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  * Also close if our net namespace is exiting; in that case there is no
  50  * hope of ever communicating again since all netns interfaces are already
  51  * down (or about to be down), and we need to release our dst references,
  52  * which have been moved to the netns loopback interface, so the namespace
  53  * can finish exiting.  This condition is only possible if we are a kernel
  54  * socket, as those do not hold references to the namespace.
  55  *
  56  * Criteria is still not confirmed experimentally and may change.
  57  * We kill the socket, if:
  58  * 1. If number of orphaned sockets exceeds an administratively configured
  59  *    limit.
  60  * 2. If we have strong memory pressure.
  61  * 3. If our net namespace is exiting.
  62  */
  63 static int tcp_out_of_resources(struct sock *sk, bool do_reset)
  64 {
  65         struct tcp_sock *tp = tcp_sk(sk);
  66         int shift = 0;
  67
  68         /* If peer does not open window for long time, or did not transmit
  69          * anything for long time, penalize it. */
  70         if ((s32)(tcp_time_stamp - tp->lsndtime) > 2*TCP_RTO_MAX || !do_reset)
  71                 shift++;
  72
  73         /* If some dubious ICMP arrived, penalize even more. */
  74         if (sk->sk_err_soft)
  75                 shift++;
  76
  77         if (tcp_check_oom(sk, shift)) {
  78                 /* Catch exceptional cases, when connection requires reset.
  79                  *      1. Last segment was sent recently. */
  80                 if ((s32)(tcp_time_stamp - tp->lsndtime) <= TCP_TIMEWAIT_LEN ||
  81                     /*  2. Window is closed. */
  82                     (!tp->snd_wnd && !tp->packets_out))
  83                         do_reset = true;
  84                 if (do_reset)
  85                         tcp_send_active_reset(sk, GFP_ATOMIC);
  86                 tcp_done(sk);
  87                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPABORTONMEMORY);
  88                 return 1;
  89         }
  90
  91         if (!check_net(sock_net(sk))) {
  92                 /* Not possible to send reset; just close */
  93                 tcp_done(sk);
  94                 return 1;
  95         }
  96
  97         return 0;
  98 }
  99
 100 /* Calculate maximal number or retries on an orphaned socket. */
 101 static int tcp_orphan_retries(struct sock *sk, bool 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
 117 static void tcp_mtu_probing(struct inet_connection_sock *icsk, struct sock *sk)
 118 {
 119         struct net *net = sock_net(sk);
 120
 121         /* Black hole detection */
 122         if (net->ipv4.sysctl_tcp_mtu_probing) {
 123                 if (!icsk->icsk_mtup.enabled) {
 124                         icsk->icsk_mtup.enabled = 1;
 125                         icsk->icsk_mtup.probe_timestamp = tcp_time_stamp;
 126                         tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
 127                 } else {
 128                         struct net *net = sock_net(sk);
 129                         struct tcp_sock *tp = tcp_sk(sk);
 130                         int mss;
 131
 132                         mss = tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low) >> 1;
 133                         mss = min(net->ipv4.sysctl_tcp_base_mss, mss);
 134                         mss = max(mss, 68 - tp->tcp_header_len);
 135                         mss = max(mss, net->ipv4.sysctl_tcp_min_snd_mss);
 136                         icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, mss);
 137                         tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
 138                 }
 139         }
 140 }
 141
 142 /* This function calculates a "timeout" which is equivalent to the timeout of a
 143  * TCP connection after "boundary" unsuccessful, exponentially backed-off
 144  * retransmissions with an initial RTO of TCP_RTO_MIN or TCP_TIMEOUT_INIT if
 145  * syn_set flag is set.
