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_thin_linear_timeouts __read_mostly;
  26
  27 static void tcp_write_err(struct sock *sk)
  28 {
  29         sk->sk_err = sk->sk_err_soft ? : ETIMEDOUT;
  30         sk->sk_error_report(sk);
  31
  32         tcp_done(sk);
  33         __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTONTIMEOUT);
  34 }
  35
  36 /* Do not allow orphaned sockets to eat all our resources.
  37  * This is direct violation of TCP specs, but it is required
  38  * to prevent DoS attacks. It is called when a retransmission timeout
  39  * or zero probe timeout occurs on orphaned socket.
  40  *
  41  * Criteria is still not confirmed experimentally and may change.
  42  * We kill the socket, if:
  43  * 1. If number of orphaned sockets exceeds an administratively configured
  44  *    limit.
  45  * 2. If we have strong memory pressure.
  46  */
  47 static int tcp_out_of_resources(struct sock *sk, bool do_reset)
  48 {
  49         struct tcp_sock *tp = tcp_sk(sk);
  50         int shift = 0;
  51
  52         /* If peer does not open window for long time, or did not transmit
  53          * anything for long time, penalize it. */
  54         if ((s32)(tcp_time_stamp - tp->lsndtime) > 2*TCP_RTO_MAX || !do_reset)
  55                 shift++;
  56
  57         /* If some dubious ICMP arrived, penalize even more. */
  58         if (sk->sk_err_soft)
  59                 shift++;
  60
  61         if (tcp_check_oom(sk, shift)) {
  62                 /* Catch exceptional cases, when connection requires reset.
  63                  *      1. Last segment was sent recently. */
  64                 if ((s32)(tcp_time_stamp - tp->lsndtime) <= TCP_TIMEWAIT_LEN ||
  65                     /*  2. Window is closed. */
  66                     (!tp->snd_wnd && !tp->packets_out))
  67                         do_reset = true;
  68                 if (do_reset)
  69                         tcp_send_active_reset(sk, GFP_ATOMIC);
  70                 tcp_done(sk);
  71                 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTONMEMORY);
  72                 return 1;
  73         }
  74         return 0;
  75 }
  76
  77 /* Calculate maximal number or retries on an orphaned socket. */
  78 static int tcp_orphan_retries(struct sock *sk, bool alive)
  79 {
  80         int retries = sock_net(sk)->ipv4.sysctl_tcp_orphan_retries; /* May be zero. */
  81
  82         /* We know from an ICMP that something is wrong. */
  83         if (sk->sk_err_soft && !alive)
  84                 retries = 0;
  85
  86         /* However, if socket sent something recently, select some safe
  87          * number of retries. 8 corresponds to >100 seconds with minimal
  88          * RTO of 200msec. */
  89         if (retries == 0 && alive)
  90                 retries = 8;
  91         return retries;
  92 }
  93
  94 static void tcp_mtu_probing(struct inet_connection_sock *icsk, struct sock *sk)
  95 {
  96         struct net *net = sock_net(sk);
  97
  98         /* Black hole detection */
  99         if (net->ipv4.sysctl_tcp_mtu_probing) {
 100                 if (!icsk->icsk_mtup.enabled) {
 101                         icsk->icsk_mtup.enabled = 1;
 102                         icsk->icsk_mtup.probe_timestamp = tcp_time_stamp;
 103                         tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
 104                 } else {
 105                         struct net *net = sock_net(sk);
 106                         struct tcp_sock *tp = tcp_sk(sk);
 107                         int mss;
 108
 109                         mss = tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low) >> 1;
 110                         mss = min(net->ipv4.sysctl_tcp_base_mss, mss);
 111                         mss = max(mss, 68 - tp->tcp_header_len);
 112                         icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, mss);
 113                         tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
 114                 }
 115         }
 116 }
 117
 118 /* This function calculates a "timeout" which is equivalent to the timeout of a
 119  * TCP connection after "boundary" unsuccessful, exponentially backed-off
 120  * retransmissions with an initial RTO of TCP_RTO_MIN or TCP_TIMEOUT_INIT if
 121  * syn_set flag is set.
