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 /* A write timeout has occurred. Process the after effects. */
 118 static int tcp_write_timeout(struct sock *sk)
 119 {
 120         struct inet_connection_sock *icsk = inet_csk(sk);
 121         struct tcp_sock *tp = tcp_sk(sk);
 122         int retry_until;
 123         int mss;
 124
 125         if ((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV)) {
 126                 if (icsk->icsk_retransmits)
 127                         dst_negative_advice(&sk->sk_dst_cache);
 128                 retry_until = icsk->icsk_syn_retries ? : sysctl_tcp_syn_retries;
 129         } else {
 130                 if (icsk->icsk_retransmits >= sysctl_tcp_retries1) {
 131                         /* Black hole detection */
 132                         if (sysctl_tcp_mtu_probing) {
 133                                 if (!icsk->icsk_mtup.enabled) {
 134                                         icsk->icsk_mtup.enabled = 1;
 135                                         tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
 136                                 } else {
 137                                         mss = min(sysctl_tcp_base_mss,
 138                                                   tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low)/2);
 139                                         mss = max(mss, 68 - tp->tcp_header_len);
 140                                         icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, mss);
 141                                         tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
 142                                 }
 143                         }
 144
 145                         dst_negative_advice(&sk->sk_dst_cache);
 146                 }
 147
 148                 retry_until = sysctl_tcp_retries2;
 149                 if (sock_flag(sk, SOCK_DEAD)) {
 150                         const int alive = (icsk->icsk_rto < TCP_RTO_MAX);
 151
 152                         retry_until = tcp_orphan_retries(sk, alive);
 153
 154                         if (tcp_out_of_resources(sk, alive || icsk->icsk_retransmits < retry_until))
 155                                 return 1;
 156                 }
 157         }
 158
 159         if (icsk->icsk_retransmits >= retry_until) {
 160                 /* Has it gone just too far? */
 161                 tcp_write_err(sk);
 162                 return 1;
 163         }
 164         return 0;
 165 }
 166
 167 static void tcp_delack_timer(unsigned long data)
 168 {
 169         struct sock *sk = (struct sock*)data;
 170         struct tcp_sock *tp = tcp_sk(sk);
 171         struct inet_connection_sock *icsk = inet_csk(sk);
 172
 173         bh_lock_sock(sk);
 174         if (sock_owned_by_user(sk)) {
 175                 /* Try again later. */
 176                 icsk->icsk_ack.blocked = 1;
 177                 NET_INC_STATS_BH(LINUX_MIB_DELAYEDACKLOCKED);
 178                 sk_reset_timer(sk, &icsk->icsk_delack_timer, jiffies + TCP_DELACK_MIN);
 179                 goto out_unlock;
 180         }
 181
 182         sk_stream_mem_reclaim(sk);
 183
 184         if (sk->sk_state == TCP_CLOSE || !(icsk->icsk_ack.pending & ICSK_ACK_TIMER))
 185                 goto out;
 186
 187         if (time_after(icsk->icsk_ack.timeout, jiffies)) {
 188                 sk_reset_timer(sk, &icsk->icsk_delack_timer, icsk->icsk_ack.timeout);
 189                 goto out;
 190         }
 191         icsk->icsk_ack.pending &= ~ICSK_ACK_TIMER;
 192
 193         if (!skb_queue_empty(&tp->ucopy.prequeue)) {
 194                 struct sk_buff *skb;
 195
 196                 NET_INC_STATS_BH(LINUX_MIB_TCPSCHEDULERFAILED);
 197
 198                 while ((skb = __skb_dequeue(&tp->ucopy.prequeue)) != NULL)
 199                         sk->sk_backlog_rcv(sk, skb);
 200
 201                 tp->ucopy.memory = 0;
 202         }
 203
 204         if (inet_csk_ack_scheduled(sk)) {
 205                 if (!icsk->icsk_ack.pingpong) {
 206                         /* Delayed ACK missed: inflate ATO. */
 207                         icsk->icsk_ack.ato = min(icsk->icsk_ack.ato << 1, icsk->icsk_rto);
 208                 } else {
 209                         /* Delayed ACK missed: leave pingpong mode and
 210                          * deflate ATO.
