linux/net/ipv4/tcp_timer.c
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   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
  25int sysctl_tcp_syn_retries __read_mostly = TCP_SYN_RETRIES;
  26int sysctl_tcp_synack_retries __read_mostly = TCP_SYNACK_RETRIES;
  27int sysctl_tcp_keepalive_time __read_mostly = TCP_KEEPALIVE_TIME;
  28int sysctl_tcp_keepalive_probes __read_mostly = TCP_KEEPALIVE_PROBES;
  29int sysctl_tcp_keepalive_intvl __read_mostly = TCP_KEEPALIVE_INTVL;
  30int sysctl_tcp_retries1 __read_mostly = TCP_RETR1;
  31int sysctl_tcp_retries2 __read_mostly = TCP_RETR2;
  32int sysctl_tcp_orphan_retries __read_mostly;
  33int sysctl_tcp_thin_linear_timeouts __read_mostly;
  34
  35static 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 */
  55static 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. */
  86static 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
 102static void tcp_mtu_probing(struct inet_connection_sock *icsk, struct sock *sk)
 103{
 104        /* Black hole detection */
 105        if (sysctl_tcp_mtu_probing) {
 106                if (!icsk->icsk_mtup.enabled) {
 107                        icsk->icsk_mtup.enabled = 1;
 108                        tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
 109                } else {
 110                        struct tcp_sock *tp = tcp_sk(sk);
 111                        int mss;
 112
 113                        mss = tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low) >> 1;
 114                        mss = min(sysctl_tcp_base_mss, mss);
 115                        mss = max(mss, 68 - tp->tcp_header_len);
 116                        icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, mss);
 117                        tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
 118                }
 119        }
 120}
 121
 122/* This function calculates a "timeout" which is equivalent to the timeout of a
 123 * TCP connection after "boundary" unsuccessful, exponentially backed-off
 124 * retransmissions with an initial RTO of TCP_RTO_MIN or TCP_TIMEOUT_INIT if
 125 * syn_set flag is set.
 126 */
 127static bool retransmits_timed_out(struct sock *sk,
 128                                  unsigned int boundary,
 129                                  unsigned int timeout,
 130                                  bool syn_set)
 131{
 132        unsigned int linear_backoff_thresh, start_ts;
 133        unsigned int rto_base = syn_set ? TCP_TIMEOUT_INIT : TCP_RTO_MIN;
 134
 135        if (!inet_csk(sk)->icsk_retransmits)
 136                return false;
 137
 138        start_ts = tcp_sk(sk)->retrans_stamp;
 139        if (unlikely(!start_ts))
 140                start_ts = tcp_skb_timestamp(tcp_write_queue_head(sk));
 141
 142        if (likely(timeout == 0)) {
 143                linear_backoff_thresh = ilog2(TCP_RTO_MAX/rto_base);
 144
 145                if (boundary <= linear_backoff_thresh)
 146                        timeout = ((2 << boundary) - 1) * rto_base;
 147                else
 148                        timeout = ((2 << linear_backoff_thresh) - 1) * rto_base +
 149                                (boundary - linear_backoff_thresh) * TCP_RTO_MAX;
 150        }
 151        return (tcp_time_stamp - start_ts) >= timeout;
 152}
 153
 154/* A write timeout has occurred. Process the after effects. */
 155static int tcp_write_timeout(struct sock *sk)
 156{
 157        struct inet_connection_sock *icsk = inet_csk(sk);
 158        struct tcp_sock *tp = tcp_sk(sk);
 159        int retry_until;
 160        bool do_reset, syn_set = false;
 161
 162        if ((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV)) {
 163                if (icsk->icsk_retransmits) {
 164                        dst_negative_advice(sk);
 165                        if (tp->syn_fastopen || tp->syn_data)
 166                                tcp_fastopen_cache_set(sk, 0, NULL, true);
 167                        if (tp->syn_data)
 168                                NET_INC_STATS_BH(sock_net(sk),
 169                                                 LINUX_MIB_TCPFASTOPENACTIVEFAIL);
 170                }
 171                retry_until = icsk->icsk_syn_retries ? : sysctl_tcp_syn_retries;
 172                syn_set = true;
 173        } else {
 174                if (retransmits_timed_out(sk, sysctl_tcp_retries1, 0, 0)) {
 175                        /* Black hole detection */
