
2532                cnt = tp->lost_cnt_hint;
2533                /* Head already handled? */
2534                if (mark_head && skb != tcp_write_queue_head(sk))
2535                        return;
2536        } else {
2537                skb = tcp_write_queue_head(sk);
2538                cnt = 0;
2539        }
2540
2541        tcp_for_write_queue_from(skb, sk) {
2542                if (skb == tcp_send_head(sk))
2543                        break;
2544                /* TODO: do this better */
2545                /* this is not the most efficient way to do this... */
2546                tp->lost_skb_hint = skb;
2547                tp->lost_cnt_hint = cnt;
2548
2549                if (after(TCP_SKB_CB(skb)->end_seq, tp->high_seq))
2550                        break;
2551
2552                oldcnt = cnt;
2553                if (tcp_is_fack(tp) || tcp_is_reno(tp) ||
2554                    (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED))
2555                        cnt += tcp_skb_pcount(skb);
2556
2557                if (cnt > packets) {
2558                        if ((tcp_is_sack(tp) && !tcp_is_fack(tp)) ||
2559                            (oldcnt >= packets))
2560                                break;
2561
2562                        mss = skb_shinfo(skb)->gso_size;
2563                        err = tcp_fragment(sk, skb, (packets - oldcnt) * mss, mss);
2564                        if (err < 0)
2565                                break;
2566                        cnt = packets;
2567                }
2568
2569                tcp_skb_mark_lost(tp, skb);
2570
2571                if (mark_head)
2572                        break;
2573        }
2574        tcp_verify_left_out(tp);
2575}
2576
2577/* Account newly detected lost packet(s) */
2578
2579static void tcp_update_scoreboard(struct sock *sk, int fast_rexmit)
2580{
2581        struct tcp_sock *tp = tcp_sk(sk);
2582
2583        if (tcp_is_reno(tp)) {
2584                tcp_mark_head_lost(sk, 1, 1);
2585        } else if (tcp_is_fack(tp)) {
2586                int lost = tp->fackets_out - tp->reordering;
2587                if (lost <= 0)
2588                        lost = 1;
2589                tcp_mark_head_lost(sk, lost, 0);
2590        } else {
2591                int sacked_upto = tp->sacked_out - tp->reordering;
2592                if (sacked_upto >= 0)
2593                        tcp_mark_head_lost(sk, sacked_upto, 0);
2594                else if (fast_rexmit)
2595                        tcp_mark_head_lost(sk, 1, 1);
2596        }
2597
2598        tcp_timeout_skbs(sk);
2599}
2600
2601/* CWND moderation, preventing bursts due to too big ACKs
2602 * in dubious situations.
2603 */
2604static inline void tcp_moderate_cwnd(struct tcp_sock *tp)
2605{
2606        tp->snd_cwnd = min(tp->snd_cwnd,
2607                           tcp_packets_in_flight(tp) + tcp_max_burst(tp));
2608        tp->snd_cwnd_stamp = tcp_time_stamp;
2609}
2610
2611/* Lower bound on congestion window is slow start threshold
2612 * unless congestion avoidance choice decides to overide it.
2613 */
2614static inline u32 tcp_cwnd_min(const struct sock *sk)
2615{
2616        const struct tcp_congestion_ops *ca_ops = inet_csk(sk)->icsk_ca_ops;
2617
2618        return ca_ops->min_cwnd ? ca_ops->min_cwnd(sk) : tcp_sk(sk)->snd_ssthresh;
2619}
2620
2621/* Decrease cwnd each second ack. */
2622static void tcp_cwnd_down(struct sock *sk, int flag)
2623{
2624        struct tcp_sock *tp = tcp_sk(sk);
2625        int decr = tp->snd_cwnd_cnt + 1;
2626
2627        if ((flag & (FLAG_ANY_PROGRESS | FLAG_DSACKING_ACK)) ||
2628            (tcp_is_reno(tp) && !(flag & FLAG_NOT_DUP))) {
2629                tp->snd_cwnd_cnt = decr & 1;
2630                decr >>= 1;
2631
2632                if (decr && tp->snd_cwnd > tcp_cwnd_min(sk))
2633                        tp->snd_cwnd -= decr;
2634
2635                tp->snd_cwnd = min(tp->snd_cwnd, tcp_packets_in_flight(tp) + 1);
2636                tp->snd_cwnd_stamp = tcp_time_stamp;
2637        }
2638}
2639
2640/* Nothing was retransmitted or returned timestamp is less
2641 * than timestamp of the first retransmission.
2642 */
2643static inline int tcp_packet_delayed(const struct tcp_sock *tp)
2644{
2645        return !tp->retrans_stamp ||
2646                (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
2647                 before(tp->rx_opt.rcv_tsecr, tp->retrans_stamp));
2648}
2649
2650/* Undo procedures. */
2651
2652#if FASTRETRANS_DEBUG > 1
2653static void DBGUNDO(struct sock *sk, const char *msg)
2654{
2655        struct tcp_sock *tp = tcp_sk(sk);
2656        struct inet_sock *inet = inet_sk(sk);
2657
2658        if (sk->sk_family == AF_INET) {
2659                printk(KERN_DEBUG "Undo %s %pI4/%u c%u l%u ss%u/%u p%u\n",
2660                       msg,
2661                       &inet->inet_daddr, ntohs(inet->inet_dport),
2662                       tp->snd_cwnd, tcp_left_out(tp),
2663                       tp->snd_ssthresh, tp->prior_ssthresh,
2664                       tp->packets_out);
2665        }
2666#if defined(CONFIG_IPV6) || defined(CONFIG_IPV6_MODULE)
2667        else if (sk->sk_family == AF_INET6) {
2668                struct ipv6_pinfo *np = inet6_sk(sk);
2669                printk(KERN_DEBUG "Undo %s %pI6/%u c%u l%u ss%u/%u p%u\n",
2670                       msg,
2671                       &np->daddr, ntohs(inet->inet_dport),
2672                       tp->snd_cwnd, tcp_left_out(tp),
2673                       tp->snd_ssthresh, tp->prior_ssthresh,
2674                       tp->packets_out);
2675        }
2676#endif
2677}
2678#else
2679#define DBGUNDO(x...) do { } while (0)
2680#endif
2681
2682static void tcp_undo_cwr(struct sock *sk, const bool undo_ssthresh)
2683{
2684        struct tcp_sock *tp = tcp_sk(sk);
2685
2686        if (tp->prior_ssthresh) {
2687                const struct inet_connection_sock *icsk = inet_csk(sk);
2688
2689                if (icsk->icsk_ca_ops->undo_cwnd)
2690                        tp->snd_cwnd = icsk->icsk_ca_ops->undo_cwnd(sk);
2691                else
2692                        tp->snd_cwnd = max(tp->snd_cwnd, tp->snd_ssthresh << 1);
2693
2694                if (undo_ssthresh && tp->prior_ssthresh > tp->snd_ssthresh) {
2695                        tp->snd_ssthresh = tp->prior_ssthresh;
2696                        TCP_ECN_withdraw_cwr(tp);
2697                }
2698        } else {
2699                tp->snd_cwnd = max(tp->snd_cwnd, tp->snd_ssthresh);
2700        }
2701        tp->snd_cwnd_stamp = tcp_time_stamp;
2702}
2703
2704static inline int tcp_may_undo(const struct tcp_sock *tp)
2705{
2706        return tp->undo_marker && (!tp->undo_retrans || tcp_packet_delayed(tp));
2707}
2708
2709/* People celebrate: "We love our President!" */
2710static int tcp_try_undo_recovery(struct sock *sk)
2711{
2712        struct tcp_sock *tp = tcp_sk(sk);
2713
2714        if (tcp_may_undo(tp)) {
2715                int mib_idx;
2716
2717                /* Happy end! We did not retransmit anything
2718                 * or our original transmission succeeded.
2719                 */
2720                DBGUNDO(sk, inet_csk(sk)->icsk_ca_state == TCP_CA_Loss ? "loss" : "retrans");
2721                tcp_undo_cwr(sk, true);
2722                if (inet_csk(sk)->icsk_ca_state == TCP_CA_Loss)
2723                        mib_idx = LINUX_MIB_TCPLOSSUNDO;
2724                else
2725                        mib_idx = LINUX_MIB_TCPFULLUNDO;
2726
2727                NET_INC_STATS_BH(sock_net(sk), mib_idx);
2728                tp->undo_marker = 0;
2729        }
2730        if (tp->snd_una == tp->high_seq && tcp_is_reno(tp)) {
2731                /* Hold old state until something *above* high_seq
2732                 * is ACKed. For Reno it is MUST to prevent false
2733                 * fast retransmits (RFC2582). SACK TCP is safe. */
2734                tcp_moderate_cwnd(tp);
2735                return 1;
2736        }
2737        tcp_set_ca_state(sk, TCP_CA_Open);
2738        return 0;
2739}
2740
2741/* Try to undo cwnd reduction, because D-SACKs acked all retransmitted data */
2742static void tcp_try_undo_dsack(struct sock *sk)
2743{
2744        struct tcp_sock *tp = tcp_sk(sk);
2745
2746        if (tp->undo_marker && !tp->undo_retrans) {
2747                DBGUNDO(sk, "D-SACK");
2748                tcp_undo_cwr(sk, true);
2749                tp->undo_marker = 0;
2750                NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPDSACKUNDO);
2751        }
2752}
2753
2754/* We can clear retrans_stamp when there are no retransmissions in the
2755 * window. It would seem that it is trivially available for us in
2756 * tp->retrans_out, however, that kind of assumptions doesn't consider
2757 * what will happen if errors occur when sending retransmission for the
2758 * second time. ...It could the that such segment has only
2759 * TCPCB_EVER_RETRANS set at the present time. It seems that checking
2760 * the head skb is enough except for some reneging corner cases that
2761 * are not worth the effort.
2762 *
2763 * Main reason for all this complexity is the fact that connection dying
2764 * time now depends on the validity of the retrans_stamp, in particular,
2765 * that successive retransmissions of a segment must not advance
2766 * retrans_stamp under any conditions.
2767 */
2768static int tcp_any_retrans_done(const struct sock *sk)
2769{
2770        const struct tcp_sock *tp = tcp_sk(sk);
2771        struct sk_buff *skb;
2772
2773        if (tp->retrans_out)
2774                return 1;
2775
2776        skb = tcp_write_queue_head(sk);
2777        if (unlikely(skb && TCP_SKB_CB(skb)->sacked & TCPCB_EVER_RETRANS))
2778                return 1;
2779
2780        return 0;
2781}
2782
2783/* Undo during fast recovery after partial ACK. */
2784
2785static int tcp_try_undo_partial(struct sock *sk, int acked)
2786{
2787        struct tcp_sock *tp = tcp_sk(sk);
2788        /* Partial ACK arrived. Force Hoe's retransmit. */
2789        int failed = tcp_is_reno(tp) || (tcp_fackets_out(tp) > tp->reordering);
2790
2791        if (tcp_may_undo(tp)) {
2792                /* Plain luck! Hole if filled with delayed
2793                 * packet, rather than with a retransmit.
2794                 */
2795                if (!tcp_any_retrans_done(sk))
2796                        tp->retrans_stamp = 0;
2797
2798                tcp_update_reordering(sk, tcp_fackets_out(tp) + acked, 1);
2799
2800                DBGUNDO(sk, "Hoe");
2801                tcp_undo_cwr(sk, false);
2802                NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPPARTIALUNDO);
2803
2804                /* So... Do not make Hoe's retransmit yet.
2805                 * If the first packet was delayed, the rest
2806                 * ones are most probably delayed as well.
2807                 */
2808                failed = 0;
2809        }
2810        return failed;
2811}
2812
2813/* Undo during loss recovery after partial ACK. */
2814static int tcp_try_undo_loss(struct sock *sk)
2815{
2816        struct tcp_sock *tp = tcp_sk(sk);
2817
2818        if (tcp_may_undo(tp)) {
2819                struct sk_buff *skb;
2820                tcp_for_write_queue(skb, sk) {
2821                        if (skb == tcp_send_head(sk))
2822                                break;
2823                        TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST;
2824                }
2825
2826                tcp_clear_all_retrans_hints(tp);
2827
2828                DBGUNDO(sk, "partial loss");
2829                tp->lost_out = 0;
2830                tcp_undo_cwr(sk, true);
2831                NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPLOSSUNDO);
2832                inet_csk(sk)->icsk_retransmits = 0;
2833                tp->undo_marker = 0;
2834                if (tcp_is_sack(tp))
2835                        tcp_set_ca_state(sk, TCP_CA_Open);
2836                return 1;
2837        }
2838        return 0;
2839}
2840
2841static inline void tcp_complete_cwr(struct sock *sk)
2842{
2843        struct tcp_sock *tp = tcp_sk(sk);
2844
2845        /* Do not moderate cwnd if it's already undone in cwr or recovery. */
2846        if (tp->undo_marker) {
2847                if (inet_csk(sk)->icsk_ca_state == TCP_CA_CWR)
2848                        tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_ssthresh);
2849                else /* PRR */
2850                        tp->snd_cwnd = tp->snd_ssthresh;
2851                tp->snd_cwnd_stamp = tcp_time_stamp;
2852        }
2853        tcp_ca_event(sk, CA_EVENT_COMPLETE_CWR);
2854}
2855
2856static void tcp_try_keep_open(struct sock *sk)
2857{
2858        struct tcp_sock *tp = tcp_sk(sk);
2859        int state = TCP_CA_Open;
2860
2861        if (tcp_left_out(tp) || tcp_any_retrans_done(sk) || tp->undo_marker)
2862                state = TCP_CA_Disorder;
2863
2864        if (inet_csk(sk)->icsk_ca_state != state) {
2865                tcp_set_ca_state(sk, state);
2866                tp->high_seq = tp->snd_nxt;
2867        }
2868}
2869
2870static void tcp_try_to_open(struct sock *sk, int flag)
2871{
2872        struct tcp_sock *tp = tcp_sk(sk);
2873
2874        tcp_verify_left_out(tp);
2875
2876        if (!tp->frto_counter && !tcp_any_retrans_done(sk))
2877                tp->retrans_stamp = 0;
2878
2879        if (flag & FLAG_ECE)
2880                tcp_enter_cwr(sk, 1);
2881
2882        if (inet_csk(sk)->icsk_ca_state != TCP_CA_CWR) {
2883                tcp_try_keep_open(sk);
2884                tcp_moderate_cwnd(tp);
2885        } else {
2886                tcp_cwnd_down(sk, flag);
2887        }
2888}
2889
2890static void tcp_mtup_probe_failed(struct sock *sk)
2891{
2892        struct inet_connection_sock *icsk = inet_csk(sk);
2893
2894        icsk->icsk_mtup.search_high = icsk->icsk_mtup.probe_size - 1;
2895        icsk->icsk_mtup.probe_size = 0;
2896}
2897
2898static void tcp_mtup_probe_success(struct sock *sk)
2899{
2900        struct tcp_sock *tp = tcp_sk(sk);
2901        struct inet_connection_sock *icsk = inet_csk(sk);
2902
2903        /* FIXME: breaks with very large cwnd */
2904        tp->prior_ssthresh = tcp_current_ssthresh(sk);
2905        tp->snd_cwnd = tp->snd_cwnd *
2906                       tcp_mss_to_mtu(sk, tp->mss_cache) /
2907                       icsk->icsk_mtup.probe_size;
2908        tp->snd_cwnd_cnt = 0;
2909        tp->snd_cwnd_stamp = tcp_time_stamp;
2910        tp->snd_ssthresh = tcp_current_ssthresh(sk);
2911
2912        icsk->icsk_mtup.search_low = icsk->icsk_mtup.probe_size;
2913        icsk->icsk_mtup.probe_size = 0;
2914        tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
2915}
2916
2917/* Do a simple retransmit without using the backoff mechanisms in
2918 * tcp_timer. This is used for path mtu discovery.
