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_syn_retries __read_mostly = TCP_SYN_RETRIES;
  26int sysctl_tcp_synack_retries __read_mostly = TCP_SYNACK_RETRIES;
  27int sysctl_tcp_keepalive_time __read_mostly = TCP_KEEPALIVE_TIME;
  28int sysctl_tcp_keepalive_probes __read_mostly = TCP_KEEPALIVE_PROBES;
  29int sysctl_tcp_keepalive_intvl __read_mostly = TCP_KEEPALIVE_INTVL;
  30int sysctl_tcp_retries1 __read_mostly = TCP_RETR1;
  31int sysctl_tcp_retries2 __read_mostly = TCP_RETR2;
  32int sysctl_tcp_orphan_retries __read_mostly;
  33int sysctl_tcp_thin_linear_timeouts __read_mostly;
  34
  35static void tcp_write_err(struct sock *sk)
  36{
  37        sk->sk_err = sk->sk_err_soft ? : ETIMEDOUT;
  38        sk->sk_error_report(sk);
  39
  40        tcp_done(sk);
  41        NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPABORTONTIMEOUT);
  42}
  43
  44/* Do not allow orphaned sockets to eat all our resources.
  45 * This is direct violation of TCP specs, but it is required
  46 * to prevent DoS attacks. It is called when a retransmission timeout
  47 * or zero probe timeout occurs on orphaned socket.
  48 *
  49 * Criteria is still not confirmed experimentally and may change.
  50 * We kill the socket, if:
  51 * 1. If number of orphaned sockets exceeds an administratively configured
  52 *    limit.
  53 * 2. If we have strong memory pressure.
  54 */
  55static int tcp_out_of_resources(struct sock *sk, int do_reset)
  56{
  57        struct tcp_sock *tp = tcp_sk(sk);
  58        int shift = 0;
  59
  60        /* If peer does not open window for long time, or did not transmit
  61         * anything for long time, penalize it. */
  62        if ((s32)(tcp_time_stamp - tp->lsndtime) > 2*TCP_RTO_MAX || !do_reset)
  63                shift++;
  64
  65        /* If some dubious ICMP arrived, penalize even more. */
  66        if (sk->sk_err_soft)
  67                shift++;
  68
  69        if (tcp_check_oom(sk, shift)) {
  70                /* Catch exceptional cases, when connection requires reset.
  71                 *      1. Last segment was sent recently. */
  72                if ((s32)(tcp_time_stamp - tp->lsndtime) <= TCP_TIMEWAIT_LEN ||
  73                    /*  2. Window is closed. */
  74                    (!tp->snd_wnd && !tp->packets_out))
  75                        do_reset = 1;
  76                if (do_reset)
  77                        tcp_send_active_reset(sk, GFP_ATOMIC);
  78                tcp_done(sk);
  79                NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPABORTONMEMORY);
  80                return 1;
  81        }
  82        return 0;
  83}
  84
  85/* Calculate maximal number or retries on an orphaned socket. */
  86static int tcp_orphan_retries(struct sock *sk, int alive)
  87{
  88        int retries = sysctl_tcp_orphan_retries; /* May be zero. */
  89
  90        /* We know from an ICMP that something is wrong. */
  91        if (sk->sk_err_soft && !alive)
  92                retries = 0;
  93
  94        /* However, if socket sent something recently, select some safe
  95         * number of retries. 8 corresponds to >100 seconds with minimal
  96         * RTO of 200msec. */
  97        if (retries == 0 && alive)
  98                retries = 8;
  99        return retries;
 100}
 101
 102static void tcp_mtu_probing(struct inet_connection_sock *icsk, struct sock *sk)
 103{
 104        /* Black hole detection */
 105        if (sysctl_tcp_mtu_probing) {
 106                if (!icsk->icsk_mtup.enabled) {
 107                        icsk->icsk_mtup.enabled = 1;
 108                        tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
 109                } else {
 110                        struct tcp_sock *tp = tcp_sk(sk);
 111                        int mss;
 112
 113                        mss = tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low) >> 1;
 114                        mss = min(sysctl_tcp_base_mss, mss);
 115                        mss = max(mss, 68 - tp->tcp_header_len);
 116                        icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, mss);
 117                        tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
 118                }
 119        }
 120}
 121
 122/* This function calculates a "timeout" which is equivalent to the timeout of a
 123 * TCP connection after "boundary" unsuccessful, exponentially backed-off
 124 * retransmissions with an initial RTO of TCP_RTO_MIN or TCP_TIMEOUT_INIT if
 125 * syn_set flag is set.
