linux/net/ipv4/tcp_timer.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#include <linux/module.h>
  22#include <linux/gfp.h>
  23#include <net/tcp.h>
  24
  25int sysctl_tcp_thin_linear_timeouts __read_mostly;
  26
  27/**
  28 *  tcp_write_err() - close socket and save error info
  29 *  @sk:  The socket the error has appeared on.
  30 *
  31 *  Returns: Nothing (void)
  32 */
  33
  34static void tcp_write_err(struct sock *sk)
  35{
  36        sk->sk_err = sk->sk_err_soft ? : ETIMEDOUT;
  37        sk->sk_error_report(sk);
  38
  39        tcp_done(sk);
  40        __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTONTIMEOUT);
  41}
  42
  43/**
  44 *  tcp_out_of_resources() - Close socket if out of resources
  45 *  @sk:        pointer to current socket
  46 *  @do_reset:  send a last packet with reset flag
  47 *
  48 *  Do not allow orphaned sockets to eat all our resources.
  49 *  This is direct violation of TCP specs, but it is required
  50 *  to prevent DoS attacks. It is called when a retransmission timeout
  51 *  or zero probe timeout occurs on orphaned socket.
  52 *
  53 *  Criteria is still not confirmed experimentally and may change.
  54 *  We kill the socket, if:
  55 *  1. If number of orphaned sockets exceeds an administratively configured
  56 *     limit.
  57 *  2. If we have strong memory pressure.
  58 */
  59static int tcp_out_of_resources(struct sock *sk, bool do_reset)
  60{
  61        struct tcp_sock *tp = tcp_sk(sk);
  62        int shift = 0;
  63
  64        /* If peer does not open window for long time, or did not transmit
  65         * anything for long time, penalize it. */
  66        if ((s32)(tcp_time_stamp - tp->lsndtime) > 2*TCP_RTO_MAX || !do_reset)
  67                shift++;
  68
  69        /* If some dubious ICMP arrived, penalize even more. */
  70        if (sk->sk_err_soft)
  71                shift++;
  72
  73        if (tcp_check_oom(sk, shift)) {
  74                /* Catch exceptional cases, when connection requires reset.
  75                 *      1. Last segment was sent recently. */
  76                if ((s32)(tcp_time_stamp - tp->lsndtime) <= TCP_TIMEWAIT_LEN ||
  77                    /*  2. Window is closed. */
  78                    (!tp->snd_wnd && !tp->packets_out))
  79                        do_reset = true;
  80                if (do_reset)
  81                        tcp_send_active_reset(sk, GFP_ATOMIC);
  82                tcp_done(sk);
  83                __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTONMEMORY);
  84                return 1;
  85        }
  86        return 0;
  87}
  88
  89/**
  90 *  tcp_orphan_retries() - Returns maximal number of retries on an orphaned socket
  91 *  @sk:    Pointer to the current socket.
  92 *  @alive: bool, socket alive state
  93 */
  94static int tcp_orphan_retries(struct sock *sk, bool alive)
  95{
  96        int retries = sock_net(sk)->ipv4.sysctl_tcp_orphan_retries; /* May be zero. */
  97
  98        /* We know from an ICMP that something is wrong. */
  99        if (sk->sk_err_soft && !alive)
 100                retries = 0;
 101
 102        /* However, if socket sent something recently, select some safe
 103         * number of retries. 8 corresponds to >100 seconds with minimal
 104         * RTO of 200msec. */
 105        if (retries == 0 && alive)
 106                retries = 8;
 107        return retries;
 108}
 109
 110static void tcp_mtu_probing(struct inet_connection_sock *icsk, struct sock *sk)
 111{
 112        struct net *net = sock_net(sk);
 113
 114        /* Black hole detection */
 115        if (net->ipv4.sysctl_tcp_mtu_probing) {
 116                if (!icsk->icsk_mtup.enabled) {
 117                        icsk->icsk_mtup.enabled = 1;
 118                        icsk->icsk_mtup.probe_timestamp = tcp_time_stamp;
 119                        tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
 120                } else {
 121                        struct net *net = sock_net(sk);
 122                        struct tcp_sock *tp = tcp_sk(sk);
 123                        int mss;
 124
 125                        mss = tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low) >> 1;
 126                        mss = min(net->ipv4.sysctl_tcp_base_mss, mss);
 127                        mss = max(mss, 68 - tp->tcp_header_len);
 128                        icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, mss);
 129                        tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
 130                }
 131        }
 132}
 133
 134
 135/**
 136 *  retransmits_timed_out() - returns true if this connection has timed out
 137 *  @sk:       The current socket
 138 *  @boundary: max number of retransmissions
 139 *  @timeout:  A custom timeout value.
