1 /* 2 * INET An implementation of the TCP/IP protocol suite for the LINUX 3 * operating system. INET is implemented using the BSD Socket 4 * interface as the means of communication with the user level. 5 * 6 * Implementation of the Transmission Control Protocol(TCP). 7 * 8 * Authors: Ross Biro 9 * Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG> 10 * Mark Evans, <evansmp@uhura.aston.ac.uk> 11 * Corey Minyard <wf-rch!minyard@relay.EU.net> 12 * Florian La Roche, <flla@stud.uni-sb.de> 13 * Charles Hedrick, <hedrick@klinzhai.rutgers.edu> 14 * Linus Torvalds, <torvalds@cs.helsinki.fi> 15 * Alan Cox, <gw4pts@gw4pts.ampr.org> 16 * Matthew Dillon, <dillon@apollo.west.oic.com> 17 * Arnt Gulbrandsen, <agulbra@nvg.unit.no> 18 * Jorge Cwik, <jorge@laser.satlink.net> 19 */ 20 21 #include <linux/module.h> 22 #include <linux/gfp.h> 23 #include <net/tcp.h> 24 25 int sysctl_tcp_syn_retries __read_mostly = TCP_SYN_RETRIES; 26 int sysctl_tcp_synack_retries __read_mostly = TCP_SYNACK_RETRIES; 27 int sysctl_tcp_keepalive_time __read_mostly = TCP_KEEPALIVE_TIME; 28 int sysctl_tcp_keepalive_probes __read_mostly = TCP_KEEPALIVE_PROBES; 29 int sysctl_tcp_keepalive_intvl __read_mostly = TCP_KEEPALIVE_INTVL; 30 int sysctl_tcp_retries1 __read_mostly = TCP_RETR1; 31 int sysctl_tcp_retries2 __read_mostly = TCP_RETR2; 32 int sysctl_tcp_orphan_retries __read_mostly; 33 int sysctl_tcp_thin_linear_timeouts __read_mostly; 34 35 static 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 */ 55 static int tcp_out_of_resources(struct sock *sk, int 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 = 1; 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. */ 86 static 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 } 101 102 static 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 */ 127 static 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 if (unlikely(!tcp_sk(sk)->retrans_stamp)) 139 start_ts = TCP_SKB_CB(tcp_write_queue_head(sk))->when; 140 else 141 start_ts = tcp_sk(sk)->retrans_stamp; 142 143 if (likely(timeout == 0)) { 144 linear_backoff_thresh = ilog2(TCP_RTO_MAX/rto_base); 145 146 if (boundary <= linear_backoff_thresh) 147 timeout = ((2 << boundary) - 1) * rto_base; 148 else 149 timeout = ((2 << linear_backoff_thresh) - 1) * rto_base + 150 (boundary - linear_backoff_thresh) * TCP_RTO_MAX; 151 } 152 return (tcp_time_stamp - start_ts) >= timeout; 153 } 154 155 /* A write timeout has occurred. Process the after effects. */ 156 static int tcp_write_timeout(struct sock *sk) 157 { 158 struct inet_connection_sock *icsk = inet_csk(sk); 159 struct tcp_sock *tp = tcp_sk(sk); 160 int retry_until; 161 bool do_reset, syn_set = false; 162 163 if ((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV)) { 164 if (icsk->icsk_retransmits) { 165 dst_negative_advice(sk); 166 if (tp->syn_fastopen || tp->syn_data) 167 tcp_fastopen_cache_set(sk, 0, NULL, true); 168 } 169 retry_until = icsk->icsk_syn_retries ? : sysctl_tcp_syn_retries; 170 syn_set = true; 171 } else { 172 if (retransmits_timed_out(sk, sysctl_tcp_retries1, 0, 0)) { 173 /* Black hole detection */ 174 tcp_mtu_probing(icsk, sk); 175 176 dst_negative_advice(sk); 177 } 178 179 retry_until = sysctl_tcp_retries2; 180 if (sock_flag(sk, SOCK_DEAD)) { 181 const int alive = (icsk->icsk_rto < TCP_RTO_MAX); 182 183 retry_until = tcp_orphan_retries(sk, alive); 184 do_reset = alive || 185 !retransmits_timed_out(sk, retry_until, 0, 0); 186 187 if (tcp_out_of_resources(sk, do_reset)) 188 return 1; 189 } 190 } 191 192 if (retransmits_timed_out(sk, retry_until, 193 syn_set ? 