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/module.h>
  66#include <linux/sysctl.h>
  67#include <linux/kernel.h>
  68#include <net/dst.h>
  69#include <net/tcp.h>
  70#include <net/inet_common.h>
  71#include <linux/ipsec.h>
  72#include <asm/unaligned.h>
  73#include <net/netdma.h>
  74
  75int sysctl_tcp_timestamps __read_mostly = 1;
  76int sysctl_tcp_window_scaling __read_mostly = 1;
  77int sysctl_tcp_sack __read_mostly = 1;
  78int sysctl_tcp_fack __read_mostly = 1;
  79int sysctl_tcp_reordering __read_mostly = TCP_FASTRETRANS_THRESH;
  80int sysctl_tcp_ecn __read_mostly;
  81int sysctl_tcp_dsack __read_mostly = 1;
  82int sysctl_tcp_app_win __read_mostly = 31;
  83int sysctl_tcp_adv_win_scale __read_mostly = 2;
  84
  85int sysctl_tcp_stdurg __read_mostly;
  86int sysctl_tcp_rfc1337 __read_mostly;
  87int sysctl_tcp_max_orphans __read_mostly = NR_FILE;
  88int sysctl_tcp_frto __read_mostly = 2;
  89int sysctl_tcp_frto_response __read_mostly;
  90int sysctl_tcp_nometrics_save __read_mostly;
  91
  92int sysctl_tcp_moderate_rcvbuf __read_mostly = 1;
  93int sysctl_tcp_abc __read_mostly;
  94
  95#define FLAG_DATA               0x01 /* Incoming frame contained data.          */
  96#define FLAG_WIN_UPDATE         0x02 /* Incoming ACK was a window update.       */
  97#define FLAG_DATA_ACKED         0x04 /* This ACK acknowledged new data.         */
  98#define FLAG_RETRANS_DATA_ACKED 0x08 /* "" "" some of which was retransmitted.  */
  99#define FLAG_SYN_ACKED          0x10 /* This ACK acknowledged SYN.              */
 100#define FLAG_DATA_SACKED        0x20 /* New SACK.                               */
 101#define FLAG_ECE                0x40 /* ECE in this ACK                         */
 102#define FLAG_DATA_LOST          0x80 /* SACK detected data lossage.             */
 103#define FLAG_SLOWPATH           0x100 /* Do not skip RFC checks for window update.*/
 104#define FLAG_ONLY_ORIG_SACKED   0x200 /* SACKs only non-rexmit sent before RTO */
 105#define FLAG_SND_UNA_ADVANCED   0x400 /* Snd_una was changed (!= FLAG_DATA_ACKED) */
 106#define FLAG_DSACKING_ACK       0x800 /* SACK blocks contained D-SACK info */
 107#define FLAG_NONHEAD_RETRANS_ACKED      0x1000 /* Non-head rexmitted data was ACKed */
 108#define FLAG_SACK_RENEGING      0x2000 /* snd_una advanced to a sacked seq */
 109
 110#define FLAG_ACKED              (FLAG_DATA_ACKED|FLAG_SYN_ACKED)
 111#define FLAG_NOT_DUP            (FLAG_DATA|FLAG_WIN_UPDATE|FLAG_ACKED)
 112#define FLAG_CA_ALERT           (FLAG_DATA_SACKED|FLAG_ECE)
 113#define FLAG_FORWARD_PROGRESS   (FLAG_ACKED|FLAG_DATA_SACKED)
 114#define FLAG_ANY_PROGRESS       (FLAG_FORWARD_PROGRESS|FLAG_SND_UNA_ADVANCED)
 115
 116#define TCP_REMNANT (TCP_FLAG_FIN|TCP_FLAG_URG|TCP_FLAG_SYN|TCP_FLAG_PSH)
 117#define TCP_HP_BITS (~(TCP_RESERVED_BITS|TCP_FLAG_PSH))
 118
 119/* Adapt the MSS value used to make delayed ack decision to the
 120 * real world.
 121 */
 122static void tcp_measure_rcv_mss(struct sock *sk, const struct sk_buff *skb)
 123{
 124        struct inet_connection_sock *icsk = inet_csk(sk);
 125        const unsigned int lss = icsk->icsk_ack.last_seg_size;
 126        unsigned int len;
 127
 128        icsk->icsk_ack.last_seg_size = 0;
 129
 130        /* skb->len may jitter because of SACKs, even if peer
 131         * sends good full-sized frames.
 132         */
 133        len = skb_shinfo(skb)->gso_size ? : skb->len;
 134        if (len >= icsk->icsk_ack.rcv_mss) {
 135                icsk->icsk_ack.rcv_mss = len;
 136        } else {
 137                /* Otherwise, we make more careful check taking into account,
 138                 * that SACKs block is variable.
 139                 *
 140                 * "len" is invariant segment length, including TCP header.
 141                 */
 142                len += skb->data - skb_transport_header(skb);
 143                if (len >= TCP_MIN_RCVMSS + sizeof(struct tcphdr) ||
 144                    /* If PSH is not set, packet should be
 145                     * full sized, provided peer TCP is not badly broken.
 146                     * This observation (if it is correct 8)) allows
 147                     * to handle super-low mtu links fairly.
 148                     */
 149                    (len >= TCP_MIN_MSS + sizeof(struct tcphdr) &&
 150                     !(tcp_flag_word(tcp_hdr(skb)) & TCP_REMNANT))) {
 151                        /* Subtract also invariant (if peer is RFC compliant),
 152                         * tcp header plus fixed timestamp option length.
 153                         * Resulting "len" is MSS free of SACK jitter.
 154                         */
 155                        len -= tcp_sk(sk)->tcp_header_len;
 156                        icsk->icsk_ack.last_seg_size = len;
 157                        if (len == lss) {
 158                                icsk->icsk_ack.rcv_mss = len;
 159                                return;
 160                        }
 161                }
 162                if (icsk->icsk_ack.pending & ICSK_ACK_PUSHED)
 163                        icsk->icsk_ack.pending |= ICSK_ACK_PUSHED2;
 164                icsk->icsk_ack.pending |= ICSK_ACK_PUSHED;
 165        }
 166}
 167
 168static void tcp_incr_quickack(struct sock *sk)
 169{
 170        struct inet_connection_sock *icsk = inet_csk(sk);
 171        unsigned quickacks = tcp_sk(sk)->rcv_wnd / (2 * icsk->icsk_ack.rcv_mss);
 172
 173        if (quickacks == 0)
 174                quickacks = 2;
 175        if (quickacks > icsk->icsk_ack.quick)
 176                icsk->icsk_ack.quick = min(quickacks, TCP_MAX_QUICKACKS);
 177}
 178
 179void tcp_enter_quickack_mode(struct sock *sk)
 180{
 181        struct inet_connection_sock *icsk = inet_csk(sk);
 182        tcp_incr_quickack(sk);
 183        icsk->icsk_ack.pingpong = 0;
 184        icsk->icsk_ack.ato = TCP_ATO_MIN;
 185}
 186
 187/* Send ACKs quickly, if "quick" count is not exhausted
 188 * and the session is not interactive.
 189 */
 190
 191static inline int tcp_in_quickack_mode(const struct sock *sk)
 192{
 193        const struct inet_connection_sock *icsk = inet_csk(sk);
 194        return icsk->icsk_ack.quick && !icsk->icsk_ack.pingpong;
 195}
 196
 197static inline void TCP_ECN_queue_cwr(struct tcp_sock *tp)
 198{
 199        if (tp->ecn_flags & TCP_ECN_OK)
 200                tp->ecn_flags |= TCP_ECN_QUEUE_CWR;
 201}
 202
 203static inline void TCP_ECN_accept_cwr(struct tcp_sock *tp, struct sk_buff *skb)
 204{
 205        if (tcp_hdr(skb)->cwr)
 206                tp->ecn_flags &= ~TCP_ECN_DEMAND_CWR;
 207}
 208
 209static inline void TCP_ECN_withdraw_cwr(struct tcp_sock *tp)
 210{
 211        tp->ecn_flags &= ~TCP_ECN_DEMAND_CWR;
 212}
 213
 214static inline void TCP_ECN_check_ce(struct tcp_sock *tp, struct sk_buff *skb)
 215{
 216        if (tp->ecn_flags & TCP_ECN_OK) {
 217                if (INET_ECN_is_ce(TCP_SKB_CB(skb)->flags))
 218                        tp->ecn_flags |= TCP_ECN_DEMAND_CWR;
 219                /* Funny extension: if ECT is not set on a segment,
 220                 * it is surely retransmit. It is not in ECN RFC,
 221                 * but Linux follows this rule. */
 222                else if (INET_ECN_is_not_ect((TCP_SKB_CB(skb)->flags)))
 223                        tcp_enter_quickack_mode((struct sock *)tp);
 224        }
 225}
 226
 227static inline void TCP_ECN_rcv_synack(struct tcp_sock *tp, struct tcphdr *th)
 228{
 229        if ((tp->ecn_flags & TCP_ECN_OK) && (!th->ece || th->cwr))
 230                tp->ecn_flags &= ~TCP_ECN_OK;
 231}
 232
 233static inline void TCP_ECN_rcv_syn(struct tcp_sock *tp, struct tcphdr *th)
 234{
 235        if ((tp->ecn_flags & TCP_ECN_OK) && (!th->ece || !th->cwr))
 236                tp->ecn_flags &= ~TCP_ECN_OK;
 237}
 238
 239static inline int TCP_ECN_rcv_ecn_echo(struct tcp_sock *tp, struct tcphdr *th)
 240{
 241        if (th->ece && !th->syn && (tp->ecn_flags & TCP_ECN_OK))
 242                return 1;
 243        return 0;
 244}
 245
 246/* Buffer size and advertised window tuning.
 247 *
 248 * 1. Tuning sk->sk_sndbuf, when connection enters established state.
 249 */
 250
 251static void tcp_fixup_sndbuf(struct sock *sk)
 252{
 253        int sndmem = tcp_sk(sk)->rx_opt.mss_clamp + MAX_TCP_HEADER + 16 +
 254                     sizeof(struct sk_buff);
 255
 256        if (sk->sk_sndbuf < 3 * sndmem)
 257                sk->sk_sndbuf = min(3 * sndmem, sysctl_tcp_wmem[2]);
 258}
 259
 260/* 2. Tuning advertised window (window_clamp, rcv_ssthresh)
 261 *
 262 * All tcp_full_space() is split to two parts: "network" buffer, allocated
 263 * forward and advertised in receiver window (tp->rcv_wnd) and
 264 * "application buffer", required to isolate scheduling/application
 265 * latencies from network.
 266 * window_clamp is maximal advertised window. It can be less than
 267 * tcp_full_space(), in this case tcp_full_space() - window_clamp
 268 * is reserved for "application" buffer. The less window_clamp is
 269 * the smoother our behaviour from viewpoint of network, but the lower
 270 * throughput and the higher sensitivity of the connection to losses. 8)
 271 *
 272 * rcv_ssthresh is more strict window_clamp used at "slow start"
 273 * phase to predict further behaviour of this connection.
 274 * It is used for two goals:
 275 * - to enforce header prediction at sender, even when application
 276 *   requires some significant "application buffer". It is check #1.
 277 * - to prevent pruning of receive queue because of misprediction
 278 *   of receiver window. Check #2.
 279 *
 280 * The scheme does not work when sender sends good segments opening
 281 * window and then starts to feed us spaghetti. But it should work
 282 * in common situations. Otherwise, we have to rely on queue collapsing.
 283 */
 284
 285/* Slow part of check#2. */
 286static int __tcp_grow_window(const struct sock *sk, const struct sk_buff *skb)
 287{
 288        struct tcp_sock *tp = tcp_sk(sk);
 289        /* Optimize this! */
 290        int truesize = tcp_win_from_space(skb->truesize) >> 1;
 291        int window = tcp_win_from_space(sysctl_tcp_rmem[2]) >> 1;
 292
 293        while (tp->rcv_ssthresh <= window) {
 294                if (truesize <= skb->len)
 295                        return 2 * inet_csk(sk)->icsk_ack.rcv_mss;
 296
 297                truesize >>= 1;
 298                window >>= 1;
 299        }
 300        return 0;
 301}
 302
 303static void tcp_grow_window(struct sock *sk, struct sk_buff *skb)
 304{
 305        struct tcp_sock *tp = tcp_sk(sk);
 306
 307        /* Check #1 */
 308        if (tp->rcv_ssthresh < tp->window_clamp &&
 309            (int)tp->rcv_ssthresh < tcp_space(sk) &&
 310            !tcp_memory_pressure) {
 311                int incr;
 312
 313                /* Check #2. Increase window, if skb with such overhead
 314                 * will fit to rcvbuf in future.
 315                 */
 316                if (tcp_win_from_space(skb->truesize) <= skb->len)
 317                        incr = 2 * tp->advmss;
 318                else
 319                        incr = __tcp_grow_window(sk, skb);
 320
 321                if (incr) {
 322                        tp->rcv_ssthresh = min(tp->rcv_ssthresh + incr,
 323                                               tp->window_clamp);
 324                        inet_csk(sk)->icsk_ack.quick |= 1;
 325                }
 326        }
 327}
 328
 329/* 3. Tuning rcvbuf, when connection enters established state. */
 330
 331static void tcp_fixup_rcvbuf(struct sock *sk)
 332{
 333        struct tcp_sock *tp = tcp_sk(sk);
 334        int rcvmem = tp->advmss + MAX_TCP_HEADER + 16 + sizeof(struct sk_buff);
 335
 336        /* Try to select rcvbuf so that 4 mss-sized segments
 337         * will fit to window and corresponding skbs will fit to our rcvbuf.
 338         * (was 3; 4 is minimum to allow fast retransmit to work.)
 339         */
 340        while (tcp_win_from_space(rcvmem) < tp->advmss)
 341                rcvmem += 128;
 342        if (sk->sk_rcvbuf < 4 * rcvmem)
 343                sk->sk_rcvbuf = min(4 * rcvmem, sysctl_tcp_rmem[2]);
 344}
 345
 346/* 4. Try to fixup all. It is made immediately after connection enters
 347 *    established state.
 348 */
 349static void tcp_init_buffer_space(struct sock *sk)
 350{
 351        struct tcp_sock *tp = tcp_sk(sk);
 352        int maxwin;
 353
 354        if (!(sk->sk_userlocks & SOCK_RCVBUF_LOCK))
 355                tcp_fixup_rcvbuf(sk);
 356        if (!(sk->sk_userlocks & SOCK_SNDBUF_LOCK))
 357                tcp_fixup_sndbuf(sk);
 358
 359        tp->rcvq_space.space = tp->rcv_wnd;
 360
 361        maxwin = tcp_full_space(sk);
 362
 363        if (tp->window_clamp >= maxwin) {
 364                tp->window_clamp = maxwin;
 365
 366                if (sysctl_tcp_app_win && maxwin > 4 * tp->advmss)
 367                        tp->window_clamp = max(maxwin -
 368                                               (maxwin >> sysctl_tcp_app_win),
 369                                               4 * tp->advmss);
 370        }
 371
 372        /* Force reservation of one segment. */
 373        if (sysctl_tcp_app_win &&
 374            tp->window_clamp > 2 * tp->advmss &&
 375            tp->window_clamp + tp->advmss > maxwin)
 376                tp->window_clamp = max(2 * tp->advmss, maxwin - tp->advmss);
 377
 378        tp->rcv_ssthresh = min(tp->rcv_ssthresh, tp->window_clamp);
 379        tp->snd_cwnd_stamp = tcp_time_stamp;
 380}
 381
 382/* 5. Recalculate window clamp after socket hit its memory bounds. */
 383static void tcp_clamp_window(struct sock *sk)
 384{
 385        struct tcp_sock *tp = tcp_sk(sk);
 386        struct inet_connection_sock *icsk = inet_csk(sk);
 387
 388        icsk->icsk_ack.quick = 0;
 389
 390        if (sk->sk_rcvbuf < sysctl_tcp_rmem[2] &&
 391            !(sk->sk_userlocks & SOCK_RCVBUF_LOCK) &&
 392            !tcp_memory_pressure &&
 393            atomic_read(&tcp_memory_allocated) < sysctl_tcp_mem[0]) {
 394                sk->sk_rcvbuf = min(atomic_read(&sk->sk_rmem_alloc),
 395                                    sysctl_tcp_rmem[2]);
 396        }
 397        if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf)
 398                tp->rcv_ssthresh = min(tp->window_clamp, 2U * tp->advmss);
 399}
 400
 401/* Initialize RCV_MSS value.
 402 * RCV_MSS is an our guess about MSS used by the peer.
 403 * We haven't any direct information about the MSS.
 404 * It's better to underestimate the RCV_MSS rather than overestimate.
 405 * Overestimations make us ACKing less frequently than needed.
 406 * Underestimations are more easy to detect and fix by tcp_measure_rcv_mss().
 407 */
 408void tcp_initialize_rcv_mss(struct sock *sk)
 409{
 410        struct tcp_sock *tp = tcp_sk(sk);
 411        unsigned int hint = min_t(unsigned int, tp->advmss, tp->mss_cache);
 412
 413        hint = min(hint, tp->rcv_wnd / 2);
 414        hint = min(hint, TCP_MIN_RCVMSS);
 415        hint = max(hint, TCP_MIN_MSS);
 416
 417        inet_csk(sk)->icsk_ack.rcv_mss = hint;
 418}
 419
 420/* Receiver "autotuning" code.
 421 *
 422 * The algorithm for RTT estimation w/o timestamps is based on
 423 * Dynamic Right-Sizing (DRS) by Wu Feng and Mike Fisk of LANL.
 424 * <http://www.lanl.gov/radiant/website/pubs/drs/lacsi2001.ps>
 425 *
 426 * More detail on this code can be found at
 427 * <http://www.psc.edu/~jheffner/senior_thesis.ps>,
 428 * though this reference is out of date.  A new paper
 429 * is pending.
 430 */
 431static void tcp_rcv_rtt_update(struct tcp_sock *tp, u32 sample, int win_dep)
 432{
 433        u32 new_sample = tp->rcv_rtt_est.rtt;
 434        long m = sample;
 435
 436        if (m == 0)
 437                m = 1;
 438
 439        if (new_sample != 0) {
 440                /* If we sample in larger samples in the non-timestamp
 441                 * case, we could grossly overestimate the RTT especially
 442                 * with chatty applications or bulk transfer apps which
 443                 * are stalled on filesystem I/O.
 444                 *
 445                 * Also, since we are only going for a minimum in the
 446                 * non-timestamp case, we do not smooth things out
 447                 * else with timestamps disabled convergence takes too
 448                 * long.
 449                 */
 450                if (!win_dep) {
 451                        m -= (new_sample >> 3);
 452                        new_sample += m;
 453                } else if (m < new_sample)
 454                        new_sample = m << 3;
 455        } else {
 456                /* No previous measure. */
 457                new_sample = m << 3;
 458        }
 459
 460        if (tp->rcv_rtt_est.rtt != new_sample)
 461                tp->rcv_rtt_est.rtt = new_sample;
 462}
 463
 464static inline void tcp_rcv_rtt_measure(struct tcp_sock *tp)
 465{
 466        if (tp->rcv_rtt_est.time == 0)
 467                goto new_measure;
 468        if (before(tp->rcv_nxt, tp->rcv_rtt_est.seq))
 469                return;
 470        tcp_rcv_rtt_update(tp, jiffies - tp->rcv_rtt_est.time, 1);
 471
 472new_measure:
 473        tp->rcv_rtt_est.seq = tp->rcv_nxt + tp->rcv_wnd;
 474        tp->rcv_rtt_est.time = tcp_time_stamp;
 475}
 476
 477static inline void tcp_rcv_rtt_measure_ts(struct sock *sk,
 478                                          const struct sk_buff *skb)
 479{
 480        struct tcp_sock *tp = tcp_sk(sk);
 481        if (tp->rx_opt.rcv_tsecr &&
 482            (TCP_SKB_CB(skb)->end_seq -
 483             TCP_SKB_CB(skb)->seq >= inet_csk(sk)->icsk_ack.rcv_mss))
 484                tcp_rcv_rtt_update(tp, tcp_time_stamp - tp->rx_opt.rcv_tsecr, 0);
 485}
 486
 487/*
 488 * This function should be called every time data is copied to user space.
 489 * It calculates the appropriate TCP receive buffer space.
 490 */
 491void tcp_rcv_space_adjust(struct sock *sk)
 492{
 493        struct tcp_sock *tp = tcp_sk(sk);
 494        int time;
 495        int space;
 496
 497        if (tp->rcvq_space.time == 0)
 498                goto new_measure;
 499
 500        time = tcp_time_stamp - tp->rcvq_space.time;
 501        if (time < (tp->rcv_rtt_est.rtt >> 3) || tp->rcv_rtt_est.rtt == 0)
 502                return;
 503
 504        space = 2 * (tp->copied_seq - tp->rcvq_space.seq);
 505
 506        space = max(tp->rcvq_space.space, space);
 507
 508        if (tp->rcvq_space.space != space) {
 509                int rcvmem;
 510
 511                tp->rcvq_space.space = space;
 512
 513                if (sysctl_tcp_moderate_rcvbuf &&
 514                    !(sk->sk_userlocks & SOCK_RCVBUF_LOCK)) {
 515                        int new_clamp = space;
 516
 517                        /* Receive space grows, normalize in order to
 518                         * take into account packet headers and sk_buff
 519                         * structure overhead.
 520                         */
 521                        space /= tp->advmss;
 522                        if (!space)
 523                                space = 1;
 524                        rcvmem = (tp->advmss + MAX_TCP_HEADER +
 525                                  16 + sizeof(struct sk_buff));
 526                        while (tcp_win_from_space(rcvmem) < tp->advmss)
 527                                rcvmem += 128;
 528                        space *= rcvmem;
 529                        space = min(space, sysctl_tcp_rmem[2]);
 530                        if (space > sk->sk_rcvbuf) {
 531                                sk->sk_rcvbuf = space;
 532
 533                                /* Make the window clamp follow along.  */
 534                                tp->window_clamp = new_clamp;
 535                        }
 536                }
 537        }
 538
 539new_measure:
 540        tp->rcvq_space.seq = tp->copied_seq;
 541        tp->rcvq_space.time = tcp_time_stamp;
 542}
 543
 544/* There is something which you must keep in mind when you analyze the
 545 * behavior of the tp->ato delayed ack timeout interval.  When a
 546 * connection starts up, we want to ack as quickly as possible.  The
 547 * problem is that "good" TCP's do slow start at the beginning of data
 548 * transmission.  The means that until we send the first few ACK's the
 549 * sender will sit on his end and only queue most of his data, because
 550 * he can only send snd_cwnd unacked packets at any given time.  For
 551 * each ACK we send, he increments snd_cwnd and transmits more of his
 552 * queue.  -DaveM
 553 */
 554static void tcp_event_data_recv(struct sock *sk, struct sk_buff *skb)
 555{
 556        struct tcp_sock *tp = tcp_sk(sk);
 557        struct inet_connection_sock *icsk = inet_csk(sk);
 558        u32 now;
 559
 560        inet_csk_schedule_ack(sk);
 561
 562        tcp_measure_rcv_mss(sk, skb);
 563
 564        tcp_rcv_rtt_measure(tp);
 565
 566        now = tcp_time_stamp;
 567
 568        if (!icsk->icsk_ack.ato) {
 569                /* The _first_ data packet received, initialize
 570                 * delayed ACK engine.
