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_thin_linear_timeouts __read_mostly; 26 27 /** 28 * tcp_write_err() - close socket and save error info 29 * @sk: The socket the error has appeared on. 30 * 31 * Returns: Nothing (void) 32 */ 33 34 static void tcp_write_err(struct sock *sk) 35 { 36 sk->sk_err = sk->sk_err_soft ? : ETIMEDOUT; 37 sk->sk_error_report(sk); 38 39 tcp_done(sk); 40 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTONTIMEOUT); 41 } 42 43 /** 44 * tcp_out_of_resources() - Close socket if out of resources 45 * @sk: pointer to current socket 46 * @do_reset: send a last packet with reset flag 47 * 48 * Do not allow orphaned sockets to eat all our resources. 49 * This is direct violation of TCP specs, but it is required 50 * to prevent DoS attacks. It is called when a retransmission timeout 51 * or zero probe timeout occurs on orphaned socket. 52 * 53 * Criteria is still not confirmed experimentally and may change. 54 * We kill the socket, if: 55 * 1. If number of orphaned sockets exceeds an administratively configured 56 * limit. 57 * 2. If we have strong memory pressure. 58 */ 59 static int tcp_out_of_resources(struct sock *sk, bool do_reset) 60 { 61 struct tcp_sock *tp = tcp_sk(sk); 62 int shift = 0; 63 64 /* If peer does not open window for long time, or did not transmit 65 * anything for long time, penalize it. */ 66 if ((s32)(tcp_time_stamp - tp->lsndtime) > 2*TCP_RTO_MAX || !do_reset) 67 shift++; 68 69 /* If some dubious ICMP arrived, penalize even more. */ 70 if (sk->sk_err_soft) 71 shift++; 72 73 if (tcp_check_oom(sk, shift)) { 74 /* Catch exceptional cases, when connection requires reset. 75 * 1. Last segment was sent recently. */ 76 if ((s32)(tcp_time_stamp - tp->lsndtime) <= TCP_TIMEWAIT_LEN || 77 /* 2. Window is closed. */ 78 (!tp->snd_wnd && !tp->packets_out)) 79 do_reset = true; 80 if (do_reset) 81 tcp_send_active_reset(sk, GFP_ATOMIC); 82 tcp_done(sk); 83 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTONMEMORY); 84 return 1; 85 } 86 return 0; 87 } 88 89 /** 90 * tcp_orphan_retries() - Returns maximal number of retries on an orphaned socket 91 * @sk: Pointer to the current socket. 92 * @alive: bool, socket alive state 93 */ 94 static int tcp_orphan_retries(struct sock *sk, bool alive) 95 { 96 int retries = sock_net(sk)->ipv4.sysctl_tcp_orphan_retries; /* May be zero. */ 97 98 /* We know from an ICMP that something is wrong. */ 99 if (sk->sk_err_soft && !alive) 100 retries = 0; 101 102 /* However, if socket sent something recently, select some safe 103 * number of retries. 8 corresponds to >100 seconds with minimal 104 * RTO of 200msec. */ 105 if (retries == 0 && alive) 106 retries = 8; 107 return retries; 108 } 109 110 static void tcp_mtu_probing(struct inet_connection_sock *icsk, struct sock *sk) 111 { 112 struct net *net = sock_net(sk); 113 114 /* Black hole detection */ 115 if (net->ipv4.sysctl_tcp_mtu_probing) { 116 if (!icsk->icsk_mtup.enabled) { 117 icsk->icsk_mtup.enabled = 1; 118 icsk->icsk_mtup.probe_timestamp = tcp_time_stamp; 119 