 146  */
 147 static bool retransmits_timed_out(struct sock *sk,
 148                                   unsigned int boundary,
 149                                   unsigned int timeout,
 150                                   bool syn_set)
 151 {
 152         unsigned int linear_backoff_thresh, start_ts;
 153         unsigned int rto_base = syn_set ? TCP_TIMEOUT_INIT : TCP_RTO_MIN;
 154
 155         if (!inet_csk(sk)->icsk_retransmits)
 156                 return false;
 157
 158         start_ts = tcp_sk(sk)->retrans_stamp;
 159         if (unlikely(!start_ts))
 160                 start_ts = tcp_skb_timestamp(tcp_write_queue_head(sk));
 161
 162         if (likely(timeout == 0)) {
 163                 linear_backoff_thresh = ilog2(TCP_RTO_MAX/rto_base);
 164
 165                 if (boundary <= linear_backoff_thresh)
 166                         timeout = ((2 << boundary) - 1) * rto_base;
 167                 else
 168                         timeout = ((2 << linear_backoff_thresh) - 1) * rto_base +
 169                                 (boundary - linear_backoff_thresh) * TCP_RTO_MAX;
 170         }
 171         return (tcp_time_stamp - start_ts) >= timeout;
 172 }
 173
 174 /* A write timeout has occurred. Process the after effects. */
 175 static int tcp_write_timeout(struct sock *sk)
 176 {
 177         struct inet_connection_sock *icsk = inet_csk(sk);
 178         struct tcp_sock *tp = tcp_sk(sk);
 179         int retry_until;
 180         bool do_reset, syn_set = false;
 181
 182         if ((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV)) {
 183                 if (icsk->icsk_retransmits) {
 184                         dst_negative_advice(sk);
 185                         if (tp->syn_fastopen || tp->syn_data)
 186                                 tcp_fastopen_cache_set(sk, 0, NULL, true, 0);
 187                         if (tp->syn_data && icsk->icsk_retransmits == 1)
 188                                 NET_INC_STATS_BH(sock_net(sk),
 189                                                  LINUX_MIB_TCPFASTOPENACTIVEFAIL);
 190                 }
 191                 retry_until = icsk->icsk_syn_retries ? : sysctl_tcp_syn_retries;
 192                 syn_set = true;
 193         } else {
 194                 if (retransmits_timed_out(sk, sysctl_tcp_retries1, 0, 0)) {
 195                         /* Some middle-boxes may black-hole Fast Open _after_
 196                          * the handshake. Therefore we conservatively disable
 197                          * Fast Open on this path on recurring timeouts with
 198                          * few or zero bytes acked after Fast Open.
 199                          */
 200                         if (tp->syn_data_acked &&
 201                             tp->bytes_acked <= tp->rx_opt.mss_clamp) {
 202                                 tcp_fastopen_cache_set(sk, 0, NULL, true, 0);
 203                                 if (icsk->icsk_retransmits == sysctl_tcp_retries1)
 204                                         NET_INC_STATS_BH(sock_net(sk),
 205                                                          LINUX_MIB_TCPFASTOPENACTIVEFAIL);
 206                         }
 207                         /* Black hole detection */
 208                         tcp_mtu_probing(icsk, sk);
 209
 210                         dst_negative_advice(sk);
 211                 }
 212
 213                 retry_until = sysctl_tcp_retries2;
 214                 if (sock_flag(sk, SOCK_DEAD)) {
 215                         const bool alive = icsk->icsk_rto < TCP_RTO_MAX;
 216
 217                         retry_until = tcp_orphan_retries(sk, alive);
 218                         do_reset = alive ||
 219                                 !retransmits_timed_out(sk, retry_until, 0, 0);
 220
 221                         if (tcp_out_of_resources(sk, do_reset))
 222                                 return 1;
