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_retries1 __read_mostly = TCP_RETR1;
  28 int sysctl_tcp_retries2 __read_mostly = TCP_RETR2;
  29 int sysctl_tcp_orphan_retries __read_mostly;
  30 int sysctl_tcp_thin_linear_timeouts __read_mostly;
  31
  32 static void tcp_write_err(struct sock *sk)
  33 {
  34         sk->sk_err = sk->sk_err_soft ? : ETIMEDOUT;
  35         sk->sk_error_report(sk);
  36
  37         tcp_done(sk);
  38         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPABORTONTIMEOUT);
  39 }
  40
  41 /* Do not allow orphaned sockets to eat all our resources.
  42  * This is direct violation of TCP specs, but it is required
  43  * to prevent DoS attacks. It is called when a retransmission timeout
  44  * or zero probe timeout occurs on orphaned socket.
  45  *
  46  * Criteria is still not confirmed experimentally and may change.
  47  * We kill the socket, if:
  48  * 1. If number of orphaned sockets exceeds an administratively configured
  49  *    limit.
  50  * 2. If we have strong memory pressure.
  51  */
  52 static int tcp_out_of_resources(struct sock *sk, bool do_reset)
  53 {
  54         struct tcp_sock *tp = tcp_sk(sk);
  55         int shift = 0;
  56
  57         /* If peer does not open window for long time, or did not transmit
  58          * anything for long time, penalize it. */
  59         if ((s32)(tcp_time_stamp - tp->lsndtime) > 2*TCP_RTO_MAX || !do_reset)
  60                 shift++;
  61
  62         /* If some dubious ICMP arrived, penalize even more. */
  63         if (sk->sk_err_soft)
  64                 shift++;
  65
  66         if (tcp_check_oom(sk, shift)) {
  67                 /* Catch exceptional cases, when connection requires reset.
  68                  *      1. Last segment was sent recently. */
  69                 if ((s32)(tcp_time_stamp - tp->lsndtime) <= TCP_TIMEWAIT_LEN ||
  70                     /*  2. Window is closed. */
  71                     (!tp->snd_wnd && !tp->packets_out))
  72                         do_reset = true;
  73                 if (do_reset)
  74                         tcp_send_active_reset(sk, GFP_ATOMIC);
  75                 tcp_done(sk);
  76                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPABORTONMEMORY);
  77                 return 1;
  78         }
  79         return 0;
  80 }
  81
  82 /* Calculate maximal number or retries on an orphaned socket. */
  83 static int tcp_orphan_retries(struct sock *sk, bool alive)
  84 {
  85         int retries = sysctl_tcp_orphan_retries; /* May be zero. */
  86
  87         /* We know from an ICMP that something is wrong. */
  88         if (sk->sk_err_soft && !alive)
  89                 retries = 0;
  90
  91         /* However, if socket sent something recently, select some safe
  92          * number of retries. 8 corresponds to >100 seconds with minimal
  93          * RTO of 200msec. */
  94         if (retries == 0 && alive)
  95                 retries = 8;
  96         return retries;
  97 }
  98
  99 static void tcp_mtu_probing(struct inet_connection_sock *icsk, struct sock *sk)
 100 {
 101         struct net *net = sock_net(sk);
 102
 103         /* Black hole detection */
 104         if (net->ipv4.sysctl_tcp_mtu_probing) {
 105                 if (!icsk->icsk_mtup.enabled) {
 106                         icsk->icsk_mtup.enabled = 1;
 107                         icsk->icsk_mtup.probe_timestamp = tcp_time_stamp;
 108                         tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
 109                 } else {
 110                         struct net *net = sock_net(sk);
 111                         struct tcp_sock *tp = tcp_sk(sk);
 112                         int mss;
 113
 114                         mss = tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low) >> 1;
 115                         mss = min(net->ipv4.sysctl_tcp_base_mss, mss);
 116                         mss = max(mss, 68 - tp->tcp_header_len);
 117                         icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, mss);
 118                         tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
 119                 }
 120         }
 121 }
 122
 123 /* This function calculates a "timeout" which is equivalent to the timeout of a
 124  * TCP connection after "boundary" unsuccessful, exponentially backed-off
 125  * retransmissions with an initial RTO of TCP_RTO_MIN or TCP_TIMEOUT_INIT if
 126  * syn_set flag is set.