 126 */
 127static bool retransmits_timed_out(struct sock *sk,
 128                                  unsigned int boundary,
 129                                  unsigned int timeout,
 130                                  bool syn_set)
 131{
 132        unsigned int linear_backoff_thresh, start_ts;
 133        unsigned int rto_base = syn_set ? TCP_TIMEOUT_INIT : TCP_RTO_MIN;
 134
 135        if (!inet_csk(sk)->icsk_retransmits)
 136                return false;
 137
 138        if (unlikely(!tcp_sk(sk)->retrans_stamp))
 139                start_ts = TCP_SKB_CB(tcp_write_queue_head(sk))->when;
 140        else
 141                start_ts = tcp_sk(sk)->retrans_stamp;
 142
 143        if (likely(timeout == 0)) {
 144                linear_backoff_thresh = ilog2(TCP_RTO_MAX/rto_base);
 145
 146                if (boundary <= linear_backoff_thresh)
 147                        timeout = ((2 << boundary) - 1) * rto_base;
 148                else
 149                        timeout = ((2 << linear_backoff_thresh) - 1) * rto_base +
 150                                (boundary - linear_backoff_thresh) * TCP_RTO_MAX;
 151        }
 152        return (tcp_time_stamp - start_ts) >= timeout;
 153}
 154
 155/* A write timeout has occurred. Process the after effects. */
 156static int tcp_write_timeout(struct sock *sk)
 157{
 158        struct inet_connection_sock *icsk = inet_csk(sk);
 159        struct tcp_sock *tp = tcp_sk(sk);
 160        int retry_until;
 161        bool do_reset, syn_set = false;
 162
 163        if ((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV)) {
 164                if (icsk->icsk_retransmits) {
 165                        dst_negative_advice(sk);
 166                        if (tp->syn_fastopen || tp->syn_data)
 167                                tcp_fastopen_cache_set(sk, 0, NULL, true);
 168                }
 169                retry_until = icsk->icsk_syn_retries ? : sysctl_tcp_syn_retries;
 170                syn_set = true;
 171        } else {
 172                if (retransmits_timed_out(sk, sysctl_tcp_retries1, 0, 0)) {
 173                        /* Black hole detection */
 174                        tcp_mtu_probing(icsk, sk);
 175
 176                        dst_negative_advice(sk);
 177                }
 178
 179                retry_until = sysctl_tcp_retries2;
 180                if (sock_flag(sk, SOCK_DEAD)) {
 181                        const int alive = (icsk->icsk_rto < TCP_RTO_MAX);
 182
 183                        retry_until = tcp_orphan_retries(sk, alive);
 184                        do_reset = alive ||
 185                                !retransmits_timed_out(sk, retry_until, 0, 0);
 186
 187                        if (tcp_out_of_resources(sk, do_reset))
 188                                return 1;
 189                }
 190        }
 191
 192        if (retransmits_timed_out(sk, retry_until,
 193                                  syn_set ? 0 : icsk->icsk_user_timeout, syn_set)) {
 194                /* Has it gone just too far? */
 195                tcp_write_err(sk);
 196                return 1;
 197        }
 198        return 0;
 199}
 200
 201void tcp_delack_timer_handler(struct sock *sk)
 202{
 203        struct tcp_sock *tp = tcp_sk(sk);
 204        struct inet_connection_sock *icsk = inet_csk(sk);
 205
 206        sk_mem_reclaim_partial(sk);
 207
 208        if (sk->sk_state == TCP_CLOSE || !(icsk->icsk_ack.pending & ICSK_ACK_TIMER))
 209                goto out;
 210
 211        if (time_after(icsk->icsk_ack.timeout, jiffies)) {
 212                sk_reset_timer(sk, &icsk->icsk_delack_timer, icsk->icsk_ack.timeout);
 213                goto out;
 214        }
 215        icsk->icsk_ack.pending &= ~ICSK_ACK_TIMER;
 216
 217        if (!skb_queue_empty(&tp->ucopy.prequeue)) {
 218                struct sk_buff *skb;
 219
 220                NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSCHEDULERFAILED);
 221
 222                while ((skb = __skb_dequeue(&tp->ucopy.prequeue)) != NULL)
 223                        sk_backlog_rcv(sk, skb);
 224
 225                tp->ucopy.memory = 0;
 226        }
 227
 228        if (inet_csk_ack_scheduled(sk)) {
 229                if (!icsk->icsk_ack.pingpong) {
 230                        /* Delayed ACK missed: inflate ATO. */
 231                        icsk->icsk_ack.ato = min(icsk->icsk_ack.ato << 1, icsk->icsk_rto);
 232                } else {
 233                        /* Delayed ACK missed: leave pingpong mode and
 234                         * deflate ATO.