0 : icsk->icsk_user_timeout, syn_set)) { 194 /* Has it gone just too far? */ 195 tcp_write_err(sk); 196 return 1; 197 } 198 return 0; 199 } 200 201 void tcp_delack_timer_handler(struct sock *sk) 202 { 203 struct tcp_sock *tp = tcp_sk(sk); 204 struct inet_connection_sock *icsk = inet_csk(sk); 205 206 sk_mem_reclaim_partial(sk); 207 208 if (sk->sk_state == TCP_CLOSE || !(icsk->icsk_ack.pending & ICSK_ACK_TIMER)) 209 goto out; 210 211 if (time_after(icsk->icsk_ack.timeout, jiffies)) { 212 sk_reset_timer(sk, &icsk->icsk_delack_timer, icsk->icsk_ack.timeout); 213 goto out; 214 } 215 icsk->icsk_ack.pending &= ~ICSK_ACK_TIMER; 216 217 if (!skb_queue_empty(&tp->ucopy.prequeue)) { 218 struct sk_buff *skb; 219 220 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSCHEDULERFAILED); 221 222 while ((skb = __skb_dequeue(&tp->ucopy.prequeue)) != NULL) 223 sk_backlog_rcv(sk, skb); 224 225 tp->ucopy.memory = 0; 226 } 227 228 if (inet_csk_ack_scheduled(sk)) { 229 if (!icsk->icsk_ack.pingpong) { 230 /* Delayed ACK missed: inflate ATO. */ 231 icsk->icsk_ack.ato = min(icsk->icsk_ack.ato << 1, icsk->icsk_rto); 232 } else { 233 /* Delayed ACK missed: leave pingpong mode and 234 * deflate ATO. 235 */ 236 icsk->icsk_ack.pingpong = 0; 237 icsk->icsk_ack.ato = TCP_ATO_MIN; 238 } 239 tcp_send_ack(sk); 240 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKS); 241 } 242 243 out: 244 if (sk_under_memory_pressure(sk)) 245 sk_mem_reclaim(sk); 246 } 247 248 static void tcp_delack_timer(unsigned long data) 249 { 250 struct sock *sk = (struct sock *)data; 251 252 bh_lock_sock(sk); 253 if (!sock_owned_by_user(sk)) { 254 tcp_delack_timer_handler(sk); 255 } else { 256 inet_csk(sk)->icsk_ack.blocked = 1; 257 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKLOCKED); 258 /* deleguate our work to tcp_release_cb() */ 259 if (!test_and_set_bit(TCP_DELACK_TIMER_DEFERRED, &tcp_sk(sk)->tsq_flags)) 260 sock_hold(sk); 261 } 262 bh_unlock_sock(sk); 263 sock_put(sk); 264 } 265 266 static void tcp_probe_timer(struct sock *sk) 267 { 268 struct inet_connection_sock *icsk = inet_csk(sk); 269 struct tcp_sock *tp = tcp_sk(sk); 270 int max_probes; 271 272 if (tp->packets_out || !tcp_send_head(sk)) { 273 icsk->icsk_probes_out = 0; 274 return; 275 } 276 277 /* *WARNING* RFC 1122 forbids this 278 * 279 * It doesn't AFAIK, because we kill the retransmit timer -AK 280 * 281 * FIXME: We ought not to do it, Solaris 2.5 actually has fixing 282 * this behaviour in Solaris down as a bug fix. [AC] 283 * 284 * Let me to explain. icsk_probes_out is zeroed by incoming ACKs 285 * even if they advertise zero window. Hence, connection is killed only 286 * if we received no ACKs for normal connection timeout. It is not killed 287 * only because window stays zero for some time, window may be zero 288 * until armageddon and even later. We are in full accordance 289 * with RFCs, only probe timer combines both retransmission timeout 290 * and probe timeout in one bottle. --ANK 291 */ 292 max_probes = sysctl_tcp_retries2; 293 294 if (sock_flag(sk, SOCK_DEAD)) { 295 const int alive = ((icsk->icsk_rto << icsk->icsk_backoff) < TCP_RTO_MAX); 296 297 max_probes = tcp_orphan_retries(sk, alive); 298 299 if (tcp_out_of_resources(sk, alive || icsk->icsk_probes_out <= max_probes)) 300 return; 301 } 302 303 if (icsk->icsk_probes_out > max_probes) { 304 tcp_write_err(sk); 305 } else { 306 /* Only send another probe if we didn't close things up. */ 307 tcp_send_probe0(sk); 308 } 309 } 310 311 /* 312 * Timer for Fast Open socket to retransmit SYNACK. Note that the 313 * sk here is the child socket, not the parent (listener) socket. 