 571                 */
 572                tcp_incr_quickack(sk);
 573                icsk->icsk_ack.ato = TCP_ATO_MIN;
 574        } else {
 575                int m = now - icsk->icsk_ack.lrcvtime;
 576
 577                if (m <= TCP_ATO_MIN / 2) {
 578                        /* The fastest case is the first. */
 579                        icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + TCP_ATO_MIN / 2;
 580                } else if (m < icsk->icsk_ack.ato) {
 581                        icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + m;
 582                        if (icsk->icsk_ack.ato > icsk->icsk_rto)
 583                                icsk->icsk_ack.ato = icsk->icsk_rto;
 584                } else if (m > icsk->icsk_rto) {
 585                        /* Too long gap. Apparently sender failed to
 586                         * restart window, so that we send ACKs quickly.
 587                         */
 588                        tcp_incr_quickack(sk);
 589                        sk_mem_reclaim(sk);
 590                }
 591        }
 592        icsk->icsk_ack.lrcvtime = now;
 593
 594        TCP_ECN_check_ce(tp, skb);
 595
 596        if (skb->len >= 128)
 597                tcp_grow_window(sk, skb);
 598}
 599
 600/* Called to compute a smoothed rtt estimate. The data fed to this
 601 * routine either comes from timestamps, or from segments that were
 602 * known _not_ to have been retransmitted [see Karn/Partridge
 603 * Proceedings SIGCOMM 87]. The algorithm is from the SIGCOMM 88
 604 * piece by Van Jacobson.
 605 * NOTE: the next three routines used to be one big routine.
 606 * To save cycles in the RFC 1323 implementation it was better to break
 607 * it up into three procedures. -- erics
 608 */
 609static void tcp_rtt_estimator(struct sock *sk, const __u32 mrtt)
 610{
 611        struct tcp_sock *tp = tcp_sk(sk);
 612        long m = mrtt; /* RTT */
 613
 614        /*      The following amusing code comes from Jacobson's
 615         *      article in SIGCOMM '88.  Note that rtt and mdev
 616         *      are scaled versions of rtt and mean deviation.
 617         *      This is designed to be as fast as possible
 618         *      m stands for "measurement".
 619         *
 620         *      On a 1990 paper the rto value is changed to:
 621         *      RTO = rtt + 4 * mdev
 622         *
 623         * Funny. This algorithm seems to be very broken.
 624         * These formulae increase RTO, when it should be decreased, increase
 625         * too slowly, when it should be increased quickly, decrease too quickly
 626         * etc. I guess in BSD RTO takes ONE value, so that it is absolutely
 627         * does not matter how to _calculate_ it. Seems, it was trap
 628         * that VJ failed to avoid. 8)
 629         */
 630        if (m == 0)
 631                m = 1;
 632        if (tp->srtt != 0) {
 633                m -= (tp->srtt >> 3);   /* m is now error in rtt est */
 634                tp->srtt += m;          /* rtt = 7/8 rtt + 1/8 new */
 635                if (m < 0) {
 636                        m = -m;         /* m is now abs(error) */
 637                        m -= (tp->mdev >> 2);   /* similar update on mdev */
 638                        /* This is similar to one of Eifel findings.
 639                         * Eifel blocks mdev updates when rtt decreases.
 640                         * This solution is a bit different: we use finer gain
 641                         * for mdev in this case (alpha*beta).
 642                         * Like Eifel it also prevents growth of rto,
 643                         * but also it limits too fast rto decreases,
 644                         * happening in pure Eifel.
 645                         */
 646                        if (m > 0)
 647                                m >>= 3;
 648                } else {
 649                        m -= (tp->mdev >> 2);   /* similar update on mdev */
 650                }
 651                tp->mdev += m;          /* mdev = 3/4 mdev + 1/4 new */
 652                if (tp->mdev > tp->mdev_max) {
 653                        tp->mdev_max = tp->mdev;
 654                        if (tp->mdev_max > tp->rttvar)
 655                                tp->rttvar = tp->mdev_max;
 656                }
 657                if (after(tp->snd_una, tp->rtt_seq)) {
 658                        if (tp->mdev_max < tp->rttvar)
 659                                tp->rttvar -= (tp->rttvar - tp->mdev_max) >> 2;
 660                        tp->rtt_seq = tp->snd_nxt;
 661                        tp->mdev_max = tcp_rto_min(sk);
 662                }
 663        } else {
 664                /* no previous measure. */
 665                tp->srtt = m << 3;      /* take the measured time to be rtt */
 666                tp->mdev = m << 1;      /* make sure rto = 3*rtt */
 667                tp->mdev_max = tp->rttvar = max(tp->mdev, tcp_rto_min(sk));
 668                tp->rtt_seq = tp->snd_nxt;
 669        }
 670}
 671
 672/* Calculate rto without backoff.  This is the second half of Van Jacobson's
 673 * routine referred to above.
 674 */
 675static inline void tcp_set_rto(struct sock *sk)
 676{
 677        const struct tcp_sock *tp = tcp_sk(sk);
 678        /* Old crap is replaced with new one. 8)
 679         *
 680         * More seriously:
 681         * 1. If rtt variance happened to be less 50msec, it is hallucination.
 682         *    It cannot be less due to utterly erratic ACK generation made
 683         *    at least by solaris and freebsd. "Erratic ACKs" has _nothing_
 684         *    to do with delayed acks, because at cwnd>2 true delack timeout
 685         *    is invisible. Actually, Linux-2.4 also generates erratic
 686         *    ACKs in some circumstances.
 687         */
 688        inet_csk(sk)->icsk_rto = (tp->srtt >> 3) + tp->rttvar;
 689
 690        /* 2. Fixups made earlier cannot be right.
 691         *    If we do not estimate RTO correctly without them,
 692         *    all the algo is pure shit and should be replaced
 693         *    with correct one. It is exactly, which we pretend to do.
 694         */
 695
 696        /* NOTE: clamping at TCP_RTO_MIN is not required, current algo
 697         * guarantees that rto is higher.
 698         */
 699        if (inet_csk(sk)->icsk_rto > TCP_RTO_MAX)
 700                inet_csk(sk)->icsk_rto = TCP_RTO_MAX;
 701}
 702
 703/* Save metrics learned by this TCP session.
 704   This function is called only, when TCP finishes successfully
 705   i.e. when it enters TIME-WAIT or goes from LAST-ACK to CLOSE.
 706 */
 707void tcp_update_metrics(struct sock *sk)
 708{
 709        struct tcp_sock *tp = tcp_sk(sk);
 710        struct dst_entry *dst = __sk_dst_get(sk);
 711
 712        if (sysctl_tcp_nometrics_save)
 713                return;
 714
 715        dst_confirm(dst);
 716
 717        if (dst && (dst->flags & DST_HOST)) {
 718                const struct inet_connection_sock *icsk = inet_csk(sk);
 719                int m;
 720                unsigned long rtt;
 721
 722                if (icsk->icsk_backoff || !tp->srtt) {
 723                        /* This session failed to estimate rtt. Why?
 724                         * Probably, no packets returned in time.
 725                         * Reset our results.
 726                         */
 727                        if (!(dst_metric_locked(dst, RTAX_RTT)))
 728                                dst->metrics[RTAX_RTT - 1] = 0;
 729                        return;
 730                }
 731
 732                rtt = dst_metric_rtt(dst, RTAX_RTT);
 733                m = rtt - tp->srtt;
 734
 735                /* If newly calculated rtt larger than stored one,
 736                 * store new one. Otherwise, use EWMA. Remember,
 737                 * rtt overestimation is always better than underestimation.
 738                 */
 739                if (!(dst_metric_locked(dst, RTAX_RTT))) {
 740                        if (m <= 0)
 741                                set_dst_metric_rtt(dst, RTAX_RTT, tp->srtt);
 742                        else
 743                                set_dst_metric_rtt(dst, RTAX_RTT, rtt - (m >> 3));
 744                }
 745
 746                if (!(dst_metric_locked(dst, RTAX_RTTVAR))) {
 747                        unsigned long var;
 748                        if (m < 0)
 749                                m = -m;
 750
 751                        /* Scale deviation to rttvar fixed point */
 752                        m >>= 1;
 753                        if (m < tp->mdev)
 754                                m = tp->mdev;
 755
 756                        var = dst_metric_rtt(dst, RTAX_RTTVAR);
 757                        if (m >= var)
 758                                var = m;
 759                        else
 760                                var -= (var - m) >> 2;
 761
 762                        set_dst_metric_rtt(dst, RTAX_RTTVAR, var);
 763                }
 764
 765                if (tp->snd_ssthresh >= 0xFFFF) {
 766                        /* Slow start still did not finish. */
 767                        if (dst_metric(dst, RTAX_SSTHRESH) &&
 768                            !dst_metric_locked(dst, RTAX_SSTHRESH) &&
 769                            (tp->snd_cwnd >> 1) > dst_metric(dst, RTAX_SSTHRESH))
 770                                dst->metrics[RTAX_SSTHRESH-1] = tp->snd_cwnd >> 1;
 771                        if (!dst_metric_locked(dst, RTAX_CWND) &&
 772                            tp->snd_cwnd > dst_metric(dst, RTAX_CWND))
 773                                dst->metrics[RTAX_CWND - 1] = tp->snd_cwnd;
 774                } else if (tp->snd_cwnd > tp->snd_ssthresh &&
 775                           icsk->icsk_ca_state == TCP_CA_Open) {
 776                        /* Cong. avoidance phase, cwnd is reliable. */
 777                        if (!dst_metric_locked(dst, RTAX_SSTHRESH))
 778                                dst->metrics[RTAX_SSTHRESH-1] =
 779                                        max(tp->snd_cwnd >> 1, tp->snd_ssthresh);
 780                        if (!dst_metric_locked(dst, RTAX_CWND))
 781                                dst->metrics[RTAX_CWND-1] = (dst_metric(dst, RTAX_CWND) + tp->snd_cwnd) >> 1;
 782                } else {
 783                        /* Else slow start did not finish, cwnd is non-sense,
 784                           ssthresh may be also invalid.
 785                         */
 786                        if (!dst_metric_locked(dst, RTAX_CWND))
 787                                dst->metrics[RTAX_CWND-1] = (dst_metric(dst, RTAX_CWND) + tp->snd_ssthresh) >> 1;
 788                        if (dst_metric(dst, RTAX_SSTHRESH) &&
 789                            !dst_metric_locked(dst, RTAX_SSTHRESH) &&
 790                            tp->snd_ssthresh > dst_metric(dst, RTAX_SSTHRESH))
 791                                dst->metrics[RTAX_SSTHRESH-1] = tp->snd_ssthresh;
 792                }
 793
 794                if (!dst_metric_locked(dst, RTAX_REORDERING)) {
 795                        if (dst_metric(dst, RTAX_REORDERING) < tp->reordering &&
 796                            tp->reordering != sysctl_tcp_reordering)
 797                                dst->metrics[RTAX_REORDERING-1] = tp->reordering;
 798                }
 799        }
 800}
 801
 802/* Numbers are taken from RFC3390.
 803 *
 804 * John Heffner states:
 805 *
 806 *      The RFC specifies a window of no more than 4380 bytes
 807 *      unless 2*MSS > 4380.  Reading the pseudocode in the RFC
 808 *      is a bit misleading because they use a clamp at 4380 bytes
 809 *      rather than use a multiplier in the relevant range.
 810 */
 811__u32 tcp_init_cwnd(struct tcp_sock *tp, struct dst_entry *dst)
 812{
 813        __u32 cwnd = (dst ? dst_metric(dst, RTAX_INITCWND) : 0);
 814
 815        if (!cwnd) {
 816                if (tp->mss_cache > 1460)
 817                        cwnd = 2;
 818                else
 819                        cwnd = (tp->mss_cache > 1095) ? 3 : 4;
 820        }
 821        return min_t(__u32, cwnd, tp->snd_cwnd_clamp);
 822}
 823
 824/* Set slow start threshold and cwnd not falling to slow start */
 825void tcp_enter_cwr(struct sock *sk, const int set_ssthresh)
 826{
 827        struct tcp_sock *tp = tcp_sk(sk);
 828        const struct inet_connection_sock *icsk = inet_csk(sk);
 829
 830        tp->prior_ssthresh = 0;
 831        tp->bytes_acked = 0;
 832        if (icsk->icsk_ca_state < TCP_CA_CWR) {
 833                tp->undo_marker = 0;
 834                if (set_ssthresh)
 835                        tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
 836                tp->snd_cwnd = min(tp->snd_cwnd,
 837                                   tcp_packets_in_flight(tp) + 1U);
 838                tp->snd_cwnd_cnt = 0;
 839                tp->high_seq = tp->snd_nxt;
 840                tp->snd_cwnd_stamp = tcp_time_stamp;
 841                TCP_ECN_queue_cwr(tp);
 842
 843                tcp_set_ca_state(sk, TCP_CA_CWR);
 844        }
 845}
 846
 847/*
 848 * Packet counting of FACK is based on in-order assumptions, therefore TCP
 849 * disables it when reordering is detected
 850 */
 851static void tcp_disable_fack(struct tcp_sock *tp)
 852{
 853        /* RFC3517 uses different metric in lost marker => reset on change */
 854        if (tcp_is_fack(tp))
 855                tp->lost_skb_hint = NULL;
 856        tp->rx_opt.sack_ok &= ~2;
 857}
 858
 859/* Take a notice that peer is sending D-SACKs */
 860static void tcp_dsack_seen(struct tcp_sock *tp)
 861{
 862        tp->rx_opt.sack_ok |= 4;
 863}
 864
 865/* Initialize metrics on socket. */
 866
 867static void tcp_init_metrics(struct sock *sk)
 868{
 869        struct tcp_sock *tp = tcp_sk(sk);
 870        struct dst_entry *dst = __sk_dst_get(sk);
 871
 872        if (dst == NULL)
 873                goto reset;
 874
 875        dst_confirm(dst);
 876
 877        if (dst_metric_locked(dst, RTAX_CWND))
 878                tp->snd_cwnd_clamp = dst_metric(dst, RTAX_CWND);
 879        if (dst_metric(dst, RTAX_SSTHRESH)) {
 880                tp->snd_ssthresh = dst_metric(dst, RTAX_SSTHRESH);
 881                if (tp->snd_ssthresh > tp->snd_cwnd_clamp)
 882                        tp->snd_ssthresh = tp->snd_cwnd_clamp;
 883        }
 884        if (dst_metric(dst, RTAX_REORDERING) &&
 885            tp->reordering != dst_metric(dst, RTAX_REORDERING)) {
 886                tcp_disable_fack(tp);
 887                tp->reordering = dst_metric(dst, RTAX_REORDERING);
 888        }
 889
 890        if (dst_metric(dst, RTAX_RTT) == 0)
 891                goto reset;
 892
 893        if (!tp->srtt && dst_metric_rtt(dst, RTAX_RTT) < (TCP_TIMEOUT_INIT << 3))
 894                goto reset;
 895
 896        /* Initial rtt is determined from SYN,SYN-ACK.
 897         * The segment is small and rtt may appear much
 898         * less than real one. Use per-dst memory
 899         * to make it more realistic.
 900         *
 901         * A bit of theory. RTT is time passed after "normal" sized packet
 902         * is sent until it is ACKed. In normal circumstances sending small
 903         * packets force peer to delay ACKs and calculation is correct too.
 904         * The algorithm is adaptive and, provided we follow specs, it
 905         * NEVER underestimate RTT. BUT! If peer tries to make some clever
 906         * tricks sort of "quick acks" for time long enough to decrease RTT
 907         * to low value, and then abruptly stops to do it and starts to delay
 908         * ACKs, wait for troubles.
 909         */
 910        if (dst_metric_rtt(dst, RTAX_RTT) > tp->srtt) {
 911                tp->srtt = dst_metric_rtt(dst, RTAX_RTT);
 912                tp->rtt_seq = tp->snd_nxt;
 913        }
 914        if (dst_metric_rtt(dst, RTAX_RTTVAR) > tp->mdev) {
 915                tp->mdev = dst_metric_rtt(dst, RTAX_RTTVAR);
 916                tp->mdev_max = tp->rttvar = max(tp->mdev, tcp_rto_min(sk));
 917        }
 918        tcp_set_rto(sk);
 919        if (inet_csk(sk)->icsk_rto < TCP_TIMEOUT_INIT && !tp->rx_opt.saw_tstamp)
 920                goto reset;
 921
 922cwnd:
 923        tp->snd_cwnd = tcp_init_cwnd(tp, dst);
 924        tp->snd_cwnd_stamp = tcp_time_stamp;
 925        return;
 926
 927reset:
 928        /* Play conservative. If timestamps are not
 929         * supported, TCP will fail to recalculate correct
 930         * rtt, if initial rto is too small. FORGET ALL AND RESET!
 931         */
 932        if (!tp->rx_opt.saw_tstamp && tp->srtt) {
 933                tp->srtt = 0;
 934                tp->mdev = tp->mdev_max = tp->rttvar = TCP_TIMEOUT_INIT;
 935                inet_csk(sk)->icsk_rto = TCP_TIMEOUT_INIT;
 936        }
 937        goto cwnd;
 938}
 939
 940static void tcp_update_reordering(struct sock *sk, const int metric,
 941                                  const int ts)
 942{
 943        struct tcp_sock *tp = tcp_sk(sk);
 944        if (metric > tp->reordering) {
 945                int mib_idx;
 946
 947                tp->reordering = min(TCP_MAX_REORDERING, metric);
 948
 949                /* This exciting event is worth to be remembered. 8) */
 950                if (ts)
 951                        mib_idx = LINUX_MIB_TCPTSREORDER;
 952                else if (tcp_is_reno(tp))
 953                        mib_idx = LINUX_MIB_TCPRENOREORDER;
 954                else if (tcp_is_fack(tp))
 955                        mib_idx = LINUX_MIB_TCPFACKREORDER;
 956                else
 957                        mib_idx = LINUX_MIB_TCPSACKREORDER;
 958
 959                NET_INC_STATS_BH(sock_net(sk), mib_idx);
 960#if FASTRETRANS_DEBUG > 1
 961                printk(KERN_DEBUG "Disorder%d %d %u f%u s%u rr%d\n",
 962                       tp->rx_opt.sack_ok, inet_csk(sk)->icsk_ca_state,
 963                       tp->reordering,
 964                       tp->fackets_out,
 965                       tp->sacked_out,
 966                       tp->undo_marker ? tp->undo_retrans : 0);
 967#endif
 968                tcp_disable_fack(tp);
 969        }
 970}
 971
 972/* This must be called before lost_out is incremented */
 973static void tcp_verify_retransmit_hint(struct tcp_sock *tp, struct sk_buff *skb)
 974{
 975        if ((tp->retransmit_skb_hint == NULL) ||
 976            before(TCP_SKB_CB(skb)->seq,
 977                   TCP_SKB_CB(tp->retransmit_skb_hint)->seq))
 978                tp->retransmit_skb_hint = skb;
 979
 980        if (!tp->lost_out ||
 981            after(TCP_SKB_CB(skb)->end_seq, tp->retransmit_high))
 982                tp->retransmit_high = TCP_SKB_CB(skb)->end_seq;
 983}
 984
 985static void tcp_skb_mark_lost(struct tcp_sock *tp, struct sk_buff *skb)
 986{
 987        if (!(TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_ACKED))) {
 988                tcp_verify_retransmit_hint(tp, skb);
 989
 990                tp->lost_out += tcp_skb_pcount(skb);
 991                TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
 992        }
 993}
 994
 995static void tcp_skb_mark_lost_uncond_verify(struct tcp_sock *tp,
 996                                            struct sk_buff *skb)
 997{
 998        tcp_verify_retransmit_hint(tp, skb);
 999
1000        if (!(TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_ACKED))) {
1001                tp->lost_out += tcp_skb_pcount(skb);
1002                TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
1003        }
1004}
1005
1006/* This procedure tags the retransmission queue when SACKs arrive.
1007 *
1008 * We have three tag bits: SACKED(S), RETRANS(R) and LOST(L).
1009 * Packets in queue with these bits set are counted in variables
1010 * sacked_out, retrans_out and lost_out, correspondingly.
1011 *
1012 * Valid combinations are:
1013 * Tag  InFlight        Description
1014 * 0    1               - orig segment is in flight.
1015 * S    0               - nothing flies, orig reached receiver.
1016 * L    0               - nothing flies, orig lost by net.
1017 * R    2               - both orig and retransmit are in flight.
1018 * L|R  1               - orig is lost, retransmit is in flight.
1019 * S|R  1               - orig reached receiver, retrans is still in flight.
1020 * (L|S|R is logically valid, it could occur when L|R is sacked,
1021 *  but it is equivalent to plain S and code short-curcuits it to S.
1022 *  L|S is logically invalid, it would mean -1 packet in flight 8))
1023 *
1024 * These 6 states form finite state machine, controlled by the following events:
1025 * 1. New ACK (+SACK) arrives. (tcp_sacktag_write_queue())
1026 * 2. Retransmission. (tcp_retransmit_skb(), tcp_xmit_retransmit_queue())
1027 * 3. Loss detection event of one of three flavors:
1028 *      A. Scoreboard estimator decided the packet is lost.
1029 *         A'. Reno "three dupacks" marks head of queue lost.
1030 *         A''. Its FACK modfication, head until snd.fack is lost.
1031 *      B. SACK arrives sacking data transmitted after never retransmitted
1032 *         hole was sent out.
1033 *      C. SACK arrives sacking SND.NXT at the moment, when the
1034 *         segment was retransmitted.
1035 * 4. D-SACK added new rule: D-SACK changes any tag to S.
1036 *
1037 * It is pleasant to note, that state diagram turns out to be commutative,
1038 * so that we are allowed not to be bothered by order of our actions,
1039 * when multiple events arrive simultaneously. (see the function below).
1040 *
1041 * Reordering detection.
1042 * --------------------
1043 * Reordering metric is maximal distance, which a packet can be displaced
1044 * in packet stream. With SACKs we can estimate it:
1045 *
1046 * 1. SACK fills old hole and the corresponding segment was not
1047 *    ever retransmitted -> reordering. Alas, we cannot use it
1048 *    when segment was retransmitted.
1049 * 2. The last flaw is solved with D-SACK. D-SACK arrives
1050 *    for retransmitted and already SACKed segment -> reordering..
1051 * Both of these heuristics are not used in Loss state, when we cannot
1052 * account for retransmits accurately.
1053 *
1054 * SACK block validation.
1055 * ----------------------
1056 *
1057 * SACK block range validation checks that the received SACK block fits to
1058 * the expected sequence limits, i.e., it is between SND.UNA and SND.NXT.
1059 * Note that SND.UNA is not included to the range though being valid because
1060 * it means that the receiver is rather inconsistent with itself reporting
1061 * SACK reneging when it should advance SND.UNA. Such SACK block this is
1062 * perfectly valid, however, in light of RFC2018 which explicitly states
1063 * that "SACK block MUST reflect the newest segment.  Even if the newest
1064 * segment is going to be discarded ...", not that it looks very clever
1065 * in case of head skb. Due to potentional receiver driven attacks, we
1066 * choose to avoid immediate execution of a walk in write queue due to
1067 * reneging and defer head skb's loss recovery to standard loss recovery
1068 * procedure that will eventually trigger (nothing forbids us doing this).
