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