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  * Version:     $Id: tcp_timer.c,v 1.88 2002/02/01 22:01:04 davem Exp $
   9  *
  10  * Authors:     Ross Biro
  11  *              Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>
  12  *              Mark Evans, <evansmp@uhura.aston.ac.uk>
  13  *              Corey Minyard <wf-rch!minyard@relay.EU.net>
  14  *              Florian La Roche, <flla@stud.uni-sb.de>
  15  *              Charles Hedrick, <hedrick@klinzhai.rutgers.edu>
  16  *              Linus Torvalds, <torvalds@cs.helsinki.fi>
  17  *              Alan Cox, <gw4pts@gw4pts.ampr.org>
  18  *              Matthew Dillon, <dillon@apollo.west.oic.com>
  19  *              Arnt Gulbrandsen, <agulbra@nvg.unit.no>
  20  *              Jorge Cwik, <jorge@laser.satlink.net>
  21  */
  22
  23 #include <linux/module.h>
  24 #include <net/tcp.h>
  25
  26 int sysctl_tcp_syn_retries __read_mostly = TCP_SYN_RETRIES;
  27 int sysctl_tcp_synack_retries __read_mostly = TCP_SYNACK_RETRIES;
  28 int sysctl_tcp_keepalive_time __read_mostly = TCP_KEEPALIVE_TIME;
  29 int sysctl_tcp_keepalive_probes __read_mostly = TCP_KEEPALIVE_PROBES;
  30 int sysctl_tcp_keepalive_intvl __read_mostly = TCP_KEEPALIVE_INTVL;
  31 int sysctl_tcp_retries1 __read_mostly = TCP_RETR1;
  32 int sysctl_tcp_retries2 __read_mostly = TCP_RETR2;
  33 int sysctl_tcp_orphan_retries __read_mostly;
  34
  35 static void tcp_write_timer(unsigned long);
  36 static void tcp_delack_timer(unsigned long);
  37 static void tcp_keepalive_timer (unsigned long data);
  38
  39 void tcp_init_xmit_timers(struct sock *sk)
  40 {
  41         inet_csk_init_xmit_timers(sk, &tcp_write_timer, &tcp_delack_timer,
  42                                   &tcp_keepalive_timer);
  43 }
  44
  45 EXPORT_SYMBOL(tcp_init_xmit_timers);
  46
  47 static void tcp_write_err(struct sock *sk)
  48 {
  49         sk->sk_err = sk->sk_err_soft ? : ETIMEDOUT;
  50         sk->sk_error_report(sk);
  51
  52         tcp_done(sk);
  53         NET_INC_STATS_BH(LINUX_MIB_TCPABORTONTIMEOUT);
  54 }
  55
  56 /* Do not allow orphaned sockets to eat all our resources.
  57  * This is direct violation of TCP specs, but it is required
  58  * to prevent DoS attacks. It is called when a retransmission timeout
  59  * or zero probe timeout occurs on orphaned socket.
  60  *
  61  * Criteria is still not confirmed experimentally and may change.
  62  * We kill the socket, if:
  63  * 1. If number of orphaned sockets exceeds an administratively configured
  64  *    limit.
  65  * 2. If we have strong memory pressure.
  66  */
  67 static int tcp_out_of_resources(struct sock *sk, int do_reset)
  68 {
  69         struct tcp_sock *tp = tcp_sk(sk);
  70         int orphans = atomic_read(&tcp_orphan_count);
  71
  72         /* If peer does not open window for long time, or did not transmit
  73          * anything for long time, penalize it. */
  74         if ((s32)(tcp_time_stamp - tp->lsndtime) > 2*TCP_RTO_MAX || !do_reset)
  75                 orphans <<= 1;
  76
  77         /* If some dubious ICMP arrived, penalize even more. */
  78         if (sk->sk_err_soft)
  79                 orphans <<= 1;
  80
  81         if (tcp_too_many_orphans(sk, orphans)) {
  82                 if (net_ratelimit())
  83                         printk(KERN_INFO "Out of socket memory\n");
  84
  85                 /* Catch exceptional cases, when connection requires reset.