 223                 }
 224         }
 225
 226         if (retransmits_timed_out(sk, retry_until,
 227                                   syn_set ? 0 : icsk->icsk_user_timeout, syn_set)) {
 228                 /* Has it gone just too far? */
 229                 tcp_write_err(sk);
 230                 return 1;
 231         }
 232         return 0;
 233 }
 234
 235 void tcp_delack_timer_handler(struct sock *sk)
 236 {
 237         struct tcp_sock *tp = tcp_sk(sk);
 238         struct inet_connection_sock *icsk = inet_csk(sk);
 239
 240         sk_mem_reclaim_partial(sk);
 241
 242         if (((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN)) ||
 243             !(icsk->icsk_ack.pending & ICSK_ACK_TIMER))
 244                 goto out;
 245
 246         if (time_after(icsk->icsk_ack.timeout, jiffies)) {
 247                 sk_reset_timer(sk, &icsk->icsk_delack_timer, icsk->icsk_ack.timeout);
 248                 goto out;
 249         }
 250         icsk->icsk_ack.pending &= ~ICSK_ACK_TIMER;
 251
 252         if (!skb_queue_empty(&tp->ucopy.prequeue)) {
 253                 struct sk_buff *skb;
 254
 255                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSCHEDULERFAILED);
 256
 257                 while ((skb = __skb_dequeue(&tp->ucopy.prequeue)) != NULL)
 258                         sk_backlog_rcv(sk, skb);
 259
 260                 tp->ucopy.memory = 0;
 261         }
 262
 263         if (inet_csk_ack_scheduled(sk)) {
 264                 if (!icsk->icsk_ack.pingpong) {
 265                         /* Delayed ACK missed: inflate ATO. */
 266                         icsk->icsk_ack.ato = min(icsk->icsk_ack.ato << 1, icsk->icsk_rto);
 267                 } else {
 268                         /* Delayed ACK missed: leave pingpong mode and
 269                          * deflate ATO.
 270                          */
 271                         icsk->icsk_ack.pingpong = 0;
 272                         icsk->icsk_ack.ato      = TCP_ATO_MIN;
 273                 }
 274                 tcp_send_ack(sk);
 275                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKS);
 276         }
 277
 278 out:
 279         if (tcp_under_memory_pressure(sk))
 280                 sk_mem_reclaim(sk);
 281 }
 282
 283 static void tcp_delack_timer(unsigned long data)
 284 {
 285         struct sock *sk = (struct sock *)data;
 286
 287         bh_lock_sock(sk);
 288         if (!sock_owned_by_user(sk)) {
 289                 tcp_delack_timer_handler(sk);
 290         } else {
 291                 inet_csk(sk)->icsk_ack.blocked = 1;
 292                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKLOCKED);
 293                 /* deleguate our work to tcp_release_cb() */
 294                 if (!test_and_set_bit(TCP_DELACK_TIMER_DEFERRED, &tcp_sk(sk)->tsq_flags))
 295                         sock_hold(sk);
 296         }
 297         bh_unlock_sock(sk);
 298         sock_put(sk);
 299 }
 300
 301 static void tcp_probe_timer(struct sock *sk)
 302 {
 303         struct inet_connection_sock *icsk = inet_csk(sk);
 304         struct tcp_sock *tp = tcp_sk(sk);
 305         int max_probes;
 306         u32 start_ts;
 307
 308         if (tp->packets_out || !tcp_send_head(sk)) {
 309                 icsk->icsk_probes_out = 0;
 310                 return;
 311         }
 312
 313         /* RFC 1122 4.2.2.17 requires the sender to stay open indefinitely as
 314          * long as the receiver continues to respond probes. We support this by
 315          * default and reset icsk_probes_out with incoming ACKs. But if the
 316          * socket is orphaned or the user specifies TCP_USER_TIMEOUT, we
 317          * kill the socket when the retry count and the time exceeds the
 318          * corresponding system limit. We also implement similar policy when
 319          * we use RTO to probe window in tcp_retransmit_timer().