 127  */
 128 static bool retransmits_timed_out(struct sock *sk,
 129                                   unsigned int boundary,
 130                                   unsigned int timeout,
 131                                   bool syn_set)
 132 {
 133         unsigned int linear_backoff_thresh, start_ts;
 134         unsigned int rto_base = syn_set ? TCP_TIMEOUT_INIT : TCP_RTO_MIN;
 135
 136         if (!inet_csk(sk)->icsk_retransmits)
 137                 return false;
 138
 139         start_ts = tcp_sk(sk)->retrans_stamp;
 140         if (unlikely(!start_ts))
 141                 start_ts = tcp_skb_timestamp(tcp_write_queue_head(sk));
 142
 143         if (likely(timeout == 0)) {
 144                 linear_backoff_thresh = ilog2(TCP_RTO_MAX/rto_base);
 145
 146                 if (boundary <= linear_backoff_thresh)
 147                         timeout = ((2 << boundary) - 1) * rto_base;
 148                 else
 149                         timeout = ((2 << linear_backoff_thresh) - 1) * rto_base +
 150                                 (boundary - linear_backoff_thresh) * TCP_RTO_MAX;
 151         }
 152         return (tcp_time_stamp - start_ts) >= timeout;
 153 }
 154
 155 /* A write timeout has occurred. Process the after effects. */
 156 static int tcp_write_timeout(struct sock *sk)
 157 {
 158         struct inet_connection_sock *icsk = inet_csk(sk);
 159         struct tcp_sock *tp = tcp_sk(sk);
 160         int retry_until;
 161         bool do_reset, syn_set = false;
 162
 163         if ((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV)) {
 164                 if (icsk->icsk_retransmits) {
 165                         dst_negative_advice(sk);
 166                         if (tp->syn_fastopen || tp->syn_data)
 167                                 tcp_fastopen_cache_set(sk, 0, NULL, true, 0);
 168                         if (tp->syn_data && icsk->icsk_retransmits == 1)
 169                                 NET_INC_STATS_BH(sock_net(sk),
 170                                                  LINUX_MIB_TCPFASTOPENACTIVEFAIL);
 171                 }
 172                 retry_until = icsk->icsk_syn_retries ? : sysctl_tcp_syn_retries;
 173                 syn_set = true;
 174         } else {
 175                 if (retransmits_timed_out(sk, sysctl_tcp_retries1, 0, 0)) {
 176                         /* Some middle-boxes may black-hole Fast Open _after_
 177                          * the handshake. Therefore we conservatively disable
 178                          * Fast Open on this path on recurring timeouts with
 179                          * few or zero bytes acked after Fast Open.
