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_timer(unsigned long);
  36static void tcp_delack_timer(unsigned long);
  37static void tcp_keepalive_timer (unsigned long data);
  38
  39void tcp_init_xmit_timers(struct sock *sk)
  40{
  41        inet_csk_init_xmit_timers(sk, &tcp_write_timer, &tcp_delack_timer,
  42                                  &tcp_keepalive_timer);
  43}
  44
  45EXPORT_SYMBOL(tcp_init_xmit_timers);
  46
  47static void tcp_write_err(struct sock *sk)
  48{
  49        sk->sk_err = sk->sk_err_soft ? : ETIMEDOUT;
  50        sk->sk_error_report(sk);
  51
  52        tcp_done(sk);
  53        NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPABORTONTIMEOUT);
  54}
  55
  56/* Do not allow orphaned sockets to eat all our resources.
  57 * This is direct violation of TCP specs, but it is required
  58 * to prevent DoS attacks. It is called when a retransmission timeout
  59 * or zero probe timeout occurs on orphaned socket.
  60 *
  61 * Criteria is still not confirmed experimentally and may change.
  62 * We kill the socket, if:
  63 * 1. If number of orphaned sockets exceeds an administratively configured
  64 *    limit.
  65 * 2. If we have strong memory pressure.
  66 */
  67static int tcp_out_of_resources(struct sock *sk, int do_reset)
  68{
  69        struct tcp_sock *tp = tcp_sk(sk);
  70        int orphans = percpu_counter_read_positive(&tcp_orphan_count);
  71
  72        /* If peer does not open window for long time, or did not transmit
  73         * anything for long time, penalize it. */
  74        if ((s32)(tcp_time_stamp - tp->lsndtime) > 2*TCP_RTO_MAX || !do_reset)
  75                orphans <<= 1;
  76
  77        /* If some dubious ICMP arrived, penalize even more. */
  78        if (sk->sk_err_soft)
  79                orphans <<= 1;
  80
  81        if (tcp_too_many_orphans(sk, orphans)) {
  82                if (net_ratelimit())
  83                        printk(KERN_INFO "Out of socket memory\n");
  84
  85                /* Catch exceptional cases, when connection requires reset.
  86                 *      1. Last segment was sent recently. */
  87                if ((s32)(tcp_time_stamp - tp->lsndtime) <= TCP_TIMEWAIT_LEN ||
  88                    /*  2. Window is closed. */
  89                    (!tp->snd_wnd && !tp->packets_out))
  90                        do_reset = 1;
  91                if (do_reset)
  92                        tcp_send_active_reset(sk, GFP_ATOMIC);
  93                tcp_done(sk);
  94                NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPABORTONMEMORY);
  95                return 1;
  96        }
  97        return 0;
  98}
  99
 100/* Calculate maximal number or retries on an orphaned socket. */
 101static int tcp_orphan_retries(struct sock *sk, int alive)
 102{
 103        int retries = sysctl_tcp_orphan_retries; /* May be zero. */
 104
 105        /* We know from an ICMP that something is wrong. */
 106        if (sk->sk_err_soft && !alive)
 107                retries = 0;
 108
 109        /* However, if socket sent something recently, select some safe
 110         * number of retries. 8 corresponds to >100 seconds with minimal
 111         * RTO of 200msec. */
 112        if (retries == 0 && alive)
 113                retries = 8;
 114        return retries;
 115}
 116
 117static void tcp_mtu_probing(struct inet_connection_sock *icsk, struct sock *sk)
 118{
 119        /* Black hole detection */
 120        if (sysctl_tcp_mtu_probing) {
 121                if (!icsk->icsk_mtup.enabled) {
 122                        icsk->icsk_mtup.enabled = 1;
 123                        tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
 124                } else {
 125                        struct tcp_sock *tp = tcp_sk(sk);
 126                        int mss;
 127
 128                        mss = tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low) >> 1;
 129                        mss = min(sysctl_tcp_base_mss, mss);
 130                        mss = max(mss, 68 - tp->tcp_header_len);
 131                        icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, mss);
 132                        tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
 133                }
 134        }
 135}
 136
 137/* This function calculates a "timeout" which is equivalent to the timeout of a
 138 * TCP connection after "boundary" unsuccessful, exponentially backed-off
 139 * retransmissions with an initial RTO of TCP_RTO_MIN.