2919 * The socket is already locked here.
2920 */
2921void tcp_simple_retransmit(struct sock *sk)
2922{
2923        const struct inet_connection_sock *icsk = inet_csk(sk);
2924        struct tcp_sock *tp = tcp_sk(sk);
2925        struct sk_buff *skb;
2926        unsigned int mss = tcp_current_mss(sk);
2927        u32 prior_lost = tp->lost_out;
2928
2929        tcp_for_write_queue(skb, sk) {
2930                if (skb == tcp_send_head(sk))
2931                        break;
2932                if (tcp_skb_seglen(skb) > mss &&
2933                    !(TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)) {
2934                        if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) {
2935                                TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
2936                                tp->retrans_out -= tcp_skb_pcount(skb);
2937                        }
2938                        tcp_skb_mark_lost_uncond_verify(tp, skb);
2939                }
2940        }
2941
2942        tcp_clear_retrans_hints_partial(tp);
2943
2944        if (prior_lost == tp->lost_out)
2945                return;
2946
2947        if (tcp_is_reno(tp))
2948                tcp_limit_reno_sacked(tp);
2949
2950        tcp_verify_left_out(tp);
2951
2952        /* Don't muck with the congestion window here.
2953         * Reason is that we do not increase amount of _data_
2954         * in network, but units changed and effective
2955         * cwnd/ssthresh really reduced now.
2956         */
2957        if (icsk->icsk_ca_state != TCP_CA_Loss) {
2958                tp->high_seq = tp->snd_nxt;
2959                tp->snd_ssthresh = tcp_current_ssthresh(sk);
2960                tp->prior_ssthresh = 0;
2961                tp->undo_marker = 0;
2962                tcp_set_ca_state(sk, TCP_CA_Loss);
2963        }
2964        tcp_xmit_retransmit_queue(sk);
2965}
2966EXPORT_SYMBOL(tcp_simple_retransmit);
2967
2968/* This function implements the PRR algorithm, specifcally the PRR-SSRB
2969 * (proportional rate reduction with slow start reduction bound) as described in
2970 * http://www.ietf.org/id/draft-mathis-tcpm-proportional-rate-reduction-01.txt.
2971 * It computes the number of packets to send (sndcnt) based on packets newly
2972 * delivered:
2973 *   1) If the packets in flight is larger than ssthresh, PRR spreads the
2974 *      cwnd reductions across a full RTT.
2975 *   2) If packets in flight is lower than ssthresh (such as due to excess
2976 *      losses and/or application stalls), do not perform any further cwnd
2977 *      reductions, but instead slow start up to ssthresh.
2978 */
2979static void tcp_update_cwnd_in_recovery(struct sock *sk, int newly_acked_sacked,
2980                                        int fast_rexmit, int flag)
2981{
2982        struct tcp_sock *tp = tcp_sk(sk);
2983        int sndcnt = 0;
2984        int delta = tp->snd_ssthresh - tcp_packets_in_flight(tp);
2985
2986        if (tcp_packets_in_flight(tp) > tp->snd_ssthresh) {
2987                u64 dividend = (u64)tp->snd_ssthresh * tp->prr_delivered +
2988                               tp->prior_cwnd - 1;
2989                sndcnt = div_u64(dividend, tp->prior_cwnd) - tp->prr_out;
2990        } else {
2991                sndcnt = min_t(int, delta,
2992                               max_t(int, tp->prr_delivered - tp->prr_out,
2993                                     newly_acked_sacked) + 1);
2994        }
2995
2996        sndcnt = max(sndcnt, (fast_rexmit ? 1 : 0));
2997        tp->snd_cwnd = tcp_packets_in_flight(tp) + sndcnt;
2998}
2999
3000/* Process an event, which can update packets-in-flight not trivially.
3001 * Main goal of this function is to calculate new estimate for left_out,
3002 * taking into account both packets sitting in receiver's buffer and
3003 * packets lost by network.
3004 *
3005 * Besides that it does CWND reduction, when packet loss is detected
3006 * and changes state of machine.
3007 *
3008 * It does _not_ decide what to send, it is made in function
3009 * tcp_xmit_retransmit_queue().
3010 */
3011static void tcp_fastretrans_alert(struct sock *sk, int pkts_acked,
3012                                  int newly_acked_sacked, int flag)
3013{
3014        struct inet_connection_sock *icsk = inet_csk(sk);
3015        struct tcp_sock *tp = tcp_sk(sk);
3016        int is_dupack = !(flag & (FLAG_SND_UNA_ADVANCED | FLAG_NOT_DUP));
3017        int do_lost = is_dupack || ((flag & FLAG_DATA_SACKED) &&
3018                                    (tcp_fackets_out(tp) > tp->reordering));
3019        int fast_rexmit = 0, mib_idx;
3020
3021        if (WARN_ON(!tp->packets_out && tp->sacked_out))
3022                tp->sacked_out = 0;
3023        if (WARN_ON(!tp->sacked_out && tp->fackets_out))
3024                tp->fackets_out = 0;
3025
3026        /* Now state machine starts.
3027         * A. ECE, hence prohibit cwnd undoing, the reduction is required. */
3028        if (flag & FLAG_ECE)
3029                tp->prior_ssthresh = 0;
3030
3031        /* B. In all the states check for reneging SACKs. */
3032        if (tcp_check_sack_reneging(sk, flag))
3033                return;
3034
3035        /* C. Process data loss notification, provided it is valid. */
3036        if (tcp_is_fack(tp) && (flag & FLAG_DATA_LOST) &&
3037            before(tp->snd_una, tp->high_seq) &&
3038            icsk->icsk_ca_state != TCP_CA_Open &&
3039            tp->fackets_out > tp->reordering) {
3040                tcp_mark_head_lost(sk, tp->fackets_out - tp->reordering, 0);
3041                NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPLOSS);
3042        }
3043
3044        /* D. Check consistency of the current state. */
3045        tcp_verify_left_out(tp);
3046
3047        /* E. Check state exit conditions. State can be terminated
3048         *    when high_seq is ACKed. */
3049        if (icsk->icsk_ca_state == TCP_CA_Open) {
3050                WARN_ON(tp->retrans_out != 0);
3051                tp->retrans_stamp = 0;
3052        } else if (!before(tp->snd_una, tp->high_seq)) {
3053                switch (icsk->icsk_ca_state) {
3054                case TCP_CA_Loss:
3055                        icsk->icsk_retransmits = 0;
3056                        if (tcp_try_undo_recovery(sk))
3057                                return;
3058                        break;
3059
3060                case TCP_CA_CWR:
3061                        /* CWR is to be held something *above* high_seq
3062                         * is ACKed for CWR bit to reach receiver. */
3063                        if (tp->snd_una != tp->high_seq) {
3064                                tcp_complete_cwr(sk);
3065                                tcp_set_ca_state(sk, TCP_CA_Open);
3066                        }
3067                        break;
3068
3069                case TCP_CA_Disorder:
3070                        tcp_try_undo_dsack(sk);
3071                        if (!tp->undo_marker ||
3072                            /* For SACK case do not Open to allow to undo
3073                             * catching for all duplicate ACKs. */
3074                            tcp_is_reno(tp) || tp->snd_una != tp->high_seq) {
3075                                tp->undo_marker = 0;
3076                                tcp_set_ca_state(sk, TCP_CA_Open);
3077                        }
3078                        break;
3079
3080                case TCP_CA_Recovery:
3081                        if (tcp_is_reno(tp))
3082                                tcp_reset_reno_sack(tp);
3083                        if (tcp_try_undo_recovery(sk))
3084                                return;
3085                        tcp_complete_cwr(sk);
3086                        break;
3087                }
3088        }
3089
3090        /* F. Process state. */
3091        switch (icsk->icsk_ca_state) {
3092        case TCP_CA_Recovery:
3093                if (!(flag & FLAG_SND_UNA_ADVANCED)) {
3094                        if (tcp_is_reno(tp) && is_dupack)
3095                                tcp_add_reno_sack(sk);
3096                } else
3097                        do_lost = tcp_try_undo_partial(sk, pkts_acked);
3098                break;
3099        case TCP_CA_Loss:
3100                if (flag & FLAG_DATA_ACKED)
3101                        icsk->icsk_retransmits = 0;
3102                if (tcp_is_reno(tp) && flag & FLAG_SND_UNA_ADVANCED)
3103                        tcp_reset_reno_sack(tp);
3104                if (!tcp_try_undo_loss(sk)) {
3105                        tcp_moderate_cwnd(tp);
3106                        tcp_xmit_retransmit_queue(sk);
3107                        return;
3108                }
3109                if (icsk->icsk_ca_state != TCP_CA_Open)
3110                        return;
3111                /* Loss is undone; fall through to processing in Open state. */
3112        default:
3113                if (tcp_is_reno(tp)) {
3114                        if (flag & FLAG_SND_UNA_ADVANCED)
3115                                tcp_reset_reno_sack(tp);
3116                        if (is_dupack)
3117                                tcp_add_reno_sack(sk);
3118                }
3119
3120                if (icsk->icsk_ca_state == TCP_CA_Disorder)
3121                        tcp_try_undo_dsack(sk);
3122
3123                if (!tcp_time_to_recover(sk)) {
3124                        tcp_try_to_open(sk, flag);
3125                        return;
3126                }
3127
3128                /* MTU probe failure: don't reduce cwnd */
3129                if (icsk->icsk_ca_state < TCP_CA_CWR &&
3130                    icsk->icsk_mtup.probe_size &&
3131                    tp->snd_una == tp->mtu_probe.probe_seq_start) {
3132                        tcp_mtup_probe_failed(sk);
3133                        /* Restores the reduction we did in tcp_mtup_probe() */
3134                        tp->snd_cwnd++;
3135                        tcp_simple_retransmit(sk);
3136                        return;
3137                }
3138
3139                /* Otherwise enter Recovery state */
3140
3141                if (tcp_is_reno(tp))
3142                        mib_idx = LINUX_MIB_TCPRENORECOVERY;
3143                else
3144                        mib_idx = LINUX_MIB_TCPSACKRECOVERY;
3145
3146                NET_INC_STATS_BH(sock_net(sk), mib_idx);
3147
3148                tp->high_seq = tp->snd_nxt;
3149                tp->prior_ssthresh = 0;
3150                tp->undo_marker = tp->snd_una;
3151                tp->undo_retrans = tp->retrans_out;
3152
3153                if (icsk->icsk_ca_state < TCP_CA_CWR) {
3154                        if (!(flag & FLAG_ECE))
3155                                tp->prior_ssthresh = tcp_current_ssthresh(sk);
3156                        tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
3157                        TCP_ECN_queue_cwr(tp);
3158                }
3159
3160                tp->bytes_acked = 0;
3161                tp->snd_cwnd_cnt = 0;
3162                tp->prior_cwnd = tp->snd_cwnd;
3163                tp->prr_delivered = 0;
3164                tp->prr_out = 0;
3165                tcp_set_ca_state(sk, TCP_CA_Recovery);
3166                fast_rexmit = 1;
3167        }
3168
3169        if (do_lost || (tcp_is_fack(tp) && tcp_head_timedout(sk)))
3170                tcp_update_scoreboard(sk, fast_rexmit);
3171        tp->prr_delivered += newly_acked_sacked;
3172        tcp_update_cwnd_in_recovery(sk, newly_acked_sacked, fast_rexmit, flag);
3173        tcp_xmit_retransmit_queue(sk);
3174}
3175
3176void tcp_valid_rtt_meas(struct sock *sk, u32 seq_rtt)
3177{
3178        tcp_rtt_estimator(sk, seq_rtt);
3179        tcp_set_rto(sk);
3180        inet_csk(sk)->icsk_backoff = 0;
3181}
3182EXPORT_SYMBOL(tcp_valid_rtt_meas);
3183
3184/* Read draft-ietf-tcplw-high-performance before mucking
3185 * with this code. (Supersedes RFC1323)
3186 */
3187static void tcp_ack_saw_tstamp(struct sock *sk, int flag)
3188{
3189        /* RTTM Rule: A TSecr value received in a segment is used to
3190         * update the averaged RTT measurement only if the segment
3191         * acknowledges some new data, i.e., only if it advances the
3192         * left edge of the send window.