314 */ 315 static void tcp_fastopen_synack_timer(struct sock *sk) 316 { 317 struct inet_connection_sock *icsk = inet_csk(sk); 318 int max_retries = icsk->icsk_syn_retries ? : 319 sysctl_tcp_synack_retries + 1; /* add one more retry for fastopen */ 320 struct request_sock *req; 321 322 req = tcp_sk(sk)->fastopen_rsk; 323 req->rsk_ops->syn_ack_timeout(sk, req); 324 325 if (req->num_timeout >= max_retries) { 326 tcp_write_err(sk); 327 return; 328 } 329 /* XXX (TFO) - Unlike regular SYN-ACK retransmit, we ignore error 330 * returned from rtx_syn_ack() to make it more persistent like 331 * regular retransmit because if the child socket has been accepted 332 * it's not good to give up too easily. 333 */ 334 inet_rtx_syn_ack(sk, req); 335 req->num_timeout++; 336 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, 337 TCP_TIMEOUT_INIT << req->num_timeout, TCP_RTO_MAX); 338 } 339 340 /* 341 * The TCP retransmit timer. 342 */ 343 344 void tcp_retransmit_timer(struct sock *sk) 345 { 346 struct tcp_sock *tp = tcp_sk(sk); 347 struct inet_connection_sock *icsk = inet_csk(sk); 348 349 if (tp->fastopen_rsk) { 350 WARN_ON_ONCE(sk->sk_state != TCP_SYN_RECV && 351 sk->sk_state != TCP_FIN_WAIT1); 352 tcp_fastopen_synack_timer(sk); 353 /* Before we receive ACK to our SYN-ACK don't retransmit 354 * anything else (e.g., data or FIN segments). 355 */ 356 return; 357 } 358 if (!tp->packets_out) 359 goto out; 360 361 WARN_ON(tcp_write_queue_empty(sk)); 362 363 tp->tlp_high_seq = 0; 364 365 if (!tp->snd_wnd && !sock_flag(sk, SOCK_DEAD) && 366 !((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV))) { 367 /* Receiver dastardly shrinks window. Our retransmits 368 * become zero probes, but we should not timeout this 369 * connection. If the socket is an orphan, time it out, 370 * we cannot allow such beasts to hang infinitely. 371 */ 372 struct inet_sock *inet = inet_sk(sk); 373 if (sk->sk_family == AF_INET) { 374 LIMIT_NETDEBUG(KERN_DEBUG pr_fmt("Peer %pI4:%u/%u unexpectedly shrunk window %u:%u (repaired)\n"), 375 &inet->inet_daddr, 376 ntohs(inet->inet_dport), inet->inet_num, 377 tp->snd_una, tp->snd_nxt); 378 } 379 #if IS_ENABLED(CONFIG_IPV6) 380 else if (sk->sk_family == AF_INET6) { 381 LIMIT_NETDEBUG(KERN_DEBUG pr_fmt("Peer %pI6:%u/%u unexpectedly shrunk window %u:%u (repaired)\n"), 382 &sk->sk_v6_daddr, 383 ntohs(inet->inet_dport), inet->inet_num, 384 tp->snd_una, tp->snd_nxt); 385 } 386 #endif 387 if (tcp_time_stamp - tp->rcv_tstamp > TCP_RTO_MAX) { 388 tcp_write_err(sk); 389 goto out; 390 } 391 tcp_enter_loss(sk, 0); 392 tcp_retransmit_skb(sk, tcp_write_queue_head(sk)); 393 __sk_dst_reset(sk); 394 goto out_reset_timer; 395 } 396 397 if (tcp_write_timeout(sk)) 398 goto out; 399 400 if (icsk->icsk_retransmits == 0) { 401 int mib_idx; 402 403 if (icsk->icsk_ca_state == TCP_CA_Recovery) { 404 if (tcp_is_sack(tp)) 405 mib_idx = LINUX_MIB_TCPSACKRECOVERYFAIL; 406 else 407 mib_idx = LINUX_MIB_TCPRENORECOVERYFAIL; 408 } else if (icsk->icsk_ca_state == TCP_CA_Loss) { 409 mib_idx = LINUX_MIB_TCPLOSSFAILURES; 410 } else if ((icsk->icsk_ca_state == TCP_CA_Disorder) || 411 tp->sacked_out) { 412 if (tcp_is_sack(tp)) 413 mib_idx = LINUX_MIB_TCPSACKFAILURES; 414 else 415 mib_idx = LINUX_MIB_TCPRENOFAILURES; 416 } else { 417 mib_idx = LINUX_MIB_TCPTIMEOUTS; 418 } 419 NET_INC_STATS_BH(sock_net(sk), mib_idx); 420 } 421 422 tcp_enter_loss(sk, 0); 423 424 if (tcp_retransmit_skb(sk, tcp_write_queue_head(sk)) > 0) { 425 /* Retransmission failed because of local congestion, 426 * do not backoff. 