 122  */
 123 static bool retransmits_timed_out(struct sock *sk,
 124                                   unsigned int boundary,
 125                                   unsigned int timeout,
 126                                   bool syn_set)
 127 {
 128         unsigned int linear_backoff_thresh, start_ts;
 129         unsigned int rto_base = syn_set ? TCP_TIMEOUT_INIT : TCP_RTO_MIN;
 130
 131         if (!inet_csk(sk)->icsk_retransmits)
 132                 return false;
 133
 134         start_ts = tcp_sk(sk)->retrans_stamp;
 135         if (unlikely(!start_ts))
 136                 start_ts = tcp_skb_timestamp(tcp_write_queue_head(sk));
 137
 138         if (likely(timeout == 0)) {
 139                 linear_backoff_thresh = ilog2(TCP_RTO_MAX/rto_base);
 140
 141                 if (boundary <= linear_backoff_thresh)
 142                         timeout = ((2 << boundary) - 1) * rto_base;
 143                 else
 144                         timeout = ((2 << linear_backoff_thresh) - 1) * rto_base +
 145                                 (boundary - linear_backoff_thresh) * TCP_RTO_MAX;
 146         }
 147         return (tcp_time_stamp - start_ts) >= timeout;
 148 }
 149
 150 /* A write timeout has occurred. Process the after effects. */
 151 static int tcp_write_timeout(struct sock *sk)
 152 {
 153         struct inet_connection_sock *icsk = inet_csk(sk);
 154         struct tcp_sock *tp = tcp_sk(sk);
 155         struct net *net = sock_net(sk);
 156         int retry_until;
 157         bool do_reset, syn_set = false;
 158
 159         if ((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV)) {
 160                 if (icsk->icsk_retransmits) {
 161                         dst_negative_advice(sk);
 162                         if (tp->syn_fastopen || tp->syn_data)
 163                                 tcp_fastopen_cache_set(sk, 0, NULL, true, 0);
 164                         if (tp->syn_data && icsk->icsk_retransmits == 1)
 165                                 NET_INC_STATS(sock_net(sk),
 166                                               LINUX_MIB_TCPFASTOPENACTIVEFAIL);
 167                 }
 168                 retry_until = icsk->icsk_syn_retries ? : net->ipv4.sysctl_tcp_syn_retries;
 169                 syn_set = true;
 170         } else {
 171                 if (retransmits_timed_out(sk, net->ipv4.sysctl_tcp_retries1, 0, 0)) {
 172                         /* Some middle-boxes may black-hole Fast Open _after_
 173                          * the handshake. Therefore we conservatively disable
 174                          * Fast Open on this path on recurring timeouts with
 175                          * few or zero bytes acked after Fast Open.
 176                          */
 177                         if (tp->syn_data_acked &&
 178                             tp->bytes_acked <= tp->rx_opt.mss_clamp) {
 179                                 tcp_fastopen_cache_set(sk, 0, NULL, true, 0);
 180                                 if (icsk->icsk_retransmits == net->ipv4.sysctl_tcp_retries1)
 181                                         NET_INC_STATS(sock_net(sk),
 182                                                       LINUX_MIB_TCPFASTOPENACTIVEFAIL);
 183                         }
 184                         /* Black hole detection */
 185                         tcp_mtu_probing(icsk, sk);
 186
 187                         dst_negative_advice(sk);
 188                 }
 189
 190                 retry_until = net->ipv4.sysctl_tcp_retries2;
 191                 if (sock_flag(sk, SOCK_DEAD)) {
 192                         const bool alive = icsk->icsk_rto < TCP_RTO_MAX;
 193
 194                         retry_until = tcp_orphan_retries(sk, alive);
 195                         do_reset = alive ||
 196                                 !retransmits_timed_out(sk, retry_until, 0, 0);
 197
 198                         if (tcp_out_of_resources(sk, do_reset))