1069 *
1070 * Implements also blockage to start_seq wrap-around. Problem lies in the
1071 * fact that though start_seq (s) is before end_seq (i.e., not reversed),
1072 * there's no guarantee that it will be before snd_nxt (n). The problem
1073 * happens when start_seq resides between end_seq wrap (e_w) and snd_nxt
1074 * wrap (s_w):
1075 *
1076 *         <- outs wnd ->                          <- wrapzone ->
1077 *         u     e      n                         u_w   e_w  s n_w
1078 *         |     |      |                          |     |   |  |
1079 * |<------------+------+----- TCP seqno space --------------+---------->|
1080 * ...-- <2^31 ->|                                           |<--------...
1081 * ...---- >2^31 ------>|                                    |<--------...
1082 *
1083 * Current code wouldn't be vulnerable but it's better still to discard such
1084 * crazy SACK blocks. Doing this check for start_seq alone closes somewhat
1085 * similar case (end_seq after snd_nxt wrap) as earlier reversed check in
1086 * snd_nxt wrap -> snd_una region will then become "well defined", i.e.,
1087 * equal to the ideal case (infinite seqno space without wrap caused issues).
1088 *
1089 * With D-SACK the lower bound is extended to cover sequence space below
1090 * SND.UNA down to undo_marker, which is the last point of interest. Yet
1091 * again, D-SACK block must not to go across snd_una (for the same reason as
1092 * for the normal SACK blocks, explained above). But there all simplicity
1093 * ends, TCP might receive valid D-SACKs below that. As long as they reside
1094 * fully below undo_marker they do not affect behavior in anyway and can
1095 * therefore be safely ignored. In rare cases (which are more or less
1096 * theoretical ones), the D-SACK will nicely cross that boundary due to skb
1097 * fragmentation and packet reordering past skb's retransmission. To consider
1098 * them correctly, the acceptable range must be extended even more though
1099 * the exact amount is rather hard to quantify. However, tp->max_window can
1100 * be used as an exaggerated estimate.
1101 */
1102static int tcp_is_sackblock_valid(struct tcp_sock *tp, int is_dsack,
1103                                  u32 start_seq, u32 end_seq)
1104{
1105        /* Too far in future, or reversed (interpretation is ambiguous) */
1106        if (after(end_seq, tp->snd_nxt) || !before(start_seq, end_seq))
1107                return 0;
1108
1109        /* Nasty start_seq wrap-around check (see comments above) */
1110        if (!before(start_seq, tp->snd_nxt))
1111                return 0;
1112
1113        /* In outstanding window? ...This is valid exit for D-SACKs too.
1114         * start_seq == snd_una is non-sensical (see comments above)
1115         */
1116        if (after(start_seq, tp->snd_una))
1117                return 1;
1118
1119        if (!is_dsack || !tp->undo_marker)
1120                return 0;
1121
1122        /* ...Then it's D-SACK, and must reside below snd_una completely */
1123        if (!after(end_seq, tp->snd_una))
1124                return 0;
1125
1126        if (!before(start_seq, tp->undo_marker))
1127                return 1;
1128
1129        /* Too old */
1130        if (!after(end_seq, tp->undo_marker))
1131                return 0;
1132
1133        /* Undo_marker boundary crossing (overestimates a lot). Known already:
1134         *   start_seq < undo_marker and end_seq >= undo_marker.
1135         */
1136        return !before(start_seq, end_seq - tp->max_window);
1137}
1138
1139/* Check for lost retransmit. This superb idea is borrowed from "ratehalving".
1140 * Event "C". Later note: FACK people cheated me again 8), we have to account
1141 * for reordering! Ugly, but should help.
1142 *
1143 * Search retransmitted skbs from write_queue that were sent when snd_nxt was
1144 * less than what is now known to be received by the other end (derived from
1145 * highest SACK block). Also calculate the lowest snd_nxt among the remaining
1146 * retransmitted skbs to avoid some costly processing per ACKs.
1147 */
1148static void tcp_mark_lost_retrans(struct sock *sk)
1149{
1150        const struct inet_connection_sock *icsk = inet_csk(sk);
1151        struct tcp_sock *tp = tcp_sk(sk);
1152        struct sk_buff *skb;
1153        int cnt = 0;
1154        u32 new_low_seq = tp->snd_nxt;
1155        u32 received_upto = tcp_highest_sack_seq(tp);
1156
1157        if (!tcp_is_fack(tp) || !tp->retrans_out ||
1158            !after(received_upto, tp->lost_retrans_low) ||
1159            icsk->icsk_ca_state != TCP_CA_Recovery)
1160                return;
1161
1162        tcp_for_write_queue(skb, sk) {
1163                u32 ack_seq = TCP_SKB_CB(skb)->ack_seq;
1164
1165                if (skb == tcp_send_head(sk))
1166                        break;
1167                if (cnt == tp->retrans_out)
1168                        break;
1169                if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
1170                        continue;
1171
1172                if (!(TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS))
1173                        continue;
1174
1175                /* TODO: We would like to get rid of tcp_is_fack(tp) only
1176                 * constraint here (see above) but figuring out that at
1177                 * least tp->reordering SACK blocks reside between ack_seq
1178                 * and received_upto is not easy task to do cheaply with
1179                 * the available datastructures.
1180                 *
1181                 * Whether FACK should check here for tp->reordering segs
1182                 * in-between one could argue for either way (it would be
1183                 * rather simple to implement as we could count fack_count
1184                 * during the walk and do tp->fackets_out - fack_count).
1185                 */
1186                if (after(received_upto, ack_seq)) {
1187                        TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
1188                        tp->retrans_out -= tcp_skb_pcount(skb);
1189
1190                        tcp_skb_mark_lost_uncond_verify(tp, skb);
1191                        NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPLOSTRETRANSMIT);
1192                } else {
1193                        if (before(ack_seq, new_low_seq))
1194                                new_low_seq = ack_seq;
1195                        cnt += tcp_skb_pcount(skb);
1196                }
1197        }
1198
1199        if (tp->retrans_out)
1200                tp->lost_retrans_low = new_low_seq;
1201}
1202
1203static int tcp_check_dsack(struct sock *sk, struct sk_buff *ack_skb,
1204                           struct tcp_sack_block_wire *sp, int num_sacks,
1205                           u32 prior_snd_una)
1206{
1207        struct tcp_sock *tp = tcp_sk(sk);
1208        u32 start_seq_0 = get_unaligned_be32(&sp[0].start_seq);
1209        u32 end_seq_0 = get_unaligned_be32(&sp[0].end_seq);
1210        int dup_sack = 0;
1211
1212        if (before(start_seq_0, TCP_SKB_CB(ack_skb)->ack_seq)) {
1213                dup_sack = 1;
1214                tcp_dsack_seen(tp);
1215                NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPDSACKRECV);
1216        } else if (num_sacks > 1) {
1217                u32 end_seq_1 = get_unaligned_be32(&sp[1].end_seq);
1218                u32 start_seq_1 = get_unaligned_be32(&sp[1].start_seq);
1219
1220                if (!after(end_seq_0, end_seq_1) &&
1221                    !before(start_seq_0, start_seq_1)) {
1222                        dup_sack = 1;
1223                        tcp_dsack_seen(tp);
1224                        NET_INC_STATS_BH(sock_net(sk),
1225                                        LINUX_MIB_TCPDSACKOFORECV);
1226                }
1227        }
1228
1229        /* D-SACK for already forgotten data... Do dumb counting. */
1230        if (dup_sack &&
1231            !after(end_seq_0, prior_snd_una) &&
1232            after(end_seq_0, tp->undo_marker))
1233                tp->undo_retrans--;
1234
1235        return dup_sack;
1236}
1237
1238struct tcp_sacktag_state {
1239        int reord;
1240        int fack_count;
1241        int flag;
1242};
1243
1244/* Check if skb is fully within the SACK block. In presence of GSO skbs,
1245 * the incoming SACK may not exactly match but we can find smaller MSS
1246 * aligned portion of it that matches. Therefore we might need to fragment
1247 * which may fail and creates some hassle (caller must handle error case
1248 * returns).
1249 *
1250 * FIXME: this could be merged to shift decision code
1251 */
1252static int tcp_match_skb_to_sack(struct sock *sk, struct sk_buff *skb,
1253                                 u32 start_seq, u32 end_seq)
1254{
1255        int in_sack, err;
1256        unsigned int pkt_len;
1257        unsigned int mss;
1258
1259        in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) &&
1260                  !before(end_seq, TCP_SKB_CB(skb)->end_seq);
1261
1262        if (tcp_skb_pcount(skb) > 1 && !in_sack &&
1263            after(TCP_SKB_CB(skb)->end_seq, start_seq)) {
1264                mss = tcp_skb_mss(skb);
1265                in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq);
1266
1267                if (!in_sack) {
1268                        pkt_len = start_seq - TCP_SKB_CB(skb)->seq;
1269                        if (pkt_len < mss)
1270                                pkt_len = mss;
1271                } else {
1272                        pkt_len = end_seq - TCP_SKB_CB(skb)->seq;
1273                        if (pkt_len < mss)
1274                                return -EINVAL;
1275                }
1276
1277                /* Round if necessary so that SACKs cover only full MSSes
1278                 * and/or the remaining small portion (if present)
1279                 */
1280                if (pkt_len > mss) {
1281                        unsigned int new_len = (pkt_len / mss) * mss;
1282                        if (!in_sack && new_len < pkt_len) {
1283                                new_len += mss;
1284                                if (new_len > skb->len)
1285                                        return 0;
1286                        }
1287                        pkt_len = new_len;
1288                }
1289                err = tcp_fragment(sk, skb, pkt_len, mss);
1290                if (err < 0)
1291                        return err;
1292        }
1293
1294        return in_sack;
1295}
1296
1297static u8 tcp_sacktag_one(struct sk_buff *skb, struct sock *sk,
1298                          struct tcp_sacktag_state *state,
1299                          int dup_sack, int pcount)
1300{
1301        struct tcp_sock *tp = tcp_sk(sk);
1302        u8 sacked = TCP_SKB_CB(skb)->sacked;
1303        int fack_count = state->fack_count;
1304
1305        /* Account D-SACK for retransmitted packet. */
1306        if (dup_sack && (sacked & TCPCB_RETRANS)) {
1307                if (after(TCP_SKB_CB(skb)->end_seq, tp->undo_marker))
1308                        tp->undo_retrans--;
1309                if (sacked & TCPCB_SACKED_ACKED)
1310                        state->reord = min(fack_count, state->reord);
1311        }
1312
1313        /* Nothing to do; acked frame is about to be dropped (was ACKed). */
1314        if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
1315                return sacked;
1316
1317        if (!(sacked & TCPCB_SACKED_ACKED)) {
1318                if (sacked & TCPCB_SACKED_RETRANS) {
1319                        /* If the segment is not tagged as lost,
1320                         * we do not clear RETRANS, believing
1321                         * that retransmission is still in flight.
1322                         */
1323                        if (sacked & TCPCB_LOST) {
1324                                sacked &= ~(TCPCB_LOST|TCPCB_SACKED_RETRANS);
1325                                tp->lost_out -= pcount;
1326                                tp->retrans_out -= pcount;
1327                        }
1328                } else {
1329                        if (!(sacked & TCPCB_RETRANS)) {
1330                                /* New sack for not retransmitted frame,
1331                                 * which was in hole. It is reordering.
1332                                 */
1333                                if (before(TCP_SKB_CB(skb)->seq,
1334                                           tcp_highest_sack_seq(tp)))
1335                                        state->reord = min(fack_count,
1336                                                           state->reord);
1337
1338                                /* SACK enhanced F-RTO (RFC4138; Appendix B) */
1339                                if (!after(TCP_SKB_CB(skb)->end_seq, tp->frto_highmark))
1340                                        state->flag |= FLAG_ONLY_ORIG_SACKED;
1341                        }
1342
1343                        if (sacked & TCPCB_LOST) {
1344                                sacked &= ~TCPCB_LOST;
1345                                tp->lost_out -= pcount;
1346                        }
1347                }
1348
1349                sacked |= TCPCB_SACKED_ACKED;
1350                state->flag |= FLAG_DATA_SACKED;
1351                tp->sacked_out += pcount;
1352
1353                fack_count += pcount;
1354
1355                /* Lost marker hint past SACKed? Tweak RFC3517 cnt */
1356                if (!tcp_is_fack(tp) && (tp->lost_skb_hint != NULL) &&
1357                    before(TCP_SKB_CB(skb)->seq,
1358                           TCP_SKB_CB(tp->lost_skb_hint)->seq))
1359                        tp->lost_cnt_hint += pcount;
1360
1361                if (fack_count > tp->fackets_out)
1362                        tp->fackets_out = fack_count;
1363        }
1364
1365        /* D-SACK. We can detect redundant retransmission in S|R and plain R
1366         * frames and clear it. undo_retrans is decreased above, L|R frames
1367         * are accounted above as well.
1368         */
1369        if (dup_sack && (sacked & TCPCB_SACKED_RETRANS)) {
1370                sacked &= ~TCPCB_SACKED_RETRANS;
1371                tp->retrans_out -= pcount;
1372        }
1373
1374        return sacked;
1375}
1376
1377static int tcp_shifted_skb(struct sock *sk, struct sk_buff *skb,
1378                           struct tcp_sacktag_state *state,
1379                           unsigned int pcount, int shifted, int mss,
1380                           int dup_sack)
1381{
1382        struct tcp_sock *tp = tcp_sk(sk);
1383        struct sk_buff *prev = tcp_write_queue_prev(sk, skb);
1384
1385        BUG_ON(!pcount);
1386
1387        /* Tweak before seqno plays */
1388        if (!tcp_is_fack(tp) && tcp_is_sack(tp) && tp->lost_skb_hint &&
1389            !before(TCP_SKB_CB(tp->lost_skb_hint)->seq, TCP_SKB_CB(skb)->seq))
1390                tp->lost_cnt_hint += pcount;
1391
1392        TCP_SKB_CB(prev)->end_seq += shifted;
1393        TCP_SKB_CB(skb)->seq += shifted;
1394
1395        skb_shinfo(prev)->gso_segs += pcount;
1396        BUG_ON(skb_shinfo(skb)->gso_segs < pcount);
1397        skb_shinfo(skb)->gso_segs -= pcount;
1398
1399        /* When we're adding to gso_segs == 1, gso_size will be zero,
1400         * in theory this shouldn't be necessary but as long as DSACK
1401         * code can come after this skb later on it's better to keep
1402         * setting gso_size to something.
1403         */
1404        if (!skb_shinfo(prev)->gso_size) {
1405                skb_shinfo(prev)->gso_size = mss;
1406                skb_shinfo(prev)->gso_type = sk->sk_gso_type;
1407        }
1408
1409        /* CHECKME: To clear or not to clear? Mimics normal skb currently */
1410        if (skb_shinfo(skb)->gso_segs <= 1) {
1411                skb_shinfo(skb)->gso_size = 0;
1412                skb_shinfo(skb)->gso_type = 0;
1413        }
1414
1415        /* We discard results */
1416        tcp_sacktag_one(skb, sk, state, dup_sack, pcount);
1417
1418        /* Difference in this won't matter, both ACKed by the same cumul. ACK */
1419        TCP_SKB_CB(prev)->sacked |= (TCP_SKB_CB(skb)->sacked & TCPCB_EVER_RETRANS);
1420
1421        if (skb->len > 0) {
1422                BUG_ON(!tcp_skb_pcount(skb));
1423                NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SACKSHIFTED);
1424                return 0;
1425        }
1426
1427        /* Whole SKB was eaten :-) */
1428
1429        if (skb == tp->retransmit_skb_hint)
1430                tp->retransmit_skb_hint = prev;
1431        if (skb == tp->scoreboard_skb_hint)
1432                tp->scoreboard_skb_hint = prev;
1433        if (skb == tp->lost_skb_hint) {
1434                tp->lost_skb_hint = prev;
1435                tp->lost_cnt_hint -= tcp_skb_pcount(prev);
1436        }
1437
1438        TCP_SKB_CB(skb)->flags |= TCP_SKB_CB(prev)->flags;
1439        if (skb == tcp_highest_sack(sk))
1440                tcp_advance_highest_sack(sk, skb);
1441
1442        tcp_unlink_write_queue(skb, sk);
1443        sk_wmem_free_skb(sk, skb);
1444
1445        NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SACKMERGED);
1446
1447        return 1;
1448}
1449
1450/* I wish gso_size would have a bit more sane initialization than
1451 * something-or-zero which complicates things
1452 */
1453static int tcp_skb_seglen(struct sk_buff *skb)
1454{
1455        return tcp_skb_pcount(skb) == 1 ? skb->len : tcp_skb_mss(skb);
1456}
1457
1458/* Shifting pages past head area doesn't work */
1459static int skb_can_shift(struct sk_buff *skb)
1460{
1461        return !skb_headlen(skb) && skb_is_nonlinear(skb);
1462}
1463
1464/* Try collapsing SACK blocks spanning across multiple skbs to a single
1465 * skb.
1466 */
1467static struct sk_buff *tcp_shift_skb_data(struct sock *sk, struct sk_buff *skb,
1468                                          struct tcp_sacktag_state *state,
1469                                          u32 start_seq, u32 end_seq,
1470                                          int dup_sack)
1471{
1472        struct tcp_sock *tp = tcp_sk(sk);
1473        struct sk_buff *prev;
1474        int mss;
1475        int pcount = 0;
1476        int len;
1477        int in_sack;
1478
1479        if (!sk_can_gso(sk))
1480                goto fallback;
1481
1482        /* Normally R but no L won't result in plain S */
1483        if (!dup_sack &&
1484            (TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_RETRANS)) == TCPCB_SACKED_RETRANS)
1485                goto fallback;
1486        if (!skb_can_shift(skb))
1487                goto fallback;
1488        /* This frame is about to be dropped (was ACKed). */
1489        if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
1490                goto fallback;
1491
1492        /* Can only happen with delayed DSACK + discard craziness */
1493        if (unlikely(skb == tcp_write_queue_head(sk)))
1494                goto fallback;
1495        prev = tcp_write_queue_prev(sk, skb);
1496
1497        if ((TCP_SKB_CB(prev)->sacked & TCPCB_TAGBITS) != TCPCB_SACKED_ACKED)
1498                goto fallback;
1499
1500        in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) &&
1501                  !before(end_seq, TCP_SKB_CB(skb)->end_seq);
1502
1503        if (in_sack) {
1504                len = skb->len;
1505                pcount = tcp_skb_pcount(skb);
1506                mss = tcp_skb_seglen(skb);
1507
1508                /* TODO: Fix DSACKs to not fragment already SACKed and we can
1509                 * drop this restriction as unnecessary
1510                 */
1511                if (mss != tcp_skb_seglen(prev))
1512                        goto fallback;
1513        } else {
1514                if (!after(TCP_SKB_CB(skb)->end_seq, start_seq))
1515                        goto noop;
1516                /* CHECKME: This is non-MSS split case only?, this will
1517                 * cause skipped skbs due to advancing loop btw, original
1518                 * has that feature too
1519                 */
1520                if (tcp_skb_pcount(skb) <= 1)
1521                        goto noop;
1522
1523                in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq);
1524                if (!in_sack) {
1525                        /* TODO: head merge to next could be attempted here
1526                         * if (!after(TCP_SKB_CB(skb)->end_seq, end_seq)),
1527                         * though it might not be worth of the additional hassle
1528                         *
1529                         * ...we can probably just fallback to what was done
1530                         * previously. We could try merging non-SACKed ones
1531                         * as well but it probably isn't going to buy off
1532                         * because later SACKs might again split them, and
1533                         * it would make skb timestamp tracking considerably
1534                         * harder problem.
1535                         */
1536                        goto fallback;
1537                }
1538
1539                len = end_seq - TCP_SKB_CB(skb)->seq;
1540                BUG_ON(len < 0);
1541                BUG_ON(len > skb->len);
1542
1543                /* MSS boundaries should be honoured or else pcount will
1544                 * severely break even though it makes things bit trickier.
1545                 * Optimize common case to avoid most of the divides
1546                 */
1547                mss = tcp_skb_mss(skb);
1548
1549                /* TODO: Fix DSACKs to not fragment already SACKed and we can
1550                 * drop this restriction as unnecessary
1551                 */
1552                if (mss != tcp_skb_seglen(prev))
1553                        goto fallback;
1554
1555                if (len == mss) {
1556                        pcount = 1;
1557                } else if (len < mss) {
1558                        goto noop;
1559                } else {
1560                        pcount = len / mss;
1561                        len = pcount * mss;
1562                }
1563        }
1564
1565        if (!skb_shift(prev, skb, len))
1566                goto fallback;
1567        if (!tcp_shifted_skb(sk, skb, state, pcount, len, mss, dup_sack))
1568                goto out;
1569
1570        /* Hole filled allows collapsing with the next as well, this is very
1571         * useful when hole on every nth skb pattern happens
1572         */
1573        if (prev == tcp_write_queue_tail(sk))
1574                goto out;
1575        skb = tcp_write_queue_next(sk, prev);
1576
1577        if (!skb_can_shift(skb) ||
1578            (skb == tcp_send_head(sk)) ||
1579            ((TCP_SKB_CB(skb)->sacked & TCPCB_TAGBITS) != TCPCB_SACKED_ACKED) ||
1580            (mss != tcp_skb_seglen(skb)))
1581                goto out;
1582
1583        len = skb->len;
1584        if (skb_shift(prev, skb, len)) {
1585                pcount += tcp_skb_pcount(skb);
1586                tcp_shifted_skb(sk, skb, state, tcp_skb_pcount(skb), len, mss, 0);
1587        }
1588
1589out:
1590        state->fack_count += pcount;
1591        return prev;
1592
1593noop:
1594        return skb;
1595
1596fallback:
1597        NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SACKSHIFTFALLBACK);
1598        return NULL;
1599}
1600
1601static struct sk_buff *tcp_sacktag_walk(struct sk_buff *skb, struct sock *sk,
1602                                        struct tcp_sack_block *next_dup,
1603                                        struct tcp_sacktag_state *state,
1604                                        u32 start_seq, u32 end_seq,
1605                                        int dup_sack_in)
1606{
1607        struct tcp_sock *tp = tcp_sk(sk);
1608        struct sk_buff *tmp;
1609
1610        tcp_for_write_queue_from(skb, sk) {
1611                int in_sack = 0;
1612                int dup_sack = dup_sack_in;
1613
1614                if (skb == tcp_send_head(sk))
1615                        break;
1616
1617                /* queue is in-order => we can short-circuit the walk early */
1618                if (!before(TCP_SKB_CB(skb)->seq, end_seq))
1619                        break;
1620
1621                if ((next_dup != NULL) &&
1622                    before(TCP_SKB_CB(skb)->seq, next_dup->end_seq)) {
1623                        in_sack = tcp_match_skb_to_sack(sk, skb,
1624                                                        next_dup->start_seq,
1625                                                        next_dup->end_seq);
1626                        if (in_sack > 0)
1627                                dup_sack = 1;
1628                }
1629
1630                /* skb reference here is a bit tricky to get right, since
1631                 * shifting can eat and free both this skb and the next,
1632                 * so not even _safe variant of the loop is enough.