3193         *
3194         * See draft-ietf-tcplw-high-performance-00, section 3.3.
3195         * 1998/04/10 Andrey V. Savochkin <saw@msu.ru>
3196         *
3197         * Changed: reset backoff as soon as we see the first valid sample.
3198         * If we do not, we get strongly overestimated rto. With timestamps
3199         * samples are accepted even from very old segments: f.e., when rtt=1
3200         * increases to 8, we retransmit 5 times and after 8 seconds delayed
3201         * answer arrives rto becomes 120 seconds! If at least one of segments
3202         * in window is lost... Voila.                          --ANK (010210)
3203         */
3204        struct tcp_sock *tp = tcp_sk(sk);
3205
3206        tcp_valid_rtt_meas(sk, tcp_time_stamp - tp->rx_opt.rcv_tsecr);
3207}
3208
3209static void tcp_ack_no_tstamp(struct sock *sk, u32 seq_rtt, int flag)
3210{
3211        /* We don't have a timestamp. Can only use
3212         * packets that are not retransmitted to determine
3213         * rtt estimates. Also, we must not reset the
3214         * backoff for rto until we get a non-retransmitted
3215         * packet. This allows us to deal with a situation
3216         * where the network delay has increased suddenly.
3217         * I.e. Karn's algorithm. (SIGCOMM '87, p5.)
3218         */
3219
3220        if (flag & FLAG_RETRANS_DATA_ACKED)
3221                return;
3222
3223        tcp_valid_rtt_meas(sk, seq_rtt);
3224}
3225
3226static inline void tcp_ack_update_rtt(struct sock *sk, const int flag,
3227                                      const s32 seq_rtt)
3228{
3229        const struct tcp_sock *tp = tcp_sk(sk);
3230        /* Note that peer MAY send zero echo. In this case it is ignored. (rfc1323) */
3231        if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr)
3232                tcp_ack_saw_tstamp(sk, flag);
3233        else if (seq_rtt >= 0)
3234                tcp_ack_no_tstamp(sk, seq_rtt, flag);
3235}
3236
3237static void tcp_cong_avoid(struct sock *sk, u32 ack, u32 in_flight)
3238{
3239        const struct inet_connection_sock *icsk = inet_csk(sk);
3240        icsk->icsk_ca_ops->cong_avoid(sk, ack, in_flight);
3241        tcp_sk(sk)->snd_cwnd_stamp = tcp_time_stamp;
3242}
3243
3244/* Restart timer after forward progress on connection.
3245 * RFC2988 recommends to restart timer to now+rto.
3246 */
3247static void tcp_rearm_rto(struct sock *sk)
3248{
3249        const struct tcp_sock *tp = tcp_sk(sk);
3250
3251        if (!tp->packets_out) {
3252                inet_csk_clear_xmit_timer(sk, ICSK_TIME_RETRANS);
3253        } else {
3254                inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
3255                                          inet_csk(sk)->icsk_rto, TCP_RTO_MAX);
3256        }
3257}
3258
3259/* If we get here, the whole TSO packet has not been acked. */
3260static u32 tcp_tso_acked(struct sock *sk, struct sk_buff *skb)
3261{
3262        struct tcp_sock *tp = tcp_sk(sk);
3263        u32 packets_acked;
3264
3265        BUG_ON(!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una));
3266
3267        packets_acked = tcp_skb_pcount(skb);
3268        if (tcp_trim_head(sk, skb, tp->snd_una - TCP_SKB_CB(skb)->seq))
3269                return 0;
3270        packets_acked -= tcp_skb_pcount(skb);
3271
3272        if (packets_acked) {
3273                BUG_ON(tcp_skb_pcount(skb) == 0);
3274                BUG_ON(!before(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq));
3275        }
3276
3277        return packets_acked;
3278}
3279
3280/* Remove acknowledged frames from the retransmission queue. If our packet
3281 * is before the ack sequence we can discard it as it's confirmed to have
3282 * arrived at the other end.
3283 */
3284static int tcp_clean_rtx_queue(struct sock *sk, int prior_fackets,
3285                               u32 prior_snd_una)
3286{
3287        struct tcp_sock *tp = tcp_sk(sk);
3288        const struct inet_connection_sock *icsk = inet_csk(sk);
3289        struct sk_buff *skb;
3290        u32 now = tcp_time_stamp;
3291        int fully_acked = 1;
3292        int flag = 0;
3293        u32 pkts_acked = 0;
3294        u32 reord = tp->packets_out;
3295        u32 prior_sacked = tp->sacked_out;
3296        s32 seq_rtt = -1;
3297        s32 ca_seq_rtt = -1;
3298        ktime_t last_ackt = net_invalid_timestamp();
3299
3300        while ((skb = tcp_write_queue_head(sk)) && skb != tcp_send_head(sk)) {
3301                struct tcp_skb_cb *scb = TCP_SKB_CB(skb);
3302                u32 acked_pcount;
3303                u8 sacked = scb->sacked;
3304
3305                /* Determine how many packets and what bytes were acked, tso and else */
3306                if (after(scb->end_seq, tp->snd_una)) {
3307                        if (tcp_skb_pcount(skb) == 1 ||
3308                            !after(tp->snd_una, scb->seq))
3309                                break;
3310
3311                        acked_pcount = tcp_tso_acked(sk, skb);
3312                        if (!acked_pcount)
3313                                break;
3314
3315                        fully_acked = 0;
3316                } else {
3317                        acked_pcount = tcp_skb_pcount(skb);
3318                }
3319
3320                if (sacked & TCPCB_RETRANS) {
3321                        if (sacked & TCPCB_SACKED_RETRANS)
3322                                tp->retrans_out -= acked_pcount;
3323                        flag |= FLAG_RETRANS_DATA_ACKED;
3324                        ca_seq_rtt = -1;
3325                        seq_rtt = -1;
3326                        if ((flag & FLAG_DATA_ACKED) || (acked_pcount > 1))
3327                                flag |= FLAG_NONHEAD_RETRANS_ACKED;
3328                } else {
3329                        ca_seq_rtt = now - scb->when;
3330                        last_ackt = skb->tstamp;
3331                        if (seq_rtt < 0) {
3332                                seq_rtt = ca_seq_rtt;
3333                        }
3334                        if (!(sacked & TCPCB_SACKED_ACKED))
3335                                reord = min(pkts_acked, reord);
3336                }
3337
3338                if (sacked & TCPCB_SACKED_ACKED)
3339                        tp->sacked_out -= acked_pcount;
3340                if (sacked & TCPCB_LOST)
3341                        tp->lost_out -= acked_pcount;
3342
3343                tp->packets_out -= acked_pcount;
3344                pkts_acked += acked_pcount;
3345
3346                /* Initial outgoing SYN's get put onto the write_queue
3347                 * just like anything else we transmit.  It is not
3348                 * true data, and if we misinform our callers that
3349                 * this ACK acks real data, we will erroneously exit
3350                 * connection startup slow start one packet too
3351                 * quickly.  This is severely frowned upon behavior.
3352                 */
3353                if (!(scb->tcp_flags & TCPHDR_SYN)) {
3354                        flag |= FLAG_DATA_ACKED;
3355                } else {
3356                        flag |= FLAG_SYN_ACKED;
3357                        tp->retrans_stamp = 0;
3358                }
3359
3360                if (!fully_acked)
3361                        break;
3362
3363                tcp_unlink_write_queue(skb, sk);
3364                sk_wmem_free_skb(sk, skb);
3365                tp->scoreboard_skb_hint = NULL;
3366                if (skb == tp->retransmit_skb_hint)
3367                        tp->retransmit_skb_hint = NULL;
3368                if (skb == tp->lost_skb_hint)
3369                        tp->lost_skb_hint = NULL;
3370        }
3371
3372        if (likely(between(tp->snd_up, prior_snd_una, tp->snd_una)))
3373                tp->snd_up = tp->snd_una;
3374
3375        if (skb && (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED))
3376                flag |= FLAG_SACK_RENEGING;
3377
3378        if (flag & FLAG_ACKED) {
3379                const struct tcp_congestion_ops *ca_ops
3380                        = inet_csk(sk)->icsk_ca_ops;
3381
3382                if (unlikely(icsk->icsk_mtup.probe_size &&
3383                             !after(tp->mtu_probe.probe_seq_end, tp->snd_una))) {
3384                        tcp_mtup_probe_success(sk);
3385                }
3386
3387                tcp_ack_update_rtt(sk, flag, seq_rtt);
3388                tcp_rearm_rto(sk);
3389
3390                if (tcp_is_reno(tp)) {
3391                        tcp_remove_reno_sacks(sk, pkts_acked);
3392                } else {
3393                        int delta;
3394
3395                        /* Non-retransmitted hole got filled? That's reordering */
3396                        if (reord < prior_fackets)
3397                                tcp_update_reordering(sk, tp->fackets_out - reord, 0);
3398
3399                        delta = tcp_is_fack(tp) ? pkts_acked :
3400                                                  prior_sacked - tp->sacked_out;
3401                        tp->lost_cnt_hint -= min(tp->lost_cnt_hint, delta);
3402                }
3403
3404                tp->fackets_out -= min(pkts_acked, tp->fackets_out);
3405
3406                if (ca_ops->pkts_acked) {
3407                        s32 rtt_us = -1;
3408
3409                        /* Is the ACK triggering packet unambiguous? */
3410                        if (!(flag & FLAG_RETRANS_DATA_ACKED)) {
3411                                /* High resolution needed and available? */
3412                                if (ca_ops->flags & TCP_CONG_RTT_STAMP &&
3413                                    !ktime_equal(last_ackt,
3414                                                 net_invalid_timestamp()))
3415                                        rtt_us = ktime_us_delta(ktime_get_real(),
3416                                                                last_ackt);
3417                                else if (ca_seq_rtt >= 0)
3418                                        rtt_us = jiffies_to_usecs(ca_seq_rtt);
3419                        }
3420
3421                        ca_ops->pkts_acked(sk, pkts_acked, rtt_us);
3422                }
3423        }
3424
3425#if FASTRETRANS_DEBUG > 0
3426        WARN_ON((int)tp->sacked_out < 0);
3427        WARN_ON((int)tp->lost_out < 0);
3428        WARN_ON((int)tp->retrans_out < 0);
3429        if (!tp->packets_out && tcp_is_sack(tp)) {
3430                icsk = inet_csk(sk);
3431                if (tp->lost_out) {
3432                        printk(KERN_DEBUG "Leak l=%u %d\n",
3433                               tp->lost_out, icsk->icsk_ca_state);
3434                        tp->lost_out = 0;
3435                }
3436                if (tp->sacked_out) {
3437                        printk(KERN_DEBUG "Leak s=%u %d\n",
3438                               tp->sacked_out, icsk->icsk_ca_state);
3439                        tp->sacked_out = 0;
3440                }
3441                if (tp->retrans_out) {
3442                        printk(KERN_DEBUG "Leak r=%u %d\n",
3443                               tp->retrans_out, icsk->icsk_ca_state);
3444                        tp->retrans_out = 0;
3445                }
3446        }
3447#endif
3448        return flag;
3449}
3450
3451static void tcp_ack_probe(struct sock *sk)
3452{
3453        const struct tcp_sock *tp = tcp_sk(sk);
3454        struct inet_connection_sock *icsk = inet_csk(sk);
3455
3456        /* Was it a usable window open? */
3457
3458        if (!after(TCP_SKB_CB(tcp_send_head(sk))->end_seq, tcp_wnd_end(tp))) {
3459                icsk->icsk_backoff = 0;
3460                inet_csk_clear_xmit_timer(sk, ICSK_TIME_PROBE0);
3461                /* Socket must be waked up by subsequent tcp_data_snd_check().
3462                 * This function is not for random using!
3463                 */
3464        } else {
3465                inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0,
3466                                          min(icsk->icsk_rto << icsk->icsk_backoff, TCP_RTO_MAX),
3467                                          TCP_RTO_MAX);
3468        }
3469}
3470
3471static inline int tcp_ack_is_dubious(const struct sock *sk, const int flag)
3472{
3473        return !(flag & FLAG_NOT_DUP) || (flag & FLAG_CA_ALERT) ||
3474                inet_csk(sk)->icsk_ca_state != TCP_CA_Open;
3475}
3476
3477static inline int tcp_may_raise_cwnd(const struct sock *sk, const int flag)
3478{
3479        const struct tcp_sock *tp = tcp_sk(sk);
3480        return (!(flag & FLAG_ECE) || tp->snd_cwnd < tp->snd_ssthresh) &&
3481                !((1 << inet_csk(sk)->icsk_ca_state) & (TCPF_CA_Recovery | TCPF_CA_CWR));
3482}
3483
3484/* Check that window update is acceptable.
3485 * The function assumes that snd_una<=ack<=snd_next.
3486 */
3487static inline int tcp_may_update_window(const struct tcp_sock *tp,
3488                                        const u32 ack, const u32 ack_seq,
3489                                        const u32 nwin)
3490{
3491        return  after(ack, tp->snd_una) ||
3492                after(ack_seq, tp->snd_wl1) ||
3493                (ack_seq == tp->snd_wl1 && nwin > tp->snd_wnd);
3494}
3495
3496/* Update our send window.