  86                  *      1. Last segment was sent recently. */
  87                 if ((s32)(tcp_time_stamp - tp->lsndtime) <= TCP_TIMEWAIT_LEN ||
  88                     /*  2. Window is closed. */
  89                     (!tp->snd_wnd && !tp->packets_out))
  90                         do_reset = 1;
  91                 if (do_reset)
  92                         tcp_send_active_reset(sk, GFP_ATOMIC);
  93                 tcp_done(sk);
  94                 NET_INC_STATS_BH(LINUX_MIB_TCPABORTONMEMORY);
  95                 return 1;
  96         }
  97         return 0;
  98 }
  99
 100 /* Calculate maximal number or retries on an orphaned socket. */
 101 static int tcp_orphan_retries(struct sock *sk, int alive)
 102 {
 103         int retries = sysctl_tcp_orphan_retries; /* May be zero. */
 104
 105         /* We know from an ICMP that something is wrong. */
 106         if (sk->sk_err_soft && !alive)
 107                 retries = 0;
 108
 109         /* However, if socket sent something recently, select some safe
 110          * number of retries. 8 corresponds to >100 seconds with minimal
 111          * RTO of 200msec. */
 112         if (retries == 0 && alive)
 113                 retries = 8;
 114         return retries;
 115 }
 116
 117 static void tcp_mtu_probing(struct inet_connection_sock *icsk, struct sock *sk)
 118 {
 119         /* Black hole detection */
 120         if (sysctl_tcp_mtu_probing) {
 121                 if (!icsk->icsk_mtup.enabled) {
 122                         icsk->icsk_mtup.enabled = 1;
 123                         tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
 124                 } else {
 125                         struct tcp_sock *tp = tcp_sk(sk);
 126                         int mss;
 127
 128                         mss = tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low) >> 1;
 129                         mss = min(sysctl_tcp_base_mss, mss);
 130                         mss = max(mss, 68 - tp->tcp_header_len);
 131                         icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, mss);
 132                         tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
 133                 }
 134         }
 135 }
 136
 137 /* A write timeout has occurred. Process the after effects. */
 138 static int tcp_write_timeout(struct sock *sk)
 139 {
 140         struct inet_connection_sock *icsk = inet_csk(sk);
 141         int retry_until;
 142
 143         if ((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV)) {
 144                 if (icsk->icsk_retransmits)
 145                         dst_negative_advice(&sk->sk_dst_cache);
 146                 retry_until = icsk->icsk_syn_retries ? : sysctl_tcp_syn_retries;
 147         } else {
 148                 if (icsk->icsk_retransmits >= sysctl_tcp_retries1) {
 149                         /* Black hole detection */
 150                         tcp_mtu_probing(icsk, sk);
 151
 152                         dst_negative_advice(&sk->sk_dst_cache);
 153                 }
 154
 155                 retry_until = sysctl_tcp_retries2;
 156                 if (sock_flag(sk, SOCK_DEAD)) {
 157                         const int alive = (icsk->icsk_rto < TCP_RTO_MAX);
 158
 159                         retry_until = tcp_orphan_retries(sk, alive);
 160
 161                         if (tcp_out_of_resources(sk, alive || icsk->icsk_retransmits < retry_until))
 162                                 return 1;
 163                 }
 164         }
 165
 166         if (icsk->icsk_retransmits >= retry_until) {
 167                 /* Has it gone just too far? */
 168                 tcp_write_err(sk);
 169                 return 1;
 170         }
 171         return 0;
 172 }
 173
 174 static void tcp_delack_timer(unsigned long data)
 175 {
 176         struct sock *sk = (struct sock*)data;
 177         struct tcp_sock *tp = tcp_sk(sk);
 178         struct inet_connection_sock *icsk = inet_csk(sk);
 179
 180         bh_lock_sock(sk);
 181         if (sock_owned_by_user(sk)) {