 140 */
 141static bool retransmits_timed_out(struct sock *sk,
 142                                  unsigned int boundary)
 143{
 144        unsigned int timeout, linear_backoff_thresh;
 145        unsigned int start_ts;
 146
 147        if (!inet_csk(sk)->icsk_retransmits)
 148                return false;
 149
 150        if (unlikely(!tcp_sk(sk)->retrans_stamp))
 151                start_ts = TCP_SKB_CB(tcp_write_queue_head(sk))->when;
 152        else
 153                start_ts = tcp_sk(sk)->retrans_stamp;
 154
 155        linear_backoff_thresh = ilog2(TCP_RTO_MAX/TCP_RTO_MIN);
 156
 157        if (boundary <= linear_backoff_thresh)
 158                timeout = ((2 << boundary) - 1) * TCP_RTO_MIN;
 159        else
 160                timeout = ((2 << linear_backoff_thresh) - 1) * TCP_RTO_MIN +
 161                          (boundary - linear_backoff_thresh) * TCP_RTO_MAX;
 162
 163        return (tcp_time_stamp - start_ts) >= timeout;
 164}
 165
 166/* A write timeout has occurred. Process the after effects. */
 167static int tcp_write_timeout(struct sock *sk)
 168{
 169        struct inet_connection_sock *icsk = inet_csk(sk);
 170        int retry_until;
 171        bool do_reset;
 172
 173        if ((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV)) {
 174                if (icsk->icsk_retransmits)
 175                        dst_negative_advice(sk);
 176                retry_until = icsk->icsk_syn_retries ? : sysctl_tcp_syn_retries;
 177        } else {
 178                if (retransmits_timed_out(sk, sysctl_tcp_retries1)) {
 179                        /* Black hole detection */
 180                        tcp_mtu_probing(icsk, sk);
 181
 182                        dst_negative_advice(sk);
 183                }
 184
 185                retry_until = sysctl_tcp_retries2;
 186                if (sock_flag(sk, SOCK_DEAD)) {
 187                        const int alive = (icsk->icsk_rto < TCP_RTO_MAX);
 188
 189                        retry_until = tcp_orphan_retries(sk, alive);
 190                        do_reset = alive ||
 191                                   !retransmits_timed_out(sk, retry_until);
 192
 193                        if (tcp_out_of_resources(sk, do_reset))
 194                                return 1;
 195                }
 196        }
 197
 198        if (retransmits_timed_out(sk, retry_until)) {
 199                /* Has it gone just too far? */
 200                tcp_write_err(sk);
 201                return 1;
 202        }
 203        return 0;
 204}
 205
 206static void tcp_delack_timer(unsigned long data)
 207{
 208        struct sock *sk = (struct sock *)data;
 209        struct tcp_sock *tp = tcp_sk(sk);
 210        struct inet_connection_sock *icsk = inet_csk(sk);
 211
 212        bh_lock_sock(sk);
 213        if (sock_owned_by_user(sk)) {
 214                /* Try again later. */
 215                icsk->icsk_ack.blocked = 1;
 216                NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKLOCKED);
 217                sk_reset_timer(sk, &icsk->icsk_delack_timer, jiffies + TCP_DELACK_MIN);
 218                goto out_unlock;
 219        }
 220
 221        sk_mem_reclaim_partial(sk);
 222
 223        if (sk->sk_state == TCP_CLOSE || !(icsk->icsk_ack.pending & ICSK_ACK_TIMER))
 224                goto out;
 225
 226        if (time_after(icsk->icsk_ack.timeout, jiffies)) {