 140 *             If set to 0 the default timeout is calculated and used.
 141 *             Using TCP_RTO_MIN and the number of unsuccessful retransmits.
 142 *  @syn_set:  true if the SYN Bit was set.
 143 *
 144 * The default "timeout" value this function can calculate and use
 145 * is equivalent to the timeout of a TCP Connection
 146 * after "boundary" unsuccessful, exponentially backed-off
 147 * retransmissions with an initial RTO of TCP_RTO_MIN or TCP_TIMEOUT_INIT if
 148 * syn_set flag is set.
 149 *
 150 */
 151static bool retransmits_timed_out(struct sock *sk,
 152                                  unsigned int boundary,
 153                                  unsigned int timeout,
 154                                  bool syn_set)
 155{
 156        unsigned int linear_backoff_thresh, start_ts;
 157        unsigned int rto_base = syn_set ? TCP_TIMEOUT_INIT : TCP_RTO_MIN;
 158
 159        if (!inet_csk(sk)->icsk_retransmits)
 160                return false;
 161
 162        start_ts = tcp_sk(sk)->retrans_stamp;
 163        if (unlikely(!start_ts))
 164                start_ts = tcp_skb_timestamp(tcp_write_queue_head(sk));
 165
 166        if (likely(timeout == 0)) {
 167                linear_backoff_thresh = ilog2(TCP_RTO_MAX/rto_base);
 168
 169                if (boundary <= linear_backoff_thresh)
 170                        timeout = ((2 << boundary) - 1) * rto_base;
 171                else
 172                        timeout = ((2 << linear_backoff_thresh) - 1) * rto_base +
 173                                (boundary - linear_backoff_thresh) * TCP_RTO_MAX;
 174        }
 175        return (tcp_time_stamp - start_ts) >= timeout;
 176}
 177
 178/* A write timeout has occurred. Process the after effects. */
 179static int tcp_write_timeout(struct sock *sk)
 180{
 181        struct inet_connection_sock *icsk = inet_csk(sk);
 182        struct tcp_sock *tp = tcp_sk(sk);
 183        struct net *net = sock_net(sk);
 184        int retry_until;
 185        bool do_reset, syn_set = false;
 186
 187        if ((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV)) {
 188                if (icsk->icsk_retransmits) {
 189                        dst_negative_advice(sk);
 190                        if (tp->syn_fastopen || tp->syn_data)
 191                                tcp_fastopen_cache_set(sk, 0, NULL, true, 0);
 192                        if (tp->syn_data && icsk->icsk_retransmits == 1)
 193                                NET_INC_STATS(sock_net(sk),
 194                                              LINUX_MIB_TCPFASTOPENACTIVEFAIL);
 195                }
 196                retry_until = icsk->icsk_syn_retries ? : net->ipv4.sysctl_tcp_syn_retries;
 197                syn_set = true;
 198        } else {
 199                if (retransmits_timed_out(sk, net->ipv4.sysctl_tcp_retries1, 0, 0)) {
 200                        /* Some middle-boxes may black-hole Fast Open _after_
 201                         * the handshake. Therefore we conservatively disable
 202                         * Fast Open on this path on recurring timeouts with
 203                         * few or zero bytes acked after Fast Open.