 180                          */
 181                         if (tp->syn_data_acked &&
 182                             tp->bytes_acked <= tp->rx_opt.mss_clamp) {
 183                                 tcp_fastopen_cache_set(sk, 0, NULL, true, 0);
 184                                 if (icsk->icsk_retransmits == sysctl_tcp_retries1)
 185                                         NET_INC_STATS_BH(sock_net(sk),
 186                                                          LINUX_MIB_TCPFASTOPENACTIVEFAIL);
 187                         }
 188                         /* Black hole detection */
 189                         tcp_mtu_probing(icsk, sk);
 190
 191                         dst_negative_advice(sk);
 192                 }
 193
 194                 retry_until = sysctl_tcp_retries2;
 195                 if (sock_flag(sk, SOCK_DEAD)) {
 196                         const bool alive = icsk->icsk_rto < TCP_RTO_MAX;
 197
 198                         retry_until = tcp_orphan_retries(sk, alive);
 199                         do_reset = alive ||
 200                                 !retransmits_timed_out(sk, retry_until, 0, 0);
 201
 202                         if (tcp_out_of_resources(sk, do_reset))
 203                                 return 1;
 204                 }
 205         }
 206
 207         if (retransmits_timed_out(sk, retry_until,
 208                                   syn_set ? 0 : icsk->icsk_user_timeout, syn_set)) {
 209                 /* Has it gone just too far? */
 210                 tcp_write_err(sk);
 211                 return 1;
 212         }
 213         return 0;
 214 }
 215
 216 void tcp_delack_timer_handler(struct sock *sk)
 217 {
 218         struct tcp_sock *tp = tcp_sk(sk);
 219         struct inet_connection_sock *icsk = inet_csk(sk);
 220
 221         sk_mem_reclaim_partial(sk);
 222
 223         if (sk->sk_state == TCP_CLOSE || !(icsk->icsk_ack.pending & ICSK_ACK_TIMER))
 224                 goto out;
 225
 226         if (time_after(icsk->icsk_ack.timeout, jiffies)) {
 227                 sk_reset_timer(sk, &icsk->icsk_delack_timer, icsk->icsk_ack.timeout);
 228                 goto out;
 229         }
 230         icsk->icsk_ack.pending &= ~ICSK_ACK_TIMER;
 231
 232         if (!skb_queue_empty(&tp->ucopy.prequeue)) {
 233                 struct sk_buff *skb;
 234
 235                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSCHEDULERFAILED);
 236
 237                 while ((skb = __skb_dequeue(&tp->ucopy.prequeue)) != NULL)
 238                         sk_backlog_rcv(sk, skb);
 239
 240                 tp->ucopy.memory = 0;
 241         }
 242
 243         if (inet_csk_ack_scheduled(sk)) {
 244                 if (!icsk->icsk_ack.pingpong) {
 245                         /* Delayed ACK missed: inflate ATO. */
 246                         icsk->icsk_ack.ato = min(icsk->icsk_ack.ato << 1, icsk->icsk_rto);
 247                 } else {
 248                         /* Delayed ACK missed: leave pingpong mode and
 249                          * deflate ATO.
 250                          */
 251                         icsk->icsk_ack.pingpong = 0;
 252                         icsk->icsk_ack.ato      = TCP_ATO_MIN;
 253                 }
 254                 tcp_send_ack(sk);
 255                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKS);
 256         }
 257
 258 out:
 259         if (tcp_under_memory_pressure(sk))
 260                 sk_mem_reclaim(sk);
 261 }
 262
 263 static void tcp_delack_timer(unsigned long data)
 264 {
 265         struct sock *sk = (struct sock *)data;
 266
 267         bh_lock_sock(sk);
 268         if (!sock_owned_by_user(sk)) {
 269                 tcp_delack_timer_handler(sk);
 270         } else {
 271                 inet_csk(sk)->icsk_ack.blocked = 1;
 272                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKLOCKED);
 273                 /* deleguate our work to tcp_release_cb() */
 274                 if (!test_and_set_bit(TCP_DELACK_TIMER_DEFERRED, &tcp_sk(sk)->tsq_flags))
 275                         sock_hold(sk);
 276         }
 277         bh_unlock_sock(sk);
 278         sock_put(sk);
 279 }
 280
 281 static void tcp_probe_timer(struct sock *sk)
 282 {
 283         struct inet_connection_sock *icsk = inet_csk(sk);
 284         struct tcp_sock *tp = tcp_sk(sk);
 285         int max_probes;
 286         u32 start_ts;
 287
 288         if (tp->packets_out || !tcp_send_head(sk)) {
 289                 icsk->icsk_probes_out = 0;
 290                 return;
 291         }
 292
 293         /* RFC 1122 4.2.2.17 requires the sender to stay open indefinitely as
 294          * long as the receiver continues to respond probes. We support this by
 295          * default and reset icsk_probes_out with incoming ACKs. But if the
 296          * socket is orphaned or the user specifies TCP_USER_TIMEOUT, we
 297          * kill the socket when the retry count and the time exceeds the
 298          * corresponding system limit. We also implement similar policy when
 299          * we use RTO to probe window in tcp_retransmit_timer().