 199                                 return 1;
 200                 }
 201         }
 202
 203         if (retransmits_timed_out(sk, retry_until,
 204                                   syn_set ? 0 : icsk->icsk_user_timeout, syn_set)) {
 205                 /* Has it gone just too far? */
 206                 tcp_write_err(sk);
 207                 return 1;
 208         }
 209         return 0;
 210 }
 211
 212 /* Called with BH disabled */
 213 void tcp_delack_timer_handler(struct sock *sk)
 214 {
 215         struct tcp_sock *tp = tcp_sk(sk);
 216         struct inet_connection_sock *icsk = inet_csk(sk);
 217
 218         sk_mem_reclaim_partial(sk);
 219
 220         if (sk->sk_state == TCP_CLOSE || !(icsk->icsk_ack.pending & ICSK_ACK_TIMER))
 221                 goto out;
 222
 223         if (time_after(icsk->icsk_ack.timeout, jiffies)) {
 224                 sk_reset_timer(sk, &icsk->icsk_delack_timer, icsk->icsk_ack.timeout);
 225                 goto out;
 226         }
 227         icsk->icsk_ack.pending &= ~ICSK_ACK_TIMER;
 228
 229         if (!skb_queue_empty(&tp->ucopy.prequeue)) {
 230                 struct sk_buff *skb;
 231
 232                 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPSCHEDULERFAILED);
 233
 234                 while ((skb = __skb_dequeue(&tp->ucopy.prequeue)) != NULL)
 235                         sk_backlog_rcv(sk, skb);
 236
 237                 tp->ucopy.memory = 0;
 238         }
 239
 240         if (inet_csk_ack_scheduled(sk)) {
 241                 if (!icsk->icsk_ack.pingpong) {
 242                         /* Delayed ACK missed: inflate ATO. */
 243                         icsk->icsk_ack.ato = min(icsk->icsk_ack.ato << 1, icsk->icsk_rto);
 244                 } else {
 245                         /* Delayed ACK missed: leave pingpong mode and
 246                          * deflate ATO.
 247                          */
 248                         icsk->icsk_ack.pingpong = 0;
 249                         icsk->icsk_ack.ato      = TCP_ATO_MIN;
 250                 }
 251                 tcp_send_ack(sk);
 252                 __NET_INC_STATS(sock_net(sk), LINUX_MIB_DELAYEDACKS);
 253         }
 254
 255 out:
 256         if (tcp_under_memory_pressure(sk))
 257                 sk_mem_reclaim(sk);
 258 }
 259
 260 static void tcp_delack_timer(unsigned long data)
 261 {
 262         struct sock *sk = (struct sock *)data;
 263
 264         bh_lock_sock(sk);
 265         if (!sock_owned_by_user(sk)) {
 266                 tcp_delack_timer_handler(sk);
 267         } else {
 268                 inet_csk(sk)->icsk_ack.blocked = 1;
 269                 __NET_INC_STATS(sock_net(sk), LINUX_MIB_DELAYEDACKLOCKED);
 270                 /* deleguate our work to tcp_release_cb() */
 271                 if (!test_and_set_bit(TCP_DELACK_TIMER_DEFERRED, &tcp_sk(sk)->tsq_flags))
 272                         sock_hold(sk);
 273         }
 274         bh_unlock_sock(sk);
 275         sock_put(sk);
 276 }
 277
 278 static void tcp_probe_timer(struct sock *sk)
 279 {
 280         struct inet_connection_sock *icsk = inet_csk(sk);
 281         struct tcp_sock *tp = tcp_sk(sk);
 282         int max_probes;
 283         u32 start_ts;
 284
 285         if (tp->packets_out || !tcp_send_head(sk)) {
 286                 icsk->icsk_probes_out = 0;
 287                 return;
 288         }
 289
 290         /* RFC 1122 4.2.2.17 requires the sender to stay open indefinitely as
 291          * long as the receiver continues to respond probes. We support this by
 292          * default and reset icsk_probes_out with incoming ACKs. But if the
 293          * socket is orphaned or the user specifies TCP_USER_TIMEOUT, we
 294          * kill the socket when the retry count and the time exceeds the
 295          * corresponding system limit. We also implement similar policy when
 296          * we use RTO to probe window in tcp_retransmit_timer().