3497 *
3498 * Window update algorithm, described in RFC793/RFC1122 (used in linux-2.2
3499 * and in FreeBSD. NetBSD's one is even worse.) is wrong.
3500 */
3501static int tcp_ack_update_window(struct sock *sk, const struct sk_buff *skb, u32 ack,
3502                                 u32 ack_seq)
3503{
3504        struct tcp_sock *tp = tcp_sk(sk);
3505        int flag = 0;
3506        u32 nwin = ntohs(tcp_hdr(skb)->window);
3507
3508        if (likely(!tcp_hdr(skb)->syn))
3509                nwin <<= tp->rx_opt.snd_wscale;
3510
3511        if (tcp_may_update_window(tp, ack, ack_seq, nwin)) {
3512                flag |= FLAG_WIN_UPDATE;
3513                tcp_update_wl(tp, ack_seq);
3514
3515                if (tp->snd_wnd != nwin) {
3516                        tp->snd_wnd = nwin;
3517
3518                        /* Note, it is the only place, where
3519                         * fast path is recovered for sending TCP.
3520                         */
3521                        tp->pred_flags = 0;
3522                        tcp_fast_path_check(sk);
3523
3524                        if (nwin > tp->max_window) {
3525                                tp->max_window = nwin;
3526                                tcp_sync_mss(sk, inet_csk(sk)->icsk_pmtu_cookie);
3527                        }
3528                }
3529        }
3530
3531        tp->snd_una = ack;
3532
3533        return flag;
3534}
3535
3536/* A very conservative spurious RTO response algorithm: reduce cwnd and
3537 * continue in congestion avoidance.
3538 */
3539static void tcp_conservative_spur_to_response(struct tcp_sock *tp)
3540{
3541        tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_ssthresh);
3542        tp->snd_cwnd_cnt = 0;
3543        tp->bytes_acked = 0;
3544        TCP_ECN_queue_cwr(tp);
3545        tcp_moderate_cwnd(tp);
3546}
3547
3548/* A conservative spurious RTO response algorithm: reduce cwnd using
3549 * rate halving and continue in congestion avoidance.
3550 */
3551static void tcp_ratehalving_spur_to_response(struct sock *sk)
3552{
3553        tcp_enter_cwr(sk, 0);
3554}
3555
3556static void tcp_undo_spur_to_response(struct sock *sk, int flag)
3557{
3558        if (flag & FLAG_ECE)
3559                tcp_ratehalving_spur_to_response(sk);
3560        else
3561                tcp_undo_cwr(sk, true);
3562}
3563
3564/* F-RTO spurious RTO detection algorithm (RFC4138)
3565 *
3566 * F-RTO affects during two new ACKs following RTO (well, almost, see inline
3567 * comments). State (ACK number) is kept in frto_counter. When ACK advances
3568 * window (but not to or beyond highest sequence sent before RTO):
3569 *   On First ACK,  send two new segments out.
3570 *   On Second ACK, RTO was likely spurious. Do spurious response (response
3571 *                  algorithm is not part of the F-RTO detection algorithm
3572 *                  given in RFC4138 but can be selected separately).
3573 * Otherwise (basically on duplicate ACK), RTO was (likely) caused by a loss
3574 * and TCP falls back to conventional RTO recovery. F-RTO allows overriding
3575 * of Nagle, this is done using frto_counter states 2 and 3, when a new data
3576 * segment of any size sent during F-RTO, state 2 is upgraded to 3.
3577 *
3578 * Rationale: if the RTO was spurious, new ACKs should arrive from the
3579 * original window even after we transmit two new data segments.
3580 *
3581 * SACK version:
3582 *   on first step, wait until first cumulative ACK arrives, then move to
3583 *   the second step. In second step, the next ACK decides.
3584 *
3585 * F-RTO is implemented (mainly) in four functions:
3586 *   - tcp_use_frto() is used to determine if TCP is can use F-RTO
3587 *   - tcp_enter_frto() prepares TCP state on RTO if F-RTO is used, it is
3588 *     called when tcp_use_frto() showed green light
3589 *   - tcp_process_frto() handles incoming ACKs during F-RTO algorithm
3590 *   - tcp_enter_frto_loss() is called if there is not enough evidence
3591 *     to prove that the RTO is indeed spurious. It transfers the control
3592 *     from F-RTO to the conventional RTO recovery
3593 */
3594static int tcp_process_frto(struct sock *sk, int flag)
3595{
3596        struct tcp_sock *tp = tcp_sk(sk);
3597
3598        tcp_verify_left_out(tp);
3599
3600        /* Duplicate the behavior from Loss state (fastretrans_alert) */
3601        if (flag & FLAG_DATA_ACKED)
3602                inet_csk(sk)->icsk_retransmits = 0;
3603
3604        if ((flag & FLAG_NONHEAD_RETRANS_ACKED) ||
3605            ((tp->frto_counter >= 2) && (flag & FLAG_RETRANS_DATA_ACKED)))
3606                tp->undo_marker = 0;
3607
3608        if (!before(tp->snd_una, tp->frto_highmark)) {
3609                tcp_enter_frto_loss(sk, (tp->frto_counter == 1 ? 2 : 3), flag);
3610                return 1;
3611        }
3612
3613        if (!tcp_is_sackfrto(tp)) {
3614                /* RFC4138 shortcoming in step 2; should also have case c):
3615                 * ACK isn't duplicate nor advances window, e.g., opposite dir
3616                 * data, winupdate
3617                 */
3618                if (!(flag & FLAG_ANY_PROGRESS) && (flag & FLAG_NOT_DUP))
3619                        return 1;
3620
3621                if (!(flag & FLAG_DATA_ACKED)) {
3622                        tcp_enter_frto_loss(sk, (tp->frto_counter == 1 ? 0 : 3),
3623                                            flag);
3624                        return 1;
3625                }
3626        } else {
3627                if (!(flag & FLAG_DATA_ACKED) && (tp->frto_counter == 1)) {
3628                        /* Prevent sending of new data. */
3629                        tp->snd_cwnd = min(tp->snd_cwnd,
3630                                           tcp_packets_in_flight(tp));
3631                        return 1;
3632                }
3633
3634                if ((tp->frto_counter >= 2) &&
3635                    (!(flag & FLAG_FORWARD_PROGRESS) ||
3636                     ((flag & FLAG_DATA_SACKED) &&
3637                      !(flag & FLAG_ONLY_ORIG_SACKED)))) {
3638                        /* RFC4138 shortcoming (see comment above) */
3639                        if (!(flag & FLAG_FORWARD_PROGRESS) &&
3640                            (flag & FLAG_NOT_DUP))
3641                                return 1;
3642
3643                        tcp_enter_frto_loss(sk, 3, flag);
3644                        return 1;
3645                }
3646        }
3647
3648        if (tp->frto_counter == 1) {
3649                /* tcp_may_send_now needs to see updated state */
3650                tp->snd_cwnd = tcp_packets_in_flight(tp) + 2;
3651                tp->frto_counter = 2;
3652
3653                if (!tcp_may_send_now(sk))
3654                        tcp_enter_frto_loss(sk, 2, flag);
3655
3656                return 1;
3657        } else {
3658                switch (sysctl_tcp_frto_response) {
3659                case 2:
3660                        tcp_undo_spur_to_response(sk, flag);
3661                        break;
3662                case 1:
3663                        tcp_conservative_spur_to_response(tp);
3664                        break;
3665                default:
3666                        tcp_ratehalving_spur_to_response(sk);
3667                        break;
3668                }
3669                tp->frto_counter = 0;
3670                tp->undo_marker = 0;
3671                NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSPURIOUSRTOS);
3672        }
3673        return 0;
3674}
3675
3676/* This routine deals with incoming acks, but not outgoing ones. */
3677static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
3678{
3679        struct inet_connection_sock *icsk = inet_csk(sk);
3680        struct tcp_sock *tp = tcp_sk(sk);
3681        u32 prior_snd_una = tp->snd_una;
3682        u32 ack_seq = TCP_SKB_CB(skb)->seq;
3683        u32 ack = TCP_SKB_CB(skb)->ack_seq;
3684        u32 prior_in_flight;
3685        u32 prior_fackets;
3686        int prior_packets;
3687        int prior_sacked = tp->sacked_out;
3688        int newly_acked_sacked = 0;
3689        int frto_cwnd = 0;
3690
3691        /* If the ack is older than previous acks
3692         * then we can probably ignore it.
3693         */
3694        if (before(ack, prior_snd_una))
3695                goto old_ack;
3696
3697        /* If the ack includes data we haven't sent yet, discard
3698         * this segment (RFC793 Section 3.9).
3699         */
3700        if (after(ack, tp->snd_nxt))
3701                goto invalid_ack;
3702
3703        if (after(ack, prior_snd_una))
3704                flag |= FLAG_SND_UNA_ADVANCED;
3705
3706        if (sysctl_tcp_abc) {
3707                if (icsk->icsk_ca_state < TCP_CA_CWR)
3708                        tp->bytes_acked += ack - prior_snd_una;
3709                else if (icsk->icsk_ca_state == TCP_CA_Loss)
3710                        /* we assume just one segment left network */
3711                        tp->bytes_acked += min(ack - prior_snd_una,
3712                                               tp->mss_cache);
3713        }
3714
3715        prior_fackets = tp->fackets_out;
3716        prior_in_flight = tcp_packets_in_flight(tp);
3717
3718        if (!(flag & FLAG_SLOWPATH) && after(ack, prior_snd_una)) {
3719                /* Window is constant, pure forward advance.
3720                 * No more checks are required.
3721                 * Note, we use the fact that SND.UNA>=SND.WL2.
3722                 */
3723                tcp_update_wl(tp, ack_seq);
3724                tp->snd_una = ack;
3725                flag |= FLAG_WIN_UPDATE;
3726
3727                tcp_ca_event(sk, CA_EVENT_FAST_ACK);
3728
3729                NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPHPACKS);
3730        } else {
3731                if (ack_seq != TCP_SKB_CB(skb)->end_seq)
3732                        flag |= FLAG_DATA;
3733                else
3734                        NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPPUREACKS);
3735
3736                flag |= tcp_ack_update_window(sk, skb, ack, ack_seq);
3737
3738                if (TCP_SKB_CB(skb)->sacked)
3739                        flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una);
3740
3741                if (TCP_ECN_rcv_ecn_echo(tp, tcp_hdr(skb)))
3742                        flag |= FLAG_ECE;
3743
3744                tcp_ca_event(sk, CA_EVENT_SLOW_ACK);
3745        }
3746
3747        /* We passed data and got it acked, remove any soft error
3748         * log. Something worked...
3749         */
3750        sk->sk_err_soft = 0;
3751        icsk->icsk_probes_out = 0;
3752        tp->rcv_tstamp = tcp_time_stamp;
3753        prior_packets = tp->packets_out;
3754        if (!prior_packets)
3755                goto no_queue;
3756
3757        /* See if we can take anything off of the retransmit queue. */
3758        flag |= tcp_clean_rtx_queue(sk, prior_fackets, prior_snd_una);
3759
3760        newly_acked_sacked = (prior_packets - prior_sacked) -
3761                             (tp->packets_out - tp->sacked_out);
3762
3763        if (tp->frto_counter)
3764                frto_cwnd = tcp_process_frto(sk, flag);
3765        /* Guarantee sacktag reordering detection against wrap-arounds */
3766        if (before(tp->frto_highmark, tp->snd_una))
3767                tp->frto_highmark = 0;
3768
3769        if (tcp_ack_is_dubious(sk, flag)) {
3770                /* Advance CWND, if state allows this. */
3771                if ((flag & FLAG_DATA_ACKED) && !frto_cwnd &&
3772                    tcp_may_raise_cwnd(sk, flag))
3773                        tcp_cong_avoid(sk, ack, prior_in_flight);
3774                tcp_fastretrans_alert(sk, prior_packets - tp->packets_out,
3775                                      newly_acked_sacked, flag);
3776        } else {
3777                if ((flag & FLAG_DATA_ACKED) && !frto_cwnd)
3778                        tcp_cong_avoid(sk, ack, prior_in_flight);
3779        }
3780
3781        if ((flag & FLAG_FORWARD_PROGRESS) || !(flag & FLAG_NOT_DUP))
3782                dst_confirm(__sk_dst_get(sk));
3783
3784        return 1;
3785
3786no_queue:
3787        /* If this ack opens up a zero window, clear backoff.  It was
3788         * being used to time the probes, and is probably far higher than
3789         * it needs to be for normal retransmission.
3790         */
3791        if (tcp_send_head(sk))
3792                tcp_ack_probe(sk);
3793        return 1;
3794
3795invalid_ack:
3796        SOCK_DEBUG(sk, "Ack %u after %u:%u\n", ack, tp->snd_una, tp->snd_nxt);
3797        return -1;
3798
3799old_ack:
3800        if (TCP_SKB_CB(skb)->sacked) {
3801                tcp_sacktag_write_queue(sk, skb, prior_snd_una);
3802                if (icsk->icsk_ca_state == TCP_CA_Open)
3803                        tcp_try_keep_open(sk);
3804        }
3805
3806        SOCK_DEBUG(sk, "Ack %u before %u:%u\n", ack, tp->snd_una, tp->snd_nxt);
3807        return 0;
3808}
3809
3810/* Look for tcp options. Normally only called on SYN and SYNACK packets.
3811 * But, this can also be called on packets in the established flow when
3812 * the fast version below fails.
