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