tcp_sync_mss(sk, icsk->icsk_pmtu_cookie); 120 } else { 121 struct net *net = sock_net(sk); 122 struct tcp_sock *tp = tcp_sk(sk); 123 int mss; 124 125 mss = tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low) >> 1; 126 mss = min(net->ipv4.sysctl_tcp_base_mss, mss); 127 mss = max(mss, 68 - tp->tcp_header_len); 128 icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, mss); 129 tcp_sync_mss(sk, icsk->icsk_pmtu_cookie); 130 } 131 } 132 } 133 134 135 /** 136 * retransmits_timed_out() - returns true if this connection has timed out 137 * @sk: The current socket 138 * @boundary: max number of retransmissions 139 * @timeout: A custom timeout value. 140 * If set to 0 the default timeout is calculated and used. 141 * Using TCP_RTO_MIN and the number of unsuccessful retransmits. 142 * @syn_set: true if the SYN Bit was set. 143 * 144 * The default "timeout" value this function can calculate and use 145 * is equivalent to the timeout of a TCP Connection 146 * after "boundary" unsuccessful, exponentially backed-off 147 * retransmissions with an initial RTO of TCP_RTO_MIN or TCP_TIMEOUT_INIT if 148 * syn_set flag is set. 149 * 150 */ 151 static bool retransmits_timed_out(struct sock *sk, 152 unsigned int boundary, 153 unsigned int timeout, 154 bool syn_set) 155 { 156 unsigned int linear_backoff_thresh, start_ts; 157 unsigned int rto_base = syn_set ? TCP_TIMEOUT_INIT : TCP_RTO_MIN; 158 159 if (!inet_csk(sk)->icsk_retransmits) 160 return false; 161 162 start_ts = tcp_sk(sk)->retrans_stamp; 163 if (unlikely(!start_ts)) 164 start_ts = tcp_skb_timestamp(tcp_write_queue_head(sk)); 165 166 if (likely(timeout == 0)) { 167 linear_backoff_thresh = ilog2(TCP_RTO_MAX/rto_base); 168 169 if (boundary <= linear_backoff_thresh) 170 timeout = ((2 << boundary) - 1) * rto_base; 171 else 172 timeout = ((2 << linear_backoff_thresh) - 1) * rto_base + 173 (boundary - linear_backoff_thresh) * TCP_RTO_MAX; 174 } 175 return (tcp_time_stamp - start_ts) >= timeout; 176 } 177 178 /* A write timeout has occurred. Process the after effects. */ 179 static int tcp_write_timeout(struct sock *sk) 180 { 181 struct inet_connection_sock *icsk = inet_csk(sk); 182 struct tcp_sock *tp = tcp_sk(sk); 183 struct net *net = sock_net(sk); 184 int retry_until; 185 bool do_reset, syn_set = false; 186 187 if ((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV)) { 188 if (icsk->icsk_retransmits) { 189 dst_negative_advice(sk); 190 if (tp->syn_fastopen || tp->syn_data) 191 tcp_fastopen_cache_set(sk, 0, NULL, true, 0); 192 if (tp->syn_data && icsk->icsk_retransmits == 1) 193 NET_INC_STATS(sock_net(sk), 194 LINUX_MIB_TCPFASTOPENACTIVEFAIL); 195 } else if (!tp->syn_data && !tp->syn_fastopen) { 196 sk_rethink_txhash(sk); 197 } 198 retry_until = icsk->icsk_syn_retries ? : net->ipv4.sysctl_tcp_syn_retries; 199 syn_set = true; 200 } else { 201 if (retransmits_timed_out(sk, net->ipv4.sysctl_tcp_retries1, 0, 0)) { 202 /* Some middle-boxes may black-hole Fast Open _after_ 203 * the handshake. Therefore we conservatively disable 204 * Fast Open on this path on recurring timeouts with 205 * few or zero bytes acked after Fast Open. 206 */ 207 if (tp->syn_data_acked && 208 tp->bytes_acked <= tp->rx_opt.mss_clamp) { 209 tcp_fastopen_cache_set(sk, 0, NULL, true, 0); 210 if (icsk->icsk_retransmits == net->ipv4.sysctl_tcp_retries1) 211 NET_INC_STATS(sock_net(sk), 212 LINUX_MIB_TCPFASTOPENACTIVEFAIL); 213 } 214 /* Black hole detection */ 215 tcp_mtu_probing(icsk, sk); 216 217 dst_negative_advice(sk); 218 } else { 219 sk_rethink_txhash(sk); 220 } 221 222 retry_until = net->ipv4.sysctl_tcp_retries2; 223 if (sock_flag(sk, SOCK_DEAD)) { 224 const bool alive = icsk->icsk_rto < TCP_RTO_MAX; 225 226 retry_until = tcp_orphan_retries(sk, alive); 227 do_reset = alive || 228 !retransmits_timed_out(sk, retry_until, 0, 0); 229 230 if (tcp_out_of_resources(sk, do_reset)) 231 return 1; 232 } 233 } 234 235 if (retransmits_timed_out(sk, retry_until, 236 syn_set ? 0 : icsk->icsk_user_timeout, syn_set)) { 237 /* Has it gone just too far? */ 238 tcp_write_err(sk); 239 return 1; 240 } 241 return 0; 242 } 243 244 /* Called with BH disabled */ 245 void tcp_delack_timer_handler(struct sock *sk) 246 { 247 struct tcp_sock *tp = tcp_sk(sk); 248 struct inet_connection_sock *icsk = inet_csk(sk); 249 250 sk_mem_reclaim_partial(sk); 251 252 if (sk->sk_state == TCP_CLOSE || !(icsk->icsk_ack.pending & ICSK_ACK_TIMER)) 253 goto out; 254 255 if (time_after(icsk->icsk_ack.timeout, jiffies)) { 256 sk_reset_timer(sk, &icsk->icsk_delack_timer, icsk->icsk_ack.timeout); 257 goto out; 258 } 259 icsk->icsk_ack.pending &= ~ICSK_ACK_TIMER; 260 261 if (!skb_queue_empty(&tp->ucopy.prequeue)) { 262 struct sk_buff *skb; 263 264 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPSCHEDULERFAILED); 265 266 while ((skb = __skb_dequeue(&tp->ucopy.prequeue)) != NULL) 267 sk_backlog_rcv(sk, skb); 268 269 tp->ucopy.memory = 0; 270 } 271 272 if (inet_csk_ack_scheduled(sk)) { 273 if (!icsk->icsk_ack.pingpong) { 274 /* Delayed ACK missed: inflate ATO. */ 275 icsk->icsk_ack.ato = min(icsk->icsk_ack.ato << 1, icsk->icsk_rto); 276 } else { 277 /* Delayed ACK missed: leave pingpong mode and 278 * deflate ATO. 279 */ 280 icsk->icsk_ack.pingpong = 0; 281 icsk->icsk_ack.ato = TCP_ATO_MIN; 282 } 283 tcp_send_ack(sk); 284 __NET_INC_STATS(sock_net(sk), LINUX_MIB_DELAYEDACKS); 285 } 286 287 out: 288 if (tcp_under_memory_pressure(sk)) 289 sk_mem_reclaim(sk); 290 } 291 292 293 /** 294 * tcp_delack_timer() - The TCP delayed ACK timeout handler 295 * @data: Pointer to the current socket. (gets casted to struct sock *) 296 * 297 * This function gets (indirectly) called when the kernel timer for a TCP packet 298 * of this socket expires. Calls tcp_delack_timer_handler() to do the actual work. 299 * 300 * Returns: Nothing (void) 301 */ 302 static void tcp_delack_timer(unsigned long data) 303 { 304 struct sock *sk = (struct sock *)data; 305 306 bh_lock_sock(sk); 307 if (!sock_owned_by_user(sk)) { 308 tcp_delack_timer_handler(sk); 309 } else { 310 inet_csk(sk)->icsk_ack.blocked = 1; 311 __NET_INC_STATS(sock_net(sk), LINUX_MIB_DELAYEDACKLOCKED); 312 /* deleguate our work to