 320          */
 321         start_ts = tcp_skb_timestamp(tcp_send_head(sk));
 322         if (!start_ts)
 323                 skb_mstamp_get(&tcp_send_head(sk)->skb_mstamp);
 324         else if (icsk->icsk_user_timeout &&
 325                  (s32)(tcp_time_stamp - start_ts) > icsk->icsk_user_timeout)
 326                 goto abort;
 327
 328         max_probes = sysctl_tcp_retries2;
 329         if (sock_flag(sk, SOCK_DEAD)) {
 330                 const bool alive = inet_csk_rto_backoff(icsk, TCP_RTO_MAX) < TCP_RTO_MAX;
 331
 332                 max_probes = tcp_orphan_retries(sk, alive);
 333                 if (!alive && icsk->icsk_backoff >= max_probes)
 334                         goto abort;
 335                 if (tcp_out_of_resources(sk, true))
 336                         return;
 337         }
 338
 339         if (icsk->icsk_probes_out >= max_probes) {
 340 abort:          tcp_write_err(sk);
 341         } else {
 342                 /* Only send another probe if we didn't close things up. */
 343                 tcp_send_probe0(sk);
 344         }
 345 }
 346
 347 /*
 348  *      Timer for Fast Open socket to retransmit SYNACK. Note that the
 349  *      sk here is the child socket, not the parent (listener) socket.
 350  */
 351 static void tcp_fastopen_synack_timer(struct sock *sk)
 352 {
 353         struct inet_connection_sock *icsk = inet_csk(sk);
 354         int max_retries = icsk->icsk_syn_retries ? :
 355             sysctl_tcp_synack_retries + 1; /* add one more retry for fastopen */
 356         struct request_sock *req;
 357
 358         req = tcp_sk(sk)->fastopen_rsk;
 359         req->rsk_ops->syn_ack_timeout(req);
 360
 361         if (req->num_timeout >= max_retries) {
 362                 tcp_write_err(sk);
 363                 return;
 364         }
 365         /* XXX (TFO) - Unlike regular SYN-ACK retransmit, we ignore error
 366          * returned from rtx_syn_ack() to make it more persistent like
 367          * regular retransmit because if the child socket has been accepted
 368          * it's not good to give up too easily.
 369          */
 370         inet_rtx_syn_ack(sk, req);
 371         req->num_timeout++;
 372         inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
 373                           TCP_TIMEOUT_INIT << req->num_timeout, TCP_RTO_MAX);
 374 }
 375
 376 /*
 377  *      The TCP retransmit timer.
 378  */
 379
 380 void tcp_retransmit_timer(struct sock *sk)
 381 {
 382         struct tcp_sock *tp = tcp_sk(sk);
 383         struct inet_connection_sock *icsk = inet_csk(sk);
 384
 385         if (tp->fastopen_rsk) {
 386                 WARN_ON_ONCE(sk->sk_state != TCP_SYN_RECV &&
 387                              sk->sk_state != TCP_FIN_WAIT1);
 388                 tcp_fastopen_synack_timer(sk);
 389                 /* Before we receive ACK to our SYN-ACK don't retransmit
 390                  * anything else (e.g., data or FIN segments).
 391                  */
 392                 return;
 393         }
 394         if (!tp->packets_out)
 395                 goto out;
 396
 397         WARN_ON(tcp_write_queue_empty(sk));
 398
 399         tp->tlp_high_seq = 0;
 400
 401         if (!tp->snd_wnd && !sock_flag(sk, SOCK_DEAD) &&
 402             !((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV))) {
 403                 /* Receiver dastardly shrinks window. Our retransmits
 404                  * become zero probes, but we should not timeout this
 405                  * connection. If the socket is an orphan, time it out,
 406                  * we cannot allow such beasts to hang infinitely.
