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 <net/tcp.h>
  23
  24int sysctl_tcp_syn_retries __read_mostly = TCP_SYN_RETRIES;
  25int sysctl_tcp_synack_retries __read_mostly = TCP_SYNACK_RETRIES;
  26int sysctl_tcp_keepalive_time __read_mostly = TCP_KEEPALIVE_TIME;
  27int sysctl_tcp_keepalive_probes __read_mostly = TCP_KEEPALIVE_PROBES;
  28int sysctl_tcp_keepalive_intvl __read_mostly = TCP_KEEPALIVE_INTVL;
  29int sysctl_tcp_retries1 __read_mostly = TCP_RETR1;
  30int sysctl_tcp_retries2 __read_mostly = TCP_RETR2;
  31int sysctl_tcp_orphan_retries __read_mostly;
  32
  33static void tcp_write_timer(unsigned long);
  34static void tcp_delack_timer(unsigned long);
  35static void tcp_keepalive_timer (unsigned long data);
  36
  37void tcp_init_xmit_timers(struct sock *sk)
  38{
  39        inet_csk_init_xmit_timers(sk, &tcp_write_timer, &tcp_delack_timer,
  40                                  &tcp_keepalive_timer);
  41}
  42
  43EXPORT_SYMBOL(tcp_init_xmit_timers);
  44
  45static void tcp_write_err(struct sock *sk)
  46{
  47        sk->sk_err = sk->sk_err_soft ? : ETIMEDOUT;
  48        sk->sk_error_report(sk);
  49
  50        tcp_done(sk);
  51        NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPABORTONTIMEOUT);
  52}
  53
  54/* Do not allow orphaned sockets to eat all our resources.
  55 * This is direct violation of TCP specs, but it is required
  56 * to prevent DoS attacks. It is called when a retransmission timeout
  57 * or zero probe timeout occurs on orphaned socket.
  58 *
  59 * Criteria is still not confirmed experimentally and may change.
  60 * We kill the socket, if:
  61 * 1. If number of orphaned sockets exceeds an administratively configured
  62 *    limit.
  63 * 2. If we have strong memory pressure.
  64 */
  65static int tcp_out_of_resources(struct sock *sk, int do_reset)
  66{
  67        struct tcp_sock *tp = tcp_sk(sk);
  68        int orphans = percpu_counter_read_positive(&tcp_orphan_count);
  69
  70        /* If peer does not open window for long time, or did not transmit
  71         * anything for long time, penalize it. */
  72        if ((s32)(tcp_time_stamp - tp->lsndtime) > 2*TCP_RTO_MAX || !do_reset)
  73                orphans <<= 1;
  74
  75        /* If some dubious ICMP arrived, penalize even more. */
  76        if (sk->sk_err_soft)
  77                orphans <<= 1;
  78
  79        if (tcp_too_many_orphans(sk, orphans)) {
  80                if (net_ratelimit())
  81                        printk(KERN_INFO "Out of socket memory\n");
  82
  83                /* Catch exceptional cases, when connection requires reset.
  84                 *      1. Last segment was sent recently. */
  85                if ((s32)(tcp_time_stamp - tp->lsndtime) <= TCP_TIMEWAIT_LEN ||
  86                    /*  2. Window is closed. */
  87                    (!tp->snd_wnd && !tp->packets_out))
  88                        do_reset = 1;
  89                if (do_reset)
  90                        tcp_send_active_reset(sk, GFP_ATOMIC);
  91                tcp_done(sk);
  92                NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPABORTONMEMORY);
  93                return 1;
  94        }
  95        return 0;
  96}
  97
  98/* Calculate maximal number or retries on an orphaned socket. */
  99static int tcp_orphan_retries(struct sock *sk, int alive)
 100{
 101        int retries = sysctl_tcp_orphan_retries; /* May be zero. */
 102
 103        /* We know from an ICMP that something is wrong. */
 104        if (sk->sk_err_soft && !alive)
 105                retries = 0;
 106
 107        /* However, if socket sent something recently, select some safe
 108         * number of retries. 8 corresponds to >100 seconds with minimal
 109         * RTO of 200msec. */
 110        if (retries == 0 && alive)
 111                retries = 8;
 112        return retries;
 113}
 114
 115static void tcp_mtu_probing(struct inet_connection_sock *icsk, struct sock *sk)
 116{
 117        /* Black hole detection */
 118        if (sysctl_tcp_mtu_probing) {
