net/ipv4/tcp_timer.c

   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
  25 int sysctl_tcp_syn_retries __read_mostly = TCP_SYN_RETRIES;
  26 int sysctl_tcp_synack_retries __read_mostly = TCP_SYNACK_RETRIES;
  27 int sysctl_tcp_keepalive_time __read_mostly = TCP_KEEPALIVE_TIME;
  28 int sysctl_tcp_keepalive_probes __read_mostly = TCP_KEEPALIVE_PROBES;
  29 int sysctl_tcp_keepalive_intvl __read_mostly = TCP_KEEPALIVE_INTVL;
  30 int sysctl_tcp_retries1 __read_mostly = TCP_RETR1;
  31 int sysctl_tcp_retries2 __read_mostly = TCP_RETR2;
  32 int sysctl_tcp_orphan_retries __read_mostly;
  33 int sysctl_tcp_thin_linear_timeouts __read_mostly;
  34
  35 static void tcp_write_timer(unsigned long);
  36 static void tcp_delack_timer(unsigned long);
  37 static void tcp_keepalive_timer (unsigned long data);
  38
  39 void 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 EXPORT_SYMBOL(tcp_init_xmit_timers);
  45
  46 static void tcp_write_err(struct sock *sk)
  47 {
  48         sk->sk_err = sk->sk_err_soft ? : ETIMEDOUT;
  49         sk->sk_error_report(sk);
  50
  51         tcp_done(sk);
  52         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPABORTONTIMEOUT);
  53 }
  54
  55 /* Do not allow orphaned sockets to eat all our resources.
  56  * This is direct violation of TCP specs, but it is required
  57  * to prevent DoS attacks. It is called when a retransmission timeout
  58  * or zero probe timeout occurs on orphaned socket.
  59  *
  60  * Criteria is still not confirmed experimentally and may change.
  61  * We kill the socket, if:
  62  * 1. If number of orphaned sockets exceeds an administratively configured
  63  *    limit.
  64  * 2. If we have strong memory pressure.
  65  */
  66 static int tcp_out_of_resources(struct sock *sk, int do_reset)
  67 {
  68         struct tcp_sock *tp = tcp_sk(sk);
  69         int shift = 0;
  70
  71         /* If peer does not open window for long time, or did not transmit
  72          * anything for long time, penalize it. */
  73         if ((s32)(tcp_time_stamp - tp->lsndtime) > 2*TCP_RTO_MAX || !do_reset)
  74                 shift++;
  75
  76         /* If some dubious ICMP arrived, penalize even more. */
  77         if (sk->sk_err_soft)
  78                 shift++;
  79
  80         if (tcp_check_oom(sk, shift)) {
  81                 /* Catch exceptional cases, when connection requires reset.
  82                  *      1. Last segment was sent recently. */
  83                 if ((s32)(tcp_time_stamp - tp->lsndtime) <= TCP_TIMEWAIT_LEN ||
  84                     /*  2. Window is closed. */
  85                     (!tp->snd_wnd && !tp->packets_out))
  86                         do_reset = 1;
  87                 if (do_reset)
  88                         tcp_send_active_reset(sk, GFP_ATOMIC);
  89                 tcp_done(sk);
  90                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPABORTONMEMORY);
  91                 return 1;
  92         }
  93         return 0;
  94 }
  95
  96 /* Calculate maximal number or retries on an orphaned socket. */
  97 static int tcp_orphan_retries(struct sock *sk, int alive)
  98 {
  99         int retries = sysctl_tcp_orphan_retries; /* May be zero. */
 100
 101         /* We know from an ICMP that something is wrong. */
 102         if (sk->sk_err_soft && !alive)
 103                 retries = 0;
 104
 105         /* However, if socket sent something recently, select some safe
 106          * number of retries. 8 corresponds to >100 seconds with minimal
 107          * RTO of 200msec. */
 108         if (retries == 0 && alive)
 109                 retries = 8;
 110         return retries;
 111 }
 112
 113 static void tcp_mtu_probing(struct inet_connection_sock *icsk, struct sock *sk)
 114 {
 115         /* Black hole detection */
 116         if (sysctl_tcp_mtu_probing) {
 117                 if (!icsk->icsk_mtup.enabled) {
 118                         icsk->icsk_mtup.enabled = 1;
 119                         tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
 120                 } else {
 121                         struct tcp_sock *tp = tcp_sk(sk);
 122                         int mss;
 123
 124                         mss = tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low) >> 1;
 125                         mss = min(sysctl_tcp_base_mss, mss);
 126                         mss = max(mss, 68 - tp->tcp_header_len);
 127                         icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, mss);
 128                         tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
 129                 }
 130         }
 131 }
 132
 133 /* This function calculates a "timeout" which is equivalent to the timeout of a
 134  * TCP connection after "boundary" unsuccessful, exponentially backed-off
 135  * retransmissions with an initial RTO of TCP_RTO_MIN or TCP_TIMEOUT_INIT if
 136  * syn_set flag is set.