 211                          */
 212                         icsk->icsk_ack.pingpong = 0;
 213                         icsk->icsk_ack.ato      = TCP_ATO_MIN;
 214                 }
 215                 tcp_send_ack(sk);
 216                 NET_INC_STATS_BH(LINUX_MIB_DELAYEDACKS);
 217         }
 218         TCP_CHECK_TIMER(sk);
 219
 220 out:
 221         if (tcp_memory_pressure)
 222                 sk_stream_mem_reclaim(sk);
 223 out_unlock:
 224         bh_unlock_sock(sk);
 225         sock_put(sk);
 226 }
 227
 228 static void tcp_probe_timer(struct sock *sk)
 229 {
 230         struct inet_connection_sock *icsk = inet_csk(sk);
 231         struct tcp_sock *tp = tcp_sk(sk);
 232         int max_probes;
 233
 234         if (tp->packets_out || !tcp_send_head(sk)) {
 235                 icsk->icsk_probes_out = 0;
 236                 return;
 237         }
 238
 239         /* *WARNING* RFC 1122 forbids this
 240          *
 241          * It doesn't AFAIK, because we kill the retransmit timer -AK
 242          *
 243          * FIXME: We ought not to do it, Solaris 2.5 actually has fixing
 244          * this behaviour in Solaris down as a bug fix. [AC]
 245          *
 246          * Let me to explain. icsk_probes_out is zeroed by incoming ACKs
 247          * even if they advertise zero window. Hence, connection is killed only
 248          * if we received no ACKs for normal connection timeout. It is not killed
 249          * only because window stays zero for some time, window may be zero
 250          * until armageddon and even later. We are in full accordance
 251          * with RFCs, only probe timer combines both retransmission timeout
 252          * and probe timeout in one bottle.                             --ANK
 253          */
 254         max_probes = sysctl_tcp_retries2;
 255
 256         if (sock_flag(sk, SOCK_DEAD)) {
 257                 const int alive = ((icsk->icsk_rto << icsk->icsk_backoff) < TCP_RTO_MAX);
 258
 259                 max_probes = tcp_orphan_retries(sk, alive);
 260
 261                 if (tcp_out_of_resources(sk, alive || icsk->icsk_probes_out <= max_probes))
 262                         return;
 263         }
 264
 265         if (icsk->icsk_probes_out > max_probes) {
 266                 tcp_write_err(sk);
 267         } else {
 268                 /* Only send another probe if we didn't close things up. */
 269                 tcp_send_probe0(sk);
 270         }
 271 }
 272
 273 /*
 274  *      The TCP retransmit timer.
 275  */
 276
 277 static void tcp_retransmit_timer(struct sock *sk)
 278 {
 279         struct tcp_sock *tp = tcp_sk(sk);
 280         struct inet_connection_sock *icsk = inet_csk(sk);
 281
 282         if (!tp->packets_out)
 283                 goto out;
 284
 285         BUG_TRAP(!tcp_write_queue_empty(sk));
 286
 287         if (!tp->snd_wnd && !sock_flag(sk, SOCK_DEAD) &&
 288             !((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV))) {
 289                 /* Receiver dastardly shrinks window. Our retransmits
 290                  * become zero probes, but we should not timeout this
 291                  * connection. If the socket is an orphan, time it out,
 292                  * we cannot allow such beasts to hang infinitely.