3813 */
3814void tcp_parse_options(const struct sk_buff *skb, struct tcp_options_received *opt_rx,
3815                       const u8 **hvpp, int estab)
3816{
3817        const unsigned char *ptr;
3818        const struct tcphdr *th = tcp_hdr(skb);
3819        int length = (th->doff * 4) - sizeof(struct tcphdr);
3820
3821        ptr = (const unsigned char *)(th + 1);
3822        opt_rx->saw_tstamp = 0;
3823
3824        while (length > 0) {
3825                int opcode = *ptr++;
3826                int opsize;
3827
3828                switch (opcode) {
3829                case TCPOPT_EOL:
3830                        return;
3831                case TCPOPT_NOP:        /* Ref: RFC 793 section 3.1 */
3832                        length--;
3833                        continue;
3834                default:
3835                        opsize = *ptr++;
3836                        if (opsize < 2) /* "silly options" */
3837                                return;
3838                        if (opsize > length)
3839                                return; /* don't parse partial options */
3840                        switch (opcode) {
3841                        case TCPOPT_MSS:
3842                                if (opsize == TCPOLEN_MSS && th->syn && !estab) {
3843                                        u16 in_mss = get_unaligned_be16(ptr);
3844                                        if (in_mss) {
3845                                                if (opt_rx->user_mss &&
3846                                                    opt_rx->user_mss < in_mss)
3847                                                        in_mss = opt_rx->user_mss;
3848                                                opt_rx->mss_clamp = in_mss;
3849                                        }
3850                                }
3851                                break;
3852                        case TCPOPT_WINDOW:
3853                                if (opsize == TCPOLEN_WINDOW && th->syn &&
3854                                    !estab && sysctl_tcp_window_scaling) {
3855                                        __u8 snd_wscale = *(__u8 *)ptr;
3856                                        opt_rx->wscale_ok = 1;
3857                                        if (snd_wscale > 14) {
3858                                                if (net_ratelimit())
3859                                                        printk(KERN_INFO "tcp_parse_options: Illegal window "
3860                                                               "scaling value %d >14 received.\n",
3861                                                               snd_wscale);
3862                                                snd_wscale = 14;
3863                                        }
3864                                        opt_rx->snd_wscale = snd_wscale;
3865                                }
3866                                break;
3867                        case TCPOPT_TIMESTAMP:
3868                                if ((opsize == TCPOLEN_TIMESTAMP) &&
3869                                    ((estab && opt_rx->tstamp_ok) ||
3870                                     (!estab && sysctl_tcp_timestamps))) {
3871                                        opt_rx->saw_tstamp = 1;
3872                                        opt_rx->rcv_tsval = get_unaligned_be32(ptr);
3873                                        opt_rx->rcv_tsecr = get_unaligned_be32(ptr + 4);
3874                                }
3875                                break;
3876                        case TCPOPT_SACK_PERM:
3877                                if (opsize == TCPOLEN_SACK_PERM && th->syn &&
3878                                    !estab && sysctl_tcp_sack) {
3879                                        opt_rx->sack_ok = 1;
3880                                        tcp_sack_reset(opt_rx);
3881                                }
3882                                break;
3883
3884                        case TCPOPT_SACK:
3885                                if ((opsize >= (TCPOLEN_SACK_BASE + TCPOLEN_SACK_PERBLOCK)) &&
3886                                   !((opsize - TCPOLEN_SACK_BASE) % TCPOLEN_SACK_PERBLOCK) &&
3887                                   opt_rx->sack_ok) {
3888                                        TCP_SKB_CB(skb)->sacked = (ptr - 2) - (unsigned char *)th;
3889                                }
3890                                break;
3891#ifdef CONFIG_TCP_MD5SIG
3892                        case TCPOPT_MD5SIG:
3893                                /*
3894                                 * The MD5 Hash has already been
3895                                 * checked (see tcp_v{4,6}_do_rcv()).
3896                                 */
3897                                break;
3898#endif
3899                        case TCPOPT_COOKIE:
3900                                /* This option is variable length.
3901                                 */
3902                                switch (opsize) {
3903                                case TCPOLEN_COOKIE_BASE:
3904                                        /* not yet implemented */
3905                                        break;
3906                                case TCPOLEN_COOKIE_PAIR:
3907                                        /* not yet implemented */
3908                                        break;
3909                                case TCPOLEN_COOKIE_MIN+0:
3910                                case TCPOLEN_COOKIE_MIN+2:
3911                                case TCPOLEN_COOKIE_MIN+4:
3912                                case TCPOLEN_COOKIE_MIN+6:
3913                                case TCPOLEN_COOKIE_MAX:
3914                                        /* 16-bit multiple */
3915                                        opt_rx->cookie_plus = opsize;
3916                                        *hvpp = ptr;
3917                                        break;
3918                                default:
3919                                        /* ignore option */
3920                                        break;
3921                                }
3922                                break;
3923                        }
3924
3925                        ptr += opsize-2;
3926                        length -= opsize;
3927                }
3928        }
3929}
3930EXPORT_SYMBOL(tcp_parse_options);
3931
3932static int tcp_parse_aligned_timestamp(struct tcp_sock *tp, const struct tcphdr *th)
3933{
3934        const __be32 *ptr = (const __be32 *)(th + 1);
3935
3936        if (*ptr == htonl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16)
3937                          | (TCPOPT_TIMESTAMP << 8) | TCPOLEN_TIMESTAMP)) {
3938                tp->rx_opt.saw_tstamp = 1;
3939                ++ptr;
3940                tp->rx_opt.rcv_tsval = ntohl(*ptr);
3941                ++ptr;
3942                tp->rx_opt.rcv_tsecr = ntohl(*ptr);
3943                return 1;
3944        }
3945        return 0;
3946}
3947
3948/* Fast parse options. This hopes to only see timestamps.
3949 * If it is wrong it falls back on tcp_parse_options().
3950 */
3951static int tcp_fast_parse_options(const struct sk_buff *skb,
3952                                  const struct tcphdr *th,
3953                                  struct tcp_sock *tp, const u8 **hvpp)
3954{
3955        /* In the spirit of fast parsing, compare doff directly to constant
3956         * values.  Because equality is used, short doff can be ignored here.
3957         */
3958        if (th->doff == (sizeof(*th) / 4)) {
3959                tp->rx_opt.saw_tstamp = 0;
3960                return 0;
3961        } else if (tp->rx_opt.tstamp_ok &&
3962                   th->doff == ((sizeof(*th) + TCPOLEN_TSTAMP_ALIGNED) / 4)) {
3963                if (tcp_parse_aligned_timestamp(tp, th))
3964                        return 1;
3965        }
3966        tcp_parse_options(skb, &tp->rx_opt, hvpp, 1);
3967        return 1;
3968}
3969
3970#ifdef CONFIG_TCP_MD5SIG
3971/*
3972 * Parse MD5 Signature option
3973 */
3974const u8 *tcp_parse_md5sig_option(const struct tcphdr *th)
3975{
3976        int length = (th->doff << 2) - sizeof(*th);
3977        const u8 *ptr = (const u8 *)(th + 1);
3978
3979        /* If the TCP option is too short, we can short cut */
3980        if (length < TCPOLEN_MD5SIG)
3981                return NULL;
3982
3983        while (length > 0) {
3984                int opcode = *ptr++;
3985                int opsize;
3986
3987                switch(opcode) {
3988                case TCPOPT_EOL:
3989                        return NULL;
3990                case TCPOPT_NOP:
3991                        length--;
3992                        continue;
3993                default:
3994                        opsize = *ptr++;
3995                        if (opsize < 2 || opsize > length)
3996                                return NULL;
3997                        if (opcode == TCPOPT_MD5SIG)
3998                                return opsize == TCPOLEN_MD5SIG ? ptr : NULL;
3999                }
4000                ptr += opsize - 2;
4001                length -= opsize;
4002        }
4003        return NULL;
4004}
4005EXPORT_SYMBOL(tcp_parse_md5sig_option);
4006#endif
4007
4008static inline void tcp_store_ts_recent(struct tcp_sock *tp)
4009{
4010        tp->rx_opt.ts_recent = tp->rx_opt.rcv_tsval;
4011        tp->rx_opt.ts_recent_stamp = get_seconds();
4012}
4013
4014static inline void tcp_replace_ts_recent(struct tcp_sock *tp, u32 seq)
4015{
4016        if (tp->rx_opt.saw_tstamp && !after(seq, tp->rcv_wup)) {
4017                /* PAWS bug workaround wrt. ACK frames, the PAWS discard
4018                 * extra check below makes sure this can only happen
4019                 * for pure ACK frames.  -DaveM
4020                 *
4021                 * Not only, also it occurs for expired timestamps.
4022                 */
4023
4024                if (tcp_paws_check(&tp->rx_opt, 0))
4025                        tcp_store_ts_recent(tp);
4026        }
4027}
4028
4029/* Sorry, PAWS as specified is broken wrt. pure-ACKs -DaveM
4030 *
4031 * It is not fatal. If this ACK does _not_ change critical state (seqs, window)
4032 * it can pass through stack. So, the following predicate verifies that
4033 * this segment is not used for anything but congestion avoidance or
4034 * fast retransmit. Moreover, we even are able to eliminate most of such
4035 * second order effects, if we apply some small "replay" window (~RTO)
4036 * to timestamp space.
4037 *
4038 * All these measures still do not guarantee that we reject wrapped ACKs
4039 * on networks with high bandwidth, when sequence space is recycled fastly,
4040 * but it guarantees that such events will be very rare and do not affect
4041 * connection seriously. This doesn't look nice, but alas, PAWS is really
4042 * buggy extension.
4043 *
4044 * [ Later note. Even worse! It is buggy for segments _with_ data. RFC
4045 * states that events when retransmit arrives after original data are rare.
4046 * It is a blatant lie. VJ forgot about fast retransmit! 8)8) It is
4047 * the biggest problem on large power networks even with minor reordering.
4048 * OK, let's give it small replay window. If peer clock is even 1hz, it is safe
4049 * up to bandwidth of 18Gigabit/sec. 8) ]
4050 */
4051
4052static int tcp_disordered_ack(const struct sock *sk, const struct sk_buff *skb)
4053{
4054        const struct tcp_sock *tp = tcp_sk(sk);
4055        const struct tcphdr *th = tcp_hdr(skb);
4056        u32 seq = TCP_SKB_CB(skb)->seq;
4057        u32 ack = TCP_SKB_CB(skb)->ack_seq;
4058
4059        return (/* 1. Pure ACK with correct sequence number. */
4060                (th->ack && seq == TCP_SKB_CB(skb)->end_seq && seq == tp->rcv_nxt) &&
4061
4062                /* 2. ... and duplicate ACK. */
4063                ack == tp->snd_una &&
4064
4065                /* 3. ... and does not update window. */
4066                !tcp_may_update_window(tp, ack, seq, ntohs(th->window) << tp->rx_opt.snd_wscale) &&
4067
4068                /* 4. ... and sits in replay window. */
4069                (s32)(tp->rx_opt.ts_recent - tp->rx_opt.rcv_tsval) <= (inet_csk(sk)->icsk_rto * 1024) / HZ);
4070}
4071
4072static inline int tcp_paws_discard(const struct sock *sk,
4073                                   const struct sk_buff *skb)
4074{
4075        const struct tcp_sock *tp = tcp_sk(sk);
4076
4077        return !tcp_paws_check(&tp->rx_opt, TCP_PAWS_WINDOW) &&
4078               !tcp_disordered_ack(sk, skb);
4079}
4080
4081/* Check segment sequence number for validity.
4082 *
4083 * Segment controls are considered valid, if the segment
4084 * fits to the window after truncation to the window. Acceptability
4085 * of data (and SYN, FIN, of course) is checked separately.
4086 * See tcp_data_queue(), for example.
4087 *
4088 * Also, controls (RST is main one) are accepted using RCV.WUP instead
4089 * of RCV.NXT. Peer still did not advance his SND.UNA when we
4090 * delayed ACK, so that hisSND.UNA<=ourRCV.WUP.
4091 * (borrowed from freebsd)
4092 */
4093
4094static inline int tcp_sequence(const struct tcp_sock *tp, u32 seq, u32 end_seq)
4095{
4096        return  !before(end_seq, tp->rcv_wup) &&
4097                !after(seq, tp->rcv_nxt + tcp_receive_window(tp));
4098}
4099
4100/* When we get a reset we do this. */
4101static void tcp_reset(struct sock *sk)
4102{
4103        /* We want the right error as BSD sees it (and indeed as we do). */
4104        switch (sk->sk_state) {
4105        case TCP_SYN_SENT:
4106                sk->sk_err = ECONNREFUSED;
4107                break;
4108        case TCP_CLOSE_WAIT:
4109                sk->sk_err = EPIPE;
4110                break;
4111        case TCP_CLOSE:
4112                return;
4113        default:
4114                sk->sk_err = ECONNRESET;
4115        }
4116        /* This barrier is coupled with smp_rmb() in tcp_poll() */
4117        smp_wmb();
4118
4119        if (!sock_flag(sk, SOCK_DEAD))
4120                sk->sk_error_report(sk);
4121
4122        tcp_done(sk);
4123}
4124
4125/*
4126 *      Process the FIN bit. This now behaves as it is supposed to work
4127 *      and the FIN takes effect when it is validly part of sequence
4128 *      space. Not before when we get holes.
4129 *
4130 *      If we are ESTABLISHED, a received fin moves us to CLOSE-WAIT
4131 *      (and thence onto LAST-ACK and finally, CLOSE, we never enter
4132 *      TIME-WAIT)
4133 *
4134 *      If we are in FINWAIT-1, a received FIN indicates simultaneous
4135 *      close and we go into CLOSING (and later onto TIME-WAIT)
4136 *
4137 *      If we are in FINWAIT-2, a received FIN moves us to TIME-WAIT.