 137  */
 138 static bool retransmits_timed_out(struct sock *sk,
 139                                   unsigned int boundary,
 140                                   unsigned int timeout,
 141                                   bool syn_set)
 142 {
 143         unsigned int linear_backoff_thresh, start_ts;
 144         unsigned int rto_base = syn_set ? TCP_TIMEOUT_INIT : TCP_RTO_MIN;
 145
 146         if (!inet_csk(sk)->icsk_retransmits)
 147                 return false;
 148
 149         if (unlikely(!tcp_sk(sk)->retrans_stamp))
 150                 start_ts = TCP_SKB_CB(tcp_write_queue_head(sk))->when;
 151         else
 152                 start_ts = tcp_sk(sk)->retrans_stamp;
 153
 154         if (likely(timeout == 0)) {
 155                 linear_backoff_thresh = ilog2(TCP_RTO_MAX/rto_base);
 156
 157                 if (boundary <= linear_backoff_thresh)
 158                         timeout = ((2 << boundary) - 1) * rto_base;
 159                 else
 160                         timeout = ((2 << linear_backoff_thresh) - 1) * rto_base +
 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. */
 167 static 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, syn_set = false;
 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                 syn_set = true;
 178         } else {
 179                 if (retransmits_timed_out(sk, sysctl_tcp_retries1, 0, 0)) {
 180                         /* Black hole detection */
 181                         tcp_mtu_probing(icsk, sk);
 182
 183                         dst_negative_advice(sk);
 184                 }
 185
 186                 retry_until = sysctl_tcp_retries2;
 187                 if (sock_flag(sk, SOCK_DEAD)) {
 188                         const int alive = (icsk->icsk_rto < TCP_RTO_MAX);
 189
 190                         retry_until = tcp_orphan_retries(sk, alive);
 191                         do_reset = alive ||
 192                                 !retransmits_timed_out(sk, retry_until, 0, 0);
 193
 194                         if (tcp_out_of_resources(sk, do_reset))
 195                                 return 1;
 196                 }
 197         }
 198
 199         if (retransmits_timed_out(sk, retry_until,
 200                                   syn_set ? 0 : icsk->icsk_user_timeout, syn_set)) {
 201                 /* Has it gone just too far? */
 202                 tcp_write_err(sk);
 203                 return 1;
 204         }
 205         return 0;
 206 }
 207
 208 static void tcp_delack_timer(unsigned long data)
 209 {
 210         struct sock *sk = (struct sock *)data;
 211         struct tcp_sock *tp = tcp_sk(sk);
 212         struct inet_connection_sock *icsk = inet_csk(sk);
 213
 214         bh_lock_sock(sk);
 215         if (sock_owned_by_user(sk)) {
 216                 /* Try again later. */
 217                 icsk->icsk_ack.blocked = 1;
 218                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKLOCKED);
 219                 sk_reset_timer(sk, &icsk->icsk_delack_timer, jiffies + TCP_DELACK_MIN);
 220                 goto out_unlock;
 221         }
 222
 223         sk_mem_reclaim_partial(sk);
 224
 225         if (sk->sk_state == TCP_CLOSE || !(icsk->icsk_ack.pending & ICSK_ACK_TIMER))
 226                 goto out;
 227
 228         if (time_after(icsk->icsk_ack.timeout, jiffies)) {
 229                 sk_reset_timer(sk, &icsk->icsk_delack_timer, icsk->icsk_ack.timeout);