 300          */
 301         start_ts = tcp_skb_timestamp(tcp_send_head(sk));
 302         if (!start_ts)
 303                 skb_mstamp_get(&tcp_send_head(sk)->skb_mstamp);
 304         else if (icsk->icsk_user_timeout &&
 305                  (s32)(tcp_time_stamp - start_ts) > icsk->icsk_user_timeout)
 306                 goto abort;
 307
 308         max_probes = sysctl_tcp_retries2;
 309         if (sock_flag(sk, SOCK_DEAD)) {
 310                 const bool alive = inet_csk_rto_backoff(icsk, TCP_RTO_MAX) < TCP_RTO_MAX;
 311
 312                 max_probes = tcp_orphan_retries(sk, alive);
 313                 if (!alive && icsk->icsk_backoff >= max_probes)
 314                         goto abort;
 315                 if (tcp_out_of_resources(sk, true))
 316                         return;
 317         }
 318
 319         if (icsk->icsk_probes_out > max_probes) {
 320 abort:          tcp_write_err(sk);
 321         } else {
 322                 /* Only send another probe if we didn't close things up. */
 323                 tcp_send_probe0(sk);
 324         }
 325 }
 326
 327 /*
 328  *      Timer for Fast Open socket to retransmit SYNACK. Note that the
 329  *      sk here is the child socket, not the parent (listener) socket.
 330  */
 331 static void tcp_fastopen_synack_timer(struct sock *sk)
 332 {
 333         struct inet_connection_sock *icsk = inet_csk(sk);
 334         int max_retries = icsk->icsk_syn_retries ? :
 335             sysctl_tcp_synack_retries + 1; /* add one more retry for fastopen */
 336         struct request_sock *req;
 337
 338         req = tcp_sk(sk)->fastopen_rsk;
 339         req->rsk_ops->syn_ack_timeout(req);
 340
 341         if (req->num_timeout >= max_retries) {
 342                 tcp_write_err(sk);
 343                 return;
 344         }
 345         /* XXX (TFO) - Unlike regular SYN-ACK retransmit, we ignore error
 346          * returned from rtx_syn_ack() to make it more persistent like
 347          * regular retransmit because if the child socket has been accepted
 348          * it's not good to give up too easily.
 349          */
 350         inet_rtx_syn_ack(sk, req);
 351         req->num_timeout++;
 352         inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
 353                           TCP_TIMEOUT_INIT << req->num_timeout, TCP_RTO_MAX);
 354 }
 355
 356 /*
 357  *      The TCP retransmit timer.
 358  */
 359
 360 void tcp_retransmit_timer(struct sock *sk)
 361 {
 362         struct tcp_sock *tp = tcp_sk(sk);
 363         struct inet_connection_sock *icsk = inet_csk(sk);
 364
 365         if (tp->fastopen_rsk) {
 366                 WARN_ON_ONCE(sk->sk_state != TCP_SYN_RECV &&
 367                              sk->sk_state != TCP_FIN_WAIT1);
 368                 tcp_fastopen_synack_timer(sk);
 369                 /* Before we receive ACK to our SYN-ACK don't retransmit
 370                  * anything else (e.g., data or FIN segments).
 371                  */
 372                 return;
 373         }
 374         if (!tp->packets_out)
 375                 goto out;
 376
 377         WARN_ON(tcp_write_queue_empty(sk));
 378
 379         tp->tlp_high_seq = 0;
 380
 381         if (!tp->snd_wnd && !sock_flag(sk, SOCK_DEAD) &&
 382             !((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV))) {
 383                 /* Receiver dastardly shrinks window. Our retransmits
 384                  * become zero probes, but we should not timeout this
 385                  * connection. If the socket is an orphan, time it out,
 386                  * we cannot allow such beasts to hang infinitely.