 407                  */
 408                 struct inet_sock *inet = inet_sk(sk);
 409                 if (sk->sk_family == AF_INET) {
 410                         net_dbg_ratelimited("Peer %pI4:%u/%u unexpectedly shrunk window %u:%u (repaired)\n",
 411                                             &inet->inet_daddr,
 412                                             ntohs(inet->inet_dport),
 413                                             inet->inet_num,
 414                                             tp->snd_una, tp->snd_nxt);
 415                 }
 416 #if IS_ENABLED(CONFIG_IPV6)
 417                 else if (sk->sk_family == AF_INET6) {
 418                         net_dbg_ratelimited("Peer %pI6:%u/%u unexpectedly shrunk window %u:%u (repaired)\n",
 419                                             &sk->sk_v6_daddr,
 420                                             ntohs(inet->inet_dport),
 421                                             inet->inet_num,
 422                                             tp->snd_una, tp->snd_nxt);
 423                 }
 424 #endif
 425                 if (tcp_time_stamp - tp->rcv_tstamp > TCP_RTO_MAX) {
 426                         tcp_write_err(sk);
 427                         goto out;
 428                 }
 429                 tcp_enter_loss(sk);
 430                 tcp_retransmit_skb(sk, tcp_write_queue_head(sk));
 431                 __sk_dst_reset(sk);
 432                 goto out_reset_timer;
 433         }
 434
 435         if (tcp_write_timeout(sk))
 436                 goto out;
 437
 438         if (icsk->icsk_retransmits == 0) {
 439                 int mib_idx;
 440
 441                 if (icsk->icsk_ca_state == TCP_CA_Recovery) {
 442                         if (tcp_is_sack(tp))
 443                                 mib_idx = LINUX_MIB_TCPSACKRECOVERYFAIL;
 444                         else
 445                                 mib_idx = LINUX_MIB_TCPRENORECOVERYFAIL;
 446                 } else if (icsk->icsk_ca_state == TCP_CA_Loss) {
 447                         mib_idx = LINUX_MIB_TCPLOSSFAILURES;
 448                 } else if ((icsk->icsk_ca_state == TCP_CA_Disorder) ||
 449                            tp->sacked_out) {
 450                         if (tcp_is_sack(tp))
 451                                 mib_idx = LINUX_MIB_TCPSACKFAILURES;
 452                         else
 453                                 mib_idx = LINUX_MIB_TCPRENOFAILURES;
 454                 } else {
 455                         mib_idx = LINUX_MIB_TCPTIMEOUTS;
 456                 }
 457                 NET_INC_STATS_BH(sock_net(sk), mib_idx);
 458         }
 459
 460         tcp_enter_loss(sk);
 461
 462         if (tcp_retransmit_skb(sk, tcp_write_queue_head(sk)) > 0) {
 463                 /* Retransmission failed because of local congestion,
 464                  * do not backoff.
 465                  */
 466                 if (!icsk->icsk_retransmits)
 467                         icsk->icsk_retransmits = 1;
 468                 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
 469                                           min(icsk->icsk_rto, TCP_RESOURCE_PROBE_INTERVAL),
 470                                           TCP_RTO_MAX);
 471                 goto out;
 472         }
 473
 474         /* Increase the timeout each time we retransmit.  Note that
 475          * we do not increase the rtt estimate.  rto is initialized
 476          * from rtt, but increases here.  Jacobson (SIGCOMM 88) suggests
 477          * that doubling rto each time is the least we can get away with.
 478          * In KA9Q, Karn uses this for the first few times, and then
 479          * goes to quadratic.  netBSD doubles, but only goes up to *64,
 480          * and clamps at 1 to 64 sec afterwards.  Note that 120 sec is
 481          * defined in the protocol as the maximum possible RTT.  I guess
 482          * we'll have to use something other than TCP to talk to the
 483          * University of Mars.
 484          *
 485          * PAWS allows us longer timeouts and large windows, so once
 486          * implemented ftp to mars will work nicely. We will have to fix
 487          * the 120 second clamps though!