 235                         */
 236                        icsk->icsk_ack.pingpong = 0;
 237                        icsk->icsk_ack.ato      = TCP_ATO_MIN;
 238                }
 239                tcp_send_ack(sk);
 240                NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKS);
 241        }
 242
 243out:
 244        if (sk_under_memory_pressure(sk))
 245                sk_mem_reclaim(sk);
 246}
 247
 248static void tcp_delack_timer(unsigned long data)
 249{
 250        struct sock *sk = (struct sock *)data;
 251
 252        bh_lock_sock(sk);
 253        if (!sock_owned_by_user(sk)) {
 254                tcp_delack_timer_handler(sk);
 255        } else {
 256                inet_csk(sk)->icsk_ack.blocked = 1;
 257                NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKLOCKED);
 258                /* deleguate our work to tcp_release_cb() */
 259                if (!test_and_set_bit(TCP_DELACK_TIMER_DEFERRED, &tcp_sk(sk)->tsq_flags))
 260                        sock_hold(sk);
 261        }
 262        bh_unlock_sock(sk);
 263        sock_put(sk);
 264}
 265
 266static void tcp_probe_timer(struct sock *sk)
 267{
 268        struct inet_connection_sock *icsk = inet_csk(sk);
 269        struct tcp_sock *tp = tcp_sk(sk);
 270        int max_probes;
 271
 272        if (tp->packets_out || !tcp_send_head(sk)) {
 273                icsk->icsk_probes_out = 0;
 274                return;
 275        }
 276
 277        /* *WARNING* RFC 1122 forbids this
 278         *
 279         * It doesn't AFAIK, because we kill the retransmit timer -AK
 280         *
 281         * FIXME: We ought not to do it, Solaris 2.5 actually has fixing
 282         * this behaviour in Solaris down as a bug fix. [AC]
 283         *
 284         * Let me to explain. icsk_probes_out is zeroed by incoming ACKs
 285         * even if they advertise zero window. Hence, connection is killed only
 286         * if we received no ACKs for normal connection timeout. It is not killed
 287         * only because window stays zero for some time, window may be zero
 288         * until armageddon and even later. We are in full accordance
 289         * with RFCs, only probe timer combines both retransmission timeout
 290         * and probe timeout in one bottle.                             --ANK
 291         */
 292        max_probes = sysctl_tcp_retries2;
 293
 294        if (sock_flag(sk, SOCK_DEAD)) {
 295                const int alive = ((icsk->icsk_rto << icsk->icsk_backoff) < TCP_RTO_MAX);
 296
 297                max_probes = tcp_orphan_retries(sk, alive);
 298
 299                if (tcp_out_of_resources(sk, alive || icsk->icsk_probes_out <= max_probes))
 300                        return;
 301        }
 302
 303        if (icsk->icsk_probes_out > max_probes) {
 304                tcp_write_err(sk);
 305        } else {
 306                /* Only send another probe if we didn't close things up. */
 307                tcp_send_probe0(sk);
 308        }
 309}
 310
 311/*
 312 *      Timer for Fast Open socket to retransmit SYNACK. Note that the
 313 *      sk here is the child socket, not the parent (listener) socket.
 314 */
 315static void tcp_fastopen_synack_timer(struct sock *sk)
 316{
 317        struct inet_connection_sock *icsk = inet_csk(sk);
 318        int max_retries = icsk->icsk_syn_retries ? :
 319            sysctl_tcp_synack_retries + 1; /* add one more retry for fastopen */
 320        struct request_sock *req;
 321
 322        req = tcp_sk(sk)->fastopen_rsk;
 323        req->rsk_ops->syn_ack_timeout(sk, req);
 324
 325        if (req->num_timeout >= max_retries) {
 326                tcp_write_err(sk);
 327                return;
 328        }
 329        /* XXX (TFO) - Unlike regular SYN-ACK retransmit, we ignore error
 330         * returned from rtx_syn_ack() to make it more persistent like
 331         * regular retransmit because if the child socket has been accepted
 332         * it's not good to give up too easily.
 333         */
 334        inet_rtx_syn_ack(sk, req);
 335        req->num_timeout++;
 336        inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
 337                          TCP_TIMEOUT_INIT << req->num_timeout, TCP_RTO_MAX);
 338}
 339
 340/*
 341 *      The TCP retransmit timer.
