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        int retry_until;
 160        bool do_reset, syn_set = false;
 161
 162        if ((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV)) {
 163                if (icsk->icsk_retransmits)
 164                        dst_negative_advice(sk);
 165                retry_until = icsk->icsk_syn_retries ? : sysctl_tcp_syn_retries;
 166                syn_set = true;
 167        } else {
 168                if (retransmits_timed_out(sk, sysctl_tcp_retries1, 0, 0)) {
 169                        /* Black hole detection */
 170                        tcp_mtu_probing(icsk, sk);
 171
 172                        dst_negative_advice(sk);
 173                }
 174
 175                retry_until = sysctl_tcp_retries2;
 176                if (sock_flag(sk, SOCK_DEAD)) {
 177                        const int alive = (icsk->icsk_rto < TCP_RTO_MAX);
 178
 179                        retry_until = tcp_orphan_retries(sk, alive);
 180                        do_reset = alive ||
 181                                !retransmits_timed_out(sk, retry_until, 0, 0);
 182
 183                        if (tcp_out_of_resources(sk, do_reset))
 184                                return 1;
 185                }
 186        }
 187
 188        if (retransmits_timed_out(sk, retry_until,
 189                                  syn_set ? 0 : icsk->icsk_user_timeout, syn_set)) {
 190                /* Has it gone just too far? */
 191                tcp_write_err(sk);
 192                return 1;
 193        }
 194        return 0;
 195}
 196
 197void tcp_delack_timer_handler(struct sock *sk)
 198{
 199        struct tcp_sock *tp = tcp_sk(sk);
 200        struct inet_connection_sock *icsk = inet_csk(sk);
 201
 202        sk_mem_reclaim_partial(sk);
 203
 204        if (sk->sk_state == TCP_CLOSE || !(icsk->icsk_ack.pending & ICSK_ACK_TIMER))
 205                goto out;
 206
 207        if (time_after(icsk->icsk_ack.timeout, jiffies)) {
 208                sk_reset_timer(sk, &icsk->icsk_delack_timer, icsk->icsk_ack.timeout);
 209                goto out;
 210        }
 211        icsk->icsk_ack.pending &= ~ICSK_ACK_TIMER;
 212
 213        if (!skb_queue_empty(&tp->ucopy.prequeue)) {
 214                struct sk_buff *skb;
 215
 216                NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSCHEDULERFAILED);
 217
 218                while ((skb = __skb_dequeue(&tp->ucopy.prequeue)) != NULL)
 219                        sk_backlog_rcv(sk, skb);
 220
 221                tp->ucopy.memory = 0;
 222        }
 223
 224        if (inet_csk_ack_scheduled(sk)) {
 225                if (!icsk->icsk_ack.pingpong) {
 226                        /* Delayed ACK missed: inflate ATO. */
 227                        icsk->icsk_ack.ato = min(icsk->icsk_ack.ato << 1, icsk->icsk_rto);
 228                } else {
 229                        /* Delayed ACK missed: leave pingpong mode and
 230                         * deflate ATO.