 488          */
 489         icsk->icsk_backoff++;
 490         icsk->icsk_retransmits++;
 491
 492 out_reset_timer:
 493         /* If stream is thin, use linear timeouts. Since 'icsk_backoff' is
 494          * used to reset timer, set to 0. Recalculate 'icsk_rto' as this
 495          * might be increased if the stream oscillates between thin and thick,
 496          * thus the old value might already be too high compared to the value
 497          * set by 'tcp_set_rto' in tcp_input.c which resets the rto without
 498          * backoff. Limit to TCP_THIN_LINEAR_RETRIES before initiating
 499          * exponential backoff behaviour to avoid continue hammering
 500          * linear-timeout retransmissions into a black hole
 501          */
 502         if (sk->sk_state == TCP_ESTABLISHED &&
 503             (tp->thin_lto || sysctl_tcp_thin_linear_timeouts) &&
 504             tcp_stream_is_thin(tp) &&
 505             icsk->icsk_retransmits <= TCP_THIN_LINEAR_RETRIES) {
 506                 icsk->icsk_backoff = 0;
 507                 icsk->icsk_rto = min(__tcp_set_rto(tp), TCP_RTO_MAX);
 508         } else {
 509                 /* Use normal (exponential) backoff */
 510                 icsk->icsk_rto = min(icsk->icsk_rto << 1, TCP_RTO_MAX);
 511         }
 512         inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, icsk->icsk_rto, TCP_RTO_MAX);
 513         if (retransmits_timed_out(sk, sysctl_tcp_retries1 + 1, 0, 0))
 514                 __sk_dst_reset(sk);
 515
 516 out:;
 517 }
 518
 519 void tcp_write_timer_handler(struct sock *sk)
 520 {
 521         struct inet_connection_sock *icsk = inet_csk(sk);
 522         int event;
 523
 524         if (((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN)) ||
 525             !icsk->icsk_pending)
 526                 goto out;
 527
 528         if (time_after(icsk->icsk_timeout, jiffies)) {
 529                 sk_reset_timer(sk, &icsk->icsk_retransmit_timer, icsk->icsk_timeout);
 530                 goto out;
 531         }
 532
 533         event = icsk->icsk_pending;
 534
 535         switch (event) {
 536         case ICSK_TIME_EARLY_RETRANS:
 537                 tcp_resume_early_retransmit(sk);
 538                 break;
 539         case ICSK_TIME_LOSS_PROBE:
 540                 tcp_send_loss_probe(sk);
 541                 break;
 542         case ICSK_TIME_RETRANS:
 543                 icsk->icsk_pending = 0;
 544                 tcp_retransmit_timer(sk);
 545                 break;
 546         case ICSK_TIME_PROBE0:
 547                 icsk->icsk_pending = 0;
 548                 tcp_probe_timer(sk);
 549                 break;
 550         }
 551
 552 out:
 553         sk_mem_reclaim(sk);
 554 }
 555
 556 static void tcp_write_timer(unsigned long data)
 557 {
 558         struct sock *sk = (struct sock *)data;
 559
 560         bh_lock_sock(sk);
 561         if (!sock_owned_by_user(sk)) {
 562                 tcp_write_timer_handler(sk);
 563         } else {
 564                 /* deleguate our work to tcp_release_cb() */
 565                 if (!test_and_set_bit(TCP_WRITE_TIMER_DEFERRED, &tcp_sk(sk)->tsq_flags))
 566                         sock_hold(sk);
 567         }
 568         bh_unlock_sock(sk);
 569         sock_put(sk);
 570 }
 571
 572 void tcp_syn_ack_timeout(const struct request_sock *req)
 573 {
 574         struct net *net = read_pnet(&inet_rsk(req)->ireq_net);
 575
 576         NET_INC_STATS_BH(net, LINUX_MIB_TCPTIMEOUTS);
 577 }
 578 EXPORT_SYMBOL(tcp_syn_ack_timeout);
 579
 580 void tcp_set_keepalive(struct sock *sk, int val)
 581 {
 582         if ((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN))
 583                 return;
 584