 293                  */
 294 #ifdef TCP_DEBUG
 295                 if (1) {
 296                         struct inet_sock *inet = inet_sk(sk);
 297                         LIMIT_NETDEBUG(KERN_DEBUG "TCP: Treason uncloaked! Peer %u.%u.%u.%u:%u/%u shrinks window %u:%u. Repaired.\n",
 298                                NIPQUAD(inet->daddr), ntohs(inet->dport),
 299                                inet->num, tp->snd_una, tp->snd_nxt);
 300                 }
 301 #endif
 302                 if (tcp_time_stamp - tp->rcv_tstamp > TCP_RTO_MAX) {
 303                         tcp_write_err(sk);
 304                         goto out;
 305                 }
 306                 tcp_enter_loss(sk, 0);
 307                 tcp_retransmit_skb(sk, tcp_write_queue_head(sk));
 308                 __sk_dst_reset(sk);
 309                 goto out_reset_timer;
 310         }
 311
 312         if (tcp_write_timeout(sk))
 313                 goto out;
 314
 315         if (icsk->icsk_retransmits == 0) {
 316                 if (icsk->icsk_ca_state == TCP_CA_Disorder ||
 317                     icsk->icsk_ca_state == TCP_CA_Recovery) {
 318                         if (tcp_is_sack(tp)) {
 319                                 if (icsk->icsk_ca_state == TCP_CA_Recovery)
 320                                         NET_INC_STATS_BH(LINUX_MIB_TCPSACKRECOVERYFAIL);
 321                                 else
 322                                         NET_INC_STATS_BH(LINUX_MIB_TCPSACKFAILURES);
 323                         } else {
 324                                 if (icsk->icsk_ca_state == TCP_CA_Recovery)
 325                                         NET_INC_STATS_BH(LINUX_MIB_TCPRENORECOVERYFAIL);
 326                                 else
 327                                         NET_INC_STATS_BH(LINUX_MIB_TCPRENOFAILURES);
 328                         }
 329                 } else if (icsk->icsk_ca_state == TCP_CA_Loss) {
 330                         NET_INC_STATS_BH(LINUX_MIB_TCPLOSSFAILURES);
 331                 } else {
 332                         NET_INC_STATS_BH(LINUX_MIB_TCPTIMEOUTS);
 333                 }
 334         }
 335
 336         if (tcp_use_frto(sk)) {
 337                 tcp_enter_frto(sk);
 338         } else {
 339                 tcp_enter_loss(sk, 0);
 340         }
 341
 342         if (tcp_retransmit_skb(sk, tcp_write_queue_head(sk)) > 0) {
 343                 /* Retransmission failed because of local congestion,
 344                  * do not backoff.
 345                  */
 346                 if (!icsk->icsk_retransmits)
 347                         icsk->icsk_retransmits = 1;
 348                 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
 349                                           min(icsk->icsk_rto, TCP_RESOURCE_PROBE_INTERVAL),
 350                                           TCP_RTO_MAX);
 351                 goto out;
 352         }
 353
 354         /* Increase the timeout each time we retransmit.  Note that
 355          * we do not increase the rtt estimate.  rto is initialized
 356          * from rtt, but increases here.  Jacobson (SIGCOMM 88) suggests
 357          * that doubling rto each time is the least we can get away with.
 358          * In KA9Q, Karn uses this for the first few times, and then
 359          * goes to quadratic.  netBSD doubles, but only goes up to *64,
 360          * and clamps at 1 to 64 sec afterwards.  Note that 120 sec is
 361          * defined in the protocol as the maximum possible RTT.  I guess
 362          * we'll have to use something other than TCP to talk to the
 363          * University of Mars.
 364          *
 365          * PAWS allows us longer timeouts and large windows, so once
 366          * implemented ftp to mars will work nicely. We will have to fix
 367          * the 120 second clamps though!
 368          */
 369         icsk->icsk_backoff++;
 370         icsk->icsk_retransmits++;
 371
 372 out_reset_timer:
 373         icsk->icsk_rto = min(icsk->icsk_rto << 1, TCP_RTO_MAX);
 374         inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, icsk->icsk_rto, TCP_RTO_MAX);
 375         if (icsk->icsk_retransmits > sysctl_tcp_retries1)
 376                 __sk_dst_reset(sk);
 377
 378 out:;
 379 }
 380
 381 static void tcp_write_timer(unsigned long data)
 382 {
 383         struct sock *sk = (struct sock*)data;
 384         struct inet_connection_sock *icsk = inet_csk(sk);
 385         int event;
 386
 387         bh_lock_sock(sk);
 388         if (sock_owned_by_user(sk)) {
 389                 /* Try again later */