4138 */
4139static void tcp_fin(struct sock *sk)
4140{
4141        struct tcp_sock *tp = tcp_sk(sk);
4142
4143        inet_csk_schedule_ack(sk);
4144
4145        sk->sk_shutdown |= RCV_SHUTDOWN;
4146        sock_set_flag(sk, SOCK_DONE);
4147
4148        switch (sk->sk_state) {
4149        case TCP_SYN_RECV:
4150        case TCP_ESTABLISHED:
4151                /* Move to CLOSE_WAIT */
4152                tcp_set_state(sk, TCP_CLOSE_WAIT);
4153                inet_csk(sk)->icsk_ack.pingpong = 1;
4154                break;
4155
4156        case TCP_CLOSE_WAIT:
4157        case TCP_CLOSING:
4158                /* Received a retransmission of the FIN, do
4159                 * nothing.
4160                 */
4161                break;
4162        case TCP_LAST_ACK:
4163                /* RFC793: Remain in the LAST-ACK state. */
4164                break;
4165
4166        case TCP_FIN_WAIT1:
4167                /* This case occurs when a simultaneous close
4168                 * happens, we must ack the received FIN and
4169                 * enter the CLOSING state.
4170                 */
4171                tcp_send_ack(sk);
4172                tcp_set_state(sk, TCP_CLOSING);
4173                break;
4174        case TCP_FIN_WAIT2:
4175                /* Received a FIN -- send ACK and enter TIME_WAIT. */
4176                tcp_send_ack(sk);
4177                tcp_time_wait(sk, TCP_TIME_WAIT, 0);
4178                break;
4179        default:
4180                /* Only TCP_LISTEN and TCP_CLOSE are left, in these
4181                 * cases we should never reach this piece of code.
4182                 */
4183                printk(KERN_ERR "%s: Impossible, sk->sk_state=%d\n",
4184                       __func__, sk->sk_state);
4185                break;
4186        }
4187
4188        /* It _is_ possible, that we have something out-of-order _after_ FIN.
4189         * Probably, we should reset in this case. For now drop them.
4190         */
4191        __skb_queue_purge(&tp->out_of_order_queue);
4192        if (tcp_is_sack(tp))
4193                tcp_sack_reset(&tp->rx_opt);
4194        sk_mem_reclaim(sk);
4195
4196        if (!sock_flag(sk, SOCK_DEAD)) {
4197                sk->sk_state_change(sk);
4198
4199                /* Do not send POLL_HUP for half duplex close. */
4200                if (sk->sk_shutdown == SHUTDOWN_MASK ||
4201                    sk->sk_state == TCP_CLOSE)
4202                        sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_HUP);
4203                else
4204                        sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_IN);
4205        }
4206}
4207
4208static inline int tcp_sack_extend(struct tcp_sack_block *sp, u32 seq,
4209                                  u32 end_seq)
4210{
4211        if (!after(seq, sp->end_seq) && !after(sp->start_seq, end_seq)) {
4212                if (before(seq, sp->start_seq))
4213                        sp->start_seq = seq;
4214                if (after(end_seq, sp->end_seq))
4215                        sp->end_seq = end_seq;
4216                return 1;
4217        }
4218        return 0;
4219}
4220
4221static void tcp_dsack_set(struct sock *sk, u32 seq, u32 end_seq)
4222{
4223        struct tcp_sock *tp = tcp_sk(sk);
4224
4225        if (tcp_is_sack(tp) && sysctl_tcp_dsack) {
4226                int mib_idx;
4227
4228                if (before(seq, tp->rcv_nxt))
4229                        mib_idx = LINUX_MIB_TCPDSACKOLDSENT;
4230                else
4231                        mib_idx = LINUX_MIB_TCPDSACKOFOSENT;
4232
4233                NET_INC_STATS_BH(sock_net(sk), mib_idx);
4234
4235                tp->rx_opt.dsack = 1;
4236                tp->duplicate_sack[0].start_seq = seq;
4237                tp->duplicate_sack[0].end_seq = end_seq;
4238        }
4239}
4240
4241static void tcp_dsack_extend(struct sock *sk, u32 seq, u32 end_seq)
4242{
4243        struct tcp_sock *tp = tcp_sk(sk);
4244
4245        if (!tp->rx_opt.dsack)
4246                tcp_dsack_set(sk, seq, end_seq);
4247        else
4248                tcp_sack_extend(tp->duplicate_sack, seq, end_seq);
4249}
4250
4251static void tcp_send_dupack(struct sock *sk, const struct sk_buff *skb)
4252{
4253        struct tcp_sock *tp = tcp_sk(sk);
4254
4255        if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
4256            before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
4257                NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKLOST);
4258                tcp_enter_quickack_mode(sk);
4259
4260                if (tcp_is_sack(tp) && sysctl_tcp_dsack) {
4261                        u32 end_seq = TCP_SKB_CB(skb)->end_seq;
4262
4263                        if (after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt))
4264                                end_seq = tp->rcv_nxt;
4265                        tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, end_seq);
4266                }
4267        }
4268
4269        tcp_send_ack(sk);
4270}
4271
4272/* These routines update the SACK block as out-of-order packets arrive or
4273 * in-order packets close up the sequence space.
4274 */
4275static void tcp_sack_maybe_coalesce(struct tcp_sock *tp)
4276{
4277        int this_sack;
4278        struct tcp_sack_block *sp = &tp->selective_acks[0];
4279        struct tcp_sack_block *swalk = sp + 1;
4280
4281        /* See if the recent change to the first SACK eats into
4282         * or hits the sequence space of other SACK blocks, if so coalesce.
4283         */
4284        for (this_sack = 1; this_sack < tp->rx_opt.num_sacks;) {
4285                if (tcp_sack_extend(sp, swalk->start_seq, swalk->end_seq)) {
4286                        int i;
4287
4288                        /* Zap SWALK, by moving every further SACK up by one slot.
4289                         * Decrease num_sacks.
4290                         */
4291                        tp->rx_opt.num_sacks--;
4292                        for (i = this_sack; i < tp->rx_opt.num_sacks; i++)
4293                                sp[i] = sp[i + 1];
4294                        continue;
4295                }
4296                this_sack++, swalk++;
4297        }
4298}
4299
4300static void tcp_sack_new_ofo_skb(struct sock *sk, u32 seq, u32 end_seq)
4301{
4302        struct tcp_sock *tp = tcp_sk(sk);
4303        struct tcp_sack_block *sp = &tp->selective_acks[0];
4304        int cur_sacks = tp->rx_opt.num_sacks;
4305        int this_sack;
4306
4307        if (!cur_sacks)
4308                goto new_sack;
4309
4310        for (this_sack = 0; this_sack < cur_sacks; this_sack++, sp++) {
4311                if (tcp_sack_extend(sp, seq, end_seq)) {
4312                        /* Rotate this_sack to the first one. */
4313                        for (; this_sack > 0; this_sack--, sp--)
4314                                swap(*sp, *(sp - 1));
4315                        if (cur_sacks > 1)
4316                                tcp_sack_maybe_coalesce(tp);
4317                        return;
4318                }
4319        }
4320
4321        /* Could not find an adjacent existing SACK, build a new one,
4322         * put it at the front, and shift everyone else down.  We
4323         * always know there is at least one SACK present already here.
4324         *
4325         * If the sack array is full, forget about the last one.
4326         */
4327        if (this_sack >= TCP_NUM_SACKS) {
4328                this_sack--;
4329                tp->rx_opt.num_sacks--;
4330                sp--;
4331        }
4332        for (; this_sack > 0; this_sack--, sp--)
4333                *sp = *(sp - 1);
4334
4335new_sack:
4336        /* Build the new head SACK, and we're done. */
4337        sp->start_seq = seq;
4338        sp->end_seq = end_seq;
4339        tp->rx_opt.num_sacks++;
4340}
4341
4342/* RCV.NXT advances, some SACKs should be eaten. */
4343
4344static void tcp_sack_remove(struct tcp_sock *tp)
4345{
4346        struct tcp_sack_block *sp = &tp->selective_acks[0];
4347        int num_sacks = tp->rx_opt.num_sacks;
4348        int this_sack;
4349
4350        /* Empty ofo queue, hence, all the SACKs are eaten. Clear. */
4351        if (skb_queue_empty(&tp->out_of_order_queue)) {
4352                tp->rx_opt.num_sacks = 0;
4353                return;
4354        }
4355
4356        for (this_sack = 0; this_sack < num_sacks;) {
4357                /* Check if the start of the sack is covered by RCV.NXT. */
4358                if (!before(tp->rcv_nxt, sp->start_seq)) {
4359                        int i;
4360
4361                        /* RCV.NXT must cover all the block! */
4362                        WARN_ON(before(tp->rcv_nxt, sp->end_seq));
4363
4364                        /* Zap this SACK, by moving forward any other SACKS. */
4365                        for (i=this_sack+1; i < num_sacks; i++)
4366                                tp->selective_acks[i-1] = tp->selective_acks[i];
4367                        num_sacks--;
4368                        continue;
4369                }
4370                this_sack++;
4371                sp++;
4372        }
4373        tp->rx_opt.num_sacks = num_sacks;
4374}
4375
4376/* This one checks to see if we can put data from the
4377 * out_of_order queue into the receive_queue.
4378 */
4379static void tcp_ofo_queue(struct sock *sk)
4380{
4381        struct tcp_sock *tp = tcp_sk(sk);
4382        __u32 dsack_high = tp->rcv_nxt;
4383        struct sk_buff *skb;
4384
4385        while ((skb = skb_peek(&tp->out_of_order_queue)) != NULL) {
4386                if (after(TCP_SKB_CB(skb)->seq, tp->rcv_nxt))
4387                        break;
4388
4389                if (before(TCP_SKB_CB(skb)->seq, dsack_high)) {
4390                        __u32 dsack = dsack_high;
4391                        if (before(TCP_SKB_CB(skb)->end_seq, dsack_high))
4392                                dsack_high = TCP_SKB_CB(skb)->end_seq;
4393                        tcp_dsack_extend(sk, TCP_SKB_CB(skb)->seq, dsack);
4394                }
4395
4396                if (!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) {
4397                        SOCK_DEBUG(sk, "ofo packet was already received\n");
4398                        __skb_unlink(skb, &tp->out_of_order_queue);
4399                        __kfree_skb(skb);
4400                        continue;
4401                }
4402                SOCK_DEBUG(sk, "ofo requeuing : rcv_next %X seq %X - %X\n",
4403                           tp->rcv_nxt, TCP_SKB_CB(skb)->seq,
4404                           TCP_SKB_CB(skb)->end_seq);
4405
4406                __skb_unlink(skb, &tp->out_of_order_queue);
4407                __skb_queue_tail(&sk->sk_receive_queue, skb);
4408                tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
4409                if (tcp_hdr(skb)->fin)
4410                        tcp_fin(sk);
4411        }
4412}
4413
4414static int tcp_prune_ofo_queue(struct sock *sk);
4415static int tcp_prune_queue(struct sock *sk);
4416
4417static inline int tcp_try_rmem_schedule(struct sock *sk, unsigned int size)
4418{
4419        if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf ||
4420            !sk_rmem_schedule(sk, size)) {
4421
4422                if (tcp_prune_queue(sk) < 0)
4423                        return -1;
4424
4425                if (!sk_rmem_schedule(sk, size)) {
4426                        if (!tcp_prune_ofo_queue(sk))
4427                                return -1;
4428
4429                        if (!sk_rmem_schedule(sk, size))
4430                                return -1;
4431                }
4432        }
4433        return 0;
4434}
4435
4436static void tcp_data_queue(struct sock *sk, struct sk_buff *skb)
4437{
4438        const struct tcphdr *th = tcp_hdr(skb);
4439        struct tcp_sock *tp = tcp_sk(sk);
4440        int eaten = -1;
4441
4442        if (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq)
4443                goto drop;
4444
4445        skb_dst_drop(skb);
4446        __skb_pull(skb, th->doff * 4);
4447
4448        TCP_ECN_accept_cwr(tp, skb);
4449
4450        tp->rx_opt.dsack = 0;
4451
4452        /*  Queue data for delivery to the user.
4453         *  Packets in sequence go to the receive queue.
4454         *  Out of sequence packets to the out_of_order_queue.
4455         */
4456        if (TCP_SKB_CB(skb)->seq == tp->rcv_nxt) {
4457                if (tcp_receive_window(tp) == 0)
4458                        goto out_of_window;
4459
4460                /* Ok. In sequence. In window. */
4461                if (tp->ucopy.task == current &&
4462                    tp->copied_seq == tp->rcv_nxt && tp->ucopy.len &&
4463                    sock_owned_by_user(sk) && !tp->urg_data) {
4464                        int chunk = min_t(unsigned int, skb->len,
4465                                          tp->ucopy.len);
4466
4467                        __set_current_state(TASK_RUNNING);
4468
4469                        local_bh_enable();
4470                        if (!skb_copy_datagram_iovec(skb, 0, tp->ucopy.iov, chunk)) {
4471                                tp->ucopy.len -= chunk;
4472                                tp->copied_seq += chunk;
4473                                eaten = (chunk == skb->len);
4474                                tcp_rcv_space_adjust(sk);
4475                        }
4476                        local_bh_disable();
4477                }
4478
4479                if (eaten <= 0) {
4480queue_and_out:
4481                        if (eaten < 0 &&
4482                            tcp_try_rmem_schedule(sk, skb->truesize))
4483                                goto drop;
4484
4485                        skb_set_owner_r(skb, sk);
4486                        __skb_queue_tail(&sk->sk_receive_queue, skb);
4487                }
4488                tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
4489                if (skb->len)
4490                        tcp_event_data_recv(sk, skb);
4491                if (th->fin)
4492                        tcp_fin(sk);
4493
4494                if (!skb_queue_empty(&tp->out_of_order_queue)) {
4495                        tcp_ofo_queue(sk);
4496
4497                        /* RFC2581. 4.2. SHOULD send immediate ACK, when
4498                         * gap in queue is filled.