 585         if (val && !sock_flag(sk, SOCK_KEEPOPEN))
 586                 inet_csk_reset_keepalive_timer(sk, keepalive_time_when(tcp_sk(sk)));
 587         else if (!val)
 588                 inet_csk_delete_keepalive_timer(sk);
 589 }
 590
 591
 592 static void tcp_keepalive_timer (unsigned long data)
 593 {
 594         struct sock *sk = (struct sock *) data;
 595         struct inet_connection_sock *icsk = inet_csk(sk);
 596         struct tcp_sock *tp = tcp_sk(sk);
 597         u32 elapsed;
 598
 599         /* Only process if socket is not in use. */
 600         bh_lock_sock(sk);
 601         if (sock_owned_by_user(sk)) {
 602                 /* Try again later. */
 603                 inet_csk_reset_keepalive_timer (sk, HZ/20);
 604                 goto out;
 605         }
 606
 607         if (sk->sk_state == TCP_LISTEN) {
 608                 pr_err("Hmm... keepalive on a LISTEN ???\n");
 609                 goto out;
 610         }
 611
 612         if (sk->sk_state == TCP_FIN_WAIT2 && sock_flag(sk, SOCK_DEAD)) {
 613                 if (tp->linger2 >= 0) {
 614                         const int tmo = tcp_fin_time(sk) - TCP_TIMEWAIT_LEN;
 615
 616                         if (tmo > 0) {
 617                                 tcp_time_wait(sk, TCP_FIN_WAIT2, tmo);
 618                                 goto out;
 619                         }
 620                 }
 621                 tcp_send_active_reset(sk, GFP_ATOMIC);
 622                 goto death;
 623         }
 624
 625         if (!sock_flag(sk, SOCK_KEEPOPEN) ||
 626             ((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_SYN_SENT)))
 627                 goto out;
 628
 629         elapsed = keepalive_time_when(tp);
 630
 631         /* It is alive without keepalive 8) */
 632         if (tp->packets_out || tcp_send_head(sk))
 633                 goto resched;
 634
 635         elapsed = keepalive_time_elapsed(tp);
 636
 637         if (elapsed >= keepalive_time_when(tp)) {
 638                 /* If the TCP_USER_TIMEOUT option is enabled, use that
 639                  * to determine when to timeout instead.
 640                  */
 641                 if ((icsk->icsk_user_timeout != 0 &&
 642                     elapsed >= icsk->icsk_user_timeout &&
 643                     icsk->icsk_probes_out > 0) ||
 644                     (icsk->icsk_user_timeout == 0 &&
 645                     icsk->icsk_probes_out >= keepalive_probes(tp))) {
 646                         tcp_send_active_reset(sk, GFP_ATOMIC);
 647                         tcp_write_err(sk);
 648                         goto out;
 649                 }
 650                 if (tcp_write_wakeup(sk, LINUX_MIB_TCPKEEPALIVE) <= 0) {
 651                         icsk->icsk_probes_out++;
 652                         elapsed = keepalive_intvl_when(tp);
 653                 } else {
 654                         /* If keepalive was lost due to local congestion,
 655                          * try harder.
 656                          */
 657                         elapsed = TCP_RESOURCE_PROBE_INTERVAL;
 658                 }
 659         } else {
 660                 /* It is tp->rcv_tstamp + keepalive_time_when(tp) */
 661                 elapsed = keepalive_time_when(tp) - elapsed;
 662         }
 663
 664         sk_mem_reclaim(sk);
 665
 666 resched:
 667         inet_csk_reset_keepalive_timer (sk, elapsed);
 668         goto out;
 669
 670 death:
 671         tcp_done(sk);
 672
 673 out:
 674         bh_unlock_sock(sk);
 675         sock_put(sk);
 676 }
 677
 678 void tcp_init_xmit_timers(struct sock *sk)
 679 {
 680         inet_csk_init_xmit_timers(sk, &tcp_write_timer, &tcp_delack_timer,
 681                                   &tcp_keepalive_timer);
 682 }