 119                if (!icsk->icsk_mtup.enabled) {
 120                        icsk->icsk_mtup.enabled = 1;
 121                        tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
 122                } else {
 123                        struct tcp_sock *tp = tcp_sk(sk);
 124                        int mss;
 125
 126                        mss = tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low) >> 1;
 127                        mss = min(sysctl_tcp_base_mss, mss);
 128                        mss = max(mss, 68 - tp->tcp_header_len);
 129                        icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, mss);
 130                        tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
 131                }
 132        }
 133}
 134
 135/* A write timeout has occurred. Process the after effects. */
 136static int tcp_write_timeout(struct sock *sk)
 137{
 138        struct inet_connection_sock *icsk = inet_csk(sk);
 139        int retry_until;
 140
 141        if ((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV)) {
 142                if (icsk->icsk_retransmits)
 143                        dst_negative_advice(&sk->sk_dst_cache);
 144                retry_until = icsk->icsk_syn_retries ? : sysctl_tcp_syn_retries;
 145        } else {
 146                if (icsk->icsk_retransmits >= sysctl_tcp_retries1) {
 147                        /* Black hole detection */
 148                        tcp_mtu_probing(icsk, sk);
 149
 150                        dst_negative_advice(&sk->sk_dst_cache);
 151                }
 152
 153                retry_until = sysctl_tcp_retries2;
 154                if (sock_flag(sk, SOCK_DEAD)) {
 155                        const int alive = (icsk->icsk_rto < TCP_RTO_MAX);
 156
 157                        retry_until = tcp_orphan_retries(sk, alive);
 158
 159                        if (tcp_out_of_resources(sk, alive || icsk->icsk_retransmits < retry_until))
 160                                return 1;
 161                }
 162        }
 163
 164        if (icsk->icsk_retransmits >= retry_until) {
 165                /* Has it gone just too far? */
 166                tcp_write_err(sk);
 167                return 1;
 168        }
 169        return 0;
 170}
 171
 172static void tcp_delack_timer(unsigned long data)
 173{
 174        struct sock *sk = (struct sock *)data;
 175        struct tcp_sock *tp = tcp_sk(sk);
 176        struct inet_connection_sock *icsk = inet_csk(sk);
 177
 178        bh_lock_sock(sk);
 179        if (sock_owned_by_user(sk)) {
 180                /* Try again later. */
 181                icsk->icsk_ack.blocked = 1;
 182                NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKLOCKED);
 183                sk_reset_timer(sk, &icsk->icsk_delack_timer, jiffies + TCP_DELACK_MIN);
 184                goto out_unlock;
 185        }
 186
 187        sk_mem_reclaim_partial(sk);
 188
 189        if (sk->sk_state == TCP_CLOSE || !(icsk->icsk_ack.pending & ICSK_ACK_TIMER))
 190                goto out;
 191
 192        if (time_after(icsk->icsk_ack.timeout, jiffies)) {
 193                sk_reset_timer(sk, &icsk->icsk_delack_timer, icsk->icsk_ack.timeout);
 194                goto out;
 195        }
 196        icsk->icsk_ack.pending &= ~ICSK_ACK_TIMER;
 197
 198        if (!skb_queue_empty(&tp->ucopy.prequeue)) {
 199                struct sk_buff *skb;
 200
 201                NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSCHEDULERFAILED);
 202
 203                while ((skb = __skb_dequeue(&tp->ucopy.prequeue)) != NULL)
 204                        sk_backlog_rcv(sk, skb);
 205
 206                tp->ucopy.memory = 0;
 207        }
 208
 209        if (inet_csk_ack_scheduled(sk)) {
 210                if (!icsk->icsk_ack.pingpong) {
 211                        /* Delayed ACK missed: inflate ATO. */
 212                        icsk->icsk_ack.ato = min(icsk->icsk_ack.ato << 1, icsk->icsk_rto);
 213                } else {
 214                        /* Delayed ACK missed: leave pingpong mode and
 215                         * deflate ATO.