4499                         */
4500                        if (skb_queue_empty(&tp->out_of_order_queue))
4501                                inet_csk(sk)->icsk_ack.pingpong = 0;
4502                }
4503
4504                if (tp->rx_opt.num_sacks)
4505                        tcp_sack_remove(tp);
4506
4507                tcp_fast_path_check(sk);
4508
4509                if (eaten > 0)
4510                        __kfree_skb(skb);
4511                else if (!sock_flag(sk, SOCK_DEAD))
4512                        sk->sk_data_ready(sk, 0);
4513                return;
4514        }
4515
4516        if (!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) {
4517                /* A retransmit, 2nd most common case.  Force an immediate ack. */
4518                NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKLOST);
4519                tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq);
4520
4521out_of_window:
4522                tcp_enter_quickack_mode(sk);
4523                inet_csk_schedule_ack(sk);
4524drop:
4525                __kfree_skb(skb);
4526                return;
4527        }
4528
4529        /* Out of window. F.e. zero window probe. */
4530        if (!before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt + tcp_receive_window(tp)))
4531                goto out_of_window;
4532
4533        tcp_enter_quickack_mode(sk);
4534
4535        if (before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
4536                /* Partial packet, seq < rcv_next < end_seq */
4537                SOCK_DEBUG(sk, "partial packet: rcv_next %X seq %X - %X\n",
4538                           tp->rcv_nxt, TCP_SKB_CB(skb)->seq,
4539                           TCP_SKB_CB(skb)->end_seq);
4540
4541                tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, tp->rcv_nxt);
4542
4543                /* If window is closed, drop tail of packet. But after
4544                 * remembering D-SACK for its head made in previous line.
4545                 */
4546                if (!tcp_receive_window(tp))
4547                        goto out_of_window;
4548                goto queue_and_out;
4549        }
4550
4551        TCP_ECN_check_ce(tp, skb);
4552
4553        if (tcp_try_rmem_schedule(sk, skb->truesize))
4554                goto drop;
4555
4556        /* Disable header prediction. */
4557        tp->pred_flags = 0;
4558        inet_csk_schedule_ack(sk);
4559
4560        SOCK_DEBUG(sk, "out of order segment: rcv_next %X seq %X - %X\n",
4561                   tp->rcv_nxt, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq);
4562
4563        skb_set_owner_r(skb, sk);
4564
4565        if (!skb_peek(&tp->out_of_order_queue)) {
4566                /* Initial out of order segment, build 1 SACK. */
4567                if (tcp_is_sack(tp)) {
4568                        tp->rx_opt.num_sacks = 1;
4569                        tp->selective_acks[0].start_seq = TCP_SKB_CB(skb)->seq;
4570                        tp->selective_acks[0].end_seq =
4571                                                TCP_SKB_CB(skb)->end_seq;
4572                }
4573                __skb_queue_head(&tp->out_of_order_queue, skb);
4574        } else {
4575                struct sk_buff *skb1 = skb_peek_tail(&tp->out_of_order_queue);
4576                u32 seq = TCP_SKB_CB(skb)->seq;
4577                u32 end_seq = TCP_SKB_CB(skb)->end_seq;
4578
4579                if (seq == TCP_SKB_CB(skb1)->end_seq) {
4580                        __skb_queue_after(&tp->out_of_order_queue, skb1, skb);
4581
4582                        if (!tp->rx_opt.num_sacks ||
4583                            tp->selective_acks[0].end_seq != seq)
4584                                goto add_sack;
4585
4586                        /* Common case: data arrive in order after hole. */
4587                        tp->selective_acks[0].end_seq = end_seq;
4588                        return;
4589                }
4590
4591                /* Find place to insert this segment. */
4592                while (1) {
4593                        if (!after(TCP_SKB_CB(skb1)->seq, seq))
4594                                break;
4595                        if (skb_queue_is_first(&tp->out_of_order_queue, skb1)) {
4596                                skb1 = NULL;
4597                                break;
4598                        }
4599                        skb1 = skb_queue_prev(&tp->out_of_order_queue, skb1);
4600                }
4601
4602                /* Do skb overlap to previous one? */
4603                if (skb1 && before(seq, TCP_SKB_CB(skb1)->end_seq)) {
4604                        if (!after(end_seq, TCP_SKB_CB(skb1)->end_seq)) {
4605                                /* All the bits are present. Drop. */
4606                                __kfree_skb(skb);
4607                                tcp_dsack_set(sk, seq, end_seq);
4608                                goto add_sack;
4609                        }
4610                        if (after(seq, TCP_SKB_CB(skb1)->seq)) {
4611                                /* Partial overlap. */
4612                                tcp_dsack_set(sk, seq,
4613                                              TCP_SKB_CB(skb1)->end_seq);
4614                        } else {
4615                                if (skb_queue_is_first(&tp->out_of_order_queue,
4616                                                       skb1))
4617                                        skb1 = NULL;
4618                                else
4619                                        skb1 = skb_queue_prev(
4620                                                &tp->out_of_order_queue,
4621                                                skb1);
4622                        }
4623                }
4624                if (!skb1)
4625                        __skb_queue_head(&tp->out_of_order_queue, skb);
4626                else
4627                        __skb_queue_after(&tp->out_of_order_queue, skb1, skb);
4628
4629                /* And clean segments covered by new one as whole. */
4630                while (!skb_queue_is_last(&tp->out_of_order_queue, skb)) {
4631                        skb1 = skb_queue_next(&tp->out_of_order_queue, skb);
4632
4633                        if (!after(end_seq, TCP_SKB_CB(skb1)->seq))
4634                                break;
4635                        if (before(end_seq, TCP_SKB_CB(skb1)->end_seq)) {
4636                                tcp_dsack_extend(sk, TCP_SKB_CB(skb1)->seq,
4637                                                 end_seq);
4638                                break;
4639                        }
4640                        __skb_unlink(skb1, &tp->out_of_order_queue);
4641                        tcp_dsack_extend(sk, TCP_SKB_CB(skb1)->seq,
4642                                         TCP_SKB_CB(skb1)->end_seq);
4643                        __kfree_skb(skb1);
4644                }
4645
4646add_sack:
4647                if (tcp_is_sack(tp))
4648                        tcp_sack_new_ofo_skb(sk, seq, end_seq);
4649        }
4650}
4651
4652static struct sk_buff *tcp_collapse_one(struct sock *sk, struct sk_buff *skb,
4653                                        struct sk_buff_head *list)
4654{
4655        struct sk_buff *next = NULL;
4656
4657        if (!skb_queue_is_last(list, skb))
4658                next = skb_queue_next(list, skb);
4659
4660        __skb_unlink(skb, list);
4661        __kfree_skb(skb);
4662        NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPRCVCOLLAPSED);
4663
4664        return next;
4665}
4666
4667/* Collapse contiguous sequence of skbs head..tail with
4668 * sequence numbers start..end.
4669 *
4670 * If tail is NULL, this means until the end of the list.
4671 *
4672 * Segments with FIN/SYN are not collapsed (only because this
4673 * simplifies code)
4674 */
4675static void
4676tcp_collapse(struct sock *sk, struct sk_buff_head *list,
4677             struct sk_buff *head, struct sk_buff *tail,
4678             u32 start, u32 end)
4679{
4680        struct sk_buff *skb, *n;
4681        bool end_of_skbs;
4682
4683        /* First, check that queue is collapsible and find
4684         * the point where collapsing can be useful. */
4685        skb = head;
4686restart:
4687        end_of_skbs = true;
4688        skb_queue_walk_from_safe(list, skb, n) {
4689                if (skb == tail)
4690                        break;
4691                /* No new bits? It is possible on ofo queue. */
4692                if (!before(start, TCP_SKB_CB(skb)->end_seq)) {
4693                        skb = tcp_collapse_one(sk, skb, list);
4694                        if (!skb)
4695                                break;
4696                        goto restart;
4697                }
4698
4699                /* The first skb to collapse is:
4700                 * - not SYN/FIN and
4701                 * - bloated or contains data before "start" or
4702                 *   overlaps to the next one.
4703                 */
4704                if (!tcp_hdr(skb)->syn && !tcp_hdr(skb)->fin &&
4705                    (tcp_win_from_space(skb->truesize) > skb->len ||
4706                     before(TCP_SKB_CB(skb)->seq, start))) {
4707                        end_of_skbs = false;
4708                        break;
4709                }
4710
4711                if (!skb_queue_is_last(list, skb)) {
4712                        struct sk_buff *next = skb_queue_next(list, skb);
4713                        if (next != tail &&
4714                            TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(next)->seq) {
4715                                end_of_skbs = false;
4716                                break;
4717                        }
4718                }
4719
4720                /* Decided to skip this, advance start seq. */
4721                start = TCP_SKB_CB(skb)->end_seq;
4722        }
4723        if (end_of_skbs || tcp_hdr(skb)->syn || tcp_hdr(skb)->fin)
4724                return;
4725
4726        while (before(start, end)) {
4727                struct sk_buff *nskb;
4728                unsigned int header = skb_headroom(skb);
4729                int copy = SKB_MAX_ORDER(header, 0);
4730
4731                /* Too big header? This can happen with IPv6. */
4732                if (copy < 0)
4733                        return;
4734                if (end - start < copy)
4735                        copy = end - start;
4736                nskb = alloc_skb(copy + header, GFP_ATOMIC);
4737                if (!nskb)
4738                        return;
4739
4740                skb_set_mac_header(nskb, skb_mac_header(skb) - skb->head);
4741                skb_set_network_header(nskb, (skb_network_header(skb) -
4742                                              skb->head));
4743                skb_set_transport_header(nskb, (skb_transport_header(skb) -
4744                                                skb->head));
4745                skb_reserve(nskb, header);
4746                memcpy(nskb->head, skb->head, header);
4747                memcpy(nskb->cb, skb->cb, sizeof(skb->cb));
4748                TCP_SKB_CB(nskb)->seq = TCP_SKB_CB(nskb)->end_seq = start;
4749                __skb_queue_before(list, skb, nskb);
4750                skb_set_owner_r(nskb, sk);
4751
4752                /* Copy data, releasing collapsed skbs. */
4753                while (copy > 0) {
4754                        int offset = start - TCP_SKB_CB(skb)->seq;
4755                        int size = TCP_SKB_CB(skb)->end_seq - start;
4756
4757                        BUG_ON(offset < 0);
4758                        if (size > 0) {
4759                                size = min(copy, size);
4760                                if (skb_copy_bits(skb, offset, skb_put(nskb, size), size))
4761                                        BUG();
4762                                TCP_SKB_CB(nskb)->end_seq += size;
4763                                copy -= size;
4764                                start += size;
4765                        }
4766                        if (!before(start, TCP_SKB_CB(skb)->end_seq)) {
4767                                skb = tcp_collapse_one(sk, skb, list);
4768                                if (!skb ||
4769                                    skb == tail ||
4770                                    tcp_hdr(skb)->syn ||
4771                                    tcp_hdr(skb)->fin)
4772                                        return;
4773                        }
4774                }
4775        }
4776}
4777
4778/* Collapse ofo queue. Algorithm: select contiguous sequence of skbs
4779 * and tcp_collapse() them until all the queue is collapsed.
4780 */
4781static void tcp_collapse_ofo_queue(struct sock *sk)
4782{
4783        struct tcp_sock *tp = tcp_sk(sk);
4784        struct sk_buff *skb = skb_peek(&tp->out_of_order_queue);
4785        struct sk_buff *head;
4786        u32 start, end;
4787
4788        if (skb == NULL)
4789                return;
4790
4791        start = TCP_SKB_CB(skb)->seq;
4792        end = TCP_SKB_CB(skb)->end_seq;
4793        head = skb;
4794
4795        for (;;) {
4796                struct sk_buff *next = NULL;
4797
4798                if (!skb_queue_is_last(&tp->out_of_order_queue, skb))
4799                        next = skb_queue_next(&tp->out_of_order_queue, skb);
4800                skb = next;
4801
4802                /* Segment is terminated when we see gap or when
4803                 * we are at the end of all the queue. */
4804                if (!skb ||
4805                    after(TCP_SKB_CB(skb)->seq, end) ||
4806                    before(TCP_SKB_CB(skb)->end_seq, start)) {
4807                        tcp_collapse(sk, &tp->out_of_order_queue,
4808                                     head, skb, start, end);
4809                        head = skb;
4810                        if (!skb)
4811                                break;
4812                        /* Start new segment */
4813                        start = TCP_SKB_CB(skb)->seq;
4814                        end = TCP_SKB_CB(skb)->end_seq;
4815                } else {
4816                        if (before(TCP_SKB_CB(skb)->seq, start))
4817                                start = TCP_SKB_CB(skb)->seq;
4818                        if (after(TCP_SKB_CB(skb)->end_seq, end))
4819                                end = TCP_SKB_CB(skb)->end_seq;
4820                }
4821        }
4822}
4823
4824/*
4825 * Purge the out-of-order queue.
4826 * Return true if queue was pruned.
4827 */
4828static int tcp_prune_ofo_queue(struct sock *sk)
4829{
4830        struct tcp_sock *tp = tcp_sk(sk);
4831        int res = 0;
4832
4833        if (!skb_queue_empty(&tp->out_of_order_queue)) {
4834                NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_OFOPRUNED);
4835                __skb_queue_purge(&tp->out_of_order_queue);
4836
4837                /* Reset SACK state.  A conforming SACK implementation will
4838                 * do the same at a timeout based retransmit.  When a connection
4839                 * is in a sad state like this, we care only about integrity
4840                 * of the connection not performance.
4841                 */
4842                if (tp->rx_opt.sack_ok)
4843                        tcp_sack_reset(&tp->rx_opt);
4844                sk_mem_reclaim(sk);
4845                res = 1;
4846        }
4847        return res;
4848}
4849
4850/* Reduce allocated memory if we can, trying to get
4851 * the socket within its memory limits again.
4852 *
4853 * Return less than zero if we should start dropping frames
4854 * until the socket owning process reads some of the data
4855 * to stabilize the situation.