 231                         */
 232                        icsk->icsk_ack.pingpong = 0;
 233                        icsk->icsk_ack.ato      = TCP_ATO_MIN;
 234                }
 235                tcp_send_ack(sk);
 236                NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKS);
 237        }
 238
 239out:
 240        if (sk_under_memory_pressure(sk))
 241                sk_mem_reclaim(sk);
 242}
 243
 244static void tcp_delack_timer(unsigned long data)
 245{
 246        struct sock *sk = (struct sock *)data;
 247
 248        bh_lock_sock(sk);
 249        if (!sock_owned_by_user(sk)) {
 250                tcp_delack_timer_handler(sk);
 251        } else {
 252                inet_csk(sk)->icsk_ack.blocked = 1;
 253                NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKLOCKED);
 254                /* deleguate our work to tcp_release_cb() */
 255                if (!test_and_set_bit(TCP_DELACK_TIMER_DEFERRED, &tcp_sk(sk)->tsq_flags))
 256                        sock_hold(sk);
 257        }
 258        bh_unlock_sock(sk);
 259        sock_put(sk);
 260}
 261
 262static void tcp_probe_timer(struct sock *sk)
 263{
 264        struct inet_connection_sock *icsk = inet_csk(sk);
 265        struct tcp_sock *tp = tcp_sk(sk);
 266        int max_probes;
 267
 268        if (tp->packets_out || !tcp_send_head(sk)) {
 269                icsk->icsk_probes_out = 0;
 270                return;
 271        }
 272
 273        /* *WARNING* RFC 1122 forbids this
 274         *
 275         * It doesn't AFAIK, because we kill the retransmit timer -AK
 276         *
 277         * FIXME: We ought not to do it, Solaris 2.5 actually has fixing
 278         * this behaviour in Solaris down as a bug fix. [AC]
 279         *
 280         * Let me to explain. icsk_probes_out is zeroed by incoming ACKs
 281         * even if they advertise zero window. Hence, connection is killed only
 282         * if we received no ACKs for normal connection timeout. It is not killed
 283         * only because window stays zero for some time, window may be zero
 284         * until armageddon and even later. We are in full accordance
 285         * with RFCs, only probe timer combines both retransmission timeout
 286         * and probe timeout in one bottle.                             --ANK
 287         */
 288        max_probes = sysctl_tcp_retries2;
 289
 290        if (sock_flag(sk, SOCK_DEAD)) {
 291                const int alive = ((icsk->icsk_rto << icsk->icsk_backoff) < TCP_RTO_MAX);
 292
 293                max_probes = tcp_orphan_retries(sk, alive);
 294
 295                if (tcp_out_of_resources(sk, alive || icsk->icsk_probes_out <= max_probes))
 296                        return;
 297        }
 298
 299        if (icsk->icsk_probes_out > max_probes) {
 300                tcp_write_err(sk);
 301        } else {
 302                /* Only send another probe if we didn't close things up. */
 303                tcp_send_probe0(sk);
 304        }
 305}
 306
 307/*
 308 *      Timer for Fast Open socket to retransmit SYNACK. Note that the
 309 *      sk here is the child socket, not the parent (listener) socket.
 310 */
 311static void tcp_fastopen_synack_timer(struct sock *sk)
 312{
 313        struct inet_connection_sock *icsk = inet_csk(sk);
 314        int max_retries = icsk->icsk_syn_retries ? :
 315            sysctl_tcp_synack_retries + 1; /* add one more retry for fastopen */
 316        struct request_sock *req;
 317
 318        req = tcp_sk(sk)->fastopen_rsk;
 319        req->rsk_ops->syn_ack_timeout(sk, req);
 320
 321        if (req->retrans >= max_retries) {
 322                tcp_write_err(sk);
 323                return;
 324        }
 325        /* XXX (TFO) - Unlike regular SYN-ACK retransmit, we ignore error
 326         * returned from rtx_syn_ack() to make it more persistent like
 327         * regular retransmit because if the child socket has been accepted
 328         * it's not good to give up too easily.
 329         */
 330        req->rsk_ops->rtx_syn_ack(sk, req, NULL);
 331        req->retrans++;
 332        inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
 333                          TCP_TIMEOUT_INIT << req->retrans, TCP_RTO_MAX);
 334}
 335
 336/*
 337 *      The TCP retransmit timer.
 338 */
 339
 340void tcp_retransmit_timer(struct sock *sk)
 341{
 342        struct tcp_sock *tp = tcp_sk(sk);
 343        struct inet_connection_sock *icsk = inet_csk(sk);
 344
 345        if (tp->early_retrans_delayed) {
 346                tcp_resume_early_retransmit(sk);
 347                return;
 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        if (!tp->snd_wnd && !sock_flag(sk, SOCK_DEAD) &&
 364            !((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV))) {
 365                /* Receiver dastardly shrinks window. Our retransmits
 366                 * become zero probes, but we should not timeout this
 367                 * connection. If the socket is an orphan, time it out,
 368                 * we cannot allow such beasts to hang infinitely.