 387                  */
 388                 struct inet_sock *inet = inet_sk(sk);
 389                 if (sk->sk_family == AF_INET) {
 390                         net_dbg_ratelimited("Peer %pI4:%u/%u unexpectedly shrunk window %u:%u (repaired)\n",
 391                                             &inet->inet_daddr,
 392                                             ntohs(inet->inet_dport),
 393                                             inet->inet_num,
 394                                             tp->snd_una, tp->snd_nxt);
 395                 }
 396 #if IS_ENABLED(CONFIG_IPV6)
 397                 else if (sk->sk_family == AF_INET6) {
 398                         net_dbg_ratelimited("Peer %pI6:%u/%u unexpectedly shrunk window %u:%u (repaired)\n",
 399                                             &sk->sk_v6_daddr,
 400                                             ntohs(inet->inet_dport),
 401                                             inet->inet_num,
 402                                             tp->snd_una, tp->snd_nxt);
 403                 }
 404 #endif
 405                 if (tcp_time_stamp - tp->rcv_tstamp > TCP_RTO_MAX) {
 406                         tcp_write_err(sk);
 407                         goto out;
 408                 }
 409                 tcp_enter_loss(sk);
 410                 tcp_retransmit_skb(sk, tcp_write_queue_head(sk));
 411                 __sk_dst_reset(sk);
 412                 goto out_reset_timer;
 413         }
 414
 415         if (tcp_write_timeout(sk))
 416                 goto out;
 417
 418         if (icsk->icsk_retransmits == 0) {
 419                 int mib_idx;
 420
 421                 if (icsk->icsk_ca_state == TCP_CA_Recovery) {
 422                         if (tcp_is_sack(tp))
 423                                 mib_idx = LINUX_MIB_TCPSACKRECOVERYFAIL;
 424                         else
 425                                 mib_idx = LINUX_MIB_TCPRENORECOVERYFAIL;
 426                 } else if (icsk->icsk_ca_state == TCP_CA_Loss) {
 427                         mib_idx = LINUX_MIB_TCPLOSSFAILURES;
 428                 } else if ((icsk->icsk_ca_state == TCP_CA_Disorder) ||
 429                            tp->sacked_out) {
 430                         if (tcp_is_sack(tp))
 431                                 mib_idx = LINUX_MIB_TCPSACKFAILURES;
 432                         else
 433                                 mib_idx = LINUX_MIB_TCPRENOFAILURES;
 434                 } else {
 435                         mib_idx = LINUX_MIB_TCPTIMEOUTS;
 436                 }
 437                 NET_INC_STATS_BH(sock_net(sk), mib_idx);
 438         }
 439
 440         tcp_enter_loss(sk);
 441
 442         if (tcp_retransmit_skb(sk, tcp_write_queue_head(sk)) > 0) {
 443                 /* Retransmission failed because of local congestion,
 444                  * do not backoff.
 445                  */
 446                 if (!icsk->icsk_retransmits)
 447                         icsk->icsk_retransmits = 1;
 448                 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
 449                                           min(icsk->icsk_rto, TCP_RESOURCE_PROBE_INTERVAL),
 450                                           TCP_RTO_MAX);
 451                 goto out;
 452         }
 453
 454         /* Increase the timeout each time we retransmit.  Note that
 455          * we do not increase the rtt estimate.  rto is initialized
 456          * from rtt, but increases here.  Jacobson (SIGCOMM 88) suggests
 457          * that doubling rto each time is the least we can get away with.
 458          * In KA9Q, Karn uses this for the first few times, and then
 459          * goes to quadratic.  netBSD doubles, but only goes up to *64,
 460          * and clamps at 1 to 64 sec afterwards.  Note that 120 sec is
 461          * defined in the protocol as the maximum possible RTT.  I guess
 462          * we'll have to use something other than TCP to talk to the
 463          * University of Mars.
 464          *
 465          * PAWS allows us longer timeouts and large windows, so once
 466          * implemented ftp to mars will work nicely. We will have to fix
 467          * the 120 second clamps though!