 216                         */
 217                        icsk->icsk_ack.pingpong = 0;
 218                        icsk->icsk_ack.ato      = TCP_ATO_MIN;
 219                }
 220                tcp_send_ack(sk);
 221                NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKS);
 222        }
 223        TCP_CHECK_TIMER(sk);
 224
 225out:
 226        if (tcp_memory_pressure)
 227                sk_mem_reclaim(sk);
 228out_unlock:
 229        bh_unlock_sock(sk);
 230        sock_put(sk);
 231}
 232
 233static void tcp_probe_timer(struct sock *sk)
 234{
 235        struct inet_connection_sock *icsk = inet_csk(sk);
 236        struct tcp_sock *tp = tcp_sk(sk);
 237        int max_probes;
 238
 239        if (tp->packets_out || !tcp_send_head(sk)) {
 240                icsk->icsk_probes_out = 0;
 241                return;
 242        }
 243
 244        /* *WARNING* RFC 1122 forbids this
 245         *
 246         * It doesn't AFAIK, because we kill the retransmit timer -AK
 247         *
 248         * FIXME: We ought not to do it, Solaris 2.5 actually has fixing
 249         * this behaviour in Solaris down as a bug fix. [AC]
 250         *
 251         * Let me to explain. icsk_probes_out is zeroed by incoming ACKs
 252         * even if they advertise zero window. Hence, connection is killed only
 253         * if we received no ACKs for normal connection timeout. It is not killed
 254         * only because window stays zero for some time, window may be zero
 255         * until armageddon and even later. We are in full accordance
 256         * with RFCs, only probe timer combines both retransmission timeout
 257         * and probe timeout in one bottle.                             --ANK
 258         */
 259        max_probes = sysctl_tcp_retries2;
 260
 261        if (sock_flag(sk, SOCK_DEAD)) {
 262                const int alive = ((icsk->icsk_rto << icsk->icsk_backoff) < TCP_RTO_MAX);
 263
 264                max_probes = tcp_orphan_retries(sk, alive);
 265
 266                if (tcp_out_of_resources(sk, alive || icsk->icsk_probes_out <= max_probes))
 267                        return;
 268        }
 269
 270        if (icsk->icsk_probes_out > max_probes) {
 271                tcp_write_err(sk);
 272        } else {
 273                /* Only send another probe if we didn't close things up. */
 274                tcp_send_probe0(sk);
 275        }
 276}
 277
 278/*
 279 *      The TCP retransmit timer.
 280 */
 281
 282static void tcp_retransmit_timer(struct sock *sk)
 283{
 284        struct tcp_sock *tp = tcp_sk(sk);
 285        struct inet_connection_sock *icsk = inet_csk(sk);
 286
 287        if (!tp->packets_out)
 288                goto out;
 289
 290        WARN_ON(tcp_write_queue_empty(sk));
 291
 292        if (!tp->snd_wnd && !sock_flag(sk, SOCK_DEAD) &&
 293            !((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV))) {
 294                /* Receiver dastardly shrinks window. Our retransmits
 295                 * become zero probes, but we should not timeout this
 296                 * connection. If the socket is an orphan, time it out,
 297                 * we cannot allow such beasts to hang infinitely.
 298                 */
 299#ifdef TCP_DEBUG
 300                struct inet_sock *inet = inet_sk(sk);
 301                if (sk->sk_family == AF_INET) {
 302                        LIMIT_NETDEBUG(KERN_DEBUG "TCP: Peer %pI4:%u/%u unexpectedly shrunk window %u:%u (repaired)\n",
 303                               &inet->daddr, ntohs(inet->dport),
 304                               inet->num, tp->snd_una, tp->snd_nxt);
 305                }
 306#if defined(CONFIG_IPV6) || defined(CONFIG_IPV6_MODULE)
 307                else if (sk->sk_family == AF_INET6) {
 308                        struct ipv6_pinfo *np = inet6_sk(sk);
 309                        LIMIT_NETDEBUG(KERN_DEBUG "TCP: Peer %pI6:%u/%u unexpectedly shrunk window %u:%u (repaired)\n",
 310                               &np->daddr, ntohs(inet->dport),
 311                               inet->num, tp->snd_una, tp->snd_nxt);
 312                }
 313#endif
 314#endif
 315                if (tcp_time_stamp - tp->rcv_tstamp > TCP_RTO_MAX) {