1633                 */
1634                if (in_sack <= 0) {
1635                        tmp = tcp_shift_skb_data(sk, skb, state,
1636                                                 start_seq, end_seq, dup_sack);
1637                        if (tmp != NULL) {
1638                                if (tmp != skb) {
1639                                        skb = tmp;
1640                                        continue;
1641                                }
1642
1643                                in_sack = 0;
1644                        } else {
1645                                in_sack = tcp_match_skb_to_sack(sk, skb,
1646                                                                start_seq,
1647                                                                end_seq);
1648                        }
1649                }
1650
1651                if (unlikely(in_sack < 0))
1652                        break;
1653
1654                if (in_sack) {
1655                        TCP_SKB_CB(skb)->sacked = tcp_sacktag_one(skb, sk,
1656                                                                  state,
1657                                                                  dup_sack,
1658                                                                  tcp_skb_pcount(skb));
1659
1660                        if (!before(TCP_SKB_CB(skb)->seq,
1661                                    tcp_highest_sack_seq(tp)))
1662                                tcp_advance_highest_sack(sk, skb);
1663                }
1664
1665                state->fack_count += tcp_skb_pcount(skb);
1666        }
1667        return skb;
1668}
1669
1670/* Avoid all extra work that is being done by sacktag while walking in
1671 * a normal way
1672 */
1673static struct sk_buff *tcp_sacktag_skip(struct sk_buff *skb, struct sock *sk,
1674                                        struct tcp_sacktag_state *state,
1675                                        u32 skip_to_seq)
1676{
1677        tcp_for_write_queue_from(skb, sk) {
1678                if (skb == tcp_send_head(sk))
1679                        break;
1680
1681                if (after(TCP_SKB_CB(skb)->end_seq, skip_to_seq))
1682                        break;
1683
1684                state->fack_count += tcp_skb_pcount(skb);
1685        }
1686        return skb;
1687}
1688
1689static struct sk_buff *tcp_maybe_skipping_dsack(struct sk_buff *skb,
1690                                                struct sock *sk,
1691                                                struct tcp_sack_block *next_dup,
1692                                                struct tcp_sacktag_state *state,
1693                                                u32 skip_to_seq)
1694{
1695        if (next_dup == NULL)
1696                return skb;
1697
1698        if (before(next_dup->start_seq, skip_to_seq)) {
1699                skb = tcp_sacktag_skip(skb, sk, state, next_dup->start_seq);
1700                skb = tcp_sacktag_walk(skb, sk, NULL, state,
1701                                       next_dup->start_seq, next_dup->end_seq,
1702                                       1);
1703        }
1704
1705        return skb;
1706}
1707
1708static int tcp_sack_cache_ok(struct tcp_sock *tp, struct tcp_sack_block *cache)
1709{
1710        return cache < tp->recv_sack_cache + ARRAY_SIZE(tp->recv_sack_cache);
1711}
1712
1713static int
1714tcp_sacktag_write_queue(struct sock *sk, struct sk_buff *ack_skb,
1715                        u32 prior_snd_una)
1716{
1717        const struct inet_connection_sock *icsk = inet_csk(sk);
1718        struct tcp_sock *tp = tcp_sk(sk);
1719        unsigned char *ptr = (skb_transport_header(ack_skb) +
1720                              TCP_SKB_CB(ack_skb)->sacked);
1721        struct tcp_sack_block_wire *sp_wire = (struct tcp_sack_block_wire *)(ptr+2);
1722        struct tcp_sack_block sp[TCP_NUM_SACKS];
1723        struct tcp_sack_block *cache;
1724        struct tcp_sacktag_state state;
1725        struct sk_buff *skb;
1726        int num_sacks = min(TCP_NUM_SACKS, (ptr[1] - TCPOLEN_SACK_BASE) >> 3);
1727        int used_sacks;
1728        int found_dup_sack = 0;
1729        int i, j;
1730        int first_sack_index;
1731
1732        state.flag = 0;
1733        state.reord = tp->packets_out;
1734
1735        if (!tp->sacked_out) {
1736                if (WARN_ON(tp->fackets_out))
1737                        tp->fackets_out = 0;
1738                tcp_highest_sack_reset(sk);
1739        }
1740
1741        found_dup_sack = tcp_check_dsack(sk, ack_skb, sp_wire,
1742                                         num_sacks, prior_snd_una);
1743        if (found_dup_sack)
1744                state.flag |= FLAG_DSACKING_ACK;
1745
1746        /* Eliminate too old ACKs, but take into
1747         * account more or less fresh ones, they can
1748         * contain valid SACK info.
1749         */
1750        if (before(TCP_SKB_CB(ack_skb)->ack_seq, prior_snd_una - tp->max_window))
1751                return 0;
1752
1753        if (!tp->packets_out)
1754                goto out;
1755
1756        used_sacks = 0;
1757        first_sack_index = 0;
1758        for (i = 0; i < num_sacks; i++) {
1759                int dup_sack = !i && found_dup_sack;
1760
1761                sp[used_sacks].start_seq = get_unaligned_be32(&sp_wire[i].start_seq);
1762                sp[used_sacks].end_seq = get_unaligned_be32(&sp_wire[i].end_seq);
1763
1764                if (!tcp_is_sackblock_valid(tp, dup_sack,
1765                                            sp[used_sacks].start_seq,
1766                                            sp[used_sacks].end_seq)) {
1767                        int mib_idx;
1768
1769                        if (dup_sack) {
1770                                if (!tp->undo_marker)
1771                                        mib_idx = LINUX_MIB_TCPDSACKIGNOREDNOUNDO;
1772                                else
1773                                        mib_idx = LINUX_MIB_TCPDSACKIGNOREDOLD;
1774                        } else {
1775                                /* Don't count olds caused by ACK reordering */
1776                                if ((TCP_SKB_CB(ack_skb)->ack_seq != tp->snd_una) &&
1777                                    !after(sp[used_sacks].end_seq, tp->snd_una))
1778                                        continue;
1779                                mib_idx = LINUX_MIB_TCPSACKDISCARD;
1780                        }
1781
1782                        NET_INC_STATS_BH(sock_net(sk), mib_idx);
1783                        if (i == 0)
1784                                first_sack_index = -1;
1785                        continue;
1786                }
1787
1788                /* Ignore very old stuff early */
1789                if (!after(sp[used_sacks].end_seq, prior_snd_una))
1790                        continue;
1791
1792                used_sacks++;
1793        }
1794
1795        /* order SACK blocks to allow in order walk of the retrans queue */
1796        for (i = used_sacks - 1; i > 0; i--) {
1797                for (j = 0; j < i; j++) {
1798                        if (after(sp[j].start_seq, sp[j + 1].start_seq)) {
1799                                swap(sp[j], sp[j + 1]);
1800
1801                                /* Track where the first SACK block goes to */
1802                                if (j == first_sack_index)
1803                                        first_sack_index = j + 1;
1804                        }
1805                }
1806        }
1807
1808        skb = tcp_write_queue_head(sk);
1809        state.fack_count = 0;
1810        i = 0;
1811
1812        if (!tp->sacked_out) {
1813                /* It's already past, so skip checking against it */
1814                cache = tp->recv_sack_cache + ARRAY_SIZE(tp->recv_sack_cache);
1815        } else {
1816                cache = tp->recv_sack_cache;
1817                /* Skip empty blocks in at head of the cache */
1818                while (tcp_sack_cache_ok(tp, cache) && !cache->start_seq &&
1819                       !cache->end_seq)
1820                        cache++;
1821        }
1822
1823        while (i < used_sacks) {
1824                u32 start_seq = sp[i].start_seq;
1825                u32 end_seq = sp[i].end_seq;
1826                int dup_sack = (found_dup_sack && (i == first_sack_index));
1827                struct tcp_sack_block *next_dup = NULL;
1828
1829                if (found_dup_sack && ((i + 1) == first_sack_index))
1830                        next_dup = &sp[i + 1];
1831
1832                /* Event "B" in the comment above. */
1833                if (after(end_seq, tp->high_seq))
1834                        state.flag |= FLAG_DATA_LOST;
1835
1836                /* Skip too early cached blocks */
1837                while (tcp_sack_cache_ok(tp, cache) &&
1838                       !before(start_seq, cache->end_seq))
1839                        cache++;
1840
1841                /* Can skip some work by looking recv_sack_cache? */
1842                if (tcp_sack_cache_ok(tp, cache) && !dup_sack &&
1843                    after(end_seq, cache->start_seq)) {
1844
1845                        /* Head todo? */
1846                        if (before(start_seq, cache->start_seq)) {
1847                                skb = tcp_sacktag_skip(skb, sk, &state,
1848                                                       start_seq);
1849                                skb = tcp_sacktag_walk(skb, sk, next_dup,
1850                                                       &state,
1851                                                       start_seq,
1852                                                       cache->start_seq,
1853                                                       dup_sack);
1854                        }
1855
1856                        /* Rest of the block already fully processed? */
1857                        if (!after(end_seq, cache->end_seq))
1858                                goto advance_sp;
1859
1860                        skb = tcp_maybe_skipping_dsack(skb, sk, next_dup,
1861                                                       &state,
1862                                                       cache->end_seq);
1863
1864                        /* ...tail remains todo... */
1865                        if (tcp_highest_sack_seq(tp) == cache->end_seq) {
1866                                /* ...but better entrypoint exists! */
1867                                skb = tcp_highest_sack(sk);
1868                                if (skb == NULL)
1869                                        break;
1870                                state.fack_count = tp->fackets_out;
1871                                cache++;
1872                                goto walk;
1873                        }
1874
1875                        skb = tcp_sacktag_skip(skb, sk, &state, cache->end_seq);
1876                        /* Check overlap against next cached too (past this one already) */
1877                        cache++;
1878                        continue;
1879                }
1880
1881                if (!before(start_seq, tcp_highest_sack_seq(tp))) {
1882                        skb = tcp_highest_sack(sk);
1883                        if (skb == NULL)
1884                                break;
1885                        state.fack_count = tp->fackets_out;
1886                }
1887                skb = tcp_sacktag_skip(skb, sk, &state, start_seq);
1888
1889walk:
1890                skb = tcp_sacktag_walk(skb, sk, next_dup, &state,
1891                                       start_seq, end_seq, dup_sack);
1892
1893advance_sp:
1894                /* SACK enhanced FRTO (RFC4138, Appendix B): Clearing correct
1895                 * due to in-order walk
1896                 */
1897                if (after(end_seq, tp->frto_highmark))
1898                        state.flag &= ~FLAG_ONLY_ORIG_SACKED;
1899
1900                i++;
1901        }
1902
1903        /* Clear the head of the cache sack blocks so we can skip it next time */
1904        for (i = 0; i < ARRAY_SIZE(tp->recv_sack_cache) - used_sacks; i++) {
1905                tp->recv_sack_cache[i].start_seq = 0;
1906                tp->recv_sack_cache[i].end_seq = 0;
1907        }
1908        for (j = 0; j < used_sacks; j++)
1909                tp->recv_sack_cache[i++] = sp[j];
1910
1911        tcp_mark_lost_retrans(sk);
1912
1913        tcp_verify_left_out(tp);
1914
1915        if ((state.reord < tp->fackets_out) &&
1916            ((icsk->icsk_ca_state != TCP_CA_Loss) || tp->undo_marker) &&
1917            (!tp->frto_highmark || after(tp->snd_una, tp->frto_highmark)))
1918                tcp_update_reordering(sk, tp->fackets_out - state.reord, 0);
1919
1920out:
1921
1922#if FASTRETRANS_DEBUG > 0
1923        WARN_ON((int)tp->sacked_out < 0);
1924        WARN_ON((int)tp->lost_out < 0);
1925        WARN_ON((int)tp->retrans_out < 0);
1926        WARN_ON((int)tcp_packets_in_flight(tp) < 0);
1927#endif
1928        return state.flag;
1929}
1930
1931/* Limits sacked_out so that sum with lost_out isn't ever larger than
1932 * packets_out. Returns zero if sacked_out adjustement wasn't necessary.
1933 */
1934static int tcp_limit_reno_sacked(struct tcp_sock *tp)
1935{
1936        u32 holes;
1937
1938        holes = max(tp->lost_out, 1U);
1939        holes = min(holes, tp->packets_out);
1940
1941        if ((tp->sacked_out + holes) > tp->packets_out) {
1942                tp->sacked_out = tp->packets_out - holes;
1943                return 1;
1944        }
1945        return 0;
1946}
1947
1948/* If we receive more dupacks than we expected counting segments
1949 * in assumption of absent reordering, interpret this as reordering.
1950 * The only another reason could be bug in receiver TCP.
1951 */
1952static void tcp_check_reno_reordering(struct sock *sk, const int addend)
1953{
1954        struct tcp_sock *tp = tcp_sk(sk);
1955        if (tcp_limit_reno_sacked(tp))
1956                tcp_update_reordering(sk, tp->packets_out + addend, 0);
1957}
1958
1959/* Emulate SACKs for SACKless connection: account for a new dupack. */
1960
1961static void tcp_add_reno_sack(struct sock *sk)
1962{
1963        struct tcp_sock *tp = tcp_sk(sk);
1964        tp->sacked_out++;
1965        tcp_check_reno_reordering(sk, 0);
1966        tcp_verify_left_out(tp);
1967}
1968
1969/* Account for ACK, ACKing some data in Reno Recovery phase. */
1970
1971static void tcp_remove_reno_sacks(struct sock *sk, int acked)
1972{
1973        struct tcp_sock *tp = tcp_sk(sk);
1974
1975        if (acked > 0) {
1976                /* One ACK acked hole. The rest eat duplicate ACKs. */
1977                if (acked - 1 >= tp->sacked_out)
1978                        tp->sacked_out = 0;
1979                else
1980                        tp->sacked_out -= acked - 1;
1981        }
1982        tcp_check_reno_reordering(sk, acked);
1983        tcp_verify_left_out(tp);
1984}
1985
1986static inline void tcp_reset_reno_sack(struct tcp_sock *tp)
1987{
1988        tp->sacked_out = 0;
1989}
1990
1991static int tcp_is_sackfrto(const struct tcp_sock *tp)
1992{
1993        return (sysctl_tcp_frto == 0x2) && !tcp_is_reno(tp);
1994}
1995
1996/* F-RTO can only be used if TCP has never retransmitted anything other than
1997 * head (SACK enhanced variant from Appendix B of RFC4138 is more robust here)
1998 */
1999int tcp_use_frto(struct sock *sk)
2000{
2001        const struct tcp_sock *tp = tcp_sk(sk);
2002        const struct inet_connection_sock *icsk = inet_csk(sk);
2003        struct sk_buff *skb;
2004
2005        if (!sysctl_tcp_frto)
2006                return 0;
2007
2008        /* MTU probe and F-RTO won't really play nicely along currently */
2009        if (icsk->icsk_mtup.probe_size)
2010                return 0;
2011
2012        if (tcp_is_sackfrto(tp))
2013                return 1;
2014
2015        /* Avoid expensive walking of rexmit queue if possible */
2016        if (tp->retrans_out > 1)
2017                return 0;
2018
2019        skb = tcp_write_queue_head(sk);
2020        if (tcp_skb_is_last(sk, skb))
2021                return 1;
2022        skb = tcp_write_queue_next(sk, skb);    /* Skips head */
2023        tcp_for_write_queue_from(skb, sk) {
2024                if (skb == tcp_send_head(sk))
2025                        break;
2026                if (TCP_SKB_CB(skb)->sacked & TCPCB_RETRANS)
2027                        return 0;
2028                /* Short-circuit when first non-SACKed skb has been checked */
2029                if (!(TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED))
2030                        break;
2031        }
2032        return 1;
2033}
2034
2035/* RTO occurred, but do not yet enter Loss state. Instead, defer RTO
2036 * recovery a bit and use heuristics in tcp_process_frto() to detect if
2037 * the RTO was spurious. Only clear SACKED_RETRANS of the head here to
2038 * keep retrans_out counting accurate (with SACK F-RTO, other than head
2039 * may still have that bit set); TCPCB_LOST and remaining SACKED_RETRANS
2040 * bits are handled if the Loss state is really to be entered (in
2041 * tcp_enter_frto_loss).
2042 *
2043 * Do like tcp_enter_loss() would; when RTO expires the second time it
2044 * does:
2045 *  "Reduce ssthresh if it has not yet been made inside this window."
2046 */
2047void tcp_enter_frto(struct sock *sk)
2048{
2049        const struct inet_connection_sock *icsk = inet_csk(sk);
2050        struct tcp_sock *tp = tcp_sk(sk);
2051        struct sk_buff *skb;
2052
2053        if ((!tp->frto_counter && icsk->icsk_ca_state <= TCP_CA_Disorder) ||
2054            tp->snd_una == tp->high_seq ||
2055            ((icsk->icsk_ca_state == TCP_CA_Loss || tp->frto_counter) &&
2056             !icsk->icsk_retransmits)) {
2057                tp->prior_ssthresh = tcp_current_ssthresh(sk);
2058                /* Our state is too optimistic in ssthresh() call because cwnd
2059                 * is not reduced until tcp_enter_frto_loss() when previous F-RTO
2060                 * recovery has not yet completed. Pattern would be this: RTO,
2061                 * Cumulative ACK, RTO (2xRTO for the same segment does not end
2062                 * up here twice).
2063                 * RFC4138 should be more specific on what to do, even though
2064                 * RTO is quite unlikely to occur after the first Cumulative ACK
2065                 * due to back-off and complexity of triggering events ...
2066                 */
2067                if (tp->frto_counter) {
2068                        u32 stored_cwnd;
2069                        stored_cwnd = tp->snd_cwnd;
2070                        tp->snd_cwnd = 2;
2071                        tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
2072                        tp->snd_cwnd = stored_cwnd;
2073                } else {
2074                        tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
2075                }
2076                /* ... in theory, cong.control module could do "any tricks" in
2077                 * ssthresh(), which means that ca_state, lost bits and lost_out
2078                 * counter would have to be faked before the call occurs. We
2079                 * consider that too expensive, unlikely and hacky, so modules
2080                 * using these in ssthresh() must deal these incompatibility
2081                 * issues if they receives CA_EVENT_FRTO and frto_counter != 0
2082                 */
2083                tcp_ca_event(sk, CA_EVENT_FRTO);
2084        }
2085
2086        tp->undo_marker = tp->snd_una;
2087        tp->undo_retrans = 0;
2088
2089        skb = tcp_write_queue_head(sk);
2090        if (TCP_SKB_CB(skb)->sacked & TCPCB_RETRANS)
2091                tp->undo_marker = 0;
2092        if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) {
2093                TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
2094                tp->retrans_out -= tcp_skb_pcount(skb);
2095        }
2096        tcp_verify_left_out(tp);
2097
2098        /* Too bad if TCP was application limited */
2099        tp->snd_cwnd = min(tp->snd_cwnd, tcp_packets_in_flight(tp) + 1);
2100
2101        /* Earlier loss recovery underway (see RFC4138; Appendix B).
2102         * The last condition is necessary at least in tp->frto_counter case.
2103         */
2104        if (tcp_is_sackfrto(tp) && (tp->frto_counter ||
2105            ((1 << icsk->icsk_ca_state) & (TCPF_CA_Recovery|TCPF_CA_Loss))) &&
2106            after(tp->high_seq, tp->snd_una)) {
2107                tp->frto_highmark = tp->high_seq;
2108        } else {
2109                tp->frto_highmark = tp->snd_nxt;
2110        }
2111        tcp_set_ca_state(sk, TCP_CA_Disorder);
2112        tp->high_seq = tp->snd_nxt;
2113        tp->frto_counter = 1;
2114}
2115
2116/* Enter Loss state after F-RTO was applied. Dupack arrived after RTO,
2117 * which indicates that we should follow the traditional RTO recovery,
2118 * i.e. mark everything lost and do go-back-N retransmission.
2119 */
2120static void tcp_enter_frto_loss(struct sock *sk, int allowed_segments, int flag)
2121{
2122        struct tcp_sock *tp = tcp_sk(sk);
2123        struct sk_buff *skb;
2124
2125        tp->lost_out = 0;
2126        tp->retrans_out = 0;
2127        if (tcp_is_reno(tp))
2128                tcp_reset_reno_sack(tp);
2129
2130        tcp_for_write_queue(skb, sk) {
2131                if (skb == tcp_send_head(sk))
2132                        break;
2133
2134                TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST;
2135                /*
2136                 * Count the retransmission made on RTO correctly (only when
2137                 * waiting for the first ACK and did not get it)...
2138                 */
2139                if ((tp->frto_counter == 1) && !(flag & FLAG_DATA_ACKED)) {
2140                        /* For some reason this R-bit might get cleared? */
2141                        if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS)
2142                                tp->retrans_out += tcp_skb_pcount(skb);
2143                        /* ...enter this if branch just for the first segment */
2144                        flag |= FLAG_DATA_ACKED;
2145                } else {
2146                        if (TCP_SKB_CB(skb)->sacked & TCPCB_RETRANS)
2147                                tp->undo_marker = 0;
2148                        TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
2149                }
2150
2151                /* Marking forward transmissions that were made after RTO lost
2152                 * can cause unnecessary retransmissions in some scenarios,
2153                 * SACK blocks will mitigate that in some but not in all cases.
2154                 * We used to not mark them but it was causing break-ups with
2155                 * receivers that do only in-order receival.
2156                 *
2157                 * TODO: we could detect presence of such receiver and select
2158                 * different behavior per flow.
2159                 */
2160                if (!(TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)) {
2161                        TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
2162                        tp->lost_out += tcp_skb_pcount(skb);
2163                        tp->retransmit_high = TCP_SKB_CB(skb)->end_seq;
2164                }
2165        }
2166        tcp_verify_left_out(tp);
2167
2168        tp->snd_cwnd = tcp_packets_in_flight(tp) + allowed_segments;
2169        tp->snd_cwnd_cnt = 0;
2170        tp->snd_cwnd_stamp = tcp_time_stamp;
2171        tp->frto_counter = 0;
2172        tp->bytes_acked = 0;
2173
2174        tp->reordering = min_t(unsigned int, tp->reordering,
2175                               sysctl_tcp_reordering);
2176        tcp_set_ca_state(sk, TCP_CA_Loss);
2177        tp->high_seq = tp->snd_nxt;
2178        TCP_ECN_queue_cwr(tp);
2179
2180        tcp_clear_all_retrans_hints(tp);
2181}
2182
2183static void tcp_clear_retrans_partial(struct tcp_sock *tp)
2184{
2185        tp->retrans_out = 0;
2186        tp->lost_out = 0;
2187
2188        tp->undo_marker = 0;
2189        tp->undo_retrans = 0;
2190}
2191
2192void tcp_clear_retrans(struct tcp_sock *tp)
2193{
2194        tcp_clear_retrans_partial(tp);
2195
2196        tp->fackets_out = 0;
2197        tp->sacked_out = 0;
2198}
2199
2200/* Enter Loss state. If "how" is not zero, forget all SACK information
2201 * and reset tags completely, otherwise preserve SACKs. If receiver
2202 * dropped its ofo queue, we will know this due to reneging detection.