 204                         */
 205                        if (tp->syn_data_acked &&
 206                            tp->bytes_acked <= tp->rx_opt.mss_clamp) {
 207                                tcp_fastopen_cache_set(sk, 0, NULL, true, 0);
 208                                if (icsk->icsk_retransmits == net->ipv4.sysctl_tcp_retries1)
 209                                        NET_INC_STATS(sock_net(sk),
 210                                                      LINUX_MIB_TCPFASTOPENACTIVEFAIL);
 211                        }
 212                        /* Black hole detection */
 213                        tcp_mtu_probing(icsk, sk);
 214
 215                        dst_negative_advice(sk);
 216                }
 217
 218                retry_until = net->ipv4.sysctl_tcp_retries2;
 219                if (sock_flag(sk, SOCK_DEAD)) {
 220                        const bool alive = icsk->icsk_rto < TCP_RTO_MAX;
 221
 222                        retry_until = tcp_orphan_retries(sk, alive);
 223                        do_reset = alive ||
 224                                !retransmits_timed_out(sk, retry_until, 0, 0);
 225
 226                        if (tcp_out_of_resources(sk, do_reset))
 227                                return 1;
 228                }
 229        }
 230
 231        if (retransmits_timed_out(sk, retry_until,
 232                                  syn_set ? 0 : icsk->icsk_user_timeout, syn_set)) {
 233                /* Has it gone just too far? */
 234                tcp_write_err(sk);
 235                return 1;
 236        }
 237        return 0;
 238}
 239
 240/* Called with BH disabled */
 241void tcp_delack_timer_handler(struct sock *sk)
 242{
 243        struct tcp_sock *tp = tcp_sk(sk);
 244        struct inet_connection_sock *icsk = inet_csk(sk);
 245
 246        sk_mem_reclaim_partial(sk);
 247
 248        if (sk->sk_state == TCP_CLOSE || !(icsk->icsk_ack.pending & ICSK_ACK_TIMER))
 249                goto out;
 250
 251        if (time_after(icsk->icsk_ack.timeout, jiffies)) {
 252                sk_reset_timer(sk, &icsk->icsk_delack_timer, icsk->icsk_ack.timeout);
 253                goto out;
 254        }
 255        icsk->icsk_ack.pending &= ~ICSK_ACK_TIMER;
 256
 257        if (!skb_queue_empty(&tp->ucopy.prequeue)) {
 258                struct sk_buff *skb;
 259
 260                __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPSCHEDULERFAILED);
 261
 262                while ((skb = __skb_dequeue(&tp->ucopy.prequeue)) != NULL)
 263                        sk_backlog_rcv(sk, skb);
 264
 265                tp->ucopy.memory = 0;
 266        }
 267
 268        if (inet_csk_ack_scheduled(sk)) {
 269                if (!icsk->icsk_ack.pingpong) {
 270                        /* Delayed ACK missed: inflate ATO. */
 271                        icsk->icsk_ack.ato = min(icsk->icsk_ack.ato << 1, icsk->icsk_rto);
 272                } else {
 273                        /* Delayed ACK missed: leave pingpong mode and
 274                         * deflate ATO.
 275                         */
 276                        icsk->icsk_ack.pingpong = 0;
 277                        icsk->icsk_ack.ato      = TCP_ATO_MIN;
 278                }
 279                tcp_send_ack(sk);
 280                __NET_INC_STATS(sock_net(sk), LINUX_MIB_DELAYEDACKS);
 281        }
 282
 283out:
 284        if (tcp_under_memory_pressure(sk))
 285                sk_mem_reclaim(sk);
 286}
 287
 288
 289/**
 290 *  tcp_delack_timer() - The TCP delayed ACK timeout handler
 291 *  @data:  Pointer to the current socket. (gets casted to struct sock *)
 292 *
 293 *  This function gets (indirectly) called when the kernel timer for a TCP packet
 294 *  of this socket expires. Calls tcp_delack_timer_handler() to do the actual work.
 295 *
 296 *  Returns: Nothing (void)
 297 */
 298static void tcp_delack_timer(unsigned long data)
 299{
 300        struct sock *sk = (struct sock *)data;
 301
 302        bh_lock_sock(sk);
 303        if (!sock_owned_by_user(sk)) {
 304                tcp_delack_timer_handler(sk);
 305        } else {
 306                inet_csk(sk)->icsk_ack.blocked = 1;
 307                __NET_INC_STATS(sock_net(sk), LINUX_MIB_DELAYEDACKLOCKED);
 308                /* deleguate our work to tcp_release_cb() */
 309                if (!test_and_set_bit(TCP_DELACK_TIMER_DEFERRED, &tcp_sk(sk)->tsq_flags))
 310                        sock_hold(sk);
 311        }
 312        bh_unlock_sock(sk);
 313        sock_put(sk);
 314}
 315
 316static void tcp_probe_timer(struct sock *sk)
 317{
 318        struct inet_connection_sock *icsk = inet_csk(sk);
 319        struct tcp_sock *tp = tcp_sk(sk);
 320        int max_probes;
 321        u32 start_ts;
 322
 323        if (tp->packets_out || !tcp_send_head(sk)) {
 324                icsk->icsk_probes_out = 0;
 325                return;
 326        }
 327
 328        /* RFC 1122 4.2.2.17 requires the sender to stay open indefinitely as
 329         * long as the receiver continues to respond probes. We support this by
 330         * default and reset icsk_probes_out with incoming ACKs. But if the
 331         * socket is orphaned or the user specifies TCP_USER_TIMEOUT, we
 332         * kill the socket when the retry count and the time exceeds the
 333         * corresponding system limit. We also implement similar policy when
 334         * we use RTO to probe window in tcp_retransmit_timer().