 468          */
 469         icsk->icsk_backoff++;
 470         icsk->icsk_retransmits++;
 471
 472 out_reset_timer:
 473         /* If stream is thin, use linear timeouts. Since 'icsk_backoff' is
 474          * used to reset timer, set to 0. Recalculate 'icsk_rto' as this
 475          * might be increased if the stream oscillates between thin and thick,
 476          * thus the old value might already be too high compared to the value
 477          * set by 'tcp_set_rto' in tcp_input.c which resets the rto without
 478          * backoff. Limit to TCP_THIN_LINEAR_RETRIES before initiating
 479          * exponential backoff behaviour to avoid continue hammering
 480          * linear-timeout retransmissions into a black hole
 481          */
 482         if (sk->sk_state == TCP_ESTABLISHED &&
 483             (tp->thin_lto || sysctl_tcp_thin_linear_timeouts) &&
 484             tcp_stream_is_thin(tp) &&
 485             icsk->icsk_retransmits <= TCP_THIN_LINEAR_RETRIES) {
 486                 icsk->icsk_backoff = 0;
 487                 icsk->icsk_rto = min(__tcp_set_rto(tp), TCP_RTO_MAX);
 488         } else {
 489                 /* Use normal (exponential) backoff */
 490                 icsk->icsk_rto = min(icsk->icsk_rto << 1, TCP_RTO_MAX);
 491         }
 492         inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, icsk->icsk_rto, TCP_RTO_MAX);
 493         if (retransmits_timed_out(sk, sysctl_tcp_retries1 + 1, 0, 0))
 494                 __sk_dst_reset(sk);
 495
 496 out:;
 497 }
 498
 499 void tcp_write_timer_handler(struct sock *sk)
 500 {
 501         struct inet_connection_sock *icsk = inet_csk(sk);
 502         int event;
 503
 504         if (sk->sk_state == TCP_CLOSE || !icsk->icsk_pending)
 505                 goto out;
 506
 507         if (time_after(icsk->icsk_timeout, jiffies)) {
 508                 sk_reset_timer(sk, &icsk->icsk_retransmit_timer, icsk->icsk_timeout);
 509                 goto out;
 510         }
 511
 512         event = icsk->icsk_pending;
 513
 514         switch (event) {
 515         case ICSK_TIME_EARLY_RETRANS:
 516                 tcp_resume_early_retransmit(sk);
 517                 break;
 518         case ICSK_TIME_LOSS_PROBE:
 519                 tcp_send_loss_probe(sk);
 520                 break;
 521         case ICSK_TIME_RETRANS:
 522                 icsk->icsk_pending = 0;
 523                 tcp_retransmit_timer(sk);
 524                 break;
 525         case ICSK_TIME_PROBE0:
 526                 icsk->icsk_pending = 0;
 527                 tcp_probe_timer(sk);
 528                 break;
 529         }
 530
 531 out:
 532         sk_mem_reclaim(sk);
 533 }
 534
 535 static void tcp_write_timer(unsigned long data)
 536 {
 537         struct sock *sk = (struct sock *)data;
 538
 539         bh_lock_sock(sk);
 540         if (!sock_owned_by_user(sk)) {
 541                 tcp_write_timer_handler(sk);
 542         } else {
 543                 /* deleguate our work to tcp_release_cb() */
 544                 if (!test_and_set_bit(TCP_WRITE_TIMER_DEFERRED, &tcp_sk(sk)->tsq_flags))
 545                         sock_hold(sk);
 546         }
 547         bh_unlock_sock(sk);
 548         sock_put(sk);
 549 }
 550
 551 void tcp_syn_ack_timeout(const struct request_sock *req)
 552 {
 553         struct net *net = read_pnet(&inet_rsk(req)->ireq_net);
 554
 555         NET_INC_STATS_BH(net, LINUX_MIB_TCPTIMEOUTS);
 556 }
 557 EXPORT_SYMBOL(tcp_syn_ack_timeout);
 558
 559 void tcp_set_keepalive(struct sock *sk, int val)
 560 {
 561         if ((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN))
 562                 return;
 563