tcp_release_cb() */ 313 if (!test_and_set_bit(TCP_DELACK_TIMER_DEFERRED, &sk->sk_tsq_flags)) 314 sock_hold(sk); 315 } 316 bh_unlock_sock(sk); 317 sock_put(sk); 318 } 319 320 static void tcp_probe_timer(struct sock *sk) 321 { 322 struct inet_connection_sock *icsk = inet_csk(sk); 323 struct tcp_sock *tp = tcp_sk(sk); 324 int max_probes; 325 u32 start_ts; 326 327 if (tp->packets_out || !tcp_send_head(sk)) { 328 icsk->icsk_probes_out = 0; 329 return; 330 } 331 332 /* RFC 1122 4.2.2.17 requires the sender to stay open indefinitely as 333 * long as the receiver continues to respond probes. We support this by 334 * default and reset icsk_probes_out with incoming ACKs. But if the 335 * socket is orphaned or the user specifies TCP_USER_TIMEOUT, we 336 * kill the socket when the retry count and the time exceeds the 337 * corresponding system limit. We also implement similar policy when 338 * we use RTO to probe window in tcp_retransmit_timer(). 339 */ 340 start_ts = tcp_skb_timestamp(tcp_send_head(sk)); 341 if (!start_ts) 342 skb_mstamp_get(&tcp_send_head(sk)->skb_mstamp); 343 else if (icsk->icsk_user_timeout && 344 (s32)(tcp_time_stamp - start_ts) > icsk->icsk_user_timeout) 345 goto abort; 346 347 max_probes = sock_net(sk)->ipv4.sysctl_tcp_retries2; 348 if (sock_flag(sk, SOCK_DEAD)) { 349 const bool alive = inet_csk_rto_backoff(icsk, TCP_RTO_MAX) < TCP_RTO_MAX; 350 351 max_probes = tcp_orphan_retries(sk, alive); 352 if (!alive && icsk->icsk_backoff >= max_probes) 353 goto abort; 354 if (tcp_out_of_resources(sk, true)) 355 return; 356 } 357 358 if (icsk->icsk_probes_out > max_probes) { 359 abort: tcp_write_err(sk); 360 } else { 361 /* Only send another probe if we didn't close things up. */ 362 tcp_send_probe0(sk); 363 } 364 } 365 366 /* 367 * Timer for Fast Open socket to retransmit SYNACK. Note that the 368 * sk here is the child socket, not the parent (listener) socket. 369 */ 370 static void tcp_fastopen_synack_timer(struct sock *sk) 371 { 372 struct inet_connection_sock *icsk = inet_csk(sk); 373 int max_retries = icsk->icsk_syn_retries ? : 374 sock_net(sk)->ipv4.sysctl_tcp_synack_retries + 1; /* add one more retry for fastopen */ 375 struct request_sock *req; 376 377 req = tcp_sk(sk)->fastopen_rsk; 378 req->rsk_ops->syn_ack_timeout(req); 379 380 if (req->num_timeout >= max_retries) { 381 tcp_write_err(sk); 382 return; 383 } 384 /* XXX (TFO) - Unlike regular SYN-ACK retransmit, we ignore error 385 * returned from rtx_syn_ack() to make it more persistent like 386 * regular retransmit because if the child socket has been accepted 387 * it's not good to give up too easily. 388 */ 389 inet_rtx_syn_ack(sk, req); 390 req->num_timeout++; 391 icsk->icsk_retransmits++; 392 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, 393 TCP_TIMEOUT_INIT << req->num_timeout, TCP_RTO_MAX); 394 } 395 396 397 /** 398 * tcp_retransmit_timer() - The TCP retransmit timeout handler 399 * @sk: Pointer to the current socket. 400 * 401 * This function gets called when the kernel timer for a TCP packet 402 * of this socket expires. 