 335         */
 336        start_ts = tcp_skb_timestamp(tcp_send_head(sk));
 337        if (!start_ts)
 338                skb_mstamp_get(&tcp_send_head(sk)->skb_mstamp);
 339        else if (icsk->icsk_user_timeout &&
 340                 (s32)(tcp_time_stamp - start_ts) > icsk->icsk_user_timeout)
 341                goto abort;
 342
 343        max_probes = sock_net(sk)->ipv4.sysctl_tcp_retries2;
 344        if (sock_flag(sk, SOCK_DEAD)) {
 345                const bool alive = inet_csk_rto_backoff(icsk, TCP_RTO_MAX) < TCP_RTO_MAX;
 346
 347                max_probes = tcp_orphan_retries(sk, alive);
 348                if (!alive && icsk->icsk_backoff >= max_probes)
 349                        goto abort;
 350                if (tcp_out_of_resources(sk, true))
 351                        return;
 352        }
 353
 354        if (icsk->icsk_probes_out > max_probes) {
 355abort:          tcp_write_err(sk);
 356        } else {
 357                /* Only send another probe if we didn't close things up. */
 358                tcp_send_probe0(sk);
 359        }
 360}
 361
 362/*
 363 *      Timer for Fast Open socket to retransmit SYNACK. Note that the
 364 *      sk here is the child socket, not the parent (listener) socket.
 365 */
 366static void tcp_fastopen_synack_timer(struct sock *sk)
 367{
 368        struct inet_connection_sock *icsk = inet_csk(sk);
 369        int max_retries = icsk->icsk_syn_retries ? :
 370            sock_net(sk)->ipv4.sysctl_tcp_synack_retries + 1; /* add one more retry for fastopen */
 371        struct request_sock *req;
 372
 373        req = tcp_sk(sk)->fastopen_rsk;
 374        req->rsk_ops->syn_ack_timeout(req);
 375
 376        if (req->num_timeout >= max_retries) {
 377                tcp_write_err(sk);
 378                return;
 379        }
 380        /* XXX (TFO) - Unlike regular SYN-ACK retransmit, we ignore error
 381         * returned from rtx_syn_ack() to make it more persistent like
 382         * regular retransmit because if the child socket has been accepted
 383         * it's not good to give up too easily.
 384         */
 385        inet_rtx_syn_ack(sk, req);
 386        req->num_timeout++;
 387        icsk->icsk_retransmits++;
 388        inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
 389                          TCP_TIMEOUT_INIT << req->num_timeout, TCP_RTO_MAX);
 390}
 391
 392
 393/**
 394 *  tcp_retransmit_timer() - The TCP retransmit timeout handler
 395 *  @sk:  Pointer to the current socket.
 396 *
 397 *  This function gets called when the kernel timer for a TCP packet
 398 *  of this socket expires.
 399 *
 400 *  It handles retransmission, timer adjustment and other necesarry measures.
 401 *
 402 *  Returns: Nothing (void)
 403 */
 404void tcp_retransmit_timer(struct sock *sk)
 405{
 406        struct tcp_sock *tp = tcp_sk(sk);
 407        struct net *net = sock_net(sk);
 408        struct inet_connection_sock *icsk = inet_csk(sk);
 409
 410        if (tp->fastopen_rsk) {
 411                WARN_ON_ONCE(sk->sk_state != TCP_SYN_RECV &&
 412                             sk->sk_state != TCP_FIN_WAIT1);
 413                tcp_fastopen_synack_timer(sk);
 414                /* Before we receive ACK to our SYN-ACK don't retransmit
 415                 * anything else (e.g., data or FIN segments).