 564         if (val && !sock_flag(sk, SOCK_KEEPOPEN))
 565                 inet_csk_reset_keepalive_timer(sk, keepalive_time_when(tcp_sk(sk)));
 566         else if (!val)
 567                 inet_csk_delete_keepalive_timer(sk);
 568 }
 569
 570
 571 static void tcp_keepalive_timer (unsigned long data)
 572 {
 573         struct sock *sk = (struct sock *) data;
 574         struct inet_connection_sock *icsk = inet_csk(sk);
 575         struct tcp_sock *tp = tcp_sk(sk);
 576         u32 elapsed;
 577
 578         /* Only process if socket is not in use. */
 579         bh_lock_sock(sk);
 580         if (sock_owned_by_user(sk)) {
 581                 /* Try again later. */
 582                 inet_csk_reset_keepalive_timer (sk, HZ/20);
 583                 goto out;
 584         }
 585
 586         if (sk->sk_state == TCP_LISTEN) {
 587                 pr_err("Hmm... keepalive on a LISTEN ???\n");
 588                 goto out;
 589         }
 590
 591         if (sk->sk_state == TCP_FIN_WAIT2 && sock_flag(sk, SOCK_DEAD)) {
 592                 if (tp->linger2 >= 0) {
 593                         const int tmo = tcp_fin_time(sk) - TCP_TIMEWAIT_LEN;
 594
 595                         if (tmo > 0) {
 596                                 tcp_time_wait(sk, TCP_FIN_WAIT2, tmo);
 597                                 goto out;
 598                         }
 599                 }
 600                 tcp_send_active_reset(sk, GFP_ATOMIC);
 601                 goto death;
 602         }
 603
 604         if (!sock_flag(sk, SOCK_KEEPOPEN) || sk->sk_state == TCP_CLOSE)
 605                 goto out;
 606
 607         elapsed = keepalive_time_when(tp);
 608
 609         /* It is alive without keepalive 8) */
 610         if (tp->packets_out || tcp_send_head(sk))
 611                 goto resched;
 612
 613         elapsed = keepalive_time_elapsed(tp);
 614
 615         if (elapsed >= keepalive_time_when(tp)) {
 616                 /* If the TCP_USER_TIMEOUT option is enabled, use that
 617                  * to determine when to timeout instead.
 618                  */
 619                 if ((icsk->icsk_user_timeout != 0 &&
 620                     elapsed >= icsk->icsk_user_timeout &&
 621                     icsk->icsk_probes_out > 0) ||
 622                     (icsk->icsk_user_timeout == 0 &&
 623                     icsk->icsk_probes_out >= keepalive_probes(tp))) {
 624                         tcp_send_active_reset(sk, GFP_ATOMIC);
 625                         tcp_write_err(sk);
 626                         goto out;
 627                 }
 628                 if (tcp_write_wakeup(sk, LINUX_MIB_TCPKEEPALIVE) <= 0) {
 629                         icsk->icsk_probes_out++;
 630                         elapsed = keepalive_intvl_when(tp);
 631                 } else {
 632                         /* If keepalive was lost due to local congestion,
 633                          * try harder.
 634                          */
 635                         elapsed = TCP_RESOURCE_PROBE_INTERVAL;
 636                 }
 637         } else {
 638                 /* It is tp->rcv_tstamp + keepalive_time_when(tp) */
 639                 elapsed = keepalive_time_when(tp) - elapsed;
 640         }
 641
 642         sk_mem_reclaim(sk);
 643
 644 resched:
 645         inet_csk_reset_keepalive_timer (sk, elapsed);
 646         goto out;
 647
 648 death:
 649         tcp_done(sk);
 650
 651 out:
 652         bh_unlock_sock(sk);
 653         sock_put(sk);
 654 }
 655
 656 void tcp_init_xmit_timers(struct sock *sk)
 657 {
 658         inet_csk_init_xmit_timers(sk, &tcp_write_timer, &tcp_delack_timer,
 659                                   &tcp_keepalive_timer);
 660 }