 176                        tcp_mtu_probing(icsk, sk);
 177
 178                        dst_negative_advice(sk);
 179                }
 180
 181                retry_until = sysctl_tcp_retries2;
 182                if (sock_flag(sk, SOCK_DEAD)) {
 183                        const int alive = icsk->icsk_rto < TCP_RTO_MAX;
 184
 185                        retry_until = tcp_orphan_retries(sk, alive);
 186                        do_reset = alive ||
 187                                !retransmits_timed_out(sk, retry_until, 0, 0);
 188
 189                        if (tcp_out_of_resources(sk, do_reset))
 190                                return 1;
 191                }
 192        }
 193
 194        if (retransmits_timed_out(sk, retry_until,
 195                                  syn_set ? 0 : icsk->icsk_user_timeout, syn_set)) {
 196                /* Has it gone just too far? */
 197                tcp_write_err(sk);
 198                return 1;
 199        }
 200        return 0;
 201}
 202
 203void tcp_delack_timer_handler(struct sock *sk)
 204{
 205        struct tcp_sock *tp = tcp_sk(sk);
 206        struct inet_connection_sock *icsk = inet_csk(sk);
 207
 208        sk_mem_reclaim_partial(sk);
 209
 210        if (sk->sk_state == TCP_CLOSE || !(icsk->icsk_ack.pending & ICSK_ACK_TIMER))
 211                goto out;
 212
 213        if (time_after(icsk->icsk_ack.timeout, jiffies)) {
 214                sk_reset_timer(sk, &icsk->icsk_delack_timer, icsk->icsk_ack.timeout);
 215                goto out;
 216        }
 217        icsk->icsk_ack.pending &= ~ICSK_ACK_TIMER;
 218
 219        if (!skb_queue_empty(&tp->ucopy.prequeue)) {
 220                struct sk_buff *skb;
 221
 222                NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSCHEDULERFAILED);
 223
 224                while ((skb = __skb_dequeue(&tp->ucopy.prequeue)) != NULL)
 225                        sk_backlog_rcv(sk, skb);
 226
 227                tp->ucopy.memory = 0;
 228        }
 229
 230        if (inet_csk_ack_scheduled(sk)) {
 231                if (!icsk->icsk_ack.pingpong) {
 232                        /* Delayed ACK missed: inflate ATO. */
 233                        icsk->icsk_ack.ato = min(icsk->icsk_ack.ato << 1, icsk->icsk_rto);
 234                } else {
 235                        /* Delayed ACK missed: leave pingpong mode and
 236                         * deflate ATO.
 237                         */
 238                        icsk->icsk_ack.pingpong = 0;
 239                        icsk->icsk_ack.ato      = TCP_ATO_MIN;
 240                }
 241                tcp_send_ack(sk);
 242                NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKS);
 243        }
 244
 245out:
 246        if (sk_under_memory_pressure(sk))
 247                sk_mem_reclaim(sk);
 248}
 249
 250static void tcp_delack_timer(unsigned long data)
 251{
 252        struct sock *sk = (struct sock *)data;
 253
 254        bh_lock_sock(sk);
 255        if (!sock_owned_by_user(sk)) {
 256                tcp_delack_timer_handler(sk);
 257        } else {
 258                inet_csk(sk)->icsk_ack.blocked = 1;
 259                NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKLOCKED);
 260                /* deleguate our work to tcp_release_cb() */
 261                if (!test_and_set_bit(TCP_DELACK_TIMER_DEFERRED, &tcp_sk(sk)->tsq_flags))
 262                        sock_hold(sk);
 263        }
 264        bh_unlock_sock(sk);
 265        sock_put(sk);
 266}
 267
 268static void tcp_probe_timer(struct sock *sk)
 269{
 270        struct inet_connection_sock *icsk = inet_csk(sk);
 271        struct tcp_sock *tp = tcp_sk(sk);
 272        int max_probes;
 273        u32 start_ts;
 274
 275        if (tp->packets_out || !tcp_send_head(sk)) {
 276                icsk->icsk_probes_out = 0;
 277                return;
 278        }
 279
 280        /* RFC 1122 4.2.2.17 requires the sender to stay open indefinitely as
 281         * long as the receiver continues to respond probes. We support this by
 282         * default and reset icsk_probes_out with incoming ACKs. But if the
 283         * socket is orphaned or the user specifies TCP_USER_TIMEOUT, we
 284         * kill the socket when the retry count and the time exceeds the
 285         * corresponding system limit. We also implement similar policy when
 286         * we use RTO to probe window in tcp_retransmit_timer().