 342 */
 343
 344void tcp_retransmit_timer(struct sock *sk)
 345{
 346        struct tcp_sock *tp = tcp_sk(sk);
 347        struct inet_connection_sock *icsk = inet_csk(sk);
 348
 349        if (tp->fastopen_rsk) {
 350                WARN_ON_ONCE(sk->sk_state != TCP_SYN_RECV &&
 351                             sk->sk_state != TCP_FIN_WAIT1);
 352                tcp_fastopen_synack_timer(sk);
 353                /* Before we receive ACK to our SYN-ACK don't retransmit
 354                 * anything else (e.g., data or FIN segments).
 355                 */
 356                return;
 357        }
 358        if (!tp->packets_out)
 359                goto out;
 360
 361        WARN_ON(tcp_write_queue_empty(sk));
 362
 363        tp->tlp_high_seq = 0;
 364
 365        if (!tp->snd_wnd && !sock_flag(sk, SOCK_DEAD) &&
 366            !((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV))) {
 367                /* Receiver dastardly shrinks window. Our retransmits
 368                 * become zero probes, but we should not timeout this
 369                 * connection. If the socket is an orphan, time it out,
 370                 * we cannot allow such beasts to hang infinitely.
 371                 */
 372                struct inet_sock *inet = inet_sk(sk);
 373                if (sk->sk_family == AF_INET) {
 374                        LIMIT_NETDEBUG(KERN_DEBUG pr_fmt("Peer %pI4:%u/%u unexpectedly shrunk window %u:%u (repaired)\n"),
 375                                       &inet->inet_daddr,
 376                                       ntohs(inet->inet_dport), inet->inet_num,
 377                                       tp->snd_una, tp->snd_nxt);
 378                }
 379#if IS_ENABLED(CONFIG_IPV6)
 380                else if (sk->sk_family == AF_INET6) {
 381                        LIMIT_NETDEBUG(KERN_DEBUG pr_fmt("Peer %pI6:%u/%u unexpectedly shrunk window %u:%u (repaired)\n"),
 382                                       &sk->sk_v6_daddr,
 383                                       ntohs(inet->inet_dport), inet->inet_num,
 384                                       tp->snd_una, tp->snd_nxt);
 385                }
 386#endif
 387                if (tcp_time_stamp - tp->rcv_tstamp > TCP_RTO_MAX) {
 388                        tcp_write_err(sk);
 389                        goto out;
 390                }
 391                tcp_enter_loss(sk, 0);
 392                tcp_retransmit_skb(sk, tcp_write_queue_head(sk));
 393                __sk_dst_reset(sk);
 394                goto out_reset_timer;
 395        }
 396
 397        if (tcp_write_timeout(sk))
 398                goto out;
 399
 400        if (icsk->icsk_retransmits == 0) {
 401                int mib_idx;
 402
 403                if (icsk->icsk_ca_state == TCP_CA_Recovery) {
 404                        if (tcp_is_sack(tp))
 405                                mib_idx = LINUX_MIB_TCPSACKRECOVERYFAIL;
 406                        else
 407                                mib_idx = LINUX_MIB_TCPRENORECOVERYFAIL;
 408                } else if (icsk->icsk_ca_state == TCP_CA_Loss) {
 409                        mib_idx = LINUX_MIB_TCPLOSSFAILURES;
 410                } else if ((icsk->icsk_ca_state == TCP_CA_Disorder) ||
 411                           tp->sacked_out) {
 412                        if (tcp_is_sack(tp))
 413                                mib_idx = LINUX_MIB_TCPSACKFAILURES;
 414                        else
 415                                mib_idx = LINUX_MIB_TCPRENOFAILURES;
 416                } else {
 417                        mib_idx = LINUX_MIB_TCPTIMEOUTS;
 418                }
 419                NET_INC_STATS_BH(sock_net(sk), mib_idx);
 420        }
 421
 422        tcp_enter_loss(sk, 0);
 423
 424        if (tcp_retransmit_skb(sk, tcp_write_queue_head(sk)) > 0) {
 425                /* Retransmission failed because of local congestion,
 426                 * do not backoff.