403 * 404 * It handles retransmission, timer adjustment and other necesarry measures. 405 * 406 * Returns: Nothing (void) 407 */ 408 void tcp_retransmit_timer(struct sock *sk) 409 { 410 struct tcp_sock *tp = tcp_sk(sk); 411 struct net *net = sock_net(sk); 412 struct inet_connection_sock *icsk = inet_csk(sk); 413 414 if (tp->fastopen_rsk) { 415 WARN_ON_ONCE(sk->sk_state != TCP_SYN_RECV && 416 sk->sk_state != TCP_FIN_WAIT1); 417 tcp_fastopen_synack_timer(sk); 418 /* Before we receive ACK to our SYN-ACK don't retransmit 419 * anything else (e.g., data or FIN segments). 420 */ 421 return; 422 } 423 if (!tp->packets_out) 424 goto out; 425 426 WARN_ON(tcp_write_queue_empty(sk)); 427 428 tp->tlp_high_seq = 0; 429 430 if (!tp->snd_wnd && !sock_flag(sk, SOCK_DEAD) && 431 !((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV))) { 432 /* Receiver dastardly shrinks window. Our retransmits 433 * become zero probes, but we should not timeout this 434 * connection. If the socket is an orphan, time it out, 435 * we cannot allow such beasts to hang infinitely. 436 */ 437 struct inet_sock *inet = inet_sk(sk); 438 if (sk->sk_family == AF_INET) { 439 net_dbg_ratelimited("Peer %pI4:%u/%u unexpectedly shrunk window %u:%u (repaired)\n", 440 &inet->inet_daddr, 441 ntohs(inet->inet_dport), 442 inet->inet_num, 443 tp->snd_una, tp->snd_nxt); 444 } 445 #if IS_ENABLED(CONFIG_IPV6) 446 else if (sk->sk_family == AF_INET6) { 447 net_dbg_ratelimited("Peer %pI6:%u/%u unexpectedly shrunk window %u:%u (repaired)\n", 448 &sk->sk_v6_daddr, 449 ntohs(inet->inet_dport), 450 inet->inet_num, 451 tp->snd_una, tp->snd_nxt); 452 } 453 #endif 454 if (tcp_time_stamp - tp->rcv_tstamp > TCP_RTO_MAX) { 455 tcp_write_err(sk); 456 goto out; 457 } 458 tcp_enter_loss(sk); 459 tcp_retransmit_skb(sk, tcp_write_queue_head(sk), 1); 460 __sk_dst_reset(sk); 461 goto out_reset_timer; 462 } 463 464 if (tcp_write_timeout(sk)) 465 goto out; 466 467 if (icsk->icsk_retransmits == 0) { 468 int mib_idx; 469 470 if (icsk->icsk_ca_state == TCP_CA_Recovery) { 471 if (tcp_is_sack(tp)) 472 mib_idx = LINUX_MIB_TCPSACKRECOVERYFAIL; 473 else 474 mib_idx = LINUX_MIB_TCPRENORECOVERYFAIL; 475 } else if (icsk->icsk_ca_state == TCP_CA_Loss) { 476 mib_idx = LINUX_MIB_TCPLOSSFAILURES; 477 } else if ((icsk->icsk_ca_state == TCP_CA_Disorder) || 478 tp->sacked_out) { 479 if (tcp_is_sack(tp)) 480 mib_idx = LINUX_MIB_TCPSACKFAILURES; 481 else 482 mib_idx = LINUX_MIB_TCPRENOFAILURES; 483 } else { 484 mib_idx = LINUX_MIB_TCPTIMEOUTS; 485 } 486 __NET_INC_STATS(sock_net(sk), mib_idx); 487 } 488 489 tcp_enter_loss(sk); 490 491 if (tcp_retransmit_skb(sk, tcp_write_queue_head(sk), 1) > 0) { 492 /* Retransmission failed because of local congestion, 493 * do not backoff. 