 230                 goto out;
 231         }
 232         icsk->icsk_ack.pending &= ~ICSK_ACK_TIMER;
 233
 234         if (!skb_queue_empty(&tp->ucopy.prequeue)) {
 235                 struct sk_buff *skb;
 236
 237                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSCHEDULERFAILED);
 238
 239                 while ((skb = __skb_dequeue(&tp->ucopy.prequeue)) != NULL)
 240                         sk_backlog_rcv(sk, skb);
 241
 242                 tp->ucopy.memory = 0;
 243         }
 244
 245         if (inet_csk_ack_scheduled(sk)) {
 246                 if (!icsk->icsk_ack.pingpong) {
 247                         /* Delayed ACK missed: inflate ATO. */
 248                         icsk->icsk_ack.ato = min(icsk->icsk_ack.ato << 1, icsk->icsk_rto);
 249                 } else {
 250                         /* Delayed ACK missed: leave pingpong mode and
 251                          * deflate ATO.
 252                          */
 253                         icsk->icsk_ack.pingpong = 0;
 254                         icsk->icsk_ack.ato      = TCP_ATO_MIN;
 255                 }
 256                 tcp_send_ack(sk);
 257                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKS);
 258         }
 259
 260 out:
 261         if (sk_under_memory_pressure(sk))
 262                 sk_mem_reclaim(sk);
 263 out_unlock:
 264         bh_unlock_sock(sk);
 265         sock_put(sk);
 266 }
 267
 268 static void tcp_probe_timer(struct sock *sk)
 269 {
 270         struct inet_connection_sock *icsk = inet_csk(sk);
 271         struct tcp_sock *tp = tcp_sk(sk);
 272         int max_probes;
 273
 274         if (tp->packets_out || !tcp_send_head(sk)) {
 275                 icsk->icsk_probes_out = 0;
 276                 return;
 277         }
 278
 279         /* *WARNING* RFC 1122 forbids this
 280          *
 281          * It doesn't AFAIK, because we kill the retransmit timer -AK
 282          *
 283          * FIXME: We ought not to do it, Solaris 2.5 actually has fixing
 284          * this behaviour in Solaris down as a bug fix. [AC]
 285          *
 286          * Let me to explain. icsk_probes_out is zeroed by incoming ACKs
 287          * even if they advertise zero window. Hence, connection is killed only
 288          * if we received no ACKs for normal connection timeout. It is not killed
 289          * only because window stays zero for some time, window may be zero
 290          * until armageddon and even later. We are in full accordance
 291          * with RFCs, only probe timer combines both retransmission timeout
 292          * and probe timeout in one bottle.                             --ANK
 293          */
 294         max_probes = sysctl_tcp_retries2;
 295
 296         if (sock_flag(sk, SOCK_DEAD)) {
 297                 const int alive = ((icsk->icsk_rto << icsk->icsk_backoff) < TCP_RTO_MAX);
 298
 299                 max_probes = tcp_orphan_retries(sk, alive);
 300
 301                 if (tcp_out_of_resources(sk, alive || icsk->icsk_probes_out <= max_probes))
 302                         return;
 303         }
 304
 305         if (icsk->icsk_probes_out > max_probes) {
 306                 tcp_write_err(sk);
 307         } else {
 308                 /* Only send another probe if we didn't close things up. */
 309                 tcp_send_probe0(sk);
 310         }
 311 }
 312
 313 /*
 314  *      The TCP retransmit timer.