 427                 */
 428                if (!icsk->icsk_retransmits)
 429                        icsk->icsk_retransmits = 1;
 430                inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
 431                                          min(icsk->icsk_rto, TCP_RESOURCE_PROBE_INTERVAL),
 432                                          TCP_RTO_MAX);
 433                goto out;
 434        }
 435
 436        /* Increase the timeout each time we retransmit.  Note that
 437         * we do not increase the rtt estimate.  rto is initialized
 438         * from rtt, but increases here.  Jacobson (SIGCOMM 88) suggests
 439         * that doubling rto each time is the least we can get away with.
 440         * In KA9Q, Karn uses this for the first few times, and then
 441         * goes to quadratic.  netBSD doubles, but only goes up to *64,
 442         * and clamps at 1 to 64 sec afterwards.  Note that 120 sec is
 443         * defined in the protocol as the maximum possible RTT.  I guess
 444         * we'll have to use something other than TCP to talk to the
 445         * University of Mars.
 446         *
 447         * PAWS allows us longer timeouts and large windows, so once
 448         * implemented ftp to mars will work nicely. We will have to fix
 449         * the 120 second clamps though!
 450         */
 451        icsk->icsk_backoff++;
 452        icsk->icsk_retransmits++;
 453
 454out_reset_timer:
 455        /* If stream is thin, use linear timeouts. Since 'icsk_backoff' is
 456         * used to reset timer, set to 0. Recalculate 'icsk_rto' as this
 457         * might be increased if the stream oscillates between thin and thick,
 458         * thus the old value might already be too high compared to the value
 459         * set by 'tcp_set_rto' in tcp_input.c which resets the rto without
 460         * backoff. Limit to TCP_THIN_LINEAR_RETRIES before initiating
 461         * exponential backoff behaviour to avoid continue hammering
 462         * linear-timeout retransmissions into a black hole
 463         */
 464        if (sk->sk_state == TCP_ESTABLISHED &&
 465            (tp->thin_lto || sysctl_tcp_thin_linear_timeouts) &&
 466            tcp_stream_is_thin(tp) &&
 467            icsk->icsk_retransmits <= TCP_THIN_LINEAR_RETRIES) {
 468                icsk->icsk_backoff = 0;
 469                icsk->icsk_rto = min(__tcp_set_rto(tp), TCP_RTO_MAX);
 470        } else {
 471                /* Use normal (exponential) backoff */
 472                icsk->icsk_rto = min(icsk->icsk_rto << 1, TCP_RTO_MAX);
 473        }
 474        inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, icsk->icsk_rto, TCP_RTO_MAX);
 475        if (retransmits_timed_out(sk, sysctl_tcp_retries1 + 1, 0, 0))
 476                __sk_dst_reset(sk);
 477
 478out:;
 479}
 480
 481void tcp_write_timer_handler(struct sock *sk)
 482{
 483        struct inet_connection_sock *icsk = inet_csk(sk);
 484        int event;
 485
 486        if (sk->sk_state == TCP_CLOSE || !icsk->icsk_pending)
 487                goto out;
 488
 489        if (time_after(icsk->icsk_timeout, jiffies)) {
 490                sk_reset_timer(sk, &icsk->icsk_retransmit_timer, icsk->icsk_timeout);
 491                goto out;
 492        }
 493
 494        event = icsk->icsk_pending;
 495
 496        switch (event) {
 497        case ICSK_TIME_EARLY_RETRANS:
 498                tcp_resume_early_retransmit(sk);
 499                break;
 500        case ICSK_TIME_LOSS_PROBE:
 501                tcp_send_loss_probe(sk);
 502                break;
 503        case ICSK_TIME_RETRANS:
 504                icsk->icsk_pending = 0;
 505                tcp_retransmit_timer(sk);
 506                break;
 507        case ICSK_TIME_PROBE0:
 508                icsk->icsk_pending = 0;
 509                tcp_probe_timer(sk);
 510                break;
 511        }
 512
 513out:
 514        sk_mem_reclaim(sk);
 515}
 516
 517static void tcp_write_timer(unsigned long data)
 518{
 519        struct sock *sk = (struct sock *)data;
 520
 521        bh_lock_sock(sk);
 522        if (!sock_owned_by_user(sk)) {
 523                tcp_write_timer_handler(sk);
 524        } else {
 525                /* deleguate our work to tcp_release_cb() */
 526                if (!test_and_set_bit(TCP_WRITE_TIMER_DEFERRED, &tcp_sk(sk)->tsq_flags))
 527                        sock_hold(sk);