4856 */
4857static int tcp_prune_queue(struct sock *sk)
4858{
4859        struct tcp_sock *tp = tcp_sk(sk);
4860
4861        SOCK_DEBUG(sk, "prune_queue: c=%x\n", tp->copied_seq);
4862
4863        NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_PRUNECALLED);
4864
4865        if (atomic_read(&sk->sk_rmem_alloc) >= sk->sk_rcvbuf)
4866                tcp_clamp_window(sk);
4867        else if (tcp_memory_pressure)
4868                tp->rcv_ssthresh = min(tp->rcv_ssthresh, 4U * tp->advmss);
4869
4870        tcp_collapse_ofo_queue(sk);
4871        if (!skb_queue_empty(&sk->sk_receive_queue))
4872                tcp_collapse(sk, &sk->sk_receive_queue,
4873                             skb_peek(&sk->sk_receive_queue),
4874                             NULL,
4875                             tp->copied_seq, tp->rcv_nxt);
4876        sk_mem_reclaim(sk);
4877
4878        if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
4879                return 0;
4880
4881        /* Collapsing did not help, destructive actions follow.
4882         * This must not ever occur. */
4883
4884        tcp_prune_ofo_queue(sk);
4885
4886        if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
4887                return 0;
4888
4889        /* If we are really being abused, tell the caller to silently
4890         * drop receive data on the floor.  It will get retransmitted
4891         * and hopefully then we'll have sufficient space.
4892         */
4893        NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_RCVPRUNED);
4894
4895        /* Massive buffer overcommit. */
4896        tp->pred_flags = 0;
4897        return -1;
4898}
4899
4900/* RFC2861, slow part. Adjust cwnd, after it was not full during one rto.
4901 * As additional protections, we do not touch cwnd in retransmission phases,
4902 * and if application hit its sndbuf limit recently.
4903 */
4904void tcp_cwnd_application_limited(struct sock *sk)
4905{
4906        struct tcp_sock *tp = tcp_sk(sk);
4907
4908        if (inet_csk(sk)->icsk_ca_state == TCP_CA_Open &&
4909            sk->sk_socket && !test_bit(SOCK_NOSPACE, &sk->sk_socket->flags)) {
4910                /* Limited by application or receiver window. */
4911                u32 init_win = tcp_init_cwnd(tp, __sk_dst_get(sk));
4912                u32 win_used = max(tp->snd_cwnd_used, init_win);
4913                if (win_used < tp->snd_cwnd) {
4914                        tp->snd_ssthresh = tcp_current_ssthresh(sk);
4915                        tp->snd_cwnd = (tp->snd_cwnd + win_used) >> 1;
4916                }
4917                tp->snd_cwnd_used = 0;
4918        }
4919        tp->snd_cwnd_stamp = tcp_time_stamp;
4920}
4921
4922static int tcp_should_expand_sndbuf(const struct sock *sk)
4923{
4924        const struct tcp_sock *tp = tcp_sk(sk);
4925
4926        /* If the user specified a specific send buffer setting, do
4927         * not modify it.
4928         */
4929        if (sk->sk_userlocks & SOCK_SNDBUF_LOCK)
4930                return 0;
4931
4932        /* If we are under global TCP memory pressure, do not expand.  */
4933        if (tcp_memory_pressure)
4934                return 0;
4935
4936        /* If we are under soft global TCP memory pressure, do not expand.  */
4937        if (atomic_long_read(&tcp_memory_allocated) >= sysctl_tcp_mem[0])
4938                return 0;
4939
4940        /* If we filled the congestion window, do not expand.  */
4941        if (tp->packets_out >= tp->snd_cwnd)
4942                return 0;
4943
4944        return 1;
4945}
4946
4947/* When incoming ACK allowed to free some skb from write_queue,
4948 * we remember this event in flag SOCK_QUEUE_SHRUNK and wake up socket
4949 * on the exit from tcp input handler.
4950 *
4951 * PROBLEM: sndbuf expansion does not work well with largesend.
4952 */
4953static void tcp_new_space(struct sock *sk)
4954{
4955        struct tcp_sock *tp = tcp_sk(sk);
4956
4957        if (tcp_should_expand_sndbuf(sk)) {
4958                int sndmem = SKB_TRUESIZE(max_t(u32,
4959                                                tp->rx_opt.mss_clamp,
4960                                                tp->mss_cache) +
4961                                          MAX_TCP_HEADER);
4962                int demanded = max_t(unsigned int, tp->snd_cwnd,
4963                                     tp->reordering + 1);
4964                sndmem *= 2 * demanded;
4965                if (sndmem > sk->sk_sndbuf)
4966                        sk->sk_sndbuf = min(sndmem, sysctl_tcp_wmem[2]);
4967                tp->snd_cwnd_stamp = tcp_time_stamp;
4968        }
4969
4970        sk->sk_write_space(sk);
4971}
4972
4973static void tcp_check_space(struct sock *sk)
4974{
4975        if (sock_flag(sk, SOCK_QUEUE_SHRUNK)) {
4976                sock_reset_flag(sk, SOCK_QUEUE_SHRUNK);
4977                if (sk->sk_socket &&
4978                    test_bit(SOCK_NOSPACE, &sk->sk_socket->flags))
4979                        tcp_new_space(sk);
4980        }
4981}
4982
4983static inline void tcp_data_snd_check(struct sock *sk)
4984{
4985        tcp_push_pending_frames(sk);
4986        tcp_check_space(sk);
4987}
4988
4989/*
4990 * Check if sending an ack is needed.
4991 */
4992static void __tcp_ack_snd_check(struct sock *sk, int ofo_possible)
4993{
4994        struct tcp_sock *tp = tcp_sk(sk);
4995
4996            /* More than one full frame received... */
4997        if (((tp->rcv_nxt - tp->rcv_wup) > inet_csk(sk)->icsk_ack.rcv_mss &&
4998             /* ... and right edge of window advances far enough.
4999              * (tcp_recvmsg() will send ACK otherwise). Or...
5000              */
5001             __tcp_select_window(sk) >= tp->rcv_wnd) ||
5002            /* We ACK each frame or... */
5003            tcp_in_quickack_mode(sk) ||
5004            /* We have out of order data. */
5005            (ofo_possible && skb_peek(&tp->out_of_order_queue))) {
5006                /* Then ack it now */
5007                tcp_send_ack(sk);
5008        } else {
5009                /* Else, send delayed ack. */
5010                tcp_send_delayed_ack(sk);
5011        }
5012}
5013
5014static inline void tcp_ack_snd_check(struct sock *sk)
5015{
5016        if (!inet_csk_ack_scheduled(sk)) {
5017                /* We sent a data segment already. */
5018                return;
5019        }
5020        __tcp_ack_snd_check(sk, 1);
5021}
5022
5023/*
5024 *      This routine is only called when we have urgent data
5025 *      signaled. Its the 'slow' part of tcp_urg. It could be
5026 *      moved inline now as tcp_urg is only called from one
5027 *      place. We handle URGent data wrong. We have to - as
5028 *      BSD still doesn't use the correction from RFC961.
5029 *      For 1003.1g we should support a new option TCP_STDURG to permit
5030 *      either form (or just set the sysctl tcp_stdurg).
5031 */
5032
5033static void tcp_check_urg(struct sock *sk, const struct tcphdr *th)
5034{
5035        struct tcp_sock *tp = tcp_sk(sk);
5036        u32 ptr = ntohs(th->urg_ptr);
5037
5038        if (ptr && !sysctl_tcp_stdurg)
5039                ptr--;
5040        ptr += ntohl(th->seq);
5041
5042        /* Ignore urgent data that we've already seen and read. */
5043        if (after(tp->copied_seq, ptr))
5044                return;
5045
5046        /* Do not replay urg ptr.
5047         *
5048         * NOTE: interesting situation not covered by specs.
5049         * Misbehaving sender may send urg ptr, pointing to segment,
5050         * which we already have in ofo queue. We are not able to fetch
5051         * such data and will stay in TCP_URG_NOTYET until will be eaten
5052         * by recvmsg(). Seems, we are not obliged to handle such wicked
5053         * situations. But it is worth to think about possibility of some
5054         * DoSes using some hypothetical application level deadlock.
5055         */
5056        if (before(ptr, tp->rcv_nxt))
5057                return;
5058
5059        /* Do we already have a newer (or duplicate) urgent pointer? */
5060        if (tp->urg_data && !after(ptr, tp->urg_seq))
5061                return;
5062
5063        /* Tell the world about our new urgent pointer. */
5064        sk_send_sigurg(sk);
5065
5066        /* We may be adding urgent data when the last byte read was
5067         * urgent. To do this requires some care. We cannot just ignore
5068         * tp->copied_seq since we would read the last urgent byte again
5069         * as data, nor can we alter copied_seq until this data arrives
5070         * or we break the semantics of SIOCATMARK (and thus sockatmark())
5071         *
5072         * NOTE. Double Dutch. Rendering to plain English: author of comment
5073         * above did something sort of  send("A", MSG_OOB); send("B", MSG_OOB);
5074         * and expect that both A and B disappear from stream. This is _wrong_.
5075         * Though this happens in BSD with high probability, this is occasional.
5076         * Any application relying on this is buggy. Note also, that fix "works"
5077         * only in this artificial test. Insert some normal data between A and B and we will
5078         * decline of BSD again. Verdict: it is better to remove to trap
5079         * buggy users.
5080         */
5081        if (tp->urg_seq == tp->copied_seq && tp->urg_data &&
5082            !sock_flag(sk, SOCK_URGINLINE) && tp->copied_seq != tp->rcv_nxt) {
5083                struct sk_buff *skb = skb_peek(&sk->sk_receive_queue);
5084                tp->copied_seq++;
5085                if (skb && !before(tp->copied_seq, TCP_SKB_CB(skb)->end_seq)) {
5086                        __skb_unlink(skb, &sk->sk_receive_queue);
5087                        __kfree_skb(skb);
5088                }
5089        }
5090
5091        tp->urg_data = TCP_URG_NOTYET;
5092        tp->urg_seq = ptr;
5093
5094        /* Disable header prediction. */
5095        tp->pred_flags = 0;
5096}
5097
5098/* This is the 'fast' part of urgent handling. */
5099static void tcp_urg(struct sock *sk, struct sk_buff *skb, const struct tcphdr *th)
5100{
5101        struct tcp_sock *tp = tcp_sk(sk);
5102
5103        /* Check if we get a new urgent pointer - normally not. */
5104        if (th->urg)
5105                tcp_check_urg(sk, th);
5106
5107        /* Do we wait for any urgent data? - normally not... */
5108        if (tp->urg_data == TCP_URG_NOTYET) {
5109                u32 ptr = tp->urg_seq - ntohl(th->seq) + (th->doff * 4) -
5110                          th->syn;
5111
5112                /* Is the urgent pointer pointing into this packet? */
5113                if (ptr < skb->len) {
5114                        u8 tmp;
5115                        if (skb_copy_bits(skb, ptr, &tmp, 1))
5116                                BUG();
5117                        tp->urg_data = TCP_URG_VALID | tmp;
5118                        if (!sock_flag(sk, SOCK_DEAD))
5119                                sk->sk_data_ready(sk, 0);
5120                }
5121        }
5122}
5123
5124static int tcp_copy_to_iovec(struct sock *sk, struct sk_buff *skb, int hlen)
5125{
5126        struct tcp_sock *tp = tcp_sk(sk);
5127        int chunk = skb->len - hlen;
5128        int err;
5129
5130        local_bh_enable();
5131        if (skb_csum_unnecessary(skb))
5132                err = skb_copy_datagram_iovec(skb, hlen, tp->ucopy.iov, chunk);
5133        else
5134                err = skb_copy_and_csum_datagram_iovec(skb, hlen,
5135                                                       tp->ucopy.iov);
5136
5137        if (!err) {
5138                tp->ucopy.len -= chunk;
5139                tp->copied_seq += chunk;
5140                tcp_rcv_space_adjust(sk);
5141        }
5142
5143        local_bh_disable();
5144        return err;
5145}
5146
5147static __sum16 __tcp_checksum_complete_user(struct sock *sk,
5148                                            struct sk_buff *skb)
5149{
5150        __sum16 result;
5151
5152        if (sock_owned_by_user(sk)) {
5153                local_bh_enable();
5154                result = __tcp_checksum_complete(skb);
5155                local_bh_disable();
5156        } else {
5157                result = __tcp_checksum_complete(skb);
5158        }
5159        return result;
5160}
5161
5162static inline int tcp_checksum_complete_user(struct sock *sk,
5163                                             struct sk_buff *skb)
5164{
5165        return !skb_csum_unnecessary(skb) &&
5166               __tcp_checksum_complete_user(sk, skb);
5167}
5168
5169#ifdef CONFIG_NET_DMA
5170static int tcp_dma_try_early_copy(struct sock *sk, struct sk_buff *skb,
5171                                  int hlen)
5172{
5173        struct tcp_sock *tp = tcp_sk(sk);
5174        int chunk = skb->len - hlen;
5175        int dma_cookie;
5176        int copied_early = 0;
5177
5178        if (tp->ucopy.wakeup)
5179                return 0;
5180
5181        if (!tp->ucopy.dma_chan && tp->ucopy.pinned_list)
5182                tp->ucopy.dma_chan = dma_find_channel(DMA_MEMCPY);
5183
5184        if (tp->ucopy.dma_chan && skb_csum_unnecessary(skb)) {
5185
5186                dma_cookie = dma_skb_copy_datagram_iovec(tp->ucopy.dma_chan,
5187                                                         skb, hlen,
5188                                                         tp->ucopy.iov, chunk,
5189                                                         tp->ucopy.pinned_list);
5190
5191                if (dma_cookie < 0)
5192                        goto out;
5193
5194                tp->ucopy.