 227                sk_reset_timer(sk, &icsk->icsk_delack_timer, icsk->icsk_ack.timeout);
 228                goto out;
 229        }
 230        icsk->icsk_ack.pending &= ~ICSK_ACK_TIMER;
 231
 232        if (!skb_queue_empty(&tp->ucopy.prequeue)) {
 233                struct sk_buff *skb;
 234
 235                NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSCHEDULERFAILED);
 236
 237                while ((skb = __skb_dequeue(&tp->ucopy.prequeue)) != NULL)
 238                        sk_backlog_rcv(sk, skb);
 239
 240                tp->ucopy.memory = 0;
 241        }
 242
 243        if (inet_csk_ack_scheduled(sk)) {
 244                if (!icsk->icsk_ack.pingpong) {
 245                        /* Delayed ACK missed: inflate ATO. */
 246                        icsk->icsk_ack.ato = min(icsk->icsk_ack.ato << 1, icsk->icsk_rto);
 247                } else {
 248                        /* Delayed ACK missed: leave pingpong mode and
 249                         * deflate ATO.
 250                         */
 251                        icsk->icsk_ack.pingpong = 0;
 252                        icsk->icsk_ack.ato      = TCP_ATO_MIN;
 253                }
 254                tcp_send_ack(sk);
 255                NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKS);
 256        }
 257        TCP_CHECK_TIMER(sk);
 258
 259out:
 260        if (tcp_memory_pressure)
 261                sk_mem_reclaim(sk);
 262out_unlock:
 263        bh_unlock_sock(sk);
 264        sock_put(sk);
 265}
 266
 267static void tcp_probe_timer(struct sock *sk)
 268{
 269        struct inet_connection_sock *icsk = inet_csk(sk);
 270        struct tcp_sock *tp = tcp_sk(sk);
 271        int max_probes;
 272
 273        if (tp->packets_out || !tcp_send_head(sk)) {
 274                icsk->icsk_probes_out = 0;
 275                return;
 276        }
 277
 278        /* *WARNING* RFC 1122 forbids this
 279         *
 280         * It doesn't AFAIK, because we kill the retransmit timer -AK
 281         *
 282         * FIXME: We ought not to do it, Solaris 2.5 actually has fixing
 283         * this behaviour in Solaris down as a bug fix. [AC]
 284         *
 285         * Let me to explain. icsk_probes_out is zeroed by incoming ACKs
 286         * even if they advertise zero window. Hence, connection is killed only
 287         * if we received no ACKs for normal connection timeout. It is not killed
 288         * only because window stays zero for some time, window may be zero
 289         * until armageddon and even later. We are in full accordance
 290         * with RFCs, only probe timer combines both retransmission timeout
 291         * and probe timeout in one bottle.                             --ANK
 292         */
 293        max_probes = sysctl_tcp_retries2;
 294
 295        if (sock_flag(sk, SOCK_DEAD)) {
 296                const int alive = ((icsk->icsk_rto << icsk->icsk_backoff) < TCP_RTO_MAX);
 297
 298                max_probes = tcp_orphan_retries(sk, alive);
 299
 300                if (tcp_out_of_resources(sk, alive || icsk->icsk_probes_out <= max_probes))
 301                        return;
 302        }
 303
 304        if (icsk->icsk_probes_out > max_probes) {
 305                tcp_write_err(sk);
 306        } else {
 307                /* Only send another probe if we didn't close things up. */
 308                tcp_send_probe0(sk);
 309        }
 310}
 311
 312/*
 313 *      The TCP retransmit timer.