 287         */
 288        start_ts = tcp_skb_timestamp(tcp_send_head(sk));
 289        if (!start_ts)
 290                skb_mstamp_get(&tcp_send_head(sk)->skb_mstamp);
 291        else if (icsk->icsk_user_timeout &&
 292                 (s32)(tcp_time_stamp - start_ts) > icsk->icsk_user_timeout)
 293                goto abort;
 294
 295        max_probes = sysctl_tcp_retries2;
 296        if (sock_flag(sk, SOCK_DEAD)) {
 297                const int alive = inet_csk_rto_backoff(icsk, TCP_RTO_MAX) < TCP_RTO_MAX;
 298
 299                max_probes = tcp_orphan_retries(sk, alive);
 300                if (!alive && icsk->icsk_backoff >= max_probes)
 301                        goto abort;
 302                if (tcp_out_of_resources(sk, true))
 303                        return;
 304        }
 305
 306        if (icsk->icsk_probes_out > max_probes) {
 307abort:          tcp_write_err(sk);
 308        } else {
 309                /* Only send another probe if we didn't close things up. */
 310                tcp_send_probe0(sk);
 311        }
 312}
 313
 314/*
 315 *      Timer for Fast Open socket to retransmit SYNACK. Note that the
 316 *      sk here is the child socket, not the parent (listener) socket.
 317 */
 318static void tcp_fastopen_synack_timer(struct sock *sk)
 319{
 320        struct inet_connection_sock *icsk = inet_csk(sk);
 321        int max_retries = icsk->icsk_syn_retries ? :
 322            sysctl_tcp_synack_retries + 1; /* add one more retry for fastopen */
 323        struct request_sock *req;
 324
 325        req = tcp_sk(sk)->fastopen_rsk;
 326        req->rsk_ops->syn_ack_timeout(sk, req);
 327
 328        if (req->num_timeout >= max_retries) {
 329                tcp_write_err(sk);
 330                return;
 331        }
 332        /* XXX (TFO) - Unlike regular SYN-ACK retransmit, we ignore error
 333         * returned from rtx_syn_ack() to make it more persistent like
 334         * regular retransmit because if the child socket has been accepted
 335         * it's not good to give up too easily.
 336         */
 337        inet_rtx_syn_ack(sk, req);
 338        req->num_timeout++;
 339        inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
 340                          TCP_TIMEOUT_INIT << req->num_timeout, TCP_RTO_MAX);
 341}
 342
 343/*
 344 *      The TCP retransmit timer.
 345 */
 346
 347void tcp_retransmit_timer(struct sock *sk)
 348{
 349        struct tcp_sock *tp = tcp_sk(sk);
 350        struct inet_connection_sock *icsk = inet_csk(sk);
 351
 352        if (tp->fastopen_rsk) {
 353                WARN_ON_ONCE(sk->sk_state != TCP_SYN_RECV &&
 354                             sk->sk_state != TCP_FIN_WAIT1);
 355                tcp_fastopen_synack_timer(sk);
 356                /* Before we receive ACK to our SYN-ACK don't retransmit
 357                 * anything else (e.g., data or FIN segments).
 358                 */
 359                return;
 360        }
 361        if (!tp->packets_out)
 362                goto out;
 363
 364        WARN_ON(tcp_write_queue_empty(sk));
 365
 366        tp->tlp_high_seq = 0;
 367
 368        if (!tp->snd_wnd && !sock_flag(sk, SOCK_DEAD) &&
 369            !((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV))) {
 370                /* Receiver dastardly shrinks window. Our retransmits
 371                 * become zero probes, but we should not timeout this
 372                 * connection. If the socket is an orphan, time it out,
 373                 * we cannot allow such beasts to hang infinitely.