 315  */
 316
 317 void tcp_retransmit_timer(struct sock *sk)
 318 {
 319         struct tcp_sock *tp = tcp_sk(sk);
 320         struct inet_connection_sock *icsk = inet_csk(sk);
 321
 322         if (!tp->packets_out)
 323                 goto out;
 324
 325         WARN_ON(tcp_write_queue_empty(sk));
 326
 327         if (!tp->snd_wnd && !sock_flag(sk, SOCK_DEAD) &&
 328             !((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV))) {
 329                 /* Receiver dastardly shrinks window. Our retransmits
 330                  * become zero probes, but we should not timeout this
 331                  * connection. If the socket is an orphan, time it out,
 332                  * we cannot allow such beasts to hang infinitely.
 333                  */
 334                 struct inet_sock *inet = inet_sk(sk);
 335                 if (sk->sk_family == AF_INET) {
 336                         LIMIT_NETDEBUG(KERN_DEBUG pr_fmt("Peer %pI4:%u/%u unexpectedly shrunk window %u:%u (repaired)\n"),
 337                                        &inet->inet_daddr,
 338                                        ntohs(inet->inet_dport), inet->inet_num,
 339                                        tp->snd_una, tp->snd_nxt);
 340                 }
 341 #if IS_ENABLED(CONFIG_IPV6)
 342                 else if (sk->sk_family == AF_INET6) {
 343                         struct ipv6_pinfo *np = inet6_sk(sk);
 344                         LIMIT_NETDEBUG(KERN_DEBUG pr_fmt("Peer %pI6:%u/%u unexpectedly shrunk window %u:%u (repaired)\n"),
 345                                        &np->daddr,
 346                                        ntohs(inet->inet_dport), inet->inet_num,
 347                                        tp->snd_una, tp->snd_nxt);
 348                 }
 349 #endif
 350                 if (tcp_time_stamp - tp->rcv_tstamp > TCP_RTO_MAX) {
 351                         tcp_write_err(sk);
 352                         goto out;
 353                 }
 354                 tcp_enter_loss(sk, 0);
 355                 tcp_retransmit_skb(sk, tcp_write_queue_head(sk));
 356                 __sk_dst_reset(sk);
 357                 goto out_reset_timer;
 358         }
 359
 360         if (tcp_write_timeout(sk))
 361                 goto out;
 362
 363         if (icsk->icsk_retransmits == 0) {
 364                 int mib_idx;
 365
 366                 if (icsk->icsk_ca_state == TCP_CA_Recovery) {
 367                         if (tcp_is_sack(tp))
 368                                 mib_idx = LINUX_MIB_TCPSACKRECOVERYFAIL;
 369                         else
 370                                 mib_idx = LINUX_MIB_TCPRENORECOVERYFAIL;
 371                 } else if (icsk->icsk_ca_state == TCP_CA_Loss) {
 372                         mib_idx = LINUX_MIB_TCPLOSSFAILURES;
 373                 } else if ((icsk->icsk_ca_state == TCP_CA_Disorder) ||
 374                            tp->sacked_out) {
 375                         if (tcp_is_sack(tp))
 376                                 mib_idx = LINUX_MIB_TCPSACKFAILURES;
 377                         else
 378                                 mib_idx = LINUX_MIB_TCPRENOFAILURES;
 379                 } else {
 380                         mib_idx = LINUX_MIB_TCPTIMEOUTS;
 381                 }
 382                 NET_INC_STATS_BH(sock_net(sk), mib_idx);
 383         }
 384
 385         if (tcp_use_frto(sk)) {
 386                 tcp_enter_frto(sk);
 387         } else {
 388                 tcp_enter_loss(sk, 0);
 389         }
 390
 391         if (tcp_retransmit_skb(sk, tcp_write_queue_head(sk)) > 0) {
 392                 /* Retransmission failed because of local congestion,
 393                  * do not backoff.
 394                  */
 395                 if (!icsk->icsk_retransmits)
 396                         icsk->icsk_retransmits = 1;
 397                 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
 398                                           min(icsk->icsk_rto, TCP_RESOURCE_PROBE_INTERVAL),
 399                                           TCP_RTO_MAX);
 400                 goto out;
 401         }
 402
 403         /* Increase the timeout each time we retransmit.  Note that
 404          * we do not increase the rtt estimate.  rto is initialized
 405          * from rtt, but increases here.  Jacobson (SIGCOMM 88) suggests
 406          * that doubling rto each time is the least we can get away with.