 316                        tcp_write_err(sk);
 317                        goto out;
 318                }
 319                tcp_enter_loss(sk, 0);
 320                tcp_retransmit_skb(sk, tcp_write_queue_head(sk));
 321                __sk_dst_reset(sk);
 322                goto out_reset_timer;
 323        }
 324
 325        if (tcp_write_timeout(sk))
 326                goto out;
 327
 328        if (icsk->icsk_retransmits == 0) {
 329                int mib_idx;
 330
 331                if (icsk->icsk_ca_state == TCP_CA_Disorder) {
 332                        if (tcp_is_sack(tp))
 333                                mib_idx = LINUX_MIB_TCPSACKFAILURES;
 334                        else
 335                                mib_idx = LINUX_MIB_TCPRENOFAILURES;
 336                } else if (icsk->icsk_ca_state == TCP_CA_Recovery) {
 337                        if (tcp_is_sack(tp))
 338                                mib_idx = LINUX_MIB_TCPSACKRECOVERYFAIL;
 339                        else
 340                                mib_idx = LINUX_MIB_TCPRENORECOVERYFAIL;
 341                } else if (icsk->icsk_ca_state == TCP_CA_Loss) {
 342                        mib_idx = LINUX_MIB_TCPLOSSFAILURES;
 343                } else {
 344                        mib_idx = LINUX_MIB_TCPTIMEOUTS;
 345                }
 346                NET_INC_STATS_BH(sock_net(sk), mib_idx);
 347        }
 348
 349        if (tcp_use_frto(sk)) {
 350                tcp_enter_frto(sk);
 351        } else {
 352                tcp_enter_loss(sk, 0);
 353        }
 354
 355        if (tcp_retransmit_skb(sk, tcp_write_queue_head(sk)) > 0) {
 356                /* Retransmission failed because of local congestion,
 357                 * do not backoff.
 358                 */
 359                if (!icsk->icsk_retransmits)
 360                        icsk->icsk_retransmits = 1;
 361                inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
 362                                          min(icsk->icsk_rto, TCP_RESOURCE_PROBE_INTERVAL),
 363                                          TCP_RTO_MAX);
 364                goto out;
 365        }
 366
 367        /* Increase the timeout each time we retransmit.  Note that
 368         * we do not increase the rtt estimate.  rto is initialized
 369         * from rtt, but increases here.  Jacobson (SIGCOMM 88) suggests
 370         * that doubling rto each time is the least we can get away with.
 371         * In KA9Q, Karn uses this for the first few times, and then
 372         * goes to quadratic.  netBSD doubles, but only goes up to *64,
 373         * and clamps at 1 to 64 sec afterwards.  Note that 120 sec is
 374         * defined in the protocol as the maximum possible RTT.  I guess
 375         * we'll have to use something other than TCP to talk to the
 376         * University of Mars.
 377         *
 378         * PAWS allows us longer timeouts and large windows, so once
 379         * implemented ftp to mars will work nicely. We will have to fix
 380         * the 120 second clamps though!
 381         */
 382        icsk->icsk_backoff++;
 383        icsk->icsk_retransmits++;
 384
 385out_reset_timer:
 386        icsk->icsk_rto = min(icsk->icsk_rto << 1, TCP_RTO_MAX);
 387        inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, icsk->icsk_rto, TCP_RTO_MAX);
 388        if (icsk->icsk_retransmits > sysctl_tcp_retries1)
 389                __sk_dst_reset(sk);
 390
 391out:;
 392}
 393
 394static void tcp_write_timer(unsigned long data)
 395{
 396        struct sock *sk = (struct sock *)data;
 397        struct inet_connection_sock *icsk = inet_csk(sk);
 398        int event;
 399
 400        bh_lock_sock(sk);
 401        if (sock_owned_by_user(sk)) {
 402                /* Try again later */
 403                sk_reset_timer(sk, &icsk->icsk_retransmit_timer, jiffies + (HZ / 20));
 404                goto out_unlock;
 405        }
 406
 407        if (sk->sk_state == TCP_CLOSE || !icsk->icsk_pending)
 408                goto out;
 409
 410        if (time_after(icsk->icsk_timeout, jiffies)) {