 369                 */
 370                struct inet_sock *inet = inet_sk(sk);
 371                if (sk->sk_family == AF_INET) {
 372                        LIMIT_NETDEBUG(KERN_DEBUG pr_fmt("Peer %pI4:%u/%u unexpectedly shrunk window %u:%u (repaired)\n"),
 373                                       &inet->inet_daddr,
 374                                       ntohs(inet->inet_dport), inet->inet_num,
 375                                       tp->snd_una, tp->snd_nxt);
 376                }
 377#if IS_ENABLED(CONFIG_IPV6)
 378                else if (sk->sk_family == AF_INET6) {
 379                        struct ipv6_pinfo *np = inet6_sk(sk);
 380                        LIMIT_NETDEBUG(KERN_DEBUG pr_fmt("Peer %pI6:%u/%u unexpectedly shrunk window %u:%u (repaired)\n"),
 381                                       &np->daddr,
 382                                       ntohs(inet->inet_dport), inet->inet_num,
 383                                       tp->snd_una, tp->snd_nxt);
 384                }
 385#endif
 386                if (tcp_time_stamp - tp->rcv_tstamp > TCP_RTO_MAX) {
 387                        tcp_write_err(sk);
 388                        goto out;
 389                }
 390                tcp_enter_loss(sk, 0);
 391                tcp_retransmit_skb(sk, tcp_write_queue_head(sk));
 392                __sk_dst_reset(sk);
 393                goto out_reset_timer;
 394        }
 395
 396        if (tcp_write_timeout(sk))
 397                goto out;
 398
 399        if (icsk->icsk_retransmits == 0) {
 400                int mib_idx;
 401
 402                if (icsk->icsk_ca_state == TCP_CA_Recovery) {
 403                        if (tcp_is_sack(tp))
 404                                mib_idx = LINUX_MIB_TCPSACKRECOVERYFAIL;
 405                        else
 406                                mib_idx = LINUX_MIB_TCPRENORECOVERYFAIL;
 407                } else if (icsk->icsk_ca_state == TCP_CA_Loss) {
 408                        mib_idx = LINUX_MIB_TCPLOSSFAILURES;
 409                } else if ((icsk->icsk_ca_state == TCP_CA_Disorder) ||
 410                           tp->sacked_out) {
 411                        if (tcp_is_sack(tp))
 412                                mib_idx = LINUX_MIB_TCPSACKFAILURES;
 413                        else
 414                                mib_idx = LINUX_MIB_TCPRENOFAILURES;
 415                } else {
 416                        mib_idx = LINUX_MIB_TCPTIMEOUTS;
 417                }
 418                NET_INC_STATS_BH(sock_net(sk), mib_idx);
 419        }
 420
 421        if (tcp_use_frto(sk)) {
 422                tcp_enter_frto(sk);
 423        } else {
 424                tcp_enter_loss(sk, 0);
 425        }
 426
 427        if (tcp_retransmit_skb(sk, tcp_write_queue_head(sk)) > 0) {
 428                /* Retransmission failed because of local congestion,
 429                 * do not backoff.
 430                 */
 431                if (!icsk->icsk_retransmits)
 432                        icsk->icsk_retransmits = 1;
 433                inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
 434                                          min(icsk->icsk_rto, TCP_RESOURCE_PROBE_INTERVAL),
 435                                          TCP_RTO_MAX);
 436                goto out;
 437        }
 438
 439        /* Increase the timeout each time we retransmit.  Note that
 440         * we do not increase the rtt estimate.  rto is initialized
 441         * from rtt, but increases here.  Jacobson (SIGCOMM 88) suggests
 442         * that doubling rto each time is the least we can get away with.
 443         * In KA9Q, Karn uses this for the first few times, and then
 444         * goes to quadratic.  netBSD doubles, but only goes up to *64,
 445         * and clamps at 1 to 64 sec afterwards.  Note that 120 sec is
 446         * defined in the protocol as the maximum possible RTT.  I guess
 447         * we'll have to use something other than TCP to talk to the
 448         * University of Mars.