 314 */
 315
 316void tcp_retransmit_timer(struct sock *sk)
 317{
 318        struct tcp_sock *tp = tcp_sk(sk);
 319        struct inet_connection_sock *icsk = inet_csk(sk);
 320
 321        if (!tp->packets_out)
 322                goto out;
 323
 324        WARN_ON(tcp_write_queue_empty(sk));
 325
 326        if (!tp->snd_wnd && !sock_flag(sk, SOCK_DEAD) &&
 327            !((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV))) {
 328                /* Receiver dastardly shrinks window. Our retransmits
 329                 * become zero probes, but we should not timeout this
 330                 * connection. If the socket is an orphan, time it out,
 331                 * we cannot allow such beasts to hang infinitely.
 332                 */
 333#ifdef TCP_DEBUG
 334                struct inet_sock *inet = inet_sk(sk);
 335                if (sk->sk_family == AF_INET) {
 336                        LIMIT_NETDEBUG(KERN_DEBUG "TCP: Peer %pI4:%u/%u unexpectedly shrunk window %u:%u (repaired)\n",
 337                               &inet->inet_daddr, ntohs(inet->inet_dport),
 338                               inet->inet_num, tp->snd_una, tp->snd_nxt);
 339                }
 340#if defined(CONFIG_IPV6) || defined(CONFIG_IPV6_MODULE)
 341                else if (sk->sk_family == AF_INET6) {
 342                        struct ipv6_pinfo *np = inet6_sk(sk);
 343                        LIMIT_NETDEBUG(KERN_DEBUG "TCP: Peer %pI6:%u/%u unexpectedly shrunk window %u:%u (repaired)\n",
 344                               &np->daddr, ntohs(inet->inet_dport),
 345                               inet->inet_num, tp->snd_una, tp->snd_nxt);
 346                }
 347#endif
 348#endif
 349                if (tcp_time_stamp - tp->rcv_tstamp > TCP_RTO_MAX) {
 350                        tcp_write_err(sk);
 351                        goto out;
 352                }
 353                tcp_enter_loss(sk, 0);
 354                tcp_retransmit_skb(sk, tcp_write_queue_head(sk));
 355                __sk_dst_reset(sk);
 356                goto out_reset_timer;
 357        }
 358
 359        if (tcp_write_timeout(sk))
 360                goto out;
 361
 362        if (icsk->icsk_retransmits == 0) {
 363                int mib_idx;
 364
 365                if (icsk->icsk_ca_state == TCP_CA_Disorder) {
 366                        if (tcp_is_sack(tp))
 367                                mib_idx = LINUX_MIB_TCPSACKFAILURES;
 368                        else
 369                                mib_idx = LINUX_MIB_TCPRENOFAILURES;
 370                } else if (icsk->icsk_ca_state == TCP_CA_Recovery) {
 371                        if (tcp_is_sack(tp))
 372                                mib_idx = LINUX_MIB_TCPSACKRECOVERYFAIL;
 373                        else
 374                                mib_idx = LINUX_MIB_TCPRENORECOVERYFAIL;
 375                } else if (icsk->icsk_ca_state == TCP_CA_Loss) {
 376                        mib_idx = LINUX_MIB_TCPLOSSFAILURES;
 377                } else {
 378                        mib_idx = LINUX_MIB_TCPTIMEOUTS;
 379                }
 380                NET_INC_STATS_BH(sock_net(sk), mib_idx);
 381        }
 382
 383        if (tcp_use_frto(sk)) {
 384                tcp_enter_frto(sk);
 385        } else {
 386                tcp_enter_loss(sk, 0);
 387        }
 388
 389        if (tcp_retransmit_skb(sk, tcp_write_queue_head(sk)) > 0) {
 390                /* Retransmission failed because of local congestion,
 391                 * do not backoff.
 392                 */
 393                if (!icsk->icsk_retransmits)
 394                        icsk->icsk_retransmits = 1;
 395                inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
 396                                          min(icsk->icsk_rto, TCP_RESOURCE_PROBE_INTERVAL),
 397                                          TCP_RTO_MAX);
 398                goto out;
 399        }
 400
 401        /* Increase the timeout each time we retransmit.  Note that
 402         * we do not increase the rtt estimate.  rto is initialized
 403         * from rtt, but increases here.  Jacobson (SIGCOMM 88) suggests
 404         * that doubling rto each time is the least we can get away with.