 528        }
 529        bh_unlock_sock(sk);
 530        sock_put(sk);
 531}
 532
 533/*
 534 *      Timer for listening sockets
 535 */
 536
 537static void tcp_synack_timer(struct sock *sk)
 538{
 539        inet_csk_reqsk_queue_prune(sk, TCP_SYNQ_INTERVAL,
 540                                   TCP_TIMEOUT_INIT, TCP_RTO_MAX);
 541}
 542
 543void tcp_syn_ack_timeout(struct sock *sk, struct request_sock *req)
 544{
 545        NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPTIMEOUTS);
 546}
 547EXPORT_SYMBOL(tcp_syn_ack_timeout);
 548
 549void tcp_set_keepalive(struct sock *sk, int val)
 550{
 551        if ((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN))
 552                return;
 553
 554        if (val && !sock_flag(sk, SOCK_KEEPOPEN))
 555                inet_csk_reset_keepalive_timer(sk, keepalive_time_when(tcp_sk(sk)));
 556        else if (!val)
 557                inet_csk_delete_keepalive_timer(sk);
 558}
 559
 560
 561static void tcp_keepalive_timer (unsigned long data)
 562{
 563        struct sock *sk = (struct sock *) data;
 564        struct inet_connection_sock *icsk = inet_csk(sk);
 565        struct tcp_sock *tp = tcp_sk(sk);
 566        u32 elapsed;
 567
 568        /* Only process if socket is not in use. */
 569        bh_lock_sock(sk);
 570        if (sock_owned_by_user(sk)) {
 571                /* Try again later. */
 572                inet_csk_reset_keepalive_timer (sk, HZ/20);
 573                goto out;
 574        }
 575
 576        if (sk->sk_state == TCP_LISTEN) {
 577                tcp_synack_timer(sk);
 578                goto out;
 579        }
 580
 581        if (sk->sk_state == TCP_FIN_WAIT2 && sock_flag(sk, SOCK_DEAD)) {
 582                if (tp->linger2 >= 0) {
 583                        const int tmo = tcp_fin_time(sk) - TCP_TIMEWAIT_LEN;
 584
 585                        if (tmo > 0) {
 586                                tcp_time_wait(sk, TCP_FIN_WAIT2, tmo);
 587                                goto out;
 588                        }
 589                }
 590                tcp_send_active_reset(sk, GFP_ATOMIC);
 591                goto death;
 592        }
 593
 594        if (!sock_flag(sk, SOCK_KEEPOPEN) || sk->sk_state == TCP_CLOSE)
 595                goto out;
 596
 597        elapsed = keepalive_time_when(tp);
 598
 599        /* It is alive without keepalive 8) */
 600        if (tp->packets_out || tcp_send_head(sk))
 601                goto resched;
 602
 603        elapsed = keepalive_time_elapsed(tp);
 604
 605        if (elapsed >= keepalive_time_when(tp)) {
 606                /* If the TCP_USER_TIMEOUT option is enabled, use that
 607                 * to determine when to timeout instead.
 608                 */
 609                if ((icsk->icsk_user_timeout != 0 &&
 610                    elapsed >= icsk->icsk_user_timeout &&
 611                    icsk->icsk_probes_out > 0) ||
 612                    (icsk->icsk_user_timeout == 0 &&
 613                    icsk->icsk_probes_out >= keepalive_probes(tp))) {
 614                        tcp_send_active_reset(sk, GFP_ATOMIC);
 615                        tcp_write_err(sk);
 616                        goto out;
 617                }
 618                if (tcp_write_wakeup(sk) <= 0) {
 619                        icsk->icsk_probes_out++;
 620                        elapsed = keepalive_intvl_when(tp);
 621                } else {
 622                        /* If keepalive was lost due to local congestion,
 623                         * try harder.
 624                         */
 625                        elapsed = TCP_RESOURCE_PROBE_INTERVAL;
 626                }
 627        } else {
 628                /* It is tp->rcv_tstamp + keepalive_time_when(tp) */
 629                elapsed = keepalive_time_when(tp) - elapsed;
 630        }
 631
 632        sk_mem_reclaim(sk);
 633
 634resched:
 635        inet_csk_reset_keepalive_timer (sk, elapsed);
 636        goto out;
 637
 638death:
 639        tcp_done(sk);
 640
 641out:
 642        bh_unlock_sock(sk);
 643        sock_put(sk);
 644}
 645
 646void tcp_init_xmit_timers(struct sock *sk)
 647{
 648        inet_csk_init_xmit_timers(sk, &tcp_write_timer, &tcp_delack_timer,
 649                                  &tcp_keepalive_timer);
 650}
 651EXPORT_SYMBOL(tcp_init_xmit_timers);
 652
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