 182                 /* Try again later. */
 183                 icsk->icsk_ack.blocked = 1;
 184                 NET_INC_STATS_BH(LINUX_MIB_DELAYEDACKLOCKED);
 185                 sk_reset_timer(sk, &icsk->icsk_delack_timer, jiffies + TCP_DELACK_MIN);
 186                 goto out_unlock;
 187         }
 188
 189         sk_mem_reclaim_partial(sk);
 190
 191         if (sk->sk_state == TCP_CLOSE || !(icsk->icsk_ack.pending & ICSK_ACK_TIMER))
 192                 goto out;
 193
 194         if (time_after(icsk->icsk_ack.timeout, jiffies)) {
 195                 sk_reset_timer(sk, &icsk->icsk_delack_timer, icsk->icsk_ack.timeout);
 196                 goto out;
 197         }
 198         icsk->icsk_ack.pending &= ~ICSK_ACK_TIMER;
 199
 200         if (!skb_queue_empty(&tp->ucopy.prequeue)) {
 201                 struct sk_buff *skb;
 202
 203                 NET_INC_STATS_BH(LINUX_MIB_TCPSCHEDULERFAILED);
 204
 205                 while ((skb = __skb_dequeue(&tp->ucopy.prequeue)) != NULL)
 206                         sk->sk_backlog_rcv(sk, skb);
 207
 208                 tp->ucopy.memory = 0;
 209         }
 210
 211         if (inet_csk_ack_scheduled(sk)) {
 212                 if (!icsk->icsk_ack.pingpong) {
 213                         /* Delayed ACK missed: inflate ATO. */
 214                         icsk->icsk_ack.ato = min(icsk->icsk_ack.ato << 1, icsk->icsk_rto);
 215                 } else {
 216                         /* Delayed ACK missed: leave pingpong mode and
 217                          * deflate ATO.
 218                          */
 219                         icsk->icsk_ack.pingpong = 0;
 220                         icsk->icsk_ack.ato      = TCP_ATO_MIN;
 221                 }
 222                 tcp_send_ack(sk);
 223                 NET_INC_STATS_BH(LINUX_MIB_DELAYEDACKS);
 224         }
 225         TCP_CHECK_TIMER(sk);
 226
 227 out:
 228         if (tcp_memory_pressure)
 229                 sk_mem_reclaim(sk);
 230 out_unlock:
 231         bh_unlock_sock(sk);
 232         sock_put(sk);
 233 }
 234
 235 static void tcp_probe_timer(struct sock *sk)
 236 {
 237         struct inet_connection_sock *icsk = inet_csk(sk);
 238         struct tcp_sock *tp = tcp_sk(sk);
 239         int max_probes;
 240
 241         if (tp->packets_out || !tcp_send_head(sk)) {
 242                 icsk->icsk_probes_out = 0;
 243                 return;
 244         }
 245
 246         /* *WARNING* RFC 1122 forbids this
 247          *
 248          * It doesn't AFAIK, because we kill the retransmit timer -AK
 249          *
 250          * FIXME: We ought not to do it, Solaris 2.5 actually has fixing
 251          * this behaviour in Solaris down as a bug fix. [AC]
 252          *
 253          * Let me to explain. icsk_probes_out is zeroed by incoming ACKs
 254          * even if they advertise zero window. Hence, connection is killed only
 255          * if we received no ACKs for normal connection timeout. It is not killed
 256          * only because window stays zero for some time, window may be zero
 257          * until armageddon and even later. We are in full accordance
 258          * with RFCs, only probe timer combines both retransmission timeout
 259          * and probe timeout in one bottle.                             --ANK
 260          */
 261         max_probes = sysctl_tcp_retries2;
 262
 263         if (sock_flag(sk, SOCK_DEAD)) {
 264                 const int alive = ((icsk->icsk_rto << icsk->icsk_backoff) < TCP_RTO_MAX);
 265
 266                 max_probes = tcp_orphan_retries(sk, alive);
 267
 268                 if (tcp_out_of_resources(sk, alive || icsk->icsk_probes_out <= max_probes))
 269                         return;
 270         }
 271
 272         if (icsk->icsk_probes_out > max_probes) {
 273                 tcp_write_err(sk);
 274         } else {
 275                 /* Only send another probe if we didn't close things up. */
 276                 tcp_send_probe0(sk);
 277         }
 278 }
 279
 280 /*
 281  *      The TCP retransmit timer.