494 */ 495 if (!icsk->icsk_retransmits) 496 icsk->icsk_retransmits = 1; 497 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, 498 min(icsk->icsk_rto, TCP_RESOURCE_PROBE_INTERVAL), 499 TCP_RTO_MAX); 500 goto out; 501 } 502 503 /* Increase the timeout each time we retransmit. Note that 504 * we do not increase the rtt estimate. rto is initialized 505 * from rtt, but increases here. Jacobson (SIGCOMM 88) suggests 506 * that doubling rto each time is the least we can get away with. 507 * In KA9Q, Karn uses this for the first few times, and then 508 * goes to quadratic. netBSD doubles, but only goes up to *64, 509 * and clamps at 1 to 64 sec afterwards. Note that 120 sec is 510 * defined in the protocol as the maximum possible RTT. I guess 511 * we'll have to use something other than TCP to talk to the 512 * University of Mars. 513 * 514 * PAWS allows us longer timeouts and large windows, so once 515 * implemented ftp to mars will work nicely. We will have to fix 516 * the 120 second clamps though! 517 */ 518 icsk->icsk_backoff++; 519 icsk->icsk_retransmits++; 520 521 out_reset_timer: 522 /* If stream is thin, use linear timeouts. Since 'icsk_backoff' is 523 * used to reset timer, set to 0. Recalculate 'icsk_rto' as this 524 * might be increased if the stream oscillates between thin and thick, 525 * thus the old value might already be too high compared to the value 526 * set by 'tcp_set_rto' in tcp_input.c which resets the rto without 527 * backoff. Limit to TCP_THIN_LINEAR_RETRIES before initiating 528 * exponential backoff behaviour to avoid continue hammering 529 * linear-timeout retransmissions into a black hole 530 */ 531 if (sk->sk_state == TCP_ESTABLISHED && 532 (tp->thin_lto || sysctl_tcp_thin_linear_timeouts) && 533 tcp_stream_is_thin(tp) && 534 icsk->icsk_retransmits <= TCP_THIN_LINEAR_RETRIES) { 535 icsk->icsk_backoff = 0; 536 icsk->icsk_rto = min(__tcp_set_rto(tp), TCP_RTO_MAX); 537 } else { 538 /* Use normal (exponential) backoff */ 539 icsk->icsk_rto = min(icsk->icsk_rto << 1, TCP_RTO_MAX); 540 } 541 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, icsk->icsk_rto, TCP_RTO_MAX); 542 if (retransmits_timed_out(sk, net->ipv4.sysctl_tcp_retries1 + 1, 0, 0)) 543 __sk_dst_reset(sk); 544 545 out:; 546 } 547 548 /* Called with bottom-half processing disabled. 549 Called by tcp_write_timer() */ 550 void tcp_write_timer_handler(struct sock *sk) 551 { 552 struct inet_connection_sock *icsk = inet_csk(sk); 553 int event; 554 555 if (sk->sk_state == TCP_CLOSE || !icsk->icsk_pending) 556 goto out; 557 558 if (time_after(icsk->icsk_timeout, jiffies)) { 559 sk_reset_timer(sk, &icsk->icsk_retransmit_timer, icsk->icsk_timeout); 560 goto out; 561 } 562 563 event = icsk->icsk_pending; 564 565 switch (event) { 566 case ICSK_TIME_EARLY_RETRANS: 567 tcp_resume_early_retransmit(sk); 568 break; 569 case ICSK_TIME_LOSS_PROBE: 570 tcp_send_loss_probe(sk); 571 break; 572 case ICSK_TIME_RETRANS: 573 icsk->icsk_pending = 0; 574 tcp_retransmit_timer(sk); 575 break; 576 case ICSK_TIME_PROBE0: 577 icsk->icsk_pending = 0; 578 tcp_probe_timer(sk); 579 break; 580 } 581 582 out: 583 sk_mem_reclaim(sk); 584 } 585 586 static void tcp_write_timer(unsigned long data) 587 { 588 struct sock *sk = (struct sock *)data; 589 590 bh_lock_sock(sk); 591 if (!sock_owned_by_user(sk)) { 592 tcp_write_timer_handler(sk); 593 } else { 594 /* delegate our work to tcp_release_cb() */ 