 449         *
 450         * PAWS allows us longer timeouts and large windows, so once
 451         * implemented ftp to mars will work nicely. We will have to fix
 452         * the 120 second clamps though!
 453         */
 454        icsk->icsk_backoff++;
 455        icsk->icsk_retransmits++;
 456
 457out_reset_timer:
 458        /* If stream is thin, use linear timeouts. Since 'icsk_backoff' is
 459         * used to reset timer, set to 0. Recalculate 'icsk_rto' as this
 460         * might be increased if the stream oscillates between thin and thick,
 461         * thus the old value might already be too high compared to the value
 462         * set by 'tcp_set_rto' in tcp_input.c which resets the rto without
 463         * backoff. Limit to TCP_THIN_LINEAR_RETRIES before initiating
 464         * exponential backoff behaviour to avoid continue hammering
 465         * linear-timeout retransmissions into a black hole
 466         */
 467        if (sk->sk_state == TCP_ESTABLISHED &&
 468            (tp->thin_lto || sysctl_tcp_thin_linear_timeouts) &&
 469            tcp_stream_is_thin(tp) &&
 470            icsk->icsk_retransmits <= TCP_THIN_LINEAR_RETRIES) {
 471                icsk->icsk_backoff = 0;
 472                icsk->icsk_rto = min(__tcp_set_rto(tp), TCP_RTO_MAX);
 473        } else {
 474                /* Use normal (exponential) backoff */
 475                icsk->icsk_rto = min(icsk->icsk_rto << 1, TCP_RTO_MAX);
 476        }
 477        inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, icsk->icsk_rto, TCP_RTO_MAX);
 478        if (retransmits_timed_out(sk, sysctl_tcp_retries1 + 1, 0, 0))
 479                __sk_dst_reset(sk);
 480
 481out:;
 482}
 483
 484void tcp_write_timer_handler(struct sock *sk)
 485{
 486        struct inet_connection_sock *icsk = inet_csk(sk);
 487        int event;
 488
 489        if (sk->sk_state == TCP_CLOSE || !icsk->icsk_pending)
 490                goto out;
 491
 492        if (time_after(icsk->icsk_timeout, jiffies)) {
 493                sk_reset_timer(sk, &icsk->icsk_retransmit_timer, icsk->icsk_timeout);
 494                goto out;
 495        }
 496
 497        event = icsk->icsk_pending;
 498        icsk->icsk_pending = 0;
 499
 500        switch (event) {
 501        case ICSK_TIME_RETRANS:
 502                tcp_retransmit_timer(sk);
 503                break;
 504        case ICSK_TIME_PROBE0:
 505                tcp_probe_timer(sk);
 506                break;
 507        }
 508
 509out:
 510        sk_mem_reclaim(sk);
 511}
 512
 513static void tcp_write_timer(unsigned long data)
 514{
 515        struct sock *sk = (struct sock *)data;
 516
 517        bh_lock_sock(sk);
 518        if (!sock_owned_by_user(sk)) {
 519                tcp_write_timer_handler(sk);
 520        } else {
 521                /* deleguate our work to tcp_release_cb() */
 522                if (!test_and_set_bit(TCP_WRITE_TIMER_DEFERRED, &tcp_sk(sk)->tsq_flags))
 523                        sock_hold(sk);
 524        }
 525        bh_unlock_sock(sk);
 526        sock_put(sk);
 527}
 528
 529/*
 530 *      Timer for listening sockets
 531 */
 532
 533static void tcp_synack_timer(struct sock *sk)
 534{
 535        inet_csk_reqsk_queue_prune(sk, TCP_SYNQ_INTERVAL,
 536                                   TCP_TIMEOUT_INIT, TCP_RTO_MAX);
 537}
 538
 539void tcp_syn_ack_timeout(struct sock *sk, struct request_sock *req)
 540{
 541        NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPTIMEOUTS);
 542}
 543EXPORT_SYMBOL(tcp_syn_ack_timeout);
 544
 545void tcp_set_keepalive(struct sock *sk, int val)
 546{
 547        if ((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN))