 297          */
 298         start_ts = tcp_skb_timestamp(tcp_send_head(sk));
 299         if (!start_ts)
 300                 skb_mstamp_get(&tcp_send_head(sk)->skb_mstamp);
 301         else if (icsk->icsk_user_timeout &&
 302                  (s32)(tcp_time_stamp - start_ts) > icsk->icsk_user_timeout)
 303                 goto abort;
 304
 305         max_probes = sock_net(sk)->ipv4.sysctl_tcp_retries2;
 306         if (sock_flag(sk, SOCK_DEAD)) {
 307                 const bool alive = inet_csk_rto_backoff(icsk, TCP_RTO_MAX) < TCP_RTO_MAX;
 308
 309                 max_probes = tcp_orphan_retries(sk, alive);
 310                 if (!alive && icsk->icsk_backoff >= max_probes)
 311                         goto abort;
 312                 if (tcp_out_of_resources(sk, true))
 313                         return;
 314         }
 315
 316         if (icsk->icsk_probes_out > max_probes) {
 317 abort:          tcp_write_err(sk);
 318         } else {
 319                 /* Only send another probe if we didn't close things up. */
 320                 tcp_send_probe0(sk);
 321         }
 322 }
 323
 324 /*
 325  *      Timer for Fast Open socket to retransmit SYNACK. Note that the
 326  *      sk here is the child socket, not the parent (listener) socket.
 327  */
 328 static void tcp_fastopen_synack_timer(struct sock *sk)
 329 {
 330         struct inet_connection_sock *icsk = inet_csk(sk);
 331         int max_retries = icsk->icsk_syn_retries ? :
 332             sock_net(sk)->ipv4.sysctl_tcp_synack_retries + 1; /* add one more retry for fastopen */
 333         struct request_sock *req;
 334
 335         req = tcp_sk(sk)->fastopen_rsk;
 336         req->rsk_ops->syn_ack_timeout(req);
 337
 338         if (req->num_timeout >= max_retries) {
 339                 tcp_write_err(sk);
 340                 return;
 341         }
 342         /* XXX (TFO) - Unlike regular SYN-ACK retransmit, we ignore error
 343          * returned from rtx_syn_ack() to make it more persistent like
 344          * regular retransmit because if the child socket has been accepted
 345          * it's not good to give up too easily.
 346          */
 347         inet_rtx_syn_ack(sk, req);
 348         req->num_timeout++;
 349         inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
 350                           TCP_TIMEOUT_INIT << req->num_timeout, TCP_RTO_MAX);
 351 }
 352
 353 /*
 354  *      The TCP retransmit timer.
 355  */
 356
 357 void tcp_retransmit_timer(struct sock *sk)
 358 {
 359         struct tcp_sock *tp = tcp_sk(sk);
 360         struct net *net = sock_net(sk);
 361         struct inet_connection_sock *icsk = inet_csk(sk);
 362
 363         if (tp->fastopen_rsk) {
 364                 WARN_ON_ONCE(sk->sk_state != TCP_SYN_RECV &&
 365                              sk->sk_state != TCP_FIN_WAIT1);
 366                 tcp_fastopen_synack_timer(sk);
 367                 /* Before we receive ACK to our SYN-ACK don't retransmit
 368                  * anything else (e.g., data or FIN segments).
 369                  */
 370                 return;
 371         }
 372         if (!tp->packets_out)
 373                 goto out;
 374
 375         WARN_ON(tcp_write_queue_empty(sk));
 376
 377         tp->tlp_high_seq = 0;
 378
 379         if (!tp->snd_wnd && !sock_flag(sk, SOCK_DEAD) &&
 380             !((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV))) {
 381                 /* Receiver dastardly shrinks window. Our retransmits
 382                  * become zero probes, but we should not timeout this
 383                  * connection. If the socket is an orphan, time it out,
 384                  * we cannot allow such beasts to hang infinitely.