 405         * In KA9Q, Karn uses this for the first few times, and then
 406         * goes to quadratic.  netBSD doubles, but only goes up to *64,
 407         * and clamps at 1 to 64 sec afterwards.  Note that 120 sec is
 408         * defined in the protocol as the maximum possible RTT.  I guess
 409         * we'll have to use something other than TCP to talk to the
 410         * University of Mars.
 411         *
 412         * PAWS allows us longer timeouts and large windows, so once
 413         * implemented ftp to mars will work nicely. We will have to fix
 414         * the 120 second clamps though!
 415         */
 416        icsk->icsk_backoff++;
 417        icsk->icsk_retransmits++;
 418
 419out_reset_timer:
 420        /* If stream is thin, use linear timeouts. Since 'icsk_backoff' is
 421         * used to reset timer, set to 0. Recalculate 'icsk_rto' as this
 422         * might be increased if the stream oscillates between thin and thick,
 423         * thus the old value might already be too high compared to the value
 424         * set by 'tcp_set_rto' in tcp_input.c which resets the rto without
 425         * backoff. Limit to TCP_THIN_LINEAR_RETRIES before initiating
 426         * exponential backoff behaviour to avoid continue hammering
 427         * linear-timeout retransmissions into a black hole
 428         */
 429        if (sk->sk_state == TCP_ESTABLISHED &&
 430            (tp->thin_lto || sysctl_tcp_thin_linear_timeouts) &&
 431            tcp_stream_is_thin(tp) &&
 432            icsk->icsk_retransmits <= TCP_THIN_LINEAR_RETRIES) {
 433                icsk->icsk_backoff = 0;
 434                icsk->icsk_rto = min(__tcp_set_rto(tp), TCP_RTO_MAX);
 435        } else {
 436                /* Use normal (exponential) backoff */
 437                icsk->icsk_rto = min(icsk->icsk_rto << 1, TCP_RTO_MAX);
 438        }
 439        inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, icsk->icsk_rto, TCP_RTO_MAX);
 440        if (retransmits_timed_out(sk, sysctl_tcp_retries1 + 1))
 441                __sk_dst_reset(sk);
 442
 443out:;
 444}
 445
 446static void tcp_write_timer(unsigned long data)
 447{
 448        struct sock *sk = (struct sock *)data;
 449        struct inet_connection_sock *icsk = inet_csk(sk);
 450        int event;
 451
 452        bh_lock_sock(sk);
 453        if (sock_owned_by_user(sk)) {
 454                /* Try again later */
 455                sk_reset_timer(sk, &icsk->icsk_retransmit_timer, jiffies + (HZ / 20));
 456                goto out_unlock;
 457        }
 458
 459        if (sk->sk_state == TCP_CLOSE || !icsk->icsk_pending)
 460                goto out;
 461
 462        if (time_after(icsk->icsk_timeout, jiffies)) {
 463                sk_reset_timer(sk, &icsk->icsk_retransmit_timer, icsk->icsk_timeout);
 464                goto out;
 465        }
 466
 467        event = icsk->icsk_pending;
 468        icsk->icsk_pending = 0;
 469
 470        switch (event) {
 471        case ICSK_TIME_RETRANS:
 472                tcp_retransmit_timer(sk);
 473                break;
 474        case ICSK_TIME_PROBE0:
 475                tcp_probe_timer(sk);
 476                break;
 477        }
 478        TCP_CHECK_TIMER(sk);
 479
 480out:
 481        sk_mem_reclaim(sk);
 482out_unlock:
 483        bh_unlock_sock(sk);
 484        sock_put(sk);
 485}
 486
 487/*
 488 *      Timer for listening sockets
 489 */
 490
 491static void tcp_synack_timer(struct sock *sk)
 492{