 374                 */
 375                struct inet_sock *inet = inet_sk(sk);
 376                if (sk->sk_family == AF_INET) {
 377                        net_dbg_ratelimited("Peer %pI4:%u/%u unexpectedly shrunk window %u:%u (repaired)\n",
 378                                            &inet->inet_daddr,
 379                                            ntohs(inet->inet_dport),
 380                                            inet->inet_num,
 381                                            tp->snd_una, tp->snd_nxt);
 382                }
 383#if IS_ENABLED(CONFIG_IPV6)
 384                else if (sk->sk_family == AF_INET6) {
 385                        net_dbg_ratelimited("Peer %pI6:%u/%u unexpectedly shrunk window %u:%u (repaired)\n",
 386                                            &sk->sk_v6_daddr,
 387                                            ntohs(inet->inet_dport),
 388                                            inet->inet_num,
 389                                            tp->snd_una, tp->snd_nxt);
 390                }
 391#endif
 392                if (tcp_time_stamp - tp->rcv_tstamp > TCP_RTO_MAX) {
 393                        tcp_write_err(sk);
 394                        goto out;
 395                }
 396                tcp_enter_loss(sk);
 397                tcp_retransmit_skb(sk, tcp_write_queue_head(sk));
 398                __sk_dst_reset(sk);
 399                goto out_reset_timer;
 400        }
 401
 402        if (tcp_write_timeout(sk))
 403                goto out;
 404
 405        if (icsk->icsk_retransmits == 0) {
 406                int mib_idx;
 407
 408                if (icsk->icsk_ca_state == TCP_CA_Recovery) {
 409                        if (tcp_is_sack(tp))
 410                                mib_idx = LINUX_MIB_TCPSACKRECOVERYFAIL;
 411                        else
 412                                mib_idx = LINUX_MIB_TCPRENORECOVERYFAIL;
 413                } else if (icsk->icsk_ca_state == TCP_CA_Loss) {
 414                        mib_idx = LINUX_MIB_TCPLOSSFAILURES;
 415                } else if ((icsk->icsk_ca_state == TCP_CA_Disorder) ||
 416                           tp->sacked_out) {
 417                        if (tcp_is_sack(tp))
 418                                mib_idx = LINUX_MIB_TCPSACKFAILURES;
 419                        else
 420                                mib_idx = LINUX_MIB_TCPRENOFAILURES;
 421                } else {
 422                        mib_idx = LINUX_MIB_TCPTIMEOUTS;
 423                }
 424                NET_INC_STATS_BH(sock_net(sk), mib_idx);
 425        }
 426
 427        tcp_enter_loss(sk);
 428
 429        if (tcp_retransmit_skb(sk, tcp_write_queue_head(sk)) > 0) {
 430                /* Retransmission failed because of local congestion,
 431                 * do not backoff.
 432                 */
 433                if (!icsk->icsk_retransmits)
 434                        icsk->icsk_retransmits = 1;
 435                inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
 436                                          min(icsk->icsk_rto, TCP_RESOURCE_PROBE_INTERVAL),
 437                                          TCP_RTO_MAX);
 438                goto out;
 439        }
 440
 441        /* Increase the timeout each time we retransmit.  Note that
 442         * we do not increase the rtt estimate.  rto is initialized
 443         * from rtt, but increases here.  Jacobson (SIGCOMM 88) suggests
 444         * that doubling rto each time is the least we can get away with.
 445         * In KA9Q, Karn uses this for the first few times, and then
 446         * goes to quadratic.  netBSD doubles, but only goes up to *64,
 447         * and clamps at 1 to 64 sec afterwards.  Note that 120 sec is
 448         * defined in the protocol as the maximum possible RTT.  I guess
 449         * we'll have to use something other than TCP to talk to the
 450         * University of Mars.