427 */ 428 if (!icsk->icsk_retransmits) 429 icsk->icsk_retransmits = 1; 430 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, 431 min(icsk->icsk_rto, TCP_RESOURCE_PROBE_INTERVAL), 432 TCP_RTO_MAX); 433 goto out; 434 } 435 436 /* Increase the timeout each time we retransmit. Note that 437 * we do not increase the rtt estimate. rto is initialized 438 * from rtt, but increases here. Jacobson (SIGCOMM 88) suggests 439 * that doubling rto each time is the least we can get away with. 440 * In KA9Q, Karn uses this for the first few times, and then 441 * goes to quadratic. netBSD doubles, but only goes up to *64, 442 * and clamps at 1 to 64 sec afterwards. Note that 120 sec is 443 * defined in the protocol as the maximum possible RTT. I guess 444 * we'll have to use something other than TCP to talk to the 445 * University of Mars. 446 * 447 * PAWS allows us longer timeouts and large windows, so once 448 * implemented ftp to mars will work nicely. We will have to fix 449 * the 120 second clamps though! 450 */ 451 icsk->icsk_backoff++; 452 icsk->icsk_retransmits++; 453 454 out_reset_timer: 455 /* If stream is thin, use linear timeouts. Since 'icsk_backoff' is 456 * used to reset timer, set to 0. Recalculate 'icsk_rto' as this 457 * might be increased if the stream oscillates between thin and thick, 458 * thus the old value might already be too high compared to the value 459 * set by 'tcp_set_rto' in tcp_input.c which resets the rto without 460 * backoff. Limit to TCP_THIN_LINEAR_RETRIES before initiating 461 * exponential backoff behaviour to avoid continue hammering 462 * linear-timeout retransmissions into a black hole 463 */ 464 if (sk->sk_state == TCP_ESTABLISHED && 465 (tp->thin_lto || sysctl_tcp_thin_linear_timeouts) && 466 tcp_stream_is_thin(tp) && 467 icsk->icsk_retransmits <= TCP_THIN_LINEAR_RETRIES) { 468 icsk->icsk_backoff = 0; 469 icsk->icsk_rto = min(__tcp_set_rto(tp), TCP_RTO_MAX); 470 } else { 471 /* Use normal (exponential) backoff */ 472 icsk->icsk_rto = min(icsk->icsk_rto << 1, TCP_RTO_MAX); 473 } 474 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, icsk->icsk_rto, TCP_RTO_MAX); 475 if (retransmits_timed_out(sk, sysctl_tcp_retries1 + 1, 0, 0)) 476 __sk_dst_reset(sk); 477 478 out:; 479 } 480 481 void tcp_write_timer_handler(struct sock *sk) 482 { 483 struct inet_connection_sock *icsk = inet_csk(sk); 484 int event; 485 486 if (sk->sk_state == TCP_CLOSE || !icsk->icsk_pending) 487 goto out; 488 489 if (time_after(icsk->icsk_timeout, jiffies)) { 490 sk_reset_timer(sk, &icsk->icsk_retransmit_timer, icsk->icsk_timeout); 491 goto out; 492 } 493 494 event = icsk->icsk_pending; 495 496 switch (event) { 497 case ICSK_TIME_EARLY_RETRANS: 498 tcp_resume_early_retransmit(sk); 499 break; 500 case ICSK_TIME_LOSS_PROBE: 501 tcp_send_loss_probe(sk); 502 break; 503 case ICSK_TIME_RETRANS: 504 icsk->icsk_pending = 0; 505 tcp_retransmit_timer(sk); 506 break; 507 case ICSK_TIME_PROBE0: 508 icsk->icsk_pending = 0; 509 tcp_probe_timer(sk); 510 break; 511 } 512 513 out: 514 sk_mem_reclaim(sk); 515 } 516 517 static void tcp_write_timer(unsigned