 385                  */
 386                 struct inet_sock *inet = inet_sk(sk);
 387                 if (sk->sk_family == AF_INET) {
 388                         net_dbg_ratelimited("Peer %pI4:%u/%u unexpectedly shrunk window %u:%u (repaired)\n",
 389                                             &inet->inet_daddr,
 390                                             ntohs(inet->inet_dport),
 391                                             inet->inet_num,
 392                                             tp->snd_una, tp->snd_nxt);
 393                 }
 394 #if IS_ENABLED(CONFIG_IPV6)
 395                 else if (sk->sk_family == AF_INET6) {
 396                         net_dbg_ratelimited("Peer %pI6:%u/%u unexpectedly shrunk window %u:%u (repaired)\n",
 397                                             &sk->sk_v6_daddr,
 398                                             ntohs(inet->inet_dport),
 399                                             inet->inet_num,
 400                                             tp->snd_una, tp->snd_nxt);
 401                 }
 402 #endif
 403                 if (tcp_time_stamp - tp->rcv_tstamp > TCP_RTO_MAX) {
 404                         tcp_write_err(sk);
 405                         goto out;
 406                 }
 407                 tcp_enter_loss(sk);
 408                 tcp_retransmit_skb(sk, tcp_write_queue_head(sk), 1);
 409                 __sk_dst_reset(sk);
 410                 goto out_reset_timer;
 411         }
 412
 413         if (tcp_write_timeout(sk))
 414                 goto out;
 415
 416         if (icsk->icsk_retransmits == 0) {
 417                 int mib_idx;
 418
 419                 if (icsk->icsk_ca_state == TCP_CA_Recovery) {
 420                         if (tcp_is_sack(tp))
 421                                 mib_idx = LINUX_MIB_TCPSACKRECOVERYFAIL;
 422                         else
 423                                 mib_idx = LINUX_MIB_TCPRENORECOVERYFAIL;
 424                 } else if (icsk->icsk_ca_state == TCP_CA_Loss) {
 425                         mib_idx = LINUX_MIB_TCPLOSSFAILURES;
 426                 } else if ((icsk->icsk_ca_state == TCP_CA_Disorder) ||
 427                            tp->sacked_out) {
 428                         if (tcp_is_sack(tp))
 429                                 mib_idx = LINUX_MIB_TCPSACKFAILURES;
 430                         else
 431                                 mib_idx = LINUX_MIB_TCPRENOFAILURES;
 432                 } else {
 433                         mib_idx = LINUX_MIB_TCPTIMEOUTS;
 434                 }
 435                 __NET_INC_STATS(sock_net(sk), mib_idx);
 436         }
 437
 438         tcp_enter_loss(sk);
 439
 440         if (tcp_retransmit_skb(sk, tcp_write_queue_head(sk), 1) > 0) {
 441                 /* Retransmission failed because of local congestion,
 442                  * do not backoff.
 443                  */
 444                 if (!icsk->icsk_retransmits)
 445                         icsk->icsk_retransmits = 1;
 446                 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
 447                                           min(icsk->icsk_rto, TCP_RESOURCE_PROBE_INTERVAL),
 448                                           TCP_RTO_MAX);
 449                 goto out;
 450         }
 451
 452         /* Increase the timeout each time we retransmit.  Note that
 453          * we do not increase the rtt estimate.  rto is initialized
 454          * from rtt, but increases here.  Jacobson (SIGCOMM 88) suggests
 455          * that doubling rto each time is the least we can get away with.
 456          * In KA9Q, Karn uses this for the first few times, and then
 457          * goes to quadratic.  netBSD doubles, but only goes up to *64,
 458          * and clamps at 1 to 64 sec afterwards.  Note that 120 sec is
 459          * defined in the protocol as the maximum possible RTT.  I guess
 460          * we'll have to use something other than TCP to talk to the
 461          * University of Mars.
 462          *
 463          * PAWS allows us longer timeouts and large windows, so once
 464          * implemented ftp to mars will work nicely. We will have to fix
 465          * the 120 second clamps though!