 416                 */
 417                return;
 418        }
 419        if (!tp->packets_out)
 420                goto out;
 421
 422        WARN_ON(tcp_write_queue_empty(sk));
 423
 424        tp->tlp_high_seq = 0;
 425
 426        if (!tp->snd_wnd && !sock_flag(sk, SOCK_DEAD) &&
 427            !((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV))) {
 428                /* Receiver dastardly shrinks window. Our retransmits
 429                 * become zero probes, but we should not timeout this
 430                 * connection. If the socket is an orphan, time it out,
 431                 * we cannot allow such beasts to hang infinitely.
 432                 */
 433                struct inet_sock *inet = inet_sk(sk);
 434                if (sk->sk_family == AF_INET) {
 435                        net_dbg_ratelimited("Peer %pI4:%u/%u unexpectedly shrunk window %u:%u (repaired)\n",
 436                                            &inet->inet_daddr,
 437                                            ntohs(inet->inet_dport),
 438                                            inet->inet_num,
 439                                            tp->snd_una, tp->snd_nxt);
 440                }
 441#if IS_ENABLED(CONFIG_IPV6)
 442                else if (sk->sk_family == AF_INET6) {
 443                        net_dbg_ratelimited("Peer %pI6:%u/%u unexpectedly shrunk window %u:%u (repaired)\n",
 444                                            &sk->sk_v6_daddr,
 445                                            ntohs(inet->inet_dport),
 446                                            inet->inet_num,
 447                                            tp->snd_una, tp->snd_nxt);
 448                }
 449#endif
 450                if (tcp_time_stamp - tp->rcv_tstamp > TCP_RTO_MAX) {
 451                        tcp_write_err(sk);
 452                        goto out;
 453                }
 454                tcp_enter_loss(sk);
 455                tcp_retransmit_skb(sk, tcp_write_queue_head(sk), 1);
 456                __sk_dst_reset(sk);
 457                goto out_reset_timer;
 458        }
 459
 460        if (tcp_write_timeout(sk))
 461                goto out;
 462
 463        if (icsk->icsk_retransmits == 0) {
 464                int mib_idx;
 465
 466                if (icsk->icsk_ca_state == TCP_CA_Recovery) {
 467                        if (tcp_is_sack(tp))
 468                                mib_idx = LINUX_MIB_TCPSACKRECOVERYFAIL;
 469                        else
 470                                mib_idx = LINUX_MIB_TCPRENORECOVERYFAIL;
 471                } else if (icsk->icsk_ca_state == TCP_CA_Loss) {
 472                        mib_idx = LINUX_MIB_TCPLOSSFAILURES;
 473                } else if ((icsk->icsk_ca_state == TCP_CA_Disorder) ||
 474                           tp->sacked_out) {
 475                        if (tcp_is_sack(tp))
 476                                mib_idx = LINUX_MIB_TCPSACKFAILURES;
 477                        else
 478                                mib_idx = LINUX_MIB_TCPRENOFAILURES;
 479                } else {
 480                        mib_idx = LINUX_MIB_TCPTIMEOUTS;
 481                }
 482                __NET_INC_STATS(sock_net(sk), mib_idx);
 483        }
 484
 485        tcp_enter_loss(sk);
 486
 487        if (tcp_retransmit_skb(sk, tcp_write_queue_head(sk), 1) > 0) {
 488                /* Retransmission failed because of local congestion,
 489                 * do not backoff.
 490                 */
 491                if (!icsk->icsk_retransmits)
 492                        icsk->icsk_retransmits = 1;
 493                inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
 494                                          min(icsk->icsk_rto, TCP_RESOURCE_PROBE_INTERVAL),
 495                                          TCP_RTO_MAX);
 496                goto out;
 497        }
 498
 499        /* Increase the timeout each time we retransmit.  Note that
 500         * we do not increase the rtt estimate.  rto is initialized
 501         * from rtt, but increases here.  Jacobson (SIGCOMM 88) suggests
 502         * that doubling rto each time is the least we can get away with.