2203 */
2204void tcp_enter_loss(struct sock *sk, int how)
2205{
2206        const struct inet_connection_sock *icsk = inet_csk(sk);
2207        struct tcp_sock *tp = tcp_sk(sk);
2208        struct sk_buff *skb;
2209
2210        /* Reduce ssthresh if it has not yet been made inside this window. */
2211        if (icsk->icsk_ca_state <= TCP_CA_Disorder || tp->snd_una == tp->high_seq ||
2212            (icsk->icsk_ca_state == TCP_CA_Loss && !icsk->icsk_retransmits)) {
2213                tp->prior_ssthresh = tcp_current_ssthresh(sk);
2214                tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
2215                tcp_ca_event(sk, CA_EVENT_LOSS);
2216        }
2217        tp->snd_cwnd       = 1;
2218        tp->snd_cwnd_cnt   = 0;
2219        tp->snd_cwnd_stamp = tcp_time_stamp;
2220
2221        tp->bytes_acked = 0;
2222        tcp_clear_retrans_partial(tp);
2223
2224        if (tcp_is_reno(tp))
2225                tcp_reset_reno_sack(tp);
2226
2227        if (!how) {
2228                /* Push undo marker, if it was plain RTO and nothing
2229                 * was retransmitted. */
2230                tp->undo_marker = tp->snd_una;
2231        } else {
2232                tp->sacked_out = 0;
2233                tp->fackets_out = 0;
2234        }
2235        tcp_clear_all_retrans_hints(tp);
2236
2237        tcp_for_write_queue(skb, sk) {
2238                if (skb == tcp_send_head(sk))
2239                        break;
2240
2241                if (TCP_SKB_CB(skb)->sacked & TCPCB_RETRANS)
2242                        tp->undo_marker = 0;
2243                TCP_SKB_CB(skb)->sacked &= (~TCPCB_TAGBITS)|TCPCB_SACKED_ACKED;
2244                if (!(TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_ACKED) || how) {
2245                        TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_ACKED;
2246                        TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
2247                        tp->lost_out += tcp_skb_pcount(skb);
2248                        tp->retransmit_high = TCP_SKB_CB(skb)->end_seq;
2249                }
2250        }
2251        tcp_verify_left_out(tp);
2252
2253        tp->reordering = min_t(unsigned int, tp->reordering,
2254                               sysctl_tcp_reordering);
2255        tcp_set_ca_state(sk, TCP_CA_Loss);
2256        tp->high_seq = tp->snd_nxt;
2257        TCP_ECN_queue_cwr(tp);
2258        /* Abort F-RTO algorithm if one is in progress */
2259        tp->frto_counter = 0;
2260}
2261
2262/* If ACK arrived pointing to a remembered SACK, it means that our
2263 * remembered SACKs do not reflect real state of receiver i.e.
2264 * receiver _host_ is heavily congested (or buggy).
2265 *
2266 * Do processing similar to RTO timeout.
2267 */
2268static int tcp_check_sack_reneging(struct sock *sk, int flag)
2269{
2270        if (flag & FLAG_SACK_RENEGING) {
2271                struct inet_connection_sock *icsk = inet_csk(sk);
2272                NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSACKRENEGING);
2273
2274                tcp_enter_loss(sk, 1);
2275                icsk->icsk_retransmits++;
2276                tcp_retransmit_skb(sk, tcp_write_queue_head(sk));
2277                inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
2278                                          icsk->icsk_rto, TCP_RTO_MAX);
2279                return 1;
2280        }
2281        return 0;
2282}
2283
2284static inline int tcp_fackets_out(struct tcp_sock *tp)
2285{
2286        return tcp_is_reno(tp) ? tp->sacked_out + 1 : tp->fackets_out;
2287}
2288
2289/* Heurestics to calculate number of duplicate ACKs. There's no dupACKs
2290 * counter when SACK is enabled (without SACK, sacked_out is used for
2291 * that purpose).
2292 *
2293 * Instead, with FACK TCP uses fackets_out that includes both SACKed
2294 * segments up to the highest received SACK block so far and holes in
2295 * between them.
2296 *
2297 * With reordering, holes may still be in flight, so RFC3517 recovery
2298 * uses pure sacked_out (total number of SACKed segments) even though
2299 * it violates the RFC that uses duplicate ACKs, often these are equal
2300 * but when e.g. out-of-window ACKs or packet duplication occurs,
2301 * they differ. Since neither occurs due to loss, TCP should really
2302 * ignore them.
2303 */
2304static inline int tcp_dupack_heurestics(struct tcp_sock *tp)
2305{
2306        return tcp_is_fack(tp) ? tp->fackets_out : tp->sacked_out + 1;
2307}
2308
2309static inline int tcp_skb_timedout(struct sock *sk, struct sk_buff *skb)
2310{
2311        return (tcp_time_stamp - TCP_SKB_CB(skb)->when > inet_csk(sk)->icsk_rto);
2312}
2313
2314static inline int tcp_head_timedout(struct sock *sk)
2315{
2316        struct tcp_sock *tp = tcp_sk(sk);
2317
2318        return tp->packets_out &&
2319               tcp_skb_timedout(sk, tcp_write_queue_head(sk));
2320}
2321
2322/* Linux NewReno/SACK/FACK/ECN state machine.
2323 * --------------------------------------
2324 *
2325 * "Open"       Normal state, no dubious events, fast path.
2326 * "Disorder"   In all the respects it is "Open",
2327 *              but requires a bit more attention. It is entered when
2328 *              we see some SACKs or dupacks. It is split of "Open"
2329 *              mainly to move some processing from fast path to slow one.
2330 * "CWR"        CWND was reduced due to some Congestion Notification event.
2331 *              It can be ECN, ICMP source quench, local device congestion.
2332 * "Recovery"   CWND was reduced, we are fast-retransmitting.
2333 * "Loss"       CWND was reduced due to RTO timeout or SACK reneging.
2334 *
2335 * tcp_fastretrans_alert() is entered:
2336 * - each incoming ACK, if state is not "Open"
2337 * - when arrived ACK is unusual, namely:
2338 *      * SACK
2339 *      * Duplicate ACK.
2340 *      * ECN ECE.
2341 *
2342 * Counting packets in flight is pretty simple.
2343 *
2344 *      in_flight = packets_out - left_out + retrans_out
2345 *
2346 *      packets_out is SND.NXT-SND.UNA counted in packets.
2347 *
2348 *      retrans_out is number of retransmitted segments.
2349 *
2350 *      left_out is number of segments left network, but not ACKed yet.
2351 *
2352 *              left_out = sacked_out + lost_out
2353 *
2354 *     sacked_out: Packets, which arrived to receiver out of order
2355 *                 and hence not ACKed. With SACKs this number is simply
2356 *                 amount of SACKed data. Even without SACKs
2357 *                 it is easy to give pretty reliable estimate of this number,
2358 *                 counting duplicate ACKs.
2359 *
2360 *       lost_out: Packets lost by network. TCP has no explicit
2361 *                 "loss notification" feedback from network (for now).
2362 *                 It means that this number can be only _guessed_.
2363 *                 Actually, it is the heuristics to predict lossage that
2364 *                 distinguishes different algorithms.
2365 *
2366 *      F.e. after RTO, when all the queue is considered as lost,
2367 *      lost_out = packets_out and in_flight = retrans_out.
2368 *
2369 *              Essentially, we have now two algorithms counting
2370 *              lost packets.
2371 *
2372 *              FACK: It is the simplest heuristics. As soon as we decided
2373 *              that something is lost, we decide that _all_ not SACKed
2374 *              packets until the most forward SACK are lost. I.e.
2375 *              lost_out = fackets_out - sacked_out and left_out = fackets_out.
2376 *              It is absolutely correct estimate, if network does not reorder
2377 *              packets. And it loses any connection to reality when reordering
2378 *              takes place. We use FACK by default until reordering
2379 *              is suspected on the path to this destination.
2380 *
2381 *              NewReno: when Recovery is entered, we assume that one segment
2382 *              is lost (classic Reno). While we are in Recovery and
2383 *              a partial ACK arrives, we assume that one more packet
2384 *              is lost (NewReno). This heuristics are the same in NewReno
2385 *              and SACK.
2386 *
2387 *  Imagine, that's all! Forget about all this shamanism about CWND inflation
2388 *  deflation etc. CWND is real congestion window, never inflated, changes
2389 *  only according to classic VJ rules.
2390 *
2391 * Really tricky (and requiring careful tuning) part of algorithm
2392 * is hidden in functions tcp_time_to_recover() and tcp_xmit_retransmit_queue().
2393 * The first determines the moment _when_ we should reduce CWND and,
2394 * hence, slow down forward transmission. In fact, it determines the moment
2395 * when we decide that hole is caused by loss, rather than by a reorder.
2396 *
2397 * tcp_xmit_retransmit_queue() decides, _what_ we should retransmit to fill
2398 * holes, caused by lost packets.
2399 *
2400 * And the most logically complicated part of algorithm is undo
2401 * heuristics. We detect false retransmits due to both too early
2402 * fast retransmit (reordering) and underestimated RTO, analyzing
2403 * timestamps and D-SACKs. When we detect that some segments were
2404 * retransmitted by mistake and CWND reduction was wrong, we undo
2405 * window reduction and abort recovery phase. This logic is hidden
2406 * inside several functions named tcp_try_undo_<something>.
2407 */
2408
2409/* This function decides, when we should leave Disordered state
2410 * and enter Recovery phase, reducing congestion window.
2411 *
2412 * Main question: may we further continue forward transmission
2413 * with the same cwnd?
2414 */
2415static int tcp_time_to_recover(struct sock *sk)
2416{
2417        struct tcp_sock *tp = tcp_sk(sk);
2418        __u32 packets_out;
2419
2420        /* Do not perform any recovery during F-RTO algorithm */
2421        if (tp->frto_counter)
2422                return 0;
2423
2424        /* Trick#1: The loss is proven. */
2425        if (tp->lost_out)
2426                return 1;
2427
2428        /* Not-A-Trick#2 : Classic rule... */
2429        if (tcp_dupack_heurestics(tp) > tp->reordering)
2430                return 1;
2431
2432        /* Trick#3 : when we use RFC2988 timer restart, fast
2433         * retransmit can be triggered by timeout of queue head.
2434         */
2435        if (tcp_is_fack(tp) && tcp_head_timedout(sk))
2436                return 1;
2437
2438        /* Trick#4: It is still not OK... But will it be useful to delay
2439         * recovery more?
2440         */
2441        packets_out = tp->packets_out;
2442        if (packets_out <= tp->reordering &&
2443            tp->sacked_out >= max_t(__u32, packets_out/2, sysctl_tcp_reordering) &&
2444            !tcp_may_send_now(sk)) {
2445                /* We have nothing to send. This connection is limited
2446                 * either by receiver window or by application.
2447                 */
2448                return 1;
2449        }
2450
2451        return 0;
2452}
2453
2454/* New heuristics: it is possible only after we switched to restart timer
2455 * each time when something is ACKed. Hence, we can detect timed out packets
2456 * during fast retransmit without falling to slow start.
2457 *
2458 * Usefulness of this as is very questionable, since we should know which of
2459 * the segments is the next to timeout which is relatively expensive to find
2460 * in general case unless we add some data structure just for that. The
2461 * current approach certainly won't find the right one too often and when it
2462 * finally does find _something_ it usually marks large part of the window
2463 * right away (because a retransmission with a larger timestamp blocks the
2464 * loop from advancing). -ij
2465 */
2466static void tcp_timeout_skbs(struct sock *sk)
2467{
2468        struct tcp_sock *tp = tcp_sk(sk);
2469        struct sk_buff *skb;
2470
2471        if (!tcp_is_fack(tp) || !tcp_head_timedout(sk))
2472                return;
2473
2474        skb = tp->scoreboard_skb_hint;
2475        if (tp->scoreboard_skb_hint == NULL)
2476                skb = tcp_write_queue_head(sk);
2477
2478        tcp_for_write_queue_from(skb, sk) {
2479                if (skb == tcp_send_head(sk))
2480                        break;
2481                if (!tcp_skb_timedout(sk, skb))
2482                        break;
2483
2484                tcp_skb_mark_lost(tp, skb);
2485        }
2486
2487        tp->scoreboard_skb_hint = skb;
2488
2489        tcp_verify_left_out(tp);
2490}
2491
2492/* Mark head of queue up as lost. With RFC3517 SACK, the packets is
2493 * is against sacked "cnt", otherwise it's against facked "cnt"
2494 */
2495static void tcp_mark_head_lost(struct sock *sk, int packets)
2496{
2497        struct tcp_sock *tp = tcp_sk(sk);
2498        struct sk_buff *skb;
2499        int cnt, oldcnt;
2500        int err;
2501        unsigned int mss;
2502
2503        WARN_ON(packets > tp->packets_out);
2504        if (tp->lost_skb_hint) {
2505                skb = tp->lost_skb_hint;
2506                cnt = tp->lost_cnt_hint;
2507        } else {
2508                skb = tcp_write_queue_head(sk);
2509                cnt = 0;
2510        }
2511
2512        tcp_for_write_queue_from(skb, sk) {
2513                if (skb == tcp_send_head(sk))
2514                        break;
2515                /* TODO: do this better */
2516                /* this is not the most efficient way to do this... */
2517                tp->lost_skb_hint = skb;
2518                tp->lost_cnt_hint = cnt;
2519
2520                if (after(TCP_SKB_CB(skb)->end_seq, tp->high_seq))
2521                        break;
2522
2523                oldcnt = cnt;
2524                if (tcp_is_fack(tp) || tcp_is_reno(tp) ||
2525                    (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED))
2526                        cnt += tcp_skb_pcount(skb);
2527
2528                if (cnt > packets) {
2529                        if (tcp_is_sack(tp) || (oldcnt >= packets))
2530                                break;
2531
2532                        mss = skb_shinfo(skb)->gso_size;
2533                        err = tcp_fragment(sk, skb, (packets - oldcnt) * mss, mss);
2534                        if (err < 0)
2535                                break;
2536                        cnt = packets;
2537                }
2538
2539                tcp_skb_mark_lost(tp, skb);
2540        }
2541        tcp_verify_left_out(tp);
2542}
2543
2544/* Account newly detected lost packet(s) */
2545
2546static void tcp_update_scoreboard(struct sock *sk, int fast_rexmit)
2547{
2548        struct tcp_sock *tp = tcp_sk(sk);
2549
2550        if (tcp_is_reno(tp)) {
2551                tcp_mark_head_lost(sk, 1);
2552        } else if (tcp_is_fack(tp)) {
2553                int lost = tp->fackets_out - tp->reordering;
2554                if (lost <= 0)
2555                        lost = 1;
2556                tcp_mark_head_lost(sk, lost);
2557        } else {
2558                int sacked_upto = tp->sacked_out - tp->reordering;
2559                if (sacked_upto < fast_rexmit)
2560                        sacked_upto = fast_rexmit;
2561                tcp_mark_head_lost(sk, sacked_upto);
2562        }
2563
2564        tcp_timeout_skbs(sk);
2565}
2566
2567/* CWND moderation, preventing bursts due to too big ACKs
2568 * in dubious situations.
2569 */
2570static inline void tcp_moderate_cwnd(struct tcp_sock *tp)
2571{
2572        tp->snd_cwnd = min(tp->snd_cwnd,
2573                           tcp_packets_in_flight(tp) + tcp_max_burst(tp));
2574        tp->snd_cwnd_stamp = tcp_time_stamp;
2575}
2576
2577/* Lower bound on congestion window is slow start threshold
2578 * unless congestion avoidance choice decides to overide it.
2579 */
2580static inline u32 tcp_cwnd_min(const struct sock *sk)
2581{
2582        const struct tcp_congestion_ops *ca_ops = inet_csk(sk)->icsk_ca_ops;
2583
2584        return ca_ops->min_cwnd ? ca_ops->min_cwnd(sk) : tcp_sk(sk)->snd_ssthresh;
2585}
2586
2587/* Decrease cwnd each second ack. */
2588static void tcp_cwnd_down(struct sock *sk, int flag)
2589{
2590        struct tcp_sock *tp = tcp_sk(sk);
2591        int decr = tp->snd_cwnd_cnt + 1;
2592
2593        if ((flag & (FLAG_ANY_PROGRESS | FLAG_DSACKING_ACK)) ||
2594            (tcp_is_reno(tp) && !(flag & FLAG_NOT_DUP))) {
2595                tp->snd_cwnd_cnt = decr & 1;
2596                decr >>= 1;
2597
2598                if (decr && tp->snd_cwnd > tcp_cwnd_min(sk))
2599                        tp->snd_cwnd -= decr;
2600
2601                tp->snd_cwnd = min(tp->snd_cwnd, tcp_packets_in_flight(tp) + 1);
2602                tp->snd_cwnd_stamp = tcp_time_stamp;
2603        }
2604}
2605
2606/* Nothing was retransmitted or returned timestamp is less
2607 * than timestamp of the first retransmission.
2608 */
2609static inline int tcp_packet_delayed(struct tcp_sock *tp)
2610{
2611        return !tp->retrans_stamp ||
2612                (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
2613                 before(tp->rx_opt.rcv_tsecr, tp->retrans_stamp));
2614}
2615
2616/* Undo procedures. */
2617
2618#if FASTRETRANS_DEBUG > 1
2619static void DBGUNDO(struct sock *sk, const char *msg)
2620{
2621        struct tcp_sock *tp = tcp_sk(sk);
2622        struct inet_sock *inet = inet_sk(sk);
2623
2624        if (sk->sk_family == AF_INET) {
2625                printk(KERN_DEBUG "Undo %s %pI4/%u c%u l%u ss%u/%u p%u\n",
2626                       msg,
2627                       &inet->daddr, ntohs(inet->dport),
2628                       tp->snd_cwnd, tcp_left_out(tp),
2629                       tp->snd_ssthresh, tp->prior_ssthresh,
2630                       tp->packets_out);
2631        }
2632#if defined(CONFIG_IPV6) || defined(CONFIG_IPV6_MODULE)
2633        else if (sk->sk_family == AF_INET6) {
2634                struct ipv6_pinfo *np = inet6_sk(sk);
2635                printk(KERN_DEBUG "Undo %s %pI6/%u c%u l%u ss%u/%u p%u\n",
2636                       msg,
2637                       &np->daddr, ntohs(inet->dport),
2638                       tp->snd_cwnd, tcp_left_out(tp),
2639                       tp->snd_ssthresh, tp->prior_ssthresh,
2640                       tp->packets_out);
2641        }
2642#endif
2643}
2644#else
2645#define DBGUNDO(x...) do { } while (0)
2646#endif
2647
2648static void tcp_undo_cwr(struct sock *sk, const int undo)
2649{
2650        struct tcp_sock *tp = tcp_sk(sk);
2651
2652        if (tp->prior_ssthresh) {
2653                const struct inet_connection_sock *icsk = inet_csk(sk);
2654
2655                if (icsk->icsk_ca_ops->undo_cwnd)
2656                        tp->snd_cwnd = icsk->icsk_ca_ops->undo_cwnd(sk);
2657                else
2658                        tp->snd_cwnd = max(tp->snd_cwnd, tp->snd_ssthresh << 1);
2659
2660                if (undo && tp->prior_ssthresh > tp->snd_ssthresh) {
2661                        tp->snd_ssthresh = tp->prior_ssthresh;
2662                        TCP_ECN_withdraw_cwr(tp);
2663                }
2664        } else {
2665                tp->snd_cwnd = max(tp->snd_cwnd, tp->snd_ssthresh);
2666        }
2667        tcp_moderate_cwnd(tp);
2668        tp->snd_cwnd_stamp = tcp_time_stamp;
2669}
2670
2671static inline int tcp_may_undo(struct tcp_sock *tp)
2672{
2673        return tp->undo_marker && (!tp->undo_retrans || tcp_packet_delayed(tp));
2674}
2675
2676/* People celebrate: "We love our President!" */
2677static int tcp_try_undo_recovery(struct sock *sk)
2678{
2679        struct tcp_sock *tp = tcp_sk(sk);
2680
2681        if (tcp_may_undo(tp)) {
2682                int mib_idx;
2683
2684                /* Happy end! We did not retransmit anything
2685                 * or our original transmission succeeded.
2686                 */
2687                DBGUNDO(sk, inet_csk(sk)->icsk_ca_state == TCP_CA_Loss ? "loss" : "retrans");
2688                tcp_undo_cwr(sk, 1);
2689                if (inet_csk(sk)->icsk_ca_state == TCP_CA_Loss)
2690                        mib_idx = LINUX_MIB_TCPLOSSUNDO;
2691                else
2692                        mib_idx = LINUX_MIB_TCPFULLUNDO;
2693
2694                NET_INC_STATS_BH(sock_net(sk), mib_idx);
2695                tp->undo_marker = 0;
2696        }
2697        if (tp->snd_una == tp->high_seq && tcp_is_reno(tp)) {
2698                /* Hold old state until something *above* high_seq
2699                 * is ACKed. For Reno it is MUST to prevent false
2700                 * fast retransmits (RFC2582). SACK TCP is safe. */
2701                tcp_moderate_cwnd(tp);
2702                return 1;
2703        }
2704        tcp_set_ca_state(sk, TCP_CA_Open);
2705        return 0;
2706}
2707
2708/* Try to undo cwnd reduction, because D-SACKs acked all retransmitted data */
2709static void tcp_try_undo_dsack(struct sock *sk)
2710{
2711        struct tcp_sock *tp = tcp_sk(sk);
2712
2713        if (tp->undo_marker && !tp->undo_retrans) {
2714                DBGUNDO(sk, "D-SACK");
2715                tcp_undo_cwr(sk, 1);
2716                tp->undo_marker = 0;
2717                NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPDSACKUNDO);
2718        }
2719}
2720
2721/* Undo during fast recovery after partial ACK. */
2722
2723static int tcp_try_undo_partial(struct sock *sk, int acked)
2724{
2725        struct tcp_sock *tp = tcp_sk(sk);
2726        /* Partial ACK arrived. Force Hoe's retransmit. */
2727        int failed = tcp_is_reno(tp) || (tcp_fackets_out(tp) > tp->reordering);
2728
2729        if (tcp_may_undo(tp)) {
2730                /* Plain luck! Hole if filled with delayed
2731                 * packet, rather than with a retransmit.
2732                 */
2733                if (tp->retrans_out == 0)
2734                        tp->retrans_stamp = 0;
2735
2736                tcp_update_reordering(sk, tcp_fackets_out(tp) + acked, 1);
2737
2738                DBGUNDO(sk, "Hoe");
2739                tcp_undo_cwr(sk, 0);
2740                NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPPARTIALUNDO);
2741
2742                /* So... Do not make Hoe's retransmit yet.
2743                 * If the first packet was delayed, the rest
2744                 * ones are most probably delayed as well.