 451         *
 452         * PAWS allows us longer timeouts and large windows, so once
 453         * implemented ftp to mars will work nicely. We will have to fix
 454         * the 120 second clamps though!
 455         */
 456        icsk->icsk_backoff++;
 457        icsk->icsk_retransmits++;
 458
 459out_reset_timer:
 460        /* If stream is thin, use linear timeouts. Since 'icsk_backoff' is
 461         * used to reset timer, set to 0. Recalculate 'icsk_rto' as this
 462         * might be increased if the stream oscillates between thin and thick,
 463         * thus the old value might already be too high compared to the value
 464         * set by 'tcp_set_rto' in tcp_input.c which resets the rto without
 465         * backoff. Limit to TCP_THIN_LINEAR_RETRIES before initiating
 466         * exponential backoff behaviour to avoid continue hammering
 467         * linear-timeout retransmissions into a black hole
 468         */
 469        if (sk->sk_state == TCP_ESTABLISHED &&
 470            (tp->thin_lto || sysctl_tcp_thin_linear_timeouts) &&
 471            tcp_stream_is_thin(tp) &&
 472            icsk->icsk_retransmits <= TCP_THIN_LINEAR_RETRIES) {
 473                icsk->icsk_backoff = 0;
 474                icsk->icsk_rto = min(__tcp_set_rto(tp), TCP_RTO_MAX);
 475        } else {
 476                /* Use normal (exponential) backoff */
 477                icsk->icsk_rto = min(icsk->icsk_rto << 1, TCP_RTO_MAX);
 478        }
 479        inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, icsk->icsk_rto, TCP_RTO_MAX);
 480        if (retransmits_timed_out(sk, sysctl_tcp_retries1 + 1, 0, 0))
 481                __sk_dst_reset(sk);
 482
 483out:;
 484}
 485
 486void tcp_write_timer_handler(struct sock *sk)
 487{
 488        struct inet_connection_sock *icsk = inet_csk(sk);
 489        int event;
 490
 491        if (sk->sk_state == TCP_CLOSE || !icsk->icsk_pending)
 492                goto out;
 493
 494        if (time_after(icsk->icsk_timeout, jiffies)) {
 495                sk_reset_timer(sk, &icsk->icsk_retransmit_timer, icsk->icsk_timeout);
 496                goto out;
 497        }
 498
 499        event = icsk->icsk_pending;
 500
 501        switch (event) {
 502        case ICSK_TIME_EARLY_RETRANS:
 503                tcp_resume_early_retransmit(sk);
 504                break;
 505        case ICSK_TIME_LOSS_PROBE:
 506                tcp_send_loss_probe(sk);
 507                break;
 508        case ICSK_TIME_RETRANS:
 509                icsk->icsk_pending = 0;
 510                tcp_retransmit_timer(sk);
 511                break;
 512        case ICSK_TIME_PROBE0:
 513                icsk->icsk_pending = 0;
 514                tcp_probe_timer(sk);
 515                break;
 516        }
 517
 518out:
 519        sk_mem_reclaim(sk);
 520}
 521
 522static void tcp_write_timer(unsigned long data)
 523{
 524        struct sock *sk = (struct sock *)data;
 525
 526        bh_lock_sock(sk);
 527        if (!sock_owned_by_user(sk)) {
 528                tcp_write_timer_handler(sk);
 529        } else {
 530                /* deleguate our work to tcp_release_cb() */
 531                if (!test_and_set_bit(TCP_WRITE_TIMER_DEFERRED, &tcp_sk(sk)->tsq_flags))
 532                        sock_hold(sk);
 533        }
 534        bh_unlock_sock(sk);
 535        sock_put(sk);
 536}
 537
 538/*
 539 *      Timer for listening sockets
 540 */
 541
 542static void tcp_synack_timer(struct sock *sk)
 543{
 544        inet_csk_reqsk_queue_prune(sk, TCP_SYNQ_INTERVAL,
 545                                   TCP_TIMEOUT_INIT, TCP_RTO_MAX);
 546}
 547
 548void tcp_syn_ack_timeout(struct sock *sk, struct request_sock *req)
 549{
 550        NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPTIMEOUTS);
 551}
 552EXPORT_SYMBOL(tcp_syn_ack_timeout);
 553