 411                sk_reset_timer(sk, &icsk->icsk_retransmit_timer, icsk->icsk_timeout);
 412                goto out;
 413        }
 414
 415        event = icsk->icsk_pending;
 416        icsk->icsk_pending = 0;
 417
 418        switch (event) {
 419        case ICSK_TIME_RETRANS:
 420                tcp_retransmit_timer(sk);
 421                break;
 422        case ICSK_TIME_PROBE0:
 423                tcp_probe_timer(sk);
 424                break;
 425        }
 426        TCP_CHECK_TIMER(sk);
 427
 428out:
 429        sk_mem_reclaim(sk);
 430out_unlock:
 431        bh_unlock_sock(sk);
 432        sock_put(sk);
 433}
 434
 435/*
 436 *      Timer for listening sockets
 437 */
 438
 439static void tcp_synack_timer(struct sock *sk)
 440{
 441        inet_csk_reqsk_queue_prune(sk, TCP_SYNQ_INTERVAL,
 442                                   TCP_TIMEOUT_INIT, TCP_RTO_MAX);
 443}
 444
 445void tcp_set_keepalive(struct sock *sk, int val)
 446{
 447        if ((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN))
 448                return;
 449
 450        if (val && !sock_flag(sk, SOCK_KEEPOPEN))
 451                inet_csk_reset_keepalive_timer(sk, keepalive_time_when(tcp_sk(sk)));
 452        else if (!val)
 453                inet_csk_delete_keepalive_timer(sk);
 454}
 455
 456
 457static void tcp_keepalive_timer (unsigned long data)
 458{
 459        struct sock *sk = (struct sock *) data;
 460        struct inet_connection_sock *icsk = inet_csk(sk);
 461        struct tcp_sock *tp = tcp_sk(sk);
 462        __u32 elapsed;
 463
 464        /* Only process if socket is not in use. */
 465        bh_lock_sock(sk);
 466        if (sock_owned_by_user(sk)) {
 467                /* Try again later. */
 468                inet_csk_reset_keepalive_timer (sk, HZ/20);
 469                goto out;
 470        }
 471
 472        if (sk->sk_state == TCP_LISTEN) {
 473                tcp_synack_timer(sk);
 474                goto out;
 475        }
 476
 477        if (sk->sk_state == TCP_FIN_WAIT2 && sock_flag(sk, SOCK_DEAD)) {
 478                if (tp->linger2 >= 0) {
 479                        const int tmo = tcp_fin_time(sk) - TCP_TIMEWAIT_LEN;
 480
 481                        if (tmo > 0) {
 482                                tcp_time_wait(sk, TCP_FIN_WAIT2, tmo);
 483                                goto out;
 484                        }
 485                }
 486                tcp_send_active_reset(sk, GFP_ATOMIC);
 487                goto death;
 488        }
 489
 490        if (!sock_flag(sk, SOCK_KEEPOPEN) || sk->sk_state == TCP_CLOSE)
 491                goto out;
 492
 493        elapsed = keepalive_time_when(tp);
 494
 495        /* It is alive without keepalive 8) */
 496        if (tp->packets_out || tcp_send_head(sk))
 497                goto resched;
 498
 499        elapsed = tcp_time_stamp - tp->rcv_tstamp;
 500
 501        if (elapsed >= keepalive_time_when(tp)) {
 502                if ((!tp->keepalive_probes && icsk->icsk_probes_out >= sysctl_tcp_keepalive_probes) ||
 503                     (tp->keepalive_probes && icsk->icsk_probes_out >= tp->keepalive_probes)) {
 504                        tcp_send_active_reset(sk, GFP_ATOMIC);
 505                        tcp_write_err(sk);
 506                        goto out;
 507                }
 508                if (tcp_write_wakeup(sk) <= 0) {
 509                        icsk->icsk_probes_out++;
 510                        elapsed = keepalive_intvl_when(tp);
 511                } else {
 512                        /* If keepalive was lost due to local congestion,
 513                         * try harder.
 514                         */
 515                        elapsed = TCP_RESOURCE_PROBE_INTERVAL;
 516                }
 517        } else {
 518                /* It is tp->rcv_tstamp + keepalive_time_when(tp) */
 519                elapsed = keepalive_time_when(tp) - elapsed;
 520        }
 521
 522        TCP_CHECK_TIMER(sk);
 523        sk_mem_reclaim(sk);
 524
 525resched:
 526        inet_csk_reset_keepalive_timer (sk, elapsed);
 527        goto out;
 528
 529death:
 530        tcp_done(sk);
 531
 532out:
 533        bh_unlock_sock(sk);
 534        sock_put(sk);
 535}
 536