2745                 */
2746                failed = 0;
2747        }
2748        return failed;
2749}
2750
2751/* Undo during loss recovery after partial ACK. */
2752static int tcp_try_undo_loss(struct sock *sk)
2753{
2754        struct tcp_sock *tp = tcp_sk(sk);
2755
2756        if (tcp_may_undo(tp)) {
2757                struct sk_buff *skb;
2758                tcp_for_write_queue(skb, sk) {
2759                        if (skb == tcp_send_head(sk))
2760                                break;
2761                        TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST;
2762                }
2763
2764                tcp_clear_all_retrans_hints(tp);
2765
2766                DBGUNDO(sk, "partial loss");
2767                tp->lost_out = 0;
2768                tcp_undo_cwr(sk, 1);
2769                NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPLOSSUNDO);
2770                inet_csk(sk)->icsk_retransmits = 0;
2771                tp->undo_marker = 0;
2772                if (tcp_is_sack(tp))
2773                        tcp_set_ca_state(sk, TCP_CA_Open);
2774                return 1;
2775        }
2776        return 0;
2777}
2778
2779static inline void tcp_complete_cwr(struct sock *sk)
2780{
2781        struct tcp_sock *tp = tcp_sk(sk);
2782        tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_ssthresh);
2783        tp->snd_cwnd_stamp = tcp_time_stamp;
2784        tcp_ca_event(sk, CA_EVENT_COMPLETE_CWR);
2785}
2786
2787static void tcp_try_keep_open(struct sock *sk)
2788{
2789        struct tcp_sock *tp = tcp_sk(sk);
2790        int state = TCP_CA_Open;
2791
2792        if (tcp_left_out(tp) || tp->retrans_out || tp->undo_marker)
2793                state = TCP_CA_Disorder;
2794
2795        if (inet_csk(sk)->icsk_ca_state != state) {
2796                tcp_set_ca_state(sk, state);
2797                tp->high_seq = tp->snd_nxt;
2798        }
2799}
2800
2801static void tcp_try_to_open(struct sock *sk, int flag)
2802{
2803        struct tcp_sock *tp = tcp_sk(sk);
2804
2805        tcp_verify_left_out(tp);
2806
2807        if (!tp->frto_counter && tp->retrans_out == 0)
2808                tp->retrans_stamp = 0;
2809
2810        if (flag & FLAG_ECE)
2811                tcp_enter_cwr(sk, 1);
2812
2813        if (inet_csk(sk)->icsk_ca_state != TCP_CA_CWR) {
2814                tcp_try_keep_open(sk);
2815                tcp_moderate_cwnd(tp);
2816        } else {
2817                tcp_cwnd_down(sk, flag);
2818        }
2819}
2820
2821static void tcp_mtup_probe_failed(struct sock *sk)
2822{
2823        struct inet_connection_sock *icsk = inet_csk(sk);
2824
2825        icsk->icsk_mtup.search_high = icsk->icsk_mtup.probe_size - 1;
2826        icsk->icsk_mtup.probe_size = 0;
2827}
2828
2829static void tcp_mtup_probe_success(struct sock *sk)
2830{
2831        struct tcp_sock *tp = tcp_sk(sk);
2832        struct inet_connection_sock *icsk = inet_csk(sk);
2833
2834        /* FIXME: breaks with very large cwnd */
2835        tp->prior_ssthresh = tcp_current_ssthresh(sk);
2836        tp->snd_cwnd = tp->snd_cwnd *
2837                       tcp_mss_to_mtu(sk, tp->mss_cache) /
2838                       icsk->icsk_mtup.probe_size;
2839        tp->snd_cwnd_cnt = 0;
2840        tp->snd_cwnd_stamp = tcp_time_stamp;
2841        tp->rcv_ssthresh = tcp_current_ssthresh(sk);
2842
2843        icsk->icsk_mtup.search_low = icsk->icsk_mtup.probe_size;
2844        icsk->icsk_mtup.probe_size = 0;
2845        tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
2846}
2847
2848/* Do a simple retransmit without using the backoff mechanisms in
2849 * tcp_timer. This is used for path mtu discovery.
2850 * The socket is already locked here.
2851 */
2852void tcp_simple_retransmit(struct sock *sk)
2853{
2854        const struct inet_connection_sock *icsk = inet_csk(sk);
2855        struct tcp_sock *tp = tcp_sk(sk);
2856        struct sk_buff *skb;
2857        unsigned int mss = tcp_current_mss(sk);
2858        u32 prior_lost = tp->lost_out;
2859
2860        tcp_for_write_queue(skb, sk) {
2861                if (skb == tcp_send_head(sk))
2862                        break;
2863                if (tcp_skb_seglen(skb) > mss &&
2864                    !(TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)) {
2865                        if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) {
2866                                TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
2867                                tp->retrans_out -= tcp_skb_pcount(skb);
2868                        }
2869                        tcp_skb_mark_lost_uncond_verify(tp, skb);
2870                }
2871        }
2872
2873        tcp_clear_retrans_hints_partial(tp);
2874
2875        if (prior_lost == tp->lost_out)
2876                return;
2877
2878        if (tcp_is_reno(tp))
2879                tcp_limit_reno_sacked(tp);
2880
2881        tcp_verify_left_out(tp);
2882
2883        /* Don't muck with the congestion window here.
2884         * Reason is that we do not increase amount of _data_
2885         * in network, but units changed and effective
2886         * cwnd/ssthresh really reduced now.
2887         */
2888        if (icsk->icsk_ca_state != TCP_CA_Loss) {
2889                tp->high_seq = tp->snd_nxt;
2890                tp->snd_ssthresh = tcp_current_ssthresh(sk);
2891                tp->prior_ssthresh = 0;
2892                tp->undo_marker = 0;
2893                tcp_set_ca_state(sk, TCP_CA_Loss);
2894        }
2895        tcp_xmit_retransmit_queue(sk);
2896}
2897
2898/* Process an event, which can update packets-in-flight not trivially.
2899 * Main goal of this function is to calculate new estimate for left_out,
2900 * taking into account both packets sitting in receiver's buffer and
2901 * packets lost by network.
2902 *
2903 * Besides that it does CWND reduction, when packet loss is detected
2904 * and changes state of machine.
2905 *
2906 * It does _not_ decide what to send, it is made in function
2907 * tcp_xmit_retransmit_queue().
2908 */
2909static void tcp_fastretrans_alert(struct sock *sk, int pkts_acked, int flag)
2910{
2911        struct inet_connection_sock *icsk = inet_csk(sk);
2912        struct tcp_sock *tp = tcp_sk(sk);
2913        int is_dupack = !(flag & (FLAG_SND_UNA_ADVANCED | FLAG_NOT_DUP));
2914        int do_lost = is_dupack || ((flag & FLAG_DATA_SACKED) &&
2915                                    (tcp_fackets_out(tp) > tp->reordering));
2916        int fast_rexmit = 0, mib_idx;
2917
2918        if (WARN_ON(!tp->packets_out && tp->sacked_out))
2919                tp->sacked_out = 0;
2920        if (WARN_ON(!tp->sacked_out && tp->fackets_out))
2921                tp->fackets_out = 0;
2922
2923        /* Now state machine starts.
2924         * A. ECE, hence prohibit cwnd undoing, the reduction is required. */
2925        if (flag & FLAG_ECE)
2926                tp->prior_ssthresh = 0;
2927
2928        /* B. In all the states check for reneging SACKs. */
2929        if (tcp_check_sack_reneging(sk, flag))
2930                return;
2931
2932        /* C. Process data loss notification, provided it is valid. */
2933        if (tcp_is_fack(tp) && (flag & FLAG_DATA_LOST) &&
2934            before(tp->snd_una, tp->high_seq) &&
2935            icsk->icsk_ca_state != TCP_CA_Open &&
2936            tp->fackets_out > tp->reordering) {
2937                tcp_mark_head_lost(sk, tp->fackets_out - tp->reordering);
2938                NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPLOSS);
2939        }
2940
2941        /* D. Check consistency of the current state. */
2942        tcp_verify_left_out(tp);
2943
2944        /* E. Check state exit conditions. State can be terminated
2945         *    when high_seq is ACKed. */
2946        if (icsk->icsk_ca_state == TCP_CA_Open) {
2947                WARN_ON(tp->retrans_out != 0);
2948                tp->retrans_stamp = 0;
2949        } else if (!before(tp->snd_una, tp->high_seq)) {
2950                switch (icsk->icsk_ca_state) {
2951                case TCP_CA_Loss:
2952                        icsk->icsk_retransmits = 0;
2953                        if (tcp_try_undo_recovery(sk))
2954                                return;
2955                        break;
2956
2957                case TCP_CA_CWR:
2958                        /* CWR is to be held something *above* high_seq
2959                         * is ACKed for CWR bit to reach receiver. */
2960                        if (tp->snd_una != tp->high_seq) {
2961                                tcp_complete_cwr(sk);
2962                                tcp_set_ca_state(sk, TCP_CA_Open);
2963                        }
2964                        break;
2965
2966                case TCP_CA_Disorder:
2967                        tcp_try_undo_dsack(sk);
2968                        if (!tp->undo_marker ||
2969                            /* For SACK case do not Open to allow to undo
2970                             * catching for all duplicate ACKs. */
2971                            tcp_is_reno(tp) || tp->snd_una != tp->high_seq) {
2972                                tp->undo_marker = 0;
2973                                tcp_set_ca_state(sk, TCP_CA_Open);
2974                        }
2975                        break;
2976
2977                case TCP_CA_Recovery:
2978                        if (tcp_is_reno(tp))
2979                                tcp_reset_reno_sack(tp);
2980                        if (tcp_try_undo_recovery(sk))
2981                                return;
2982                        tcp_complete_cwr(sk);
2983                        break;
2984                }
2985        }
2986
2987        /* F. Process state. */
2988        switch (icsk->icsk_ca_state) {
2989        case TCP_CA_Recovery:
2990                if (!(flag & FLAG_SND_UNA_ADVANCED)) {
2991                        if (tcp_is_reno(tp) && is_dupack)
2992                                tcp_add_reno_sack(sk);
2993                } else
2994                        do_lost = tcp_try_undo_partial(sk, pkts_acked);
2995                break;
2996        case TCP_CA_Loss:
2997                if (flag & FLAG_DATA_ACKED)
2998                        icsk->icsk_retransmits = 0;
2999                if (tcp_is_reno(tp) && flag & FLAG_SND_UNA_ADVANCED)
3000                        tcp_reset_reno_sack(tp);
3001                if (!tcp_try_undo_loss(sk)) {
3002                        tcp_moderate_cwnd(tp);
3003                        tcp_xmit_retransmit_queue(sk);
3004                        return;
3005                }
3006                if (icsk->icsk_ca_state != TCP_CA_Open)
3007                        return;
3008                /* Loss is undone; fall through to processing in Open state. */
3009        default:
3010                if (tcp_is_reno(tp)) {
3011                        if (flag & FLAG_SND_UNA_ADVANCED)
3012                                tcp_reset_reno_sack(tp);
3013                        if (is_dupack)
3014                                tcp_add_reno_sack(sk);
3015                }
3016
3017                if (icsk->icsk_ca_state == TCP_CA_Disorder)
3018                        tcp_try_undo_dsack(sk);
3019
3020                if (!tcp_time_to_recover(sk)) {
3021                        tcp_try_to_open(sk, flag);
3022                        return;
3023                }
3024
3025                /* MTU probe failure: don't reduce cwnd */
3026                if (icsk->icsk_ca_state < TCP_CA_CWR &&
3027                    icsk->icsk_mtup.probe_size &&
3028                    tp->snd_una == tp->mtu_probe.probe_seq_start) {
3029                        tcp_mtup_probe_failed(sk);
3030                        /* Restores the reduction we did in tcp_mtup_probe() */
3031                        tp->snd_cwnd++;
3032                        tcp_simple_retransmit(sk);
3033                        return;
3034                }
3035
3036                /* Otherwise enter Recovery state */
3037
3038                if (tcp_is_reno(tp))
3039                        mib_idx = LINUX_MIB_TCPRENORECOVERY;
3040                else
3041                        mib_idx = LINUX_MIB_TCPSACKRECOVERY;
3042
3043                NET_INC_STATS_BH(sock_net(sk), mib_idx);
3044
3045                tp->high_seq = tp->snd_nxt;
3046                tp->prior_ssthresh = 0;
3047                tp->undo_marker = tp->snd_una;
3048                tp->undo_retrans = tp->retrans_out;
3049
3050                if (icsk->icsk_ca_state < TCP_CA_CWR) {
3051                        if (!(flag & FLAG_ECE))
3052                                tp->prior_ssthresh = tcp_current_ssthresh(sk);
3053                        tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
3054                        TCP_ECN_queue_cwr(tp);
3055                }
3056
3057                tp->bytes_acked = 0;
3058                tp->snd_cwnd_cnt = 0;
3059                tcp_set_ca_state(sk, TCP_CA_Recovery);
3060                fast_rexmit = 1;
3061        }
3062
3063        if (do_lost || (tcp_is_fack(tp) && tcp_head_timedout(sk)))
3064                tcp_update_scoreboard(sk, fast_rexmit);
3065        tcp_cwnd_down(sk, flag);
3066        tcp_xmit_retransmit_queue(sk);
3067}
3068
3069static void tcp_valid_rtt_meas(struct sock *sk, u32 seq_rtt)
3070{
3071        tcp_rtt_estimator(sk, seq_rtt);
3072        tcp_set_rto(sk);
3073        inet_csk(sk)->icsk_backoff = 0;
3074}
3075
3076/* Read draft-ietf-tcplw-high-performance before mucking
3077 * with this code. (Supersedes RFC1323)
3078 */
3079static void tcp_ack_saw_tstamp(struct sock *sk, int flag)
3080{
3081        /* RTTM Rule: A TSecr value received in a segment is used to
3082         * update the averaged RTT measurement only if the segment
3083         * acknowledges some new data, i.e., only if it advances the
3084         * left edge of the send window.
3085         *
3086         * See draft-ietf-tcplw-high-performance-00, section 3.3.
3087         * 1998/04/10 Andrey V. Savochkin <saw@msu.ru>
3088         *
3089         * Changed: reset backoff as soon as we see the first valid sample.
3090         * If we do not, we get strongly overestimated rto. With timestamps
3091         * samples are accepted even from very old segments: f.e., when rtt=1
3092         * increases to 8, we retransmit 5 times and after 8 seconds delayed
3093         * answer arrives rto becomes 120 seconds! If at least one of segments
3094         * in window is lost... Voila.                          --ANK (010210)
3095         */
3096        struct tcp_sock *tp = tcp_sk(sk);
3097
3098        tcp_valid_rtt_meas(sk, tcp_time_stamp - tp->rx_opt.rcv_tsecr);
3099}
3100
3101static void tcp_ack_no_tstamp(struct sock *sk, u32 seq_rtt, int flag)
3102{
3103        /* We don't have a timestamp. Can only use
3104         * packets that are not retransmitted to determine
3105         * rtt estimates. Also, we must not reset the
3106         * backoff for rto until we get a non-retransmitted
3107         * packet. This allows us to deal with a situation
3108         * where the network delay has increased suddenly.
3109         * I.e. Karn's algorithm. (SIGCOMM '87, p5.)
3110         */
3111
3112        if (flag & FLAG_RETRANS_DATA_ACKED)
3113                return;
3114
3115        tcp_valid_rtt_meas(sk, seq_rtt);
3116}
3117
3118static inline void tcp_ack_update_rtt(struct sock *sk, const int flag,
3119                                      const s32 seq_rtt)
3120{
3121        const struct tcp_sock *tp = tcp_sk(sk);
3122        /* Note that peer MAY send zero echo. In this case it is ignored. (rfc1323) */
3123        if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr)
3124                tcp_ack_saw_tstamp(sk, flag);
3125        else if (seq_rtt >= 0)
3126                tcp_ack_no_tstamp(sk, seq_rtt, flag);
3127}
3128
3129static void tcp_cong_avoid(struct sock *sk, u32 ack, u32 in_flight)
3130{
3131        const struct inet_connection_sock *icsk = inet_csk(sk);
3132        icsk->icsk_ca_ops->cong_avoid(sk, ack, in_flight);
3133        tcp_sk(sk)->snd_cwnd_stamp = tcp_time_stamp;
3134}
3135
3136/* Restart timer after forward progress on connection.
3137 * RFC2988 recommends to restart timer to now+rto.
3138 */
3139static void tcp_rearm_rto(struct sock *sk)
3140{
3141        struct tcp_sock *tp = tcp_sk(sk);
3142
3143        if (!tp->packets_out) {
3144                inet_csk_clear_xmit_timer(sk, ICSK_TIME_RETRANS);
3145        } else {
3146                inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
3147                                          inet_csk(sk)->icsk_rto, TCP_RTO_MAX);
3148        }
3149}
3150
3151/* If we get here, the whole TSO packet has not been acked. */
3152static u32 tcp_tso_acked(struct sock *sk, struct sk_buff *skb)
3153{
3154        struct tcp_sock *tp = tcp_sk(sk);
3155        u32 packets_acked;
3156
3157        BUG_ON(!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una));
3158
3159        packets_acked = tcp_skb_pcount(skb);
3160        if (tcp_trim_head(sk, skb, tp->snd_una - TCP_SKB_CB(skb)->seq))
3161                return 0;
3162        packets_acked -= tcp_skb_pcount(skb);
3163
3164        if (packets_acked) {
3165                BUG_ON(tcp_skb_pcount(skb) == 0);
3166                BUG_ON(!before(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq));
3167        }
3168
3169        return packets_acked;
3170}
3171
3172/* Remove acknowledged frames from the retransmission queue. If our packet
3173 * is before the ack sequence we can discard it as it's confirmed to have
3174 * arrived at the other end.
3175 */
3176static int tcp_clean_rtx_queue(struct sock *sk, int prior_fackets,
3177                               u32 prior_snd_una)
3178{
3179        struct tcp_sock *tp = tcp_sk(sk);
3180        const struct inet_connection_sock *icsk = inet_csk(sk);
3181        struct sk_buff *skb;
3182        u32 now = tcp_time_stamp;
3183        int fully_acked = 1;
3184        int flag = 0;
3185        u32 pkts_acked = 0;
3186        u32 reord = tp->packets_out;
3187        u32 prior_sacked = tp->sacked_out;
3188        s32 seq_rtt = -1;
3189        s32 ca_seq_rtt = -1;
3190        ktime_t last_ackt = net_invalid_timestamp();
3191
3192        while ((skb = tcp_write_queue_head(sk)) && skb != tcp_send_head(sk)) {
3193                struct tcp_skb_cb *scb = TCP_SKB_CB(skb);
3194                u32 acked_pcount;
3195                u8 sacked = scb->sacked;
3196
3197                /* Determine how many packets and what bytes were acked, tso and else */
3198                if (after(scb->end_seq, tp->snd_una)) {
3199                        if (tcp_skb_pcount(skb) == 1 ||
3200                            !after(tp->snd_una, scb->seq))
3201                                break;
3202
3203                        acked_pcount = tcp_tso_acked(sk, skb);
3204                        if (!acked_pcount)
3205                                break;
3206
3207                        fully_acked = 0;
3208                } else {
3209                        acked_pcount = tcp_skb_pcount(skb);
3210                }
3211
3212                if (sacked & TCPCB_RETRANS) {
3213                        if (sacked & TCPCB_SACKED_RETRANS)
3214                                tp->retrans_out -= acked_pcount;
3215                        flag |= FLAG_RETRANS_DATA_ACKED;
3216                        ca_seq_rtt = -1;
3217                        seq_rtt = -1;
3218                        if ((flag & FLAG_DATA_ACKED) || (acked_pcount > 1))
3219                                flag |= FLAG_NONHEAD_RETRANS_ACKED;
3220                } else {
3221                        ca_seq_rtt = now - scb->when;
3222                        last_ackt = skb->tstamp;
3223                        if (seq_rtt < 0) {
3224                                seq_rtt = ca_seq_rtt;
3225                        }
3226                        if (!(sacked & TCPCB_SACKED_ACKED))
3227                                reord = min(pkts_acked, reord);
3228                }
3229
3230                if (sacked & TCPCB_SACKED_ACKED)
3231                        tp->sacked_out -= acked_pcount;
3232                if (sacked & TCPCB_LOST)
3233                        tp->lost_out -= acked_pcount;
3234
3235                tp->packets_out -= acked_pcount;
3236                pkts_acked += acked_pcount;
3237
3238                /* Initial outgoing SYN's get put onto the write_queue
3239                 * just like anything else we transmit.  It is not
3240                 * true data, and if we misinform our callers that
3241                 * this ACK acks real data, we will erroneously exit
3242                 * connection startup slow start one packet too
3243                 * quickly.  This is severely frowned upon behavior.
3244                 */
3245                if (!(scb->flags & TCPCB_FLAG_SYN)) {
3246                        flag |= FLAG_DATA_ACKED;
3247                } else {
3248                        flag |= FLAG_SYN_ACKED;
3249                        tp->retrans_stamp = 0;
3250                }
3251
3252                if (!fully_acked)
3253                        break;
3254
3255                tcp_unlink_write_queue(skb, sk);
3256                sk_wmem_free_skb(sk, skb);
3257                tp->scoreboard_skb_hint = NULL;
3258                if (skb == tp->retransmit_skb_hint)
3259                        tp->retransmit_skb_hint = NULL;
3260                if (skb == tp->lost_skb_hint)
3261                        tp->lost_skb_hint = NULL;
3262        }
3263
3264        if (likely(between(tp->snd_up, prior_snd_una, tp->snd_una)))
3265                tp->snd_up = tp->snd_una;
3266
3267        if (skb && (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED))
3268                flag |= FLAG_SACK_RENEGING;
3269
3270        if (flag & FLAG_ACKED) {
3271                const struct tcp_congestion_ops *ca_ops
3272                        = inet_csk(sk)->icsk_ca_ops;
3273
3274                if (unlikely(icsk->icsk_mtup.probe_size &&
3275                             !after(tp->mtu_probe.probe_seq_end, tp->snd_una))) {
3276                        tcp_mtup_probe_success(sk);
3277                }
3278
3279                tcp_ack_update_rtt(sk, flag, seq_rtt);
3280                tcp_rearm_rto(sk);
3281
3282                if (tcp_is_reno(tp)) {
3283                        tcp_remove_reno_sacks(sk, pkts_acked);
3284                } else {
3285                        int delta;
3286
3287                        /* Non-retransmitted hole got filled? That's reordering */
3288                        if (reord < prior_fackets)
3289                                tcp_update_reordering(sk, tp->fackets_out - reord, 0);
3290
3291                        delta = tcp_is_fack(tp) ? pkts_acked :
3292                                                  prior_sacked - tp->sacked_out;
3293                        tp->lost_cnt_hint -= min(tp->lost_cnt_hint, delta);
3294                }
3295
3296                tp->fackets_out -= min(pkts_acked, tp->fackets_out);
3297
3298                if (ca_ops->pkts_acked) {
3299                        s32 rtt_us = -1;
3300
3301                        /* Is the ACK triggering packet unambiguous? */
3302                        if (!(flag & FLAG_RETRANS_DATA_ACKED)) {
3303                                /* High resolution needed and available? */
3304                                if (ca_ops->flags & TCP_CONG_RTT_STAMP &&
3305                                    !ktime_equal(last_ackt,
3306                                                 net_invalid_timestamp()))
3307                                        rtt_us = ktime_us_delta(ktime_get_real(),
3308                                                                last_ackt);
3309                                else if (ca_seq_rtt > 0)
3310                                        rtt_us = jiffies_to_usecs(ca_seq_rtt);
3311                        }
3312
3313                        ca_ops->pkts_acked(sk, pkts_acked, rtt_us);
3314                }
3315        }
3316
3317#if FASTRETRANS_DEBUG > 0
3318        WARN_ON((int)tp->sacked_out < 0);
3319        WARN_ON((int)tp->lost_out < 0);
3320        WARN_ON((int)tp->retrans_out < 0);
3321        if (!tp->packets_out && tcp_is_sack(tp)) {
3322                icsk = inet_csk(sk);
3323                if (tp->lost_out) {
3324                        printk(KERN_DEBUG "Leak l=%u %d\n",
3325                               tp->lost_out, icsk->icsk_ca_state);
3326                        tp->lost_out = 0;
3327                }
3328                if (tp->sacked_out) {
3329                        printk(KERN_DEBUG "Leak s=%u %d\n",
3330                               tp->sacked_out, icsk->icsk_ca_state);
3331                        tp->sacked_out = 0;
3332                }
3333                if (tp->retrans_out) {
3334                        printk(KERN_DEBUG "Leak r=%u %d\n",
3335                               tp->retrans_out, icsk->icsk_ca_state);
3336                        tp->retrans_out = 0;
3337                }
3338        }
3339#endif
3340        return flag;
3341}
3342
3343static void tcp_ack_probe(struct sock *sk)
3344{
3345        const struct tcp_sock *tp = tcp_sk(sk);
3346        struct inet_connection_sock *icsk = inet_csk(sk);
3347
3348        /* Was it a usable window open? */
3349
3350        if (!after(TCP_SKB_CB(tcp_send_head(sk))->end_seq, tcp_wnd_end(tp))) {
3351                icsk->icsk_backoff = 0;
3352                inet_csk_clear_xmit_timer(sk, ICSK_TIME_PROBE0);
3353                /* Socket must be waked up by subsequent tcp_data_snd_check().