 503         * In KA9Q, Karn uses this for the first few times, and then
 504         * goes to quadratic.  netBSD doubles, but only goes up to *64,
 505         * and clamps at 1 to 64 sec afterwards.  Note that 120 sec is
 506         * defined in the protocol as the maximum possible RTT.  I guess
 507         * we'll have to use something other than TCP to talk to the
 508         * University of Mars.
 509         *
 510         * PAWS allows us longer timeouts and large windows, so once
 511         * implemented ftp to mars will work nicely. We will have to fix
 512         * the 120 second clamps though!
 513         */
 514        icsk->icsk_backoff++;
 515        icsk->icsk_retransmits++;
 516
 517out_reset_timer:
 518        /* If stream is thin, use linear timeouts. Since 'icsk_backoff' is
 519         * used to reset timer, set to 0. Recalculate 'icsk_rto' as this
 520         * might be increased if the stream oscillates between thin and thick,
 521         * thus the old value might already be too high compared to the value
 522         * set by 'tcp_set_rto' in tcp_input.c which resets the rto without
 523         * backoff. Limit to TCP_THIN_LINEAR_RETRIES before initiating
 524         * exponential backoff behaviour to avoid continue hammering
 525         * linear-timeout retransmissions into a black hole
 526         */
 527        if (sk->sk_state == TCP_ESTABLISHED &&
 528            (tp->thin_lto || sysctl_tcp_thin_linear_timeouts) &&
 529            tcp_stream_is_thin(tp) &&
 530            icsk->icsk_retransmits <= TCP_THIN_LINEAR_RETRIES) {
 531                icsk->icsk_backoff = 0;
 532                icsk->icsk_rto = min(__tcp_set_rto(tp), TCP_RTO_MAX);
 533        } else {
 534                /* Use normal (exponential) backoff */
 535                icsk->icsk_rto = min(icsk->icsk_rto << 1, TCP_RTO_MAX);
 536        }
 537        inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, icsk->icsk_rto, TCP_RTO_MAX);
 538        if (retransmits_timed_out(sk, net->ipv4.sysctl_tcp_retries1 + 1, 0, 0))
 539                __sk_dst_reset(sk);
 540
 541out:;
 542}
 543
 544/* Called with bottom-half processing disabled.
 545   Called by tcp_write_timer() */
 546void tcp_write_timer_handler(struct sock *sk)
 547{
 548        struct inet_connection_sock *icsk = inet_csk(sk);
 549        int event;
 550
 551        if (sk->sk_state == TCP_CLOSE || !icsk->icsk_pending)
 552                goto out;
 553
 554        if (time_after(icsk->icsk_timeout, jiffies)) {
 555                sk_reset_timer(sk, &icsk->icsk_retransmit_timer, icsk->icsk_timeout);
 556                goto out;
 557        }
 558
 559        event = icsk->icsk_pending;
 560
 561        switch (event) {
 562        case ICSK_TIME_EARLY_RETRANS:
 563                tcp_resume_early_retransmit(sk);
 564                break;
 565        case ICSK_TIME_LOSS_PROBE:
 566                tcp_send_loss_probe(sk);
 567                break;
 568        case ICSK_TIME_RETRANS:
 569                icsk->icsk_pending = 0;
 570                tcp_retransmit_timer(sk);
 571                break;
 572        case ICSK_TIME_PROBE0:
 573                icsk->icsk_pending = 0;
 574                tcp_probe_timer(sk);
 575                break;
 576        }
 577
 578out:
 579        sk_mem_reclaim(sk);
 580}
 581
 582static void tcp_write_timer(unsigned long data)
 583{
 584        struct sock *sk = (struct sock *)data;
 585
 586        bh_lock_sock(sk);
 587        if (!sock_owned_by_user(sk)) {
 588                tcp_write_timer_handler(sk);
 589        } else {
 590                /* delegate our work to tcp_release_cb() */
 591                if (!test_and_set_bit(TCP_WRITE_TIMER_DEFERRED, &tcp_sk(sk)->tsq_flags))
 592                        sock_hold(sk);
 593        }
 594        bh_unlock_sock(sk);
 595        sock_put(sk);
 596}
 597
 598void tcp_syn_ack_timeout(const struct request_sock *req)
 599{
 600        struct net *net = read_pnet(&inet_rsk(req)->ireq_net);