 466          */
 467         icsk->icsk_backoff++;
 468         icsk->icsk_retransmits++;
 469
 470 out_reset_timer:
 471         /* If stream is thin, use linear timeouts. Since 'icsk_backoff' is
 472          * used to reset timer, set to 0. Recalculate 'icsk_rto' as this
 473          * might be increased if the stream oscillates between thin and thick,
 474          * thus the old value might already be too high compared to the value
 475          * set by 'tcp_set_rto' in tcp_input.c which resets the rto without
 476          * backoff. Limit to TCP_THIN_LINEAR_RETRIES before initiating
 477          * exponential backoff behaviour to avoid continue hammering
 478          * linear-timeout retransmissions into a black hole
 479          */
 480         if (sk->sk_state == TCP_ESTABLISHED &&
 481             (tp->thin_lto || sysctl_tcp_thin_linear_timeouts) &&
 482             tcp_stream_is_thin(tp) &&
 483             icsk->icsk_retransmits <= TCP_THIN_LINEAR_RETRIES) {
 484                 icsk->icsk_backoff = 0;
 485                 icsk->icsk_rto = min(__tcp_set_rto(tp), TCP_RTO_MAX);
 486         } else {
 487                 /* Use normal (exponential) backoff */
 488                 icsk->icsk_rto = min(icsk->icsk_rto << 1, TCP_RTO_MAX);
 489         }
 490         inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, icsk->icsk_rto, TCP_RTO_MAX);
 491         if (retransmits_timed_out(sk, net->ipv4.sysctl_tcp_retries1 + 1, 0, 0))
 492                 __sk_dst_reset(sk);
 493
 494 out:;
 495 }
 496
 497 /* Called with BH disabled */
 498 void tcp_write_timer_handler(struct sock *sk)
 499 {
 500         struct inet_connection_sock *icsk = inet_csk(sk);
 501         int event;
 502
 503         if (sk->sk_state == TCP_CLOSE || !icsk->icsk_pending)
 504                 goto out;
 505
 506         if (time_after(icsk->icsk_timeout, jiffies)) {
 507                 sk_reset_timer(sk, &icsk->icsk_retransmit_timer, icsk->icsk_timeout);
 508                 goto out;
 509         }
 510
 511         event = icsk->icsk_pending;
 512
 513         switch (event) {
 514         case ICSK_TIME_EARLY_RETRANS:
 515                 tcp_resume_early_retransmit(sk);
 516                 break;
 517         case ICSK_TIME_LOSS_PROBE:
 518                 tcp_send_loss_probe(sk);
 519                 break;
 520         case ICSK_TIME_RETRANS:
 521                 icsk->icsk_pending = 0;
 522                 tcp_retransmit_timer(sk);
 523                 break;
 524         case ICSK_TIME_PROBE0:
 525                 icsk->icsk_pending = 0;
 526                 tcp_probe_timer(sk);
 527                 break;
 528         }
 529
 530 out:
 531         sk_mem_reclaim(sk);
 532 }
 533
 534 static void tcp_write_timer(unsigned long data)
 535 {
 536         struct sock *sk = (struct sock *)data;
 537
 538         bh_lock_sock(sk);
 539         if (!sock_owned_by_user(sk)) {
 540                 tcp_write_timer_handler(sk);
 541         } else {
 542                 /* deleguate our work to tcp_release_cb() */
 543                 if (!test_and_set_bit(TCP_WRITE_TIMER_DEFERRED, &tcp_sk(sk)->tsq_flags))
 544                         sock_hold(sk);
 545         }
 546         bh_unlock_sock(sk);
 547         sock_put(sk);
 548 }
 549
 550 void tcp_syn_ack_timeout(const struct request_sock *req)
 551 {
 552         struct net *net = read_pnet(&inet_rsk(req)->ireq_net);
 553
 554         __NET_INC_STATS(net, LINUX_MIB_TCPTIMEOUTS);
 555 }
 556 EXPORT_SYMBOL(tcp_syn_ack_timeout);
 557
 558 void tcp_set_keepalive(struct sock *sk, int val)
 559 {
 560         if ((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN))
 561                 return;
 562