3354                 * This function is not for random using!
3355                 */
3356        } else {
3357                inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0,
3358                                          min(icsk->icsk_rto << icsk->icsk_backoff, TCP_RTO_MAX),
3359                                          TCP_RTO_MAX);
3360        }
3361}
3362
3363static inline int tcp_ack_is_dubious(const struct sock *sk, const int flag)
3364{
3365        return (!(flag & FLAG_NOT_DUP) || (flag & FLAG_CA_ALERT) ||
3366                inet_csk(sk)->icsk_ca_state != TCP_CA_Open);
3367}
3368
3369static inline int tcp_may_raise_cwnd(const struct sock *sk, const int flag)
3370{
3371        const struct tcp_sock *tp = tcp_sk(sk);
3372        return (!(flag & FLAG_ECE) || tp->snd_cwnd < tp->snd_ssthresh) &&
3373                !((1 << inet_csk(sk)->icsk_ca_state) & (TCPF_CA_Recovery | TCPF_CA_CWR));
3374}
3375
3376/* Check that window update is acceptable.
3377 * The function assumes that snd_una<=ack<=snd_next.
3378 */
3379static inline int tcp_may_update_window(const struct tcp_sock *tp,
3380                                        const u32 ack, const u32 ack_seq,
3381                                        const u32 nwin)
3382{
3383        return (after(ack, tp->snd_una) ||
3384                after(ack_seq, tp->snd_wl1) ||
3385                (ack_seq == tp->snd_wl1 && nwin > tp->snd_wnd));
3386}
3387
3388/* Update our send window.
3389 *
3390 * Window update algorithm, described in RFC793/RFC1122 (used in linux-2.2
3391 * and in FreeBSD. NetBSD's one is even worse.) is wrong.
3392 */
3393static int tcp_ack_update_window(struct sock *sk, struct sk_buff *skb, u32 ack,
3394                                 u32 ack_seq)
3395{
3396        struct tcp_sock *tp = tcp_sk(sk);
3397        int flag = 0;
3398        u32 nwin = ntohs(tcp_hdr(skb)->window);
3399
3400        if (likely(!tcp_hdr(skb)->syn))
3401                nwin <<= tp->rx_opt.snd_wscale;
3402
3403        if (tcp_may_update_window(tp, ack, ack_seq, nwin)) {
3404                flag |= FLAG_WIN_UPDATE;
3405                tcp_update_wl(tp, ack_seq);
3406
3407                if (tp->snd_wnd != nwin) {
3408                        tp->snd_wnd = nwin;
3409
3410                        /* Note, it is the only place, where
3411                         * fast path is recovered for sending TCP.
3412                         */
3413                        tp->pred_flags = 0;
3414                        tcp_fast_path_check(sk);
3415
3416                        if (nwin > tp->max_window) {
3417                                tp->max_window = nwin;
3418                                tcp_sync_mss(sk, inet_csk(sk)->icsk_pmtu_cookie);
3419                        }
3420                }
3421        }
3422
3423        tp->snd_una = ack;
3424
3425        return flag;
3426}
3427
3428/* A very conservative spurious RTO response algorithm: reduce cwnd and
3429 * continue in congestion avoidance.
3430 */
3431static void tcp_conservative_spur_to_response(struct tcp_sock *tp)
3432{
3433        tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_ssthresh);
3434        tp->snd_cwnd_cnt = 0;
3435        tp->bytes_acked = 0;
3436        TCP_ECN_queue_cwr(tp);
3437        tcp_moderate_cwnd(tp);
3438}
3439
3440/* A conservative spurious RTO response algorithm: reduce cwnd using
3441 * rate halving and continue in congestion avoidance.
3442 */
3443static void tcp_ratehalving_spur_to_response(struct sock *sk)
3444{
3445        tcp_enter_cwr(sk, 0);
3446}
3447
3448static void tcp_undo_spur_to_response(struct sock *sk, int flag)
3449{
3450        if (flag & FLAG_ECE)
3451                tcp_ratehalving_spur_to_response(sk);
3452        else
3453                tcp_undo_cwr(sk, 1);
3454}
3455
3456/* F-RTO spurious RTO detection algorithm (RFC4138)
3457 *
3458 * F-RTO affects during two new ACKs following RTO (well, almost, see inline
3459 * comments). State (ACK number) is kept in frto_counter. When ACK advances
3460 * window (but not to or beyond highest sequence sent before RTO):
3461 *   On First ACK,  send two new segments out.
3462 *   On Second ACK, RTO was likely spurious. Do spurious response (response
3463 *                  algorithm is not part of the F-RTO detection algorithm
3464 *                  given in RFC4138 but can be selected separately).
3465 * Otherwise (basically on duplicate ACK), RTO was (likely) caused by a loss
3466 * and TCP falls back to conventional RTO recovery. F-RTO allows overriding
3467 * of Nagle, this is done using frto_counter states 2 and 3, when a new data
3468 * segment of any size sent during F-RTO, state 2 is upgraded to 3.
3469 *
3470 * Rationale: if the RTO was spurious, new ACKs should arrive from the
3471 * original window even after we transmit two new data segments.
3472 *
3473 * SACK version:
3474 *   on first step, wait until first cumulative ACK arrives, then move to
3475 *   the second step. In second step, the next ACK decides.
3476 *
3477 * F-RTO is implemented (mainly) in four functions:
3478 *   - tcp_use_frto() is used to determine if TCP is can use F-RTO
3479 *   - tcp_enter_frto() prepares TCP state on RTO if F-RTO is used, it is
3480 *     called when tcp_use_frto() showed green light
3481 *   - tcp_process_frto() handles incoming ACKs during F-RTO algorithm
3482 *   - tcp_enter_frto_loss() is called if there is not enough evidence
3483 *     to prove that the RTO is indeed spurious. It transfers the control
3484 *     from F-RTO to the conventional RTO recovery
3485 */
3486static int tcp_process_frto(struct sock *sk, int flag)
3487{
3488        struct tcp_sock *tp = tcp_sk(sk);
3489
3490        tcp_verify_left_out(tp);
3491
3492        /* Duplicate the behavior from Loss state (fastretrans_alert) */
3493        if (flag & FLAG_DATA_ACKED)
3494                inet_csk(sk)->icsk_retransmits = 0;
3495
3496        if ((flag & FLAG_NONHEAD_RETRANS_ACKED) ||
3497            ((tp->frto_counter >= 2) && (flag & FLAG_RETRANS_DATA_ACKED)))
3498                tp->undo_marker = 0;
3499
3500        if (!before(tp->snd_una, tp->frto_highmark)) {
3501                tcp_enter_frto_loss(sk, (tp->frto_counter == 1 ? 2 : 3), flag);
3502                return 1;
3503        }
3504
3505        if (!tcp_is_sackfrto(tp)) {
3506                /* RFC4138 shortcoming in step 2; should also have case c):
3507                 * ACK isn't duplicate nor advances window, e.g., opposite dir
3508                 * data, winupdate
3509                 */
3510                if (!(flag & FLAG_ANY_PROGRESS) && (flag & FLAG_NOT_DUP))
3511                        return 1;
3512
3513                if (!(flag & FLAG_DATA_ACKED)) {
3514                        tcp_enter_frto_loss(sk, (tp->frto_counter == 1 ? 0 : 3),
3515                                            flag);
3516                        return 1;
3517                }
3518        } else {
3519                if (!(flag & FLAG_DATA_ACKED) && (tp->frto_counter == 1)) {
3520                        /* Prevent sending of new data. */
3521                        tp->snd_cwnd = min(tp->snd_cwnd,
3522                                           tcp_packets_in_flight(tp));
3523                        return 1;
3524                }
3525
3526                if ((tp->frto_counter >= 2) &&
3527                    (!(flag & FLAG_FORWARD_PROGRESS) ||
3528                     ((flag & FLAG_DATA_SACKED) &&
3529                      !(flag & FLAG_ONLY_ORIG_SACKED)))) {
3530                        /* RFC4138 shortcoming (see comment above) */
3531                        if (!(flag & FLAG_FORWARD_PROGRESS) &&
3532                            (flag & FLAG_NOT_DUP))
3533                                return 1;
3534
3535                        tcp_enter_frto_loss(sk, 3, flag);
3536                        return 1;
3537                }
3538        }
3539
3540        if (tp->frto_counter == 1) {
3541                /* tcp_may_send_now needs to see updated state */
3542                tp->snd_cwnd = tcp_packets_in_flight(tp) + 2;
3543                tp->frto_counter = 2;
3544
3545                if (!tcp_may_send_now(sk))
3546                        tcp_enter_frto_loss(sk, 2, flag);
3547
3548                return 1;
3549        } else {
3550                switch (sysctl_tcp_frto_response) {
3551                case 2:
3552                        tcp_undo_spur_to_response(sk, flag);
3553                        break;
3554                case 1:
3555                        tcp_conservative_spur_to_response(tp);
3556                        break;
3557                default:
3558                        tcp_ratehalving_spur_to_response(sk);
3559                        break;
3560                }
3561                tp->frto_counter = 0;
3562                tp->undo_marker = 0;
3563                NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSPURIOUSRTOS);
3564        }
3565        return 0;
3566}
3567
3568/* This routine deals with incoming acks, but not outgoing ones. */
3569static int tcp_ack(struct sock *sk, struct sk_buff *skb, int flag)
3570{
3571        struct inet_connection_sock *icsk = inet_csk(sk);
3572        struct tcp_sock *tp = tcp_sk(sk);
3573        u32 prior_snd_una = tp->snd_una;
3574        u32 ack_seq = TCP_SKB_CB(skb)->seq;
3575        u32 ack = TCP_SKB_CB(skb)->ack_seq;
3576        u32 prior_in_flight;
3577        u32 prior_fackets;
3578        int prior_packets;
3579        int frto_cwnd = 0;
3580
3581        /* If the ack is older than previous acks
3582         * then we can probably ignore it.
3583         */
3584        if (before(ack, prior_snd_una))
3585                goto old_ack;
3586
3587        /* If the ack includes data we haven't sent yet, discard
3588         * this segment (RFC793 Section 3.9).
3589         */
3590        if (after(ack, tp->snd_nxt))
3591                goto invalid_ack;
3592
3593        if (after(ack, prior_snd_una))
3594                flag |= FLAG_SND_UNA_ADVANCED;
3595
3596        if (sysctl_tcp_abc) {
3597                if (icsk->icsk_ca_state < TCP_CA_CWR)
3598                        tp->bytes_acked += ack - prior_snd_una;
3599                else if (icsk->icsk_ca_state == TCP_CA_Loss)
3600                        /* we assume just one segment left network */
3601                        tp->bytes_acked += min(ack - prior_snd_una,
3602                                               tp->mss_cache);
3603        }
3604
3605        prior_fackets = tp->fackets_out;
3606        prior_in_flight = tcp_packets_in_flight(tp);
3607
3608        if (!(flag & FLAG_SLOWPATH) && after(ack, prior_snd_una)) {
3609                /* Window is constant, pure forward advance.
3610                 * No more checks are required.
3611                 * Note, we use the fact that SND.UNA>=SND.WL2.
3612                 */
3613                tcp_update_wl(tp, ack_seq);
3614                tp->snd_una = ack;
3615                flag |= FLAG_WIN_UPDATE;
3616
3617                tcp_ca_event(sk, CA_EVENT_FAST_ACK);
3618
3619                NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPHPACKS);
3620        } else {
3621                if (ack_seq != TCP_SKB_CB(skb)->end_seq)
3622                        flag |= FLAG_DATA;
3623                else
3624                        NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPPUREACKS);
3625
3626                flag |= tcp_ack_update_window(sk, skb, ack, ack_seq);
3627
3628                if (TCP_SKB_CB(skb)->sacked)
3629                        flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una);
3630
3631                if (TCP_ECN_rcv_ecn_echo(tp, tcp_hdr(skb)))
3632                        flag |= FLAG_ECE;
3633
3634                tcp_ca_event(sk, CA_EVENT_SLOW_ACK);
3635        }
3636
3637        /* We passed data and got it acked, remove any soft error
3638         * log. Something worked...
3639         */
3640        sk->sk_err_soft = 0;
3641        icsk->icsk_probes_out = 0;
3642        tp->rcv_tstamp = tcp_time_stamp;
3643        prior_packets = tp->packets_out;
3644        if (!prior_packets)
3645                goto no_queue;
3646
3647        /* See if we can take anything off of the retransmit queue. */
3648        flag |= tcp_clean_rtx_queue(sk, prior_fackets, prior_snd_una);
3649
3650        if (tp->frto_counter)
3651                frto_cwnd = tcp_process_frto(sk, flag);
3652        /* Guarantee sacktag reordering detection against wrap-arounds */
3653        if (before(tp->frto_highmark, tp->snd_una))
3654                tp->frto_highmark = 0;
3655
3656        if (tcp_ack_is_dubious(sk, flag)) {
3657                /* Advance CWND, if state allows this. */
3658                if ((flag & FLAG_DATA_ACKED) && !frto_cwnd &&
3659                    tcp_may_raise_cwnd(sk, flag))
3660                        tcp_cong_avoid(sk, ack, prior_in_flight);
3661                tcp_fastretrans_alert(sk, prior_packets - tp->packets_out,
3662                                      flag);
3663        } else {
3664                if ((flag & FLAG_DATA_ACKED) && !frto_cwnd)
3665                        tcp_cong_avoid(sk, ack, prior_in_flight);
3666        }
3667
3668        if ((flag & FLAG_FORWARD_PROGRESS) || !(flag & FLAG_NOT_DUP))
3669                dst_confirm(sk->sk_dst_cache);
3670
3671        return 1;
3672
3673no_queue:
3674        /* If this ack opens up a zero window, clear backoff.  It was
3675         * being used to time the probes, and is probably far higher than
3676         * it needs to be for normal retransmission.
3677         */
3678        if (tcp_send_head(sk))
3679                tcp_ack_probe(sk);
3680        return 1;
3681
3682invalid_ack:
3683        SOCK_DEBUG(sk, "Ack %u after %u:%u\n", ack, tp->snd_una, tp->snd_nxt);
3684        return -1;
3685
3686old_ack:
3687        if (TCP_SKB_CB(skb)->sacked) {
3688                tcp_sacktag_write_queue(sk, skb, prior_snd_una);
3689                if (icsk->icsk_ca_state == TCP_CA_Open)
3690                        tcp_try_keep_open(sk);
3691        }
3692
3693        SOCK_DEBUG(sk, "Ack %u before %u:%u\n", ack, tp->snd_una, tp->snd_nxt);
3694        return 0;
3695}
3696
3697/* Look for tcp options. Normally only called on SYN and SYNACK packets.
3698 * But, this can also be called on packets in the established flow when
3699 * the fast version below fails.
3700 */
3701void tcp_parse_options(struct sk_buff *skb, struct tcp_options_received *opt_rx,
3702                       int estab)
3703{
3704        unsigned char *ptr;
3705        struct tcphdr *th = tcp_hdr(skb);
3706        int length = (th->doff * 4) - sizeof(struct tcphdr);
3707
3708        ptr = (unsigned char *)(th + 1);
3709        opt_rx->saw_tstamp = 0;
3710
3711        while (length > 0) {
3712                int opcode = *ptr++;
3713                int opsize;
3714
3715                switch (opcode) {
3716                case TCPOPT_EOL:
3717                        return;
3718                case TCPOPT_NOP:        /* Ref: RFC 793 section 3.1 */
3719                        length--;
3720                        continue;
3721                default:
3722                        opsize = *ptr++;
3723                        if (opsize < 2) /* "silly options" */
3724                                return;
3725                        if (opsize > length)
3726                                return; /* don't parse partial options */
3727                        switch (opcode) {
3728                        case TCPOPT_MSS:
3729                                if (opsize == TCPOLEN_MSS && th->syn && !estab) {
3730                                        u16 in_mss = get_unaligned_be16(ptr);
3731                                        if (in_mss) {
3732                                                if (opt_rx->user_mss &&
3733                                                    opt_rx->user_mss < in_mss)
3734                                                        in_mss = opt_rx->user_mss;
3735                                                opt_rx->mss_clamp = in_mss;
3736                                        }
3737                                }
3738                                break;
3739                        case TCPOPT_WINDOW:
3740                                if (opsize == TCPOLEN_WINDOW && th->syn &&
3741                                    !estab && sysctl_tcp_window_scaling) {
3742                                        __u8 snd_wscale = *(__u8 *)ptr;
3743                                        opt_rx->wscale_ok = 1;
3744                                        if (snd_wscale > 14) {
3745                                                if (net_ratelimit())
3746                                                        printk(KERN_INFO "tcp_parse_options: Illegal window "
3747                                                               "scaling value %d >14 received.\n",
3748                                                               snd_wscale);
3749                                                snd_wscale = 14;
3750                                        }
3751                                        opt_rx->snd_wscale = snd_wscale;
3752                                }
3753                                break;
3754                        case TCPOPT_TIMESTAMP:
3755                                if ((opsize == TCPOLEN_TIMESTAMP) &&
3756                                    ((estab && opt_rx->tstamp_ok) ||
3757                                     (!estab && sysctl_tcp_timestamps))) {
3758                                        opt_rx->saw_tstamp = 1;
3759                                        opt_rx->rcv_tsval = get_unaligned_be32(ptr);
3760                                        opt_rx->rcv_tsecr = get_unaligned_be32(ptr + 4);
3761                                }
3762                                break;
3763                        case TCPOPT_SACK_PERM:
3764                                if (opsize == TCPOLEN_SACK_PERM && th->syn &&
3765                                    !estab && sysctl_tcp_sack) {
3766                                        opt_rx->sack_ok = 1;
3767                                        tcp_sack_reset(opt_rx);
3768                                }
3769                                break;
3770
3771                        case TCPOPT_SACK:
3772                                if ((opsize >= (TCPOLEN_SACK_BASE + TCPOLEN_SACK_PERBLOCK)) &&
3773                                   !((opsize - TCPOLEN_SACK_BASE) % TCPOLEN_SACK_PERBLOCK) &&
3774                                   opt_rx->sack_ok) {
3775                                        TCP_SKB_CB(skb)->sacked = (ptr - 2) - (unsigned char *)th;
3776                                }
3777                                break;
3778#ifdef CONFIG_TCP_MD5SIG
3779                        case TCPOPT_MD5SIG:
3780                                /*
3781                                 * The MD5 Hash has already been
3782                                 * checked (see tcp_v{4,6}_do_rcv()).
3783                                 */
3784                                break;
3785#endif
3786                        }
3787
3788                        ptr += opsize-2;
3789                        length -= opsize;
3790                }
3791        }
3792}
3793
3794static int tcp_parse_aligned_timestamp(struct tcp_sock *tp, struct tcphdr *th)
3795{
3796        __be32 *ptr = (__be32 *)(th + 1);
3797
3798        if (*ptr == htonl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16)
3799                          | (TCPOPT_TIMESTAMP << 8) | TCPOLEN_TIMESTAMP)) {
3800                tp->rx_opt.saw_tstamp = 1;
3801                ++ptr;
3802                tp->rx_opt.rcv_tsval = ntohl(*ptr);
3803                ++ptr;
3804                tp->rx_opt.rcv_tsecr = ntohl(*ptr);
3805                return 1;
3806        }
3807        return 0;
3808}
3809
3810/* Fast parse options. This hopes to only see timestamps.
3811 * If it is wrong it falls back on tcp_parse_options().
3812 */
3813static int tcp_fast_parse_options(struct sk_buff *skb, struct tcphdr *th,
3814                                  struct tcp_sock *tp)
3815{
3816        if (th->doff == sizeof(struct tcphdr) >> 2) {
3817                tp->rx_opt.saw_tstamp = 0;
3818                return 0;
3819        } else if (tp->rx_opt.tstamp_ok &&
3820                   th->doff == (sizeof(struct tcphdr)>>2)+(TCPOLEN_TSTAMP_ALIGNED>>2)) {
3821                if (tcp_parse_aligned_timestamp(tp, th))
3822                        return 1;
3823        }
3824        tcp_parse_options(skb, &tp->rx_opt, 1);
3825        return 1;
3826}
3827
3828#ifdef CONFIG_TCP_MD5SIG
3829/*
3830 * Parse MD5 Signature option
3831 */
3832u8 *tcp_parse_md5sig_option(struct tcphdr *th)
3833{
3834        int length = (th->doff << 2) - sizeof (*th);
3835        u8 *ptr = (u8*)(th + 1);
3836
3837        /* If the TCP option is too short, we can short cut */
3838        if (length < TCPOLEN_MD5SIG)
3839                return NULL;
3840
3841        while (length > 0) {
3842                int opcode = *ptr++;
3843                int opsize;
3844
3845                switch(opcode) {
3846                case TCPOPT_EOL:
3847                        return NULL;
3848                case TCPOPT_NOP:
3849                        length--;
3850                        continue;
3851                default:
3852                        opsize = *ptr++;
3853                        if (opsize < 2 || opsize > length)
3854                                return NULL;
3855                        if (opcode == TCPOPT_MD5SIG)
3856                                return ptr;
3857                }
3858                ptr += opsize - 2;
3859                length -= opsize;
3860        }
3861        return NULL;
3862}
3863#endif
3864
3865static inline void tcp_store_ts_recent(struct tcp_sock *tp)
3866{
3867        tp->rx_opt.ts_recent = tp->rx_opt.rcv_tsval;
3868        tp->rx_opt.ts_recent_stamp = get_seconds();
3869}
3870
3871static inline void tcp_replace_ts_recent(struct tcp_sock *tp, u32 seq)
3872{
3873        if (tp->rx_opt.saw_tstamp && !after(seq, tp->rcv_wup)) {
3874                /* PAWS bug workaround wrt. ACK frames, the PAWS discard
3875                 * extra check below makes sure this can only happen
3876                 * for pure ACK frames.  -DaveM
3877                 *
3878                 * Not only, also it occurs for expired timestamps.