595 if (!test_and_set_bit(TCP_WRITE_TIMER_DEFERRED, &sk->sk_tsq_flags)) 596 sock_hold(sk); 597 } 598 bh_unlock_sock(sk); 599 sock_put(sk); 600 } 601 602 void tcp_syn_ack_timeout(const struct request_sock *req) 603 { 604 struct net *net = read_pnet(&inet_rsk(req)->ireq_net); 605 606 __NET_INC_STATS(net, LINUX_MIB_TCPTIMEOUTS); 607 } 608 EXPORT_SYMBOL(tcp_syn_ack_timeout); 609 610 void tcp_set_keepalive(struct sock *sk, int val) 611 { 612 if ((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN)) 613 return; 614 615 if (val && !sock_flag(sk, SOCK_KEEPOPEN)) 616 inet_csk_reset_keepalive_timer(sk, keepalive_time_when(tcp_sk(sk))); 617 else if (!val) 618 inet_csk_delete_keepalive_timer(sk); 619 } 620 621 622 static void tcp_keepalive_timer (unsigned long data) 623 { 624 struct sock *sk = (struct sock *) data; 625 struct inet_connection_sock *icsk = inet_csk(sk); 626 struct tcp_sock *tp = tcp_sk(sk); 627 u32 elapsed; 628 629 /* Only process if socket is not in use. */ 630 bh_lock_sock(sk); 631 if (sock_owned_by_user(sk)) { 632 /* Try again later. */ 633 inet_csk_reset_keepalive_timer (sk, HZ/20); 634 goto out; 635 } 636 637 if (sk->sk_state == TCP_LISTEN) { 638 pr_err("Hmm... keepalive on a LISTEN ???\n"); 639 goto out; 640 } 641 642 if (sk->sk_state == TCP_FIN_WAIT2 && sock_flag(sk, SOCK_DEAD)) { 643 if (tp->linger2 >= 0) { 644 const int tmo = tcp_fin_time(sk) - TCP_TIMEWAIT_LEN; 645 646 if (tmo > 0) { 647 tcp_time_wait(sk, TCP_FIN_WAIT2, tmo); 648 goto out; 649 } 650 } 651 tcp_send_active_reset(sk, GFP_ATOMIC); 652 goto death; 653 } 654 655 if (!sock_flag(sk, SOCK_KEEPOPEN) || sk->sk_state == TCP_CLOSE) 656 goto out; 657 658 elapsed = keepalive_time_when(tp); 659 660 /* It is alive without keepalive 8) */ 661 if (tp->packets_out || tcp_send_head(sk)) 662 goto resched; 663 664 elapsed = keepalive_time_elapsed(tp); 665 666 if (elapsed >= keepalive_time_when(tp)) { 667 /* If the TCP_USER_TIMEOUT option is enabled, use that 668 * to determine when to timeout instead. 669 */ 670 if ((icsk->icsk_user_timeout != 0 && 671 elapsed >= icsk->icsk_user_timeout && 672 icsk->icsk_probes_out > 0) || 673 (icsk->icsk_user_timeout == 0 && 674 icsk->icsk_probes_out >= keepalive_probes(tp))) { 675 tcp_send_active_reset(sk, GFP_ATOMIC); 676 tcp_write_err(sk); 677 goto out; 678 } 679 if (tcp_write_wakeup(sk, LINUX_MIB_TCPKEEPALIVE) <= 0) { 680 icsk->icsk_probes_out++; 681 elapsed = keepalive_intvl_when(tp); 682 } else { 683 /* If keepalive was lost due to local congestion, 684 * try harder. 685 */ 686 elapsed = TCP_RESOURCE_PROBE_INTERVAL; 687 } 688 } else { 689 /* It is tp->rcv_tstamp + keepalive_time_when(tp) */ 690 elapsed = keepalive_time_when(tp) - elapsed; 691 } 692 693 sk_mem_reclaim(sk); 694 695 resched: 696 inet_csk_reset_keepalive_timer (sk, elapsed); 697 goto out; 698 699 death: 700 tcp_done(sk); 701 702 out: 703 bh_unlock_sock(sk); 704 sock_put(sk); 705 } 706 707 void tcp_init_xmit_timers(struct sock *sk) 708 { 709 inet_csk_init_xmit_timers(sk, &tcp_write_timer, &tcp_delack_timer, 710 &tcp_keepalive_timer); 711 } 712