long data) 518 { 519 struct sock *sk = (struct sock *)data; 520 521 bh_lock_sock(sk); 522 if (!sock_owned_by_user(sk)) { 523 tcp_write_timer_handler(sk); 524 } else { 525 /* deleguate our work to tcp_release_cb() */ 526 if (!test_and_set_bit(TCP_WRITE_TIMER_DEFERRED, &tcp_sk(sk)->tsq_flags)) 527 sock_hold(sk); 528 } 529 bh_unlock_sock(sk); 530 sock_put(sk); 531 } 532 533 /* 534 * Timer for listening sockets 535 */ 536 537 static void tcp_synack_timer(struct sock *sk) 538 { 539 inet_csk_reqsk_queue_prune(sk, TCP_SYNQ_INTERVAL, 540 TCP_TIMEOUT_INIT, TCP_RTO_MAX); 541 } 542 543 void tcp_syn_ack_timeout(struct sock *sk, struct request_sock *req) 544 { 545 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPTIMEOUTS); 546 } 547 EXPORT_SYMBOL(tcp_syn_ack_timeout); 548 549 void tcp_set_keepalive(struct sock *sk, int val) 550 { 551 if ((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN)) 552 return; 553 554 if (val && !sock_flag(sk, SOCK_KEEPOPEN)) 555 inet_csk_reset_keepalive_timer(sk, keepalive_time_when(tcp_sk(sk))); 556 else if (!val) 557 inet_csk_delete_keepalive_timer(sk); 558 } 559 560 561 static void tcp_keepalive_timer (unsigned long data) 562 { 563 struct sock *sk = (struct sock *) data; 564 struct inet_connection_sock *icsk = inet_csk(sk); 565 struct tcp_sock *tp = tcp_sk(sk); 566 u32 elapsed; 567 568 /* Only process if socket is not in use. */ 569 bh_lock_sock(sk); 570 if (sock_owned_by_user(sk)) { 571 /* Try again later. */ 572 inet_csk_reset_keepalive_timer (sk, HZ/20); 573 goto out; 574 } 575 576 if (sk->sk_state == TCP_LISTEN) { 577 tcp_synack_timer(sk); 578 goto out; 579 } 580 581 if (sk->sk_state == TCP_FIN_WAIT2 && sock_flag(sk, SOCK_DEAD)) { 582 if (tp->linger2 >= 0) { 583 const int tmo = tcp_fin_time(sk) - TCP_TIMEWAIT_LEN; 584 585 if (tmo > 0) { 586 tcp_time_wait(sk, TCP_FIN_WAIT2, tmo); 587 goto out; 588 } 589 } 590 tcp_send_active_reset(sk, GFP_ATOMIC); 591 goto death; 592 } 593 594 if (!sock_flag(sk, SOCK_KEEPOPEN) || sk->sk_state == TCP_CLOSE) 595 goto out; 596 597 elapsed = keepalive_time_when(tp); 598 599 /* It is alive without keepalive 8) */ 600 if (tp->packets_out || tcp_send_head(sk)) 601 goto resched; 602 603 elapsed = keepalive_time_elapsed(tp); 604 605 if (elapsed >= keepalive_time_when(tp)) { 606 /* If the TCP_USER_TIMEOUT option is enabled, use that 607 * to determine when to timeout instead. 608 */ 609 if ((icsk->icsk_user_timeout != 0 && 610 elapsed >= icsk->icsk_user_timeout && 611 icsk->icsk_probes_out > 0) || 612 (icsk->icsk_user_timeout == 0 && 613 icsk->icsk_probes_out >= keepalive_probes(tp))) { 614 tcp_send_active_reset(sk, GFP_ATOMIC); 615 tcp_write_err(sk); 616 goto out; 617 } 618 if (tcp_write_wakeup(sk) <= 0) { 619 icsk->icsk_probes_out++; 620 elapsed = keepalive_intvl_when(tp); 621 } else { 622 /* If keepalive was lost due to local congestion, 623 * try harder. 624 */ 625 elapsed = TCP_RESOURCE_PROBE_INTERVAL; 626 } 627 } else { 628 /* It is tp->rcv_tstamp + keepalive_time_when(tp) */ 629 elapsed = keepalive_time_when(tp) - elapsed; 630 } 631 632 sk_mem_reclaim(sk); 633 634 resched: 635 inet_csk_reset_keepalive_timer (sk, elapsed); 636 goto out; 637 638 death: 639 tcp_done(sk); 640 641 out: 642 bh_unlock_sock(sk); 643 sock_put(sk); 644 } 645 646 void tcp_init_xmit_timers(struct sock *sk) 647 { 648 inet_csk_init_xmit_timers(sk, &tcp_write_timer, &tcp_delack_timer, 649 &tcp_keepalive_timer); 650 } 651 EXPORT_SYMBOL(tcp_init_xmit_timers); 652