 390                 sk_reset_timer(sk, &icsk->icsk_retransmit_timer, jiffies + (HZ / 20));
 391                 goto out_unlock;
 392         }
 393
 394         if (sk->sk_state == TCP_CLOSE || !icsk->icsk_pending)
 395                 goto out;
 396
 397         if (time_after(icsk->icsk_timeout, jiffies)) {
 398                 sk_reset_timer(sk, &icsk->icsk_retransmit_timer, icsk->icsk_timeout);
 399                 goto out;
 400         }
 401
 402         event = icsk->icsk_pending;
 403         icsk->icsk_pending = 0;
 404
 405         switch (event) {
 406         case ICSK_TIME_RETRANS:
 407                 tcp_retransmit_timer(sk);
 408                 break;
 409         case ICSK_TIME_PROBE0:
 410                 tcp_probe_timer(sk);
 411                 break;
 412         }
 413         TCP_CHECK_TIMER(sk);
 414
 415 out:
 416         sk_stream_mem_reclaim(sk);
 417 out_unlock:
 418         bh_unlock_sock(sk);
 419         sock_put(sk);
 420 }
 421
 422 /*
 423  *      Timer for listening sockets
 424  */
 425
 426 static void tcp_synack_timer(struct sock *sk)
 427 {
 428         inet_csk_reqsk_queue_prune(sk, TCP_SYNQ_INTERVAL,
 429                                    TCP_TIMEOUT_INIT, TCP_RTO_MAX);
 430 }
 431
 432 void tcp_set_keepalive(struct sock *sk, int val)
 433 {
 434         if ((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN))
 435                 return;
 436
 437         if (val && !sock_flag(sk, SOCK_KEEPOPEN))
 438                 inet_csk_reset_keepalive_timer(sk, keepalive_time_when(tcp_sk(sk)));
 439         else if (!val)
 440                 inet_csk_delete_keepalive_timer(sk);
 441 }
 442
 443
 444 static void tcp_keepalive_timer (unsigned long data)
 445 {
 446         struct sock *sk = (struct sock *) data;
 447         struct inet_connection_sock *icsk = inet_csk(sk);
 448         struct tcp_sock *tp = tcp_sk(sk);
 449         __u32 elapsed;
 450
 451         /* Only process if socket is not in use. */
 452         bh_lock_sock(sk);
 453         if (sock_owned_by_user(sk)) {
 454                 /* Try again later. */
 455                 inet_csk_reset_keepalive_timer (sk, HZ/20);
 456                 goto out;
 457         }
 458
 459         if (sk->sk_state == TCP_LISTEN) {
 460                 tcp_synack_timer(sk);
 461                 goto out;
 462         }
 463
 464         if (sk->sk_state == TCP_FIN_WAIT2 && sock_flag(sk, SOCK_DEAD)) {
 465                 if (tp->linger2 >= 0) {
 466                         const int tmo = tcp_fin_time(sk) - TCP_TIMEWAIT_LEN;
 467
 468                         if (tmo > 0) {
 469                                 tcp_time_wait(sk, TCP_FIN_WAIT2, tmo);
 470                                 goto out;
 471                         }
 472                 }
 473                 tcp_send_active_reset(sk, GFP_ATOMIC);
 474                 goto death;
 475         }
 476
 477         if (!sock_flag(sk, SOCK_KEEPOPEN) || sk->sk_state == TCP_CLOSE)
 478                 goto out;
 479
 480         elapsed = keepalive_time_when(tp);
 481
 482         /* It is alive without keepalive 8) */
 483         if (tp->packets_out || tcp_send_head(sk))
 484                 goto resched;
 485
 486         elapsed = tcp_time_stamp - tp->rcv_tstamp;
 487
 488         if (elapsed >= keepalive_time_when(tp)) {
 489                 if ((!tp->keepalive_probes && icsk->icsk_probes_out >= sysctl_tcp_keepalive_probes) ||
 490                      (tp->keepalive_probes && icsk->icsk_probes_out >= tp->keepalive_probes)) {
 491                         tcp_send_active_reset(sk, GFP_ATOMIC);
 492                         tcp_write_err(sk);
 493                         goto out;
 494                 }
 495                 if (tcp_write_wakeup(sk) <= 0) {
 496                         icsk->icsk_probes_out++;
 497                         elapsed = keepalive_intvl_when(tp);
 498                 } else {
 499                         /* If keepalive was lost due to local congestion,
 500                          * try harder.
 501                          */
 502                         elapsed = TCP_RESOURCE_PROBE_INTERVAL;
 503                 }
 504         } else {
 505                 /* It is tp->rcv_tstamp + keepalive_time_when(tp) */
 506                 elapsed = keepalive_time_when(tp) - elapsed;
 507         }
 508
 509         TCP_CHECK_TIMER(sk);
 510         sk_stream_mem_reclaim(sk);
 511
 512 resched:
 513         inet_csk_reset_keepalive_timer (sk, elapsed);
 514         goto out;
 515
 516 death:
 517         tcp_done(sk);
 518
 519 out:
 520         bh_unlock_sock(sk);
 521         sock_put(sk);
 522 }