 282  */
 283
 284 static void tcp_retransmit_timer(struct sock *sk)
 285 {
 286         struct tcp_sock *tp = tcp_sk(sk);
 287         struct inet_connection_sock *icsk = inet_csk(sk);
 288
 289         if (!tp->packets_out)
 290                 goto out;
 291
 292         BUG_TRAP(!tcp_write_queue_empty(sk));
 293
 294         if (!tp->snd_wnd && !sock_flag(sk, SOCK_DEAD) &&
 295             !((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV))) {
 296                 /* Receiver dastardly shrinks window. Our retransmits
 297                  * become zero probes, but we should not timeout this
 298                  * connection. If the socket is an orphan, time it out,
 299                  * we cannot allow such beasts to hang infinitely.
 300                  */
 301 #ifdef TCP_DEBUG
 302                 struct inet_sock *inet = inet_sk(sk);
 303                 if (sk->sk_family == AF_INET) {
 304                         LIMIT_NETDEBUG(KERN_DEBUG "TCP: Treason uncloaked! Peer " NIPQUAD_FMT ":%u/%u shrinks window %u:%u. Repaired.\n",
 305                                NIPQUAD(inet->daddr), ntohs(inet->dport),
 306                                inet->num, tp->snd_una, tp->snd_nxt);
 307                 }
 308 #if defined(CONFIG_IPV6) || defined(CONFIG_IPV6_MODULE)
 309                 else if (sk->sk_family == AF_INET6) {
 310                         struct ipv6_pinfo *np = inet6_sk(sk);
 311                         LIMIT_NETDEBUG(KERN_DEBUG "TCP: Treason uncloaked! Peer " NIP6_FMT ":%u/%u shrinks window %u:%u. Repaired.\n",
 312                                NIP6(np->daddr), ntohs(inet->dport),
 313                                inet->num, tp->snd_una, tp->snd_nxt);
 314                 }
 315 #endif
 316 #endif
 317                 if (tcp_time_stamp - tp->rcv_tstamp > TCP_RTO_MAX) {
 318                         tcp_write_err(sk);
 319                         goto out;
 320                 }
 321                 tcp_enter_loss(sk, 0);
 322                 tcp_retransmit_skb(sk, tcp_write_queue_head(sk));
 323                 __sk_dst_reset(sk);
 324                 goto out_reset_timer;
 325         }
 326
 327         if (tcp_write_timeout(sk))
 328                 goto out;
 329
 330         if (icsk->icsk_retransmits == 0) {
 331                 if (icsk->icsk_ca_state == TCP_CA_Disorder ||
 332                     icsk->icsk_ca_state == TCP_CA_Recovery) {
 333                         if (tcp_is_sack(tp)) {
 334                                 if (icsk->icsk_ca_state == TCP_CA_Recovery)
 335                                         NET_INC_STATS_BH(LINUX_MIB_TCPSACKRECOVERYFAIL);
 336                                 else
 337                                         NET_INC_STATS_BH(LINUX_MIB_TCPSACKFAILURES);
 338                         } else {
 339                                 if (icsk->icsk_ca_state == TCP_CA_Recovery)
 340                                         NET_INC_STATS_BH(LINUX_MIB_TCPRENORECOVERYFAIL);
 341                                 else
 342                                         NET_INC_STATS_BH(LINUX_MIB_TCPRENOFAILURES);
 343                         }
 344                 } else if (icsk->icsk_ca_state == TCP_CA_Loss) {
 345                         NET_INC_STATS_BH(LINUX_MIB_TCPLOSSFAILURES);
 346                 } else {
 347                         NET_INC_STATS_BH(LINUX_MIB_TCPTIMEOUTS);
 348                 }
 349         }
 350
 351         if (tcp_use_frto(sk)) {
 352                 tcp_enter_frto(sk);
 353         } else {
 354                 tcp_enter_loss(sk, 0);
 355         }
 356
 357         if (tcp_retransmit_skb(sk, tcp_write_queue_head(sk)) > 0) {
 358                 /* Retransmission failed because of local congestion,
 359                  * do not backoff.