 601
 602        __NET_INC_STATS(net, LINUX_MIB_TCPTIMEOUTS);
 603}
 604EXPORT_SYMBOL(tcp_syn_ack_timeout);
 605
 606void tcp_set_keepalive(struct sock *sk, int val)
 607{
 608        if ((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN))
 609                return;
 610
 611        if (val && !sock_flag(sk, SOCK_KEEPOPEN))
 612                inet_csk_reset_keepalive_timer(sk, keepalive_time_when(tcp_sk(sk)));
 613        else if (!val)
 614                inet_csk_delete_keepalive_timer(sk);
 615}
 616
 617
 618static void tcp_keepalive_timer (unsigned long data)
 619{
 620        struct sock *sk = (struct sock *) data;
 621        struct inet_connection_sock *icsk = inet_csk(sk);
 622        struct tcp_sock *tp = tcp_sk(sk);
 623        u32 elapsed;
 624
 625        /* Only process if socket is not in use. */
 626        bh_lock_sock(sk);
 627        if (sock_owned_by_user(sk)) {
 628                /* Try again later. */
 629                inet_csk_reset_keepalive_timer (sk, HZ/20);
 630                goto out;
 631        }
 632
 633        if (sk->sk_state == TCP_LISTEN) {
 634                pr_err("Hmm... keepalive on a LISTEN ???\n");
 635                goto out;
 636        }
 637
 638        if (sk->sk_state == TCP_FIN_WAIT2 && sock_flag(sk, SOCK_DEAD)) {
 639                if (tp->linger2 >= 0) {
 640                        const int tmo = tcp_fin_time(sk) - TCP_TIMEWAIT_LEN;
 641
 642                        if (tmo > 0) {
 643                                tcp_time_wait(sk, TCP_FIN_WAIT2, tmo);
 644                                goto out;
 645                        }
 646                }
 647                tcp_send_active_reset(sk, GFP_ATOMIC);
 648                goto death;
 649        }
 650
 651        if (!sock_flag(sk, SOCK_KEEPOPEN) || sk->sk_state == TCP_CLOSE)
 652                goto out;
 653
 654        elapsed = keepalive_time_when(tp);
 655
 656        /* It is alive without keepalive 8) */
 657        if (tp->packets_out || tcp_send_head(sk))
 658                goto resched;
 659
 660        elapsed = keepalive_time_elapsed(tp);
 661
 662        if (elapsed >= keepalive_time_when(tp)) {
 663                /* If the TCP_USER_TIMEOUT option is enabled, use that
 664                 * to determine when to timeout instead.
 665                 */
 666                if ((icsk->icsk_user_timeout != 0 &&
 667                    elapsed >= icsk->icsk_user_timeout &&
 668                    icsk->icsk_probes_out > 0) ||
 669                    (icsk->icsk_user_timeout == 0 &&
 670                    icsk->icsk_probes_out >= keepalive_probes(tp))) {
 671                        tcp_send_active_reset(sk, GFP_ATOMIC);
 672                        tcp_write_err(sk);
 673                        goto out;
 674                }
 675                if (tcp_write_wakeup(sk, LINUX_MIB_TCPKEEPALIVE) <= 0) {
 676                        icsk->icsk_probes_out++;
 677                        elapsed = keepalive_intvl_when(tp);
 678                } else {
 679                        /* If keepalive was lost due to local congestion,
 680                         * try harder.
 681                         */
 682                        elapsed = TCP_RESOURCE_PROBE_INTERVAL;
 683                }
 684        } else {
 685                /* It is tp->rcv_tstamp + keepalive_time_when(tp) */
 686                elapsed = keepalive_time_when(tp) - elapsed;
 687        }
 688
 689        sk_mem_reclaim(sk);
 690
 691resched:
 692        inet_csk_reset_keepalive_timer (sk, elapsed);
 693        goto out;
 694
 695death:
 696        tcp_done(sk);
 697
 698out:
 699        bh_unlock_sock(sk);
 700        sock_put(sk);
 701}
 702
 703void tcp_init_xmit_timers(struct sock *sk)
 704{
 705        inet_csk_init_xmit_timers(sk, &tcp_write_timer, &tcp_delack_timer,
 706                                  &tcp_keepalive_timer);
 707}
 708
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