 493        inet_csk_reqsk_queue_prune(sk, TCP_SYNQ_INTERVAL,
 494                                   TCP_TIMEOUT_INIT, TCP_RTO_MAX);
 495}
 496
 497void tcp_syn_ack_timeout(struct sock *sk, struct request_sock *req)
 498{
 499        NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPTIMEOUTS);
 500}
 501EXPORT_SYMBOL(tcp_syn_ack_timeout);
 502
 503void tcp_set_keepalive(struct sock *sk, int val)
 504{
 505        if ((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN))
 506                return;
 507
 508        if (val && !sock_flag(sk, SOCK_KEEPOPEN))
 509                inet_csk_reset_keepalive_timer(sk, keepalive_time_when(tcp_sk(sk)));
 510        else if (!val)
 511                inet_csk_delete_keepalive_timer(sk);
 512}
 513
 514
 515static void tcp_keepalive_timer (unsigned long data)
 516{
 517        struct sock *sk = (struct sock *) data;
 518        struct inet_connection_sock *icsk = inet_csk(sk);
 519        struct tcp_sock *tp = tcp_sk(sk);
 520        u32 elapsed;
 521
 522        /* Only process if socket is not in use. */
 523        bh_lock_sock(sk);
 524        if (sock_owned_by_user(sk)) {
 525                /* Try again later. */
 526                inet_csk_reset_keepalive_timer (sk, HZ/20);
 527                goto out;
 528        }
 529
 530        if (sk->sk_state == TCP_LISTEN) {
 531                tcp_synack_timer(sk);
 532                goto out;
 533        }
 534
 535        if (sk->sk_state == TCP_FIN_WAIT2 && sock_flag(sk, SOCK_DEAD)) {
 536                if (tp->linger2 >= 0) {
 537                        const int tmo = tcp_fin_time(sk) - TCP_TIMEWAIT_LEN;
 538
 539                        if (tmo > 0) {
 540                                tcp_time_wait(sk, TCP_FIN_WAIT2, tmo);
 541                                goto out;
 542                        }
 543                }
 544                tcp_send_active_reset(sk, GFP_ATOMIC);
 545                goto death;
 546        }
 547
 548        if (!sock_flag(sk, SOCK_KEEPOPEN) || sk->sk_state == TCP_CLOSE)
 549                goto out;
 550
 551        elapsed = keepalive_time_when(tp);
 552
 553        /* It is alive without keepalive 8) */
 554        if (tp->packets_out || tcp_send_head(sk))
 555                goto resched;
 556
 557        elapsed = keepalive_time_elapsed(tp);
 558
 559        if (elapsed >= keepalive_time_when(tp)) {
 560                if (icsk->icsk_probes_out >= keepalive_probes(tp)) {
 561                        tcp_send_active_reset(sk, GFP_ATOMIC);
 562                        tcp_write_err(sk);
 563                        goto out;
 564                }
 565                if (tcp_write_wakeup(sk) <= 0) {
 566                        icsk->icsk_probes_out++;
 567                        elapsed = keepalive_intvl_when(tp);
 568                } else {
 569                        /* If keepalive was lost due to local congestion,
 570                         * try harder.
 571                         */
 572                        elapsed = TCP_RESOURCE_PROBE_INTERVAL;
 573                }
 574        } else {
 575                /* It is tp->rcv_tstamp + keepalive_time_when(tp) */
 576                elapsed = keepalive_time_when(tp) - elapsed;
 577        }
 578
 579        TCP_CHECK_TIMER(sk);
 580        sk_mem_reclaim(sk);
 581
 582resched:
 583        inet_csk_reset_keepalive_timer (sk, elapsed);
 584        goto out;
 585
 586death:
 587        tcp_done(sk);
 588
 589out:
 590        bh_unlock_sock(sk);
 591        sock_put(sk);
 592}
 593