 360                  */
 361                 if (!icsk->icsk_retransmits)
 362                         icsk->icsk_retransmits = 1;
 363                 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
 364                                           min(icsk->icsk_rto, TCP_RESOURCE_PROBE_INTERVAL),
 365                                           TCP_RTO_MAX);
 366                 goto out;
 367         }
 368
 369         /* Increase the timeout each time we retransmit.  Note that
 370          * we do not increase the rtt estimate.  rto is initialized
 371          * from rtt, but increases here.  Jacobson (SIGCOMM 88) suggests
 372          * that doubling rto each time is the least we can get away with.
 373          * In KA9Q, Karn uses this for the first few times, and then
 374          * goes to quadratic.  netBSD doubles, but only goes up to *64,
 375          * and clamps at 1 to 64 sec afterwards.  Note that 120 sec is
 376          * defined in the protocol as the maximum possible RTT.  I guess
 377          * we'll have to use something other than TCP to talk to the
 378          * University of Mars.
 379          *
 380          * PAWS allows us longer timeouts and large windows, so once
 381          * implemented ftp to mars will work nicely. We will have to fix
 382          * the 120 second clamps though!
 383          */
 384         icsk->icsk_backoff++;
 385         icsk->icsk_retransmits++;
 386
 387 out_reset_timer:
 388         icsk->icsk_rto = min(icsk->icsk_rto << 1, TCP_RTO_MAX);
 389         inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, icsk->icsk_rto, TCP_RTO_MAX);
 390         if (icsk->icsk_retransmits > sysctl_tcp_retries1)
 391                 __sk_dst_reset(sk);
 392
 393 out:;
 394 }
 395
 396 static void tcp_write_timer(unsigned long data)
 397 {
 398         struct sock *sk = (struct sock*)data;
 399         struct inet_connection_sock *icsk = inet_csk(sk);
 400         int event;
 401
 402         bh_lock_sock(sk);
 403         if (sock_owned_by_user(sk)) {
 404                 /* Try again later */
 405                 sk_reset_timer(sk, &icsk->icsk_retransmit_timer, jiffies + (HZ / 20));
 406                 goto out_unlock;
 407         }
 408
 409         if (sk->sk_state == TCP_CLOSE || !icsk->icsk_pending)
 410                 goto out;
 411
 412         if (time_after(icsk->icsk_timeout, jiffies)) {
 413                 sk_reset_timer(sk, &icsk->icsk_retransmit_timer, icsk->icsk_timeout);
 414                 goto out;
 415         }
 416
 417         event = icsk->icsk_pending;
 418         icsk->icsk_pending = 0;
 419
 420         switch (event) {
 421         case ICSK_TIME_RETRANS:
 422                 tcp_retransmit_timer(sk);
 423                 break;
 424         case ICSK_TIME_PROBE0:
 425                 tcp_probe_timer(sk);
 426                 break;
 427         }
 428         TCP_CHECK_TIMER(sk);
 429
 430 out:
 431         sk_mem_reclaim(sk);
 432 out_unlock:
 433         bh_unlock_sock(sk);
 434         sock_put(sk);
 435 }
 436
 437 /*
 438  *      Timer for listening sockets
 439  */
 440
 441 static void tcp_synack_timer(struct sock *sk)
 442 {
 443         inet_csk_reqsk_queue_prune(sk, TCP_SYNQ_INTERVAL,
 444                                    TCP_TIMEOUT_INIT, TCP_RTO_MAX);
 445 }
 446
 447 void tcp_set_keepalive(struct sock *sk, int val)
 448 {
 449         if ((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN))