 407          * In KA9Q, Karn uses this for the first few times, and then
 408          * goes to quadratic.  netBSD doubles, but only goes up to *64,
 409          * and clamps at 1 to 64 sec afterwards.  Note that 120 sec is
 410          * defined in the protocol as the maximum possible RTT.  I guess
 411          * we'll have to use something other than TCP to talk to the
 412          * University of Mars.
 413          *
 414          * PAWS allows us longer timeouts and large windows, so once
 415          * implemented ftp to mars will work nicely. We will have to fix
 416          * the 120 second clamps though!
 417          */
 418         icsk->icsk_backoff++;
 419         icsk->icsk_retransmits++;
 420
 421 out_reset_timer:
 422         /* If stream is thin, use linear timeouts. Since 'icsk_backoff' is
 423          * used to reset timer, set to 0. Recalculate 'icsk_rto' as this
 424          * might be increased if the stream oscillates between thin and thick,
 425          * thus the old value might already be too high compared to the value
 426          * set by 'tcp_set_rto' in tcp_input.c which resets the rto without
 427          * backoff. Limit to TCP_THIN_LINEAR_RETRIES before initiating
 428          * exponential backoff behaviour to avoid continue hammering
 429          * linear-timeout retransmissions into a black hole
 430          */
 431         if (sk->sk_state == TCP_ESTABLISHED &&
 432             (tp->thin_lto || sysctl_tcp_thin_linear_timeouts) &&
 433             tcp_stream_is_thin(tp) &&
 434             icsk->icsk_retransmits <= TCP_THIN_LINEAR_RETRIES) {
 435                 icsk->icsk_backoff = 0;
 436                 icsk->icsk_rto = min(__tcp_set_rto(tp), TCP_RTO_MAX);
 437         } else {
 438                 /* Use normal (exponential) backoff */
 439                 icsk->icsk_rto = min(icsk->icsk_rto << 1, TCP_RTO_MAX);
 440         }
 441         inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, icsk->icsk_rto, TCP_RTO_MAX);
 442         if (retransmits_timed_out(sk, sysctl_tcp_retries1 + 1, 0, 0))
 443                 __sk_dst_reset(sk);
 444
 445 out:;
 446 }
 447
 448 static void tcp_write_timer(unsigned long data)
 449 {
 450         struct sock *sk = (struct sock *)data;
 451         struct inet_connection_sock *icsk = inet_csk(sk);
 452         int event;
 453
 454         bh_lock_sock(sk);
 455         if (sock_owned_by_user(sk)) {
 456                 /* Try again later */
 457                 sk_reset_timer(sk, &icsk->icsk_retransmit_timer, jiffies + (HZ / 20));
 458                 goto out_unlock;
 459         }
 460
 461         if (sk->sk_state == TCP_CLOSE || !icsk->icsk_pending)
 462                 goto out;
 463
 464         if (time_after(icsk->icsk_timeout, jiffies)) {
 465                 sk_reset_timer(sk, &icsk->icsk_retransmit_timer, icsk->icsk_timeout);
 466                 goto out;
 467         }
 468
 469         event = icsk->icsk_pending;
 470         icsk->icsk_pending = 0;
 471
 472         switch (event) {
 473         case ICSK_TIME_RETRANS:
 474                 tcp_retransmit_timer(sk);
 475                 break;
 476         case ICSK_TIME_PROBE0:
 477                 tcp_probe_timer(sk);
 478                 break;
 479         }
 480
 481 out:
 482         sk_mem_reclaim(sk);
 483 out_unlock:
 484         bh_unlock_sock(sk);
 485         sock_put(sk);
 486 }
 487
 488 /*
 489  *      Timer for listening sockets
 490  */
 491
 492 static void tcp_synack_timer(struct sock *sk)
 493 {
 494         inet_csk_reqsk_queue_prune(sk, TCP_SYNQ_INTERVAL,
 495                                    TCP_TIMEOUT_INIT, TCP_RTO_MAX);
 496 }
 497
 498 void tcp_syn_ack_timeout(struct sock *sk, struct request_sock *req)