 554void tcp_set_keepalive(struct sock *sk, int val)
 555{
 556        if ((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN))
 557                return;
 558
 559        if (val && !sock_flag(sk, SOCK_KEEPOPEN))
 560                inet_csk_reset_keepalive_timer(sk, keepalive_time_when(tcp_sk(sk)));
 561        else if (!val)
 562                inet_csk_delete_keepalive_timer(sk);
 563}
 564
 565
 566static void tcp_keepalive_timer (unsigned long data)
 567{
 568        struct sock *sk = (struct sock *) data;
 569        struct inet_connection_sock *icsk = inet_csk(sk);
 570        struct tcp_sock *tp = tcp_sk(sk);
 571        u32 elapsed;
 572
 573        /* Only process if socket is not in use. */
 574        bh_lock_sock(sk);
 575        if (sock_owned_by_user(sk)) {
 576                /* Try again later. */
 577                inet_csk_reset_keepalive_timer (sk, HZ/20);
 578                goto out;
 579        }
 580
 581        if (sk->sk_state == TCP_LISTEN) {
 582                tcp_synack_timer(sk);
 583                goto out;
 584        }
 585
 586        if (sk->sk_state == TCP_FIN_WAIT2 && sock_flag(sk, SOCK_DEAD)) {
 587                if (tp->linger2 >= 0) {
 588                        const int tmo = tcp_fin_time(sk) - TCP_TIMEWAIT_LEN;
 589
 590                        if (tmo > 0) {
 591                                tcp_time_wait(sk, TCP_FIN_WAIT2, tmo);
 592                                goto out;
 593                        }
 594                }
 595                tcp_send_active_reset(sk, GFP_ATOMIC);
 596                goto death;
 597        }
 598
 599        if (!sock_flag(sk, SOCK_KEEPOPEN) || sk->sk_state == TCP_CLOSE)
 600                goto out;
 601
 602        elapsed = keepalive_time_when(tp);
 603
 604        /* It is alive without keepalive 8) */
 605        if (tp->packets_out || tcp_send_head(sk))
 606                goto resched;
 607
 608        elapsed = keepalive_time_elapsed(tp);
 609
 610        if (elapsed >= keepalive_time_when(tp)) {
 611                /* If the TCP_USER_TIMEOUT option is enabled, use that
 612                 * to determine when to timeout instead.
 613                 */
 614                if ((icsk->icsk_user_timeout != 0 &&
 615                    elapsed >= icsk->icsk_user_timeout &&
 616                    icsk->icsk_probes_out > 0) ||
 617                    (icsk->icsk_user_timeout == 0 &&
 618                    icsk->icsk_probes_out >= keepalive_probes(tp))) {
 619                        tcp_send_active_reset(sk, GFP_ATOMIC);
 620                        tcp_write_err(sk);
 621                        goto out;
 622                }
 623                if (tcp_write_wakeup(sk) <= 0) {
 624                        icsk->icsk_probes_out++;
 625                        elapsed = keepalive_intvl_when(tp);
 626                } else {
 627                        /* If keepalive was lost due to local congestion,
 628                         * try harder.
 629                         */
 630                        elapsed = TCP_RESOURCE_PROBE_INTERVAL;
 631                }
 632        } else {
 633                /* It is tp->rcv_tstamp + keepalive_time_when(tp) */
 634                elapsed = keepalive_time_when(tp) - elapsed;
 635        }
 636
 637        sk_mem_reclaim(sk);
 638
 639resched:
 640        inet_csk_reset_keepalive_timer (sk, elapsed);
 641        goto out;
 642
 643death:
 644        tcp_done(sk);
 645
 646out:
 647        bh_unlock_sock(sk);
 648        sock_put(sk);
 649}
 650
 651void tcp_init_xmit_timers(struct sock *sk)
 652{
 653        inet_csk_init_xmit_timers(sk, &tcp_write_timer, &tcp_delack_timer,
 654                                  &tcp_keepalive_timer);
 655}
 656EXPORT_SYMBOL(tcp_init_xmit_timers);
 657
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