 450                 return;
 451
 452         if (val && !sock_flag(sk, SOCK_KEEPOPEN))
 453                 inet_csk_reset_keepalive_timer(sk, keepalive_time_when(tcp_sk(sk)));
 454         else if (!val)
 455                 inet_csk_delete_keepalive_timer(sk);
 456 }
 457
 458
 459 static void tcp_keepalive_timer (unsigned long data)
 460 {
 461         struct sock *sk = (struct sock *) data;
 462         struct inet_connection_sock *icsk = inet_csk(sk);
 463         struct tcp_sock *tp = tcp_sk(sk);
 464         __u32 elapsed;
 465
 466         /* Only process if socket is not in use. */
 467         bh_lock_sock(sk);
 468         if (sock_owned_by_user(sk)) {
 469                 /* Try again later. */
 470                 inet_csk_reset_keepalive_timer (sk, HZ/20);
 471                 goto out;
 472         }
 473
 474         if (sk->sk_state == TCP_LISTEN) {
 475                 tcp_synack_timer(sk);
 476                 goto out;
 477         }
 478
 479         if (sk->sk_state == TCP_FIN_WAIT2 && sock_flag(sk, SOCK_DEAD)) {
 480                 if (tp->linger2 >= 0) {
 481                         const int tmo = tcp_fin_time(sk) - TCP_TIMEWAIT_LEN;
 482
 483                         if (tmo > 0) {
 484                                 tcp_time_wait(sk, TCP_FIN_WAIT2, tmo);
 485                                 goto out;
 486                         }
 487                 }
 488                 tcp_send_active_reset(sk, GFP_ATOMIC);
 489                 goto death;
 490         }
 491
 492         if (tp->defer_tcp_accept.request && sk->sk_state == TCP_ESTABLISHED) {
 493                 tcp_send_active_reset(sk, GFP_ATOMIC);
 494                 goto death;
 495         }
 496
 497         if (!sock_flag(sk, SOCK_KEEPOPEN) || sk->sk_state == TCP_CLOSE)
 498                 goto out;
 499
 500         elapsed = keepalive_time_when(tp);
 501
 502         /* It is alive without keepalive 8) */
 503         if (tp->packets_out || tcp_send_head(sk))
 504                 goto resched;
 505
 506         elapsed = tcp_time_stamp - tp->rcv_tstamp;
 507
 508         if (elapsed >= keepalive_time_when(tp)) {
 509                 if ((!tp->keepalive_probes && icsk->icsk_probes_out >= sysctl_tcp_keepalive_probes) ||
 510                      (tp->keepalive_probes && icsk->icsk_probes_out >= tp->keepalive_probes)) {
 511                         tcp_send_active_reset(sk, GFP_ATOMIC);
 512                         tcp_write_err(sk);
 513                         goto out;
 514                 }
 515                 if (tcp_write_wakeup(sk) <= 0) {
 516                         icsk->icsk_probes_out++;
 517                         elapsed = keepalive_intvl_when(tp);
 518                 } else {
 519                         /* If keepalive was lost due to local congestion,
 520                          * try harder.
 521                          */
 522                         elapsed = TCP_RESOURCE_PROBE_INTERVAL;
 523                 }
 524         } else {
 525                 /* It is tp->rcv_tstamp + keepalive_time_when(tp) */
 526                 elapsed = keepalive_time_when(tp) - elapsed;
 527         }
 528
 529         TCP_CHECK_TIMER(sk);
 530         sk_mem_reclaim(sk);
 531
 532 resched:
 533         inet_csk_reset_keepalive_timer (sk, elapsed);
 534         goto out;
 535
 536 death:
 537         tcp_done(sk);
 538
 539 out:
 540         bh_unlock_sock(sk);
 541         sock_put(sk);
 542 }