 563         if (val && !sock_flag(sk, SOCK_KEEPOPEN))
 564                 inet_csk_reset_keepalive_timer(sk, keepalive_time_when(tcp_sk(sk)));
 565         else if (!val)
 566                 inet_csk_delete_keepalive_timer(sk);
 567 }
 568
 569
 570 static void tcp_keepalive_timer (unsigned long data)
 571 {
 572         struct sock *sk = (struct sock *) data;
 573         struct inet_connection_sock *icsk = inet_csk(sk);
 574         struct tcp_sock *tp = tcp_sk(sk);
 575         u32 elapsed;
 576
 577         /* Only process if socket is not in use. */
 578         bh_lock_sock(sk);
 579         if (sock_owned_by_user(sk)) {
 580                 /* Try again later. */
 581                 inet_csk_reset_keepalive_timer (sk, HZ/20);
 582                 goto out;
 583         }
 584
 585         if (sk->sk_state == TCP_LISTEN) {
 586                 pr_err("Hmm... keepalive on a LISTEN ???\n");
 587                 goto out;
 588         }
 589
 590         if (sk->sk_state == TCP_FIN_WAIT2 && sock_flag(sk, SOCK_DEAD)) {
 591                 if (tp->linger2 >= 0) {
 592                         const int tmo = tcp_fin_time(sk) - TCP_TIMEWAIT_LEN;
 593
 594                         if (tmo > 0) {
 595                                 tcp_time_wait(sk, TCP_FIN_WAIT2, tmo);
 596                                 goto out;
 597                         }
 598                 }
 599                 tcp_send_active_reset(sk, GFP_ATOMIC);
 600                 goto death;
 601         }
 602
 603         if (!sock_flag(sk, SOCK_KEEPOPEN) || sk->sk_state == TCP_CLOSE)
 604                 goto out;
 605
 606         elapsed = keepalive_time_when(tp);
 607
 608         /* It is alive without keepalive 8) */
 609         if (tp->packets_out || tcp_send_head(sk))
 610                 goto resched;
 611
 612         elapsed = keepalive_time_elapsed(tp);
 613
 614         if (elapsed >= keepalive_time_when(tp)) {
 615                 /* If the TCP_USER_TIMEOUT option is enabled, use that
 616                  * to determine when to timeout instead.
 617                  */
 618                 if ((icsk->icsk_user_timeout != 0 &&
 619                     elapsed >= icsk->icsk_user_timeout &&
 620                     icsk->icsk_probes_out > 0) ||
 621                     (icsk->icsk_user_timeout == 0 &&
 622                     icsk->icsk_probes_out >= keepalive_probes(tp))) {
 623                         tcp_send_active_reset(sk, GFP_ATOMIC);
 624                         tcp_write_err(sk);
 625                         goto out;
 626                 }
 627                 if (tcp_write_wakeup(sk, LINUX_MIB_TCPKEEPALIVE) <= 0) {
 628                         icsk->icsk_probes_out++;
 629                         elapsed = keepalive_intvl_when(tp);
 630                 } else {
 631                         /* If keepalive was lost due to local congestion,
 632                          * try harder.
 633                          */
 634                         elapsed = TCP_RESOURCE_PROBE_INTERVAL;
 635                 }
 636         } else {
 637                 /* It is tp->rcv_tstamp + keepalive_time_when(tp) */
 638                 elapsed = keepalive_time_when(tp) - elapsed;
 639         }
 640
 641         sk_mem_reclaim(sk);
 642
 643 resched:
 644         inet_csk_reset_keepalive_timer (sk, elapsed);
 645         goto out;
 646
 647 death:
 648         tcp_done(sk);
 649
 650 out:
 651         bh_unlock_sock(sk);
 652         sock_put(sk);
 653 }
 654
 655 void tcp_init_xmit_timers(struct sock *sk)
 656 {
 657         inet_csk_init_xmit_timers(sk, &tcp_write_timer, &tcp_delack_timer,
 658                                   &tcp_keepalive_timer);
 659 }