3879                 */
3880
3881                if (tcp_paws_check(&tp->rx_opt, 0))
3882                        tcp_store_ts_recent(tp);
3883        }
3884}
3885
3886/* Sorry, PAWS as specified is broken wrt. pure-ACKs -DaveM
3887 *
3888 * It is not fatal. If this ACK does _not_ change critical state (seqs, window)
3889 * it can pass through stack. So, the following predicate verifies that
3890 * this segment is not used for anything but congestion avoidance or
3891 * fast retransmit. Moreover, we even are able to eliminate most of such
3892 * second order effects, if we apply some small "replay" window (~RTO)
3893 * to timestamp space.
3894 *
3895 * All these measures still do not guarantee that we reject wrapped ACKs
3896 * on networks with high bandwidth, when sequence space is recycled fastly,
3897 * but it guarantees that such events will be very rare and do not affect
3898 * connection seriously. This doesn't look nice, but alas, PAWS is really
3899 * buggy extension.
3900 *
3901 * [ Later note. Even worse! It is buggy for segments _with_ data. RFC
3902 * states that events when retransmit arrives after original data are rare.
3903 * It is a blatant lie. VJ forgot about fast retransmit! 8)8) It is
3904 * the biggest problem on large power networks even with minor reordering.
3905 * OK, let's give it small replay window. If peer clock is even 1hz, it is safe
3906 * up to bandwidth of 18Gigabit/sec. 8) ]
3907 */
3908
3909static int tcp_disordered_ack(const struct sock *sk, const struct sk_buff *skb)
3910{
3911        struct tcp_sock *tp = tcp_sk(sk);
3912        struct tcphdr *th = tcp_hdr(skb);
3913        u32 seq = TCP_SKB_CB(skb)->seq;
3914        u32 ack = TCP_SKB_CB(skb)->ack_seq;
3915
3916        return (/* 1. Pure ACK with correct sequence number. */
3917                (th->ack && seq == TCP_SKB_CB(skb)->end_seq && seq == tp->rcv_nxt) &&
3918
3919                /* 2. ... and duplicate ACK. */
3920                ack == tp->snd_una &&
3921
3922                /* 3. ... and does not update window. */
3923                !tcp_may_update_window(tp, ack, seq, ntohs(th->window) << tp->rx_opt.snd_wscale) &&
3924
3925                /* 4. ... and sits in replay window. */
3926                (s32)(tp->rx_opt.ts_recent - tp->rx_opt.rcv_tsval) <= (inet_csk(sk)->icsk_rto * 1024) / HZ);
3927}
3928
3929static inline int tcp_paws_discard(const struct sock *sk,
3930                                   const struct sk_buff *skb)
3931{
3932        const struct tcp_sock *tp = tcp_sk(sk);
3933
3934        return !tcp_paws_check(&tp->rx_opt, TCP_PAWS_WINDOW) &&
3935               !tcp_disordered_ack(sk, skb);
3936}
3937
3938/* Check segment sequence number for validity.
3939 *
3940 * Segment controls are considered valid, if the segment
3941 * fits to the window after truncation to the window. Acceptability
3942 * of data (and SYN, FIN, of course) is checked separately.
3943 * See tcp_data_queue(), for example.
3944 *
3945 * Also, controls (RST is main one) are accepted using RCV.WUP instead
3946 * of RCV.NXT. Peer still did not advance his SND.UNA when we
3947 * delayed ACK, so that hisSND.UNA<=ourRCV.WUP.
3948 * (borrowed from freebsd)
3949 */
3950
3951static inline int tcp_sequence(struct tcp_sock *tp, u32 seq, u32 end_seq)
3952{
3953        return  !before(end_seq, tp->rcv_wup) &&
3954                !after(seq, tp->rcv_nxt + tcp_receive_window(tp));
3955}
3956
3957/* When we get a reset we do this. */
3958static void tcp_reset(struct sock *sk)
3959{
3960        /* We want the right error as BSD sees it (and indeed as we do). */
3961        switch (sk->sk_state) {
3962        case TCP_SYN_SENT:
3963                sk->sk_err = ECONNREFUSED;
3964                break;
3965        case TCP_CLOSE_WAIT:
3966                sk->sk_err = EPIPE;
3967                break;
3968        case TCP_CLOSE:
3969                return;
3970        default:
3971                sk->sk_err = ECONNRESET;
3972        }
3973
3974        if (!sock_flag(sk, SOCK_DEAD))
3975                sk->sk_error_report(sk);
3976
3977        tcp_done(sk);
3978}
3979
3980/*
3981 *      Process the FIN bit. This now behaves as it is supposed to work
3982 *      and the FIN takes effect when it is validly part of sequence
3983 *      space. Not before when we get holes.
3984 *
3985 *      If we are ESTABLISHED, a received fin moves us to CLOSE-WAIT
3986 *      (and thence onto LAST-ACK and finally, CLOSE, we never enter
3987 *      TIME-WAIT)
3988 *
3989 *      If we are in FINWAIT-1, a received FIN indicates simultaneous
3990 *      close and we go into CLOSING (and later onto TIME-WAIT)
3991 *
3992 *      If we are in FINWAIT-2, a received FIN moves us to TIME-WAIT.
3993 */
3994static void tcp_fin(struct sk_buff *skb, struct sock *sk, struct tcphdr *th)
3995{
3996        struct tcp_sock *tp = tcp_sk(sk);
3997
3998        inet_csk_schedule_ack(sk);
3999
4000        sk->sk_shutdown |= RCV_SHUTDOWN;
4001        sock_set_flag(sk, SOCK_DONE);
4002
4003        switch (sk->sk_state) {
4004        case TCP_SYN_RECV:
4005        case TCP_ESTABLISHED:
4006                /* Move to CLOSE_WAIT */
4007                tcp_set_state(sk, TCP_CLOSE_WAIT);
4008                inet_csk(sk)->icsk_ack.pingpong = 1;
4009                break;
4010
4011        case TCP_CLOSE_WAIT:
4012        case TCP_CLOSING:
4013                /* Received a retransmission of the FIN, do
4014                 * nothing.
4015                 */
4016                break;
4017        case TCP_LAST_ACK:
4018                /* RFC793: Remain in the LAST-ACK state. */
4019                break;
4020
4021        case TCP_FIN_WAIT1:
4022                /* This case occurs when a simultaneous close
4023                 * happens, we must ack the received FIN and
4024                 * enter the CLOSING state.
4025                 */
4026                tcp_send_ack(sk);
4027                tcp_set_state(sk, TCP_CLOSING);
4028                break;
4029        case TCP_FIN_WAIT2:
4030                /* Received a FIN -- send ACK and enter TIME_WAIT. */
4031                tcp_send_ack(sk);
4032                tcp_time_wait(sk, TCP_TIME_WAIT, 0);
4033                break;
4034        default:
4035                /* Only TCP_LISTEN and TCP_CLOSE are left, in these
4036                 * cases we should never reach this piece of code.
4037                 */
4038                printk(KERN_ERR "%s: Impossible, sk->sk_state=%d\n",
4039                       __func__, sk->sk_state);
4040                break;
4041        }
4042
4043        /* It _is_ possible, that we have something out-of-order _after_ FIN.
4044         * Probably, we should reset in this case. For now drop them.
4045         */
4046        __skb_queue_purge(&tp->out_of_order_queue);
4047        if (tcp_is_sack(tp))
4048                tcp_sack_reset(&tp->rx_opt);
4049        sk_mem_reclaim(sk);
4050
4051        if (!sock_flag(sk, SOCK_DEAD)) {
4052                sk->sk_state_change(sk);
4053
4054                /* Do not send POLL_HUP for half duplex close. */
4055                if (sk->sk_shutdown == SHUTDOWN_MASK ||
4056                    sk->sk_state == TCP_CLOSE)
4057                        sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_HUP);
4058                else
4059                        sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_IN);
4060        }
4061}
4062
4063static inline int tcp_sack_extend(struct tcp_sack_block *sp, u32 seq,
4064                                  u32 end_seq)
4065{
4066        if (!after(seq, sp->end_seq) && !after(sp->start_seq, end_seq)) {
4067                if (before(seq, sp->start_seq))
4068                        sp->start_seq = seq;
4069                if (after(end_seq, sp->end_seq))
4070                        sp->end_seq = end_seq;
4071                return 1;
4072        }
4073        return 0;
4074}
4075
4076static void tcp_dsack_set(struct sock *sk, u32 seq, u32 end_seq)
4077{
4078        struct tcp_sock *tp = tcp_sk(sk);
4079
4080        if (tcp_is_sack(tp) && sysctl_tcp_dsack) {
4081                int mib_idx;
4082
4083                if (before(seq, tp->rcv_nxt))
4084                        mib_idx = LINUX_MIB_TCPDSACKOLDSENT;
4085                else
4086                        mib_idx = LINUX_MIB_TCPDSACKOFOSENT;
4087
4088                NET_INC_STATS_BH(sock_net(sk), mib_idx);
4089
4090                tp->rx_opt.dsack = 1;
4091                tp->duplicate_sack[0].start_seq = seq;
4092                tp->duplicate_sack[0].end_seq = end_seq;
4093        }
4094}
4095
4096static void tcp_dsack_extend(struct sock *sk, u32 seq, u32 end_seq)
4097{
4098        struct tcp_sock *tp = tcp_sk(sk);
4099
4100        if (!tp->rx_opt.dsack)
4101                tcp_dsack_set(sk, seq, end_seq);
4102        else
4103                tcp_sack_extend(tp->duplicate_sack, seq, end_seq);
4104}
4105
4106static void tcp_send_dupack(struct sock *sk, struct sk_buff *skb)
4107{
4108        struct tcp_sock *tp = tcp_sk(sk);
4109
4110        if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
4111            before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
4112                NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKLOST);
4113                tcp_enter_quickack_mode(sk);
4114
4115                if (tcp_is_sack(tp) && sysctl_tcp_dsack) {
4116                        u32 end_seq = TCP_SKB_CB(skb)->end_seq;
4117
4118                        if (after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt))
4119                                end_seq = tp->rcv_nxt;
4120                        tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, end_seq);
4121                }
4122        }
4123
4124        tcp_send_ack(sk);
4125}
4126
4127/* These routines update the SACK block as out-of-order packets arrive or
4128 * in-order packets close up the sequence space.
4129 */
4130static void tcp_sack_maybe_coalesce(struct tcp_sock *tp)
4131{
4132        int this_sack;
4133        struct tcp_sack_block *sp = &tp->selective_acks[0];
4134        struct tcp_sack_block *swalk = sp + 1;
4135
4136        /* See if the recent change to the first SACK eats into
4137         * or hits the sequence space of other SACK blocks, if so coalesce.
4138         */
4139        for (this_sack = 1; this_sack < tp->rx_opt.num_sacks;) {
4140                if (tcp_sack_extend(sp, swalk->start_seq, swalk->end_seq)) {
4141                        int i;
4142
4143                        /* Zap SWALK, by moving every further SACK up by one slot.
4144                         * Decrease num_sacks.
4145                         */
4146                        tp->rx_opt.num_sacks--;
4147                        for (i = this_sack; i < tp->rx_opt.num_sacks; i++)
4148                                sp[i] = sp[i + 1];
4149                        continue;
4150                }
4151                this_sack++, swalk++;
4152        }
4153}
4154
4155static void tcp_sack_new_ofo_skb(struct sock *sk, u32 seq, u32 end_seq)
4156{
4157        struct tcp_sock *tp = tcp_sk(sk);
4158        struct tcp_sack_block *sp = &tp->selective_acks[0];
4159        int cur_sacks = tp->rx_opt.num_sacks;
4160        int this_sack;
4161
4162        if (!cur_sacks)
4163                goto new_sack;
4164
4165        for (this_sack = 0; this_sack < cur_sacks; this_sack++, sp++) {
4166                if (tcp_sack_extend(sp, seq, end_seq)) {
4167                        /* Rotate this_sack to the first one. */
4168                        for (; this_sack > 0; this_sack--, sp--)
4169                                swap(*sp, *(sp - 1));
4170                        if (cur_sacks > 1)
4171                                tcp_sack_maybe_coalesce(tp);
4172                        return;
4173                }
4174        }
4175
4176        /* Could not find an adjacent existing SACK, build a new one,
4177         * put it at the front, and shift everyone else down.  We
4178         * always know there is at least one SACK present already here.
4179         *
4180         * If the sack array is full, forget about the last one.
4181         */
4182        if (this_sack >= TCP_NUM_SACKS) {
4183                this_sack--;
4184                tp->rx_opt.num_sacks--;
4185                sp--;
4186        }
4187        for (; this_sack > 0; this_sack--, sp--)
4188                *sp = *(sp - 1);
4189
4190new_sack:
4191        /* Build the new head SACK, and we're done. */
4192        sp->start_seq = seq;
4193        sp->end_seq = end_seq;
4194        tp->rx_opt.num_sacks++;
4195}
4196
4197/* RCV.NXT advances, some SACKs should be eaten. */
4198
4199static void tcp_sack_remove(struct tcp_sock *tp)
4200{
4201        struct tcp_sack_block *sp = &tp->selective_acks[0];
4202        int num_sacks = tp->rx_opt.num_sacks;
4203        int this_sack;
4204
4205        /* Empty ofo queue, hence, all the SACKs are eaten. Clear. */
4206        if (skb_queue_empty(&tp->out_of_order_queue)) {
4207                tp->rx_opt.num_sacks = 0;
4208                return;
4209        }
4210
4211        for (this_sack = 0; this_sack < num_sacks;) {
4212                /* Check if the start of the sack is covered by RCV.NXT. */
4213                if (!before(tp->rcv_nxt, sp->start_seq)) {
4214                        int i;
4215
4216                        /* RCV.NXT must cover all the block! */
4217                        WARN_ON(before(tp->rcv_nxt, sp->end_seq));
4218
4219                        /* Zap this SACK, by moving forward any other SACKS. */
4220                        for (i=this_sack+1; i < num_sacks; i++)
4221                                tp->selective_acks[i-1] = tp->selective_acks[i];
4222                        num_sacks--;
4223                        continue;
4224                }
4225                this_sack++;
4226                sp++;
4227        }
4228        tp->rx_opt.num_sacks = num_sacks;
4229}
4230
4231/* This one checks to see if we can put data from the
4232 * out_of_order queue into the receive_queue.
4233 */
4234static void tcp_ofo_queue(struct sock *sk)
4235{
4236        struct tcp_sock *tp = tcp_sk(sk);
4237        __u32 dsack_high = tp->rcv_nxt;
4238        struct sk_buff *skb;
4239
4240        while ((skb = skb_peek(&tp->out_of_order_queue)) != NULL) {
4241                if (after(TCP_SKB_CB(skb)->seq, tp->rcv_nxt))
4242                        break;
4243
4244                if (before(TCP_SKB_CB(skb)->seq, dsack_high)) {
4245                        __u32 dsack = dsack_high;
4246                        if (before(TCP_SKB_CB(skb)->end_seq, dsack_high))
4247                                dsack_high = TCP_SKB_CB(skb)->end_seq;
4248                        tcp_dsack_extend(sk, TCP_SKB_CB(skb)->seq, dsack);
4249                }
4250
4251                if (!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) {
4252                        SOCK_DEBUG(sk, "ofo packet was already received \n");
4253                        __skb_unlink(skb, &tp->out_of_order_queue);
4254                        __kfree_skb(skb);
4255                        continue;
4256                }
4257                SOCK_DEBUG(sk, "ofo requeuing : rcv_next %X seq %X - %X\n",
4258                           tp->rcv_nxt, TCP_SKB_CB(skb)->seq,
4259                           TCP_SKB_CB(skb)->end_seq);
4260
4261                __skb_unlink(skb, &tp->out_of_order_queue);
4262                __skb_queue_tail(&sk->sk_receive_queue, skb);
4263                tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
4264                if (tcp_hdr(skb)->fin)
4265                        tcp_fin(skb, sk, tcp_hdr(skb));
4266        }
4267}
4268
4269static int tcp_prune_ofo_queue(struct sock *sk);
4270static int tcp_prune_queue(struct sock *sk);
4271
4272static inline int tcp_try_rmem_schedule(struct sock *sk, unsigned int size)
4273{
4274        if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf ||
4275            !sk_rmem_schedule(sk, size)) {
4276
4277                if (tcp_prune_queue(sk) < 0)
4278                        return -1;
4279
4280                if (!sk_rmem_schedule(sk, size)) {
4281                        if (!tcp_prune_ofo_queue(sk))
4282                                return -1;
4283
4284                        if (!sk_rmem_schedule(sk, size))
4285                                return -1;
4286                }
4287        }
4288        return 0;
4289}
4290
4291static void tcp_data_queue(struct sock *sk, struct sk_buff *skb)
4292{
4293        struct tcphdr *th = tcp_hdr(skb);
4294        struct tcp_sock *tp = tcp_sk(sk);
4295        int eaten = -1;
4296
4297        if (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq)
4298                goto drop;
4299
4300        __skb_pull(skb, th->doff * 4);
4301
4302        TCP_ECN_accept_cwr(tp, skb);
4303
4304        tp->rx_opt.dsack = 0;
4305
4306        /*  Queue data for delivery to the user.
4307         *  Packets in sequence go to the receive queue.
4308         *  Out of sequence packets to the out_of_order_queue.
4309         */
4310        if (TCP_SKB_CB(skb)->seq == tp->rcv_nxt) {
4311                if (tcp_receive_window(tp) == 0)
4312                        goto out_of_window;
4313
4314                /* Ok. In sequence. In window. */
4315                if (tp->ucopy.task == current &&
4316                    tp->copied_seq == tp->rcv_nxt && tp->ucopy.len &&
4317                    sock_owned_by_user(sk) && !tp->urg_data) {
4318                        int chunk = min_t(unsigned int, skb->len,
4319                                          tp->ucopy.len);
4320
4321                        __set_current_state(TASK_RUNNING);
4322
4323                        local_bh_enable();
4324                        if (!skb_copy_datagram_iovec(skb, 0, tp->ucopy.iov, chunk)) {
4325                                tp->ucopy.len -= chunk;
4326                                tp->copied_seq += chunk;
4327                                eaten = (chunk == skb->len && !th->fin);
4328                                tcp_rcv_space_adjust(sk);
4329                        }
4330                        local_bh_disable();
4331                }
4332
4333                if (eaten <= 0) {
4334queue_and_out:
4335                        if (eaten < 0 &&
4336                            tcp_try_rmem_schedule(sk, skb->truesize))
4337                                goto drop;
4338
4339                        skb_set_owner_r(skb, sk);
4340                        __skb_queue_tail(&sk->sk_receive_queue, skb);
4341                }
4342                tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
4343                if (skb->len)
4344                        tcp_event_data_recv(sk, skb);
4345                if (th->fin)
4346                        tcp_fin(skb, sk, th);
4347
4348                if (!skb_queue_empty(&tp->out_of_order_queue)) {
4349                        tcp_ofo_queue(sk);
4350
4351                        /* RFC2581. 4.2. SHOULD send immediate ACK, when
4352                         * gap in queue is filled.
4353                         */
4354                        if (skb_queue_empty(&tp->out_of_order_queue))
4355                                inet_csk(sk)->icsk_ack.pingpong = 0;
4356                }
4357
4358                if (tp->rx_opt.num_sacks)
4359                        tcp_sack_remove(tp);
4360
4361                tcp_fast_path_check(sk);
4362
4363                if (eaten > 0)
4364                        __kfree_skb(skb);
4365                else if (!sock_flag(sk, SOCK_DEAD))
4366                        sk->sk_data_ready(sk, 0);
4367                return;
4368        }
4369
4370        if (!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) {
4371                /* A retransmit, 2nd most common case.  Force an immediate ack. */
4372                NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKLOST);
4373                tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq);
4374
4375out_of_window:
4376                tcp_enter_quickack_mode(sk);
4377                inet_csk_schedule_ack(sk);
4378drop:
4379                __kfree_skb(skb);
4380                return;
4381        }
4382
4383        /* Out of window. F.e. zero window probe. */
4384        if (!before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt + tcp_receive_window(tp)))
4385                goto out_of_window;
4386
4387        tcp_enter_quickack_mode(sk);
4388
4389        if (before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
4390                /* Partial packet, seq < rcv_next < end_seq */
4391                SOCK_DEBUG(sk, "partial packet: rcv_next %X seq %X - %X\n",
4392                           tp->rcv_nxt, TCP_SKB_CB(skb)->seq,
4393                           TCP_SKB_CB(skb)->end_seq);
4394
4395                tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, tp->rcv_nxt);
4396
4397                /* If window is closed, drop tail of packet. But after
4398                 * remembering D-SACK for its head made in previous line.
4399                 */
4400                if (!tcp_receive_window(tp))
4401                        goto out_of_window;
4402                goto queue_and_out;
4403        }
4404
4405        TCP_ECN_check_ce(tp, skb);
4406
4407        if (tcp_try_rmem_schedule(sk, skb->truesize))
4408                goto drop;
4409
4410        /* Disable header prediction. */
4411        tp->pred_flags = 0;
4412        inet_csk_schedule_ack(sk);
4413
4414        SOCK_DEBUG(sk, "out of order segment: rcv_next %X seq %X - %X\n",
4415                   tp->rcv_nxt, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq);
4416
4417        skb_set_owner_r(skb, sk);
4418
4419        if (!skb_peek(&tp->out_of_order_queue)) {
4420                /* Initial out of order segment, build 1 SACK. */
4421                if (tcp_is_sack(tp)) {
4422                        tp->rx_opt.num_sacks = 1;
4423                        tp->selective_acks[0].start_seq = TCP_SKB_CB(skb)->seq;
4424                        tp->selective_acks[0].end_seq =
4425                                                TCP_SKB_CB(skb)->end_seq;
4426                }
4427                __skb_queue_head(&tp->out_of_order_queue, skb);
4428        } else {
4429                struct sk_buff *skb1 = tp->out_of_order_queue.prev;
4430                u32 seq = TCP_SKB_CB(skb)->seq;
4431                u32 end_seq = TCP_SKB_CB(skb)->end_seq;
4432
4433                if (seq == TCP_SKB_CB(skb1)->end_seq) {
4434                        __skb_queue_after(&tp->out_of_order_queue, skb1, skb);
4435
4436                        if (!tp->rx_opt.num_sacks ||
4437                            tp->selective_acks[0].end_seq != seq)
4438                                goto add_sack;
4439
4440                        /* Common case: data arrive in order after hole. */
4441                        tp->selective_acks[0].end_seq = end_seq;
4442                        return;
4443                }
4444
4445                /* Find place to insert this segment. */
4446                do {
4447                        if (!after(TCP_SKB_CB(skb1)->seq, seq))
4448                                break;
4449                } while ((skb1 = skb1->prev) !=
4450                         (struct sk_buff *)&tp->out_of_order_queue);
4451
4452                /* Do skb overlap to previous one? */
4453                if (skb1 != (struct sk_buff *)&tp->out_of_order_queue &&
4454                    before(seq, TCP_SKB_CB(skb1)->end_seq)) {
4455                        if (!after(end_seq, TCP_SKB_CB(skb1)->end_seq)) {
4456                                /* All the bits are present. Drop. */
4457                                __kfree_skb(skb);
4458                                tcp_dsack_set(sk, seq, end_seq);
4459                                goto add_sack;
4460                        }
4461                        if (after(seq, TCP_SKB_CB(skb1)->seq)) {
4462