 548                return;
 549
 550        if (val && !sock_flag(sk, SOCK_KEEPOPEN))
 551                inet_csk_reset_keepalive_timer(sk, keepalive_time_when(tcp_sk(sk)));
 552        else if (!val)
 553                inet_csk_delete_keepalive_timer(sk);
 554}
 555
 556
 557static void tcp_keepalive_timer (unsigned long data)
 558{
 559        struct sock *sk = (struct sock *) data;
 560        struct inet_connection_sock *icsk = inet_csk(sk);
 561        struct tcp_sock *tp = tcp_sk(sk);
 562        u32 elapsed;
 563
 564        /* Only process if socket is not in use. */
 565        bh_lock_sock(sk);
 566        if (sock_owned_by_user(sk)) {
 567                /* Try again later. */
 568                inet_csk_reset_keepalive_timer (sk, HZ/20);
 569                goto out;
 570        }
 571
 572        if (sk->sk_state == TCP_LISTEN) {
 573                tcp_synack_timer(sk);
 574                goto out;
 575        }
 576
 577        if (sk->sk_state == TCP_FIN_WAIT2 && sock_flag(sk, SOCK_DEAD)) {
 578                if (tp->linger2 >= 0) {
 579                        const int tmo = tcp_fin_time(sk) - TCP_TIMEWAIT_LEN;
 580
 581                        if (tmo > 0) {
 582                                tcp_time_wait(sk, TCP_FIN_WAIT2, tmo);
 583                                goto out;
 584                        }
 585                }
 586                tcp_send_active_reset(sk, GFP_ATOMIC);
 587                goto death;
 588        }
 589
 590        if (!sock_flag(sk, SOCK_KEEPOPEN) || sk->sk_state == TCP_CLOSE)
 591                goto out;
 592
 593        elapsed = keepalive_time_when(tp);
 594
 595        /* It is alive without keepalive 8) */
 596        if (tp->packets_out || tcp_send_head(sk))
 597                goto resched;
 598
 599        elapsed = keepalive_time_elapsed(tp);
 600
 601        if (elapsed >= keepalive_time_when(tp)) {
 602                /* If the TCP_USER_TIMEOUT option is enabled, use that
 603                 * to determine when to timeout instead.
 604                 */
 605                if ((icsk->icsk_user_timeout != 0 &&
 606                    elapsed >= icsk->icsk_user_timeout &&
 607                    icsk->icsk_probes_out > 0) ||
 608                    (icsk->icsk_user_timeout == 0 &&
 609                    icsk->icsk_probes_out >= keepalive_probes(tp))) {
 610                        tcp_send_active_reset(sk, GFP_ATOMIC);
 611                        tcp_write_err(sk);
 612                        goto out;
 613                }
 614                if (tcp_write_wakeup(sk) <= 0) {
 615                        icsk->icsk_probes_out++;
 616                        elapsed = keepalive_intvl_when(tp);
 617                } else {
 618                        /* If keepalive was lost due to local congestion,
 619                         * try harder.
 620                         */
 621                        elapsed = TCP_RESOURCE_PROBE_INTERVAL;
 622                }
 623        } else {
 624                /* It is tp->rcv_tstamp + keepalive_time_when(tp) */
 625                elapsed = keepalive_time_when(tp) - elapsed;
 626        }
 627
 628        sk_mem_reclaim(sk);
 629
 630resched:
 631        inet_csk_reset_keepalive_timer (sk, elapsed);
 632        goto out;
 633
 634death:
 635        tcp_done(sk);
 636
 637out:
 638        bh_unlock_sock(sk);
 639        sock_put(sk);
 640}
 641
 642void tcp_init_xmit_timers(struct sock *sk)
 643{
 644        inet_csk_init_xmit_timers(sk, &tcp_write_timer, &tcp_delack_timer,
 645                                  &tcp_keepalive_timer);
 646}
 647EXPORT_SYMBOL(tcp_init_xmit_timers);
 648
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