 499 {
 500         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPTIMEOUTS);
 501 }
 502 EXPORT_SYMBOL(tcp_syn_ack_timeout);
 503
 504 void tcp_set_keepalive(struct sock *sk, int val)
 505 {
 506         if ((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN))
 507                 return;
 508
 509         if (val && !sock_flag(sk, SOCK_KEEPOPEN))
 510                 inet_csk_reset_keepalive_timer(sk, keepalive_time_when(tcp_sk(sk)));
 511         else if (!val)
 512                 inet_csk_delete_keepalive_timer(sk);
 513 }
 514
 515
 516 static void tcp_keepalive_timer (unsigned long data)
 517 {
 518         struct sock *sk = (struct sock *) data;
 519         struct inet_connection_sock *icsk = inet_csk(sk);
 520         struct tcp_sock *tp = tcp_sk(sk);
 521         u32 elapsed;
 522
 523         /* Only process if socket is not in use. */
 524         bh_lock_sock(sk);
 525         if (sock_owned_by_user(sk)) {
 526                 /* Try again later. */
 527                 inet_csk_reset_keepalive_timer (sk, HZ/20);
 528                 goto out;
 529         }
 530
 531         if (sk->sk_state == TCP_LISTEN) {
 532                 tcp_synack_timer(sk);
 533                 goto out;
 534         }
 535
 536         if (sk->sk_state == TCP_FIN_WAIT2 && sock_flag(sk, SOCK_DEAD)) {
 537                 if (tp->linger2 >= 0) {
 538                         const int tmo = tcp_fin_time(sk) - TCP_TIMEWAIT_LEN;
 539
 540                         if (tmo > 0) {
 541                                 tcp_time_wait(sk, TCP_FIN_WAIT2, tmo);
 542                                 goto out;
 543                         }
 544                 }
 545                 tcp_send_active_reset(sk, GFP_ATOMIC);
 546                 goto death;
 547         }
 548
 549         if (!sock_flag(sk, SOCK_KEEPOPEN) || sk->sk_state == TCP_CLOSE)
 550                 goto out;
 551
 552         elapsed = keepalive_time_when(tp);
 553
 554         /* It is alive without keepalive 8) */
 555         if (tp->packets_out || tcp_send_head(sk))
 556                 goto resched;
 557
 558         elapsed = keepalive_time_elapsed(tp);
 559
 560         if (elapsed >= keepalive_time_when(tp)) {
 561                 /* If the TCP_USER_TIMEOUT option is enabled, use that
 562                  * to determine when to timeout instead.
 563                  */
 564                 if ((icsk->icsk_user_timeout != 0 &&
 565                     elapsed >= icsk->icsk_user_timeout &&
 566                     icsk->icsk_probes_out > 0) ||
 567                     (icsk->icsk_user_timeout == 0 &&
 568                     icsk->icsk_probes_out >= keepalive_probes(tp))) {
 569                         tcp_send_active_reset(sk, GFP_ATOMIC);
 570                         tcp_write_err(sk);
 571                         goto out;
 572                 }
 573                 if (tcp_write_wakeup(sk) <= 0) {
 574                         icsk->icsk_probes_out++;
 575                         elapsed = keepalive_intvl_when(tp);
 576                 } else {
 577                         /* If keepalive was lost due to local congestion,
 578                          * try harder.
 579                          */
 580                         elapsed = TCP_RESOURCE_PROBE_INTERVAL;
 581                 }
 582         } else {
 583                 /* It is tp->rcv_tstamp + keepalive_time_when(tp) */
 584                 elapsed = keepalive_time_when(tp) - elapsed;
 585         }
 586
 587         sk_mem_reclaim(sk);
 588
 589 resched:
 590         inet_csk_reset_keepalive_timer (sk, elapsed);
 591         goto out;
 592
 593 death:
 594         tcp_done(sk);
 595
 596 out:
 597         bh_unlock_sock(sk);
 598         sock_put(sk);
 599 }