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 int retry_until; 160 bool do_reset, syn_set = false; 161 162 if ((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV)) { 163 if (icsk->icsk_retransmits) 164 dst_negative_advice(sk); 165 retry_until = icsk->icsk_syn_retries ? : sysctl_tcp_syn_retries; 166 syn_set = true; 167 } else { 168 if (retransmits_timed_out(sk, sysctl_tcp_retries1, 0, 0)) { 169 /* Black hole detection */ 170 tcp_mtu_probing(icsk, sk); 171 172 dst_negative_advice(sk); 173 } 174 175 retry_until = sysctl_tcp_retries2; 176 if (sock_flag(sk, SOCK_DEAD)) { 177 const int alive = (icsk->icsk_rto < TCP_RTO_MAX); 178 179 retry_until = tcp_orphan_retries(sk, alive); 180 do_reset = alive || 181 !retransmits_timed_out(sk, retry_until, 0, 0); 182 183 if (tcp_out_of_resources(sk, do_reset)) 184 return 1; 185 } 186 } 187 188 if (retransmits_timed_out(sk, retry_until, 189 syn_set ? 0 : icsk->icsk_user_timeout, syn_set)) { 190 /* Has it gone just too far? */ 191 tcp_write_err(sk); 192 return 1; 193 } 194 return 0; 195 } 196 197 void tcp_delack_timer_handler(struct sock *sk) 198 { 199 struct tcp_sock *tp = tcp_sk(sk); 200 struct inet_connection_sock *icsk = inet_csk(sk); 201 202 sk_mem_reclaim_partial(sk); 203 204 if (sk->sk_state == TCP_CLOSE || !(icsk->icsk_ack.pending & ICSK_ACK_TIMER)) 205 goto out; 206 207 if (time_after(icsk->icsk_ack.timeout, jiffies)) { 208 sk_reset_timer(sk, &icsk->icsk_delack_timer, icsk->icsk_ack.timeout); 209 goto out; 210 } 211 icsk->icsk_ack.pending &= ~ICSK_ACK_TIMER; 212 213 if (!skb_queue_empty(&tp->ucopy.prequeue)) { 214 struct sk_buff *skb; 215 216 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSCHEDULERFAILED); 217 218 while ((skb = __skb_dequeue(&tp->ucopy.prequeue)) != NULL) 219 sk_backlog_rcv(sk, skb); 220 221 tp->ucopy.memory = 0; 222 } 223 224 if (inet_csk_ack_scheduled(sk)) { 225 if (!icsk->icsk_ack.pingpong) { 226 /* Delayed ACK missed: inflate ATO. */ 227 icsk->icsk_ack.ato = min(icsk->icsk_ack.ato << 1, icsk->icsk_rto); 228 } else { 229 /* Delayed ACK missed: leave pingpong mode and 230 * deflate ATO. 231 */ 232 icsk->icsk_ack.pingpong = 0; 233 icsk->icsk_ack.ato = TCP_ATO_MIN; 234 } 235 tcp_send_ack(sk); 236 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKS); 237 } 238 239 out: 240 if (sk_under_memory_pressure(sk)) 241 sk_mem_reclaim(sk); 242 } 243 244 static void tcp_delack_timer(unsigned long data) 245 { 246 struct sock *sk = (struct sock *)data; 247 248 bh_lock_sock(sk); 249 if (!sock_owned_by_user(sk)) { 250 tcp_delack_timer_handler(sk); 251 } else { 252 inet_csk(sk)->icsk_ack.blocked = 1; 253 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKLOCKED); 254 /* deleguate our work to tcp_release_cb() */ 255 set_bit(TCP_WRITE_TIMER_DEFERRED, &tcp_sk(sk)->tsq_flags); 256 } 257 bh_unlock_sock(sk); 258 sock_put(sk); 259 } 260 261 static void tcp_probe_timer(struct sock *sk) 262 { 263 struct inet_connection_sock *icsk = inet_csk(sk); 264 struct tcp_sock *tp = tcp_sk(sk); 265 int max_probes; 266 267 if (tp->packets_out || !tcp_send_head(sk)) { 268 icsk->icsk_probes_out = 0; 269 return; 270 } 271 272 /* *WARNING* RFC 1122 forbids this 273 * 274 * It doesn't AFAIK, because we kill the retransmit timer -AK 275 * 276 * FIXME: We ought not to do it, Solaris 2.5 actually has fixing 277 * this behaviour in Solaris down as a bug fix. [AC] 278 * 279 * Let me to explain. icsk_probes_out is zeroed by incoming ACKs 280 * even if they advertise zero window. Hence, connection is killed only 281 * if we received no ACKs for normal connection timeout. It is not killed 282 * only because window stays zero for some time, window may be zero 283 * until armageddon and even later. We are in full accordance 284 * with RFCs, only probe timer combines both retransmission timeout 285 * and probe timeout in one bottle. --ANK 286 */ 287 max_probes = sysctl_tcp_retries2; 288 289 if (sock_flag(sk, SOCK_DEAD)) { 290 const int alive = ((icsk->icsk_rto << icsk->icsk_backoff) < TCP_RTO_MAX); 291 292 max_probes = tcp_orphan_retries(sk, alive); 293 294 if (tcp_out_of_resources(sk, alive || icsk->icsk_probes_out <= max_probes)) 295 return; 296 } 297 298 if (icsk->icsk_probes_out > max_probes) { 299 tcp_write_err(sk); 300 } else { 301 /* Only send another probe if we didn't close things up. */ 302 tcp_send_probe0(sk); 303 } 304 } 305 306 /* 307 * The TCP retransmit timer. 308 */ 309 310 void tcp_retransmit_timer(struct sock *sk) 311 { 312 struct tcp_sock *tp = tcp_sk(sk); 313 struct inet_connection_sock *icsk = inet_csk(sk); 314 315 if (tp->early_retrans_delayed) { 316 tcp_resume_early_retransmit(sk); 317 return; 318 } 319 320 if (!tp->packets_out) 321 goto out; 322 323 WARN_ON(tcp_write_queue_empty(sk)); 324 325 if (!tp->snd_wnd && !sock_flag(sk, SOCK_DEAD) && 326 !((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV))) { 327 /* Receiver dastardly shrinks window. Our retransmits 328 * become zero probes, but we should not timeout this 329 * connection. If the socket is an orphan, time it out, 330 * we cannot allow such beasts to hang infinitely. 331 */ 332 struct inet_sock *inet = inet_sk(sk); 333 if (sk->sk_family == AF_INET) { 334 LIMIT_NETDEBUG(KERN_DEBUG pr_fmt("Peer %pI4:%u/%u unexpectedly shrunk window %u:%u (repaired)\n"), 335 &inet->inet_daddr, 336 ntohs(inet->inet_dport), inet->inet_num, 337 tp->snd_una, tp->snd_nxt); 338 } 339 #if IS_ENABLED(CONFIG_IPV6) 340 else if (sk->sk_family == AF_INET6) { 341 struct ipv6_pinfo *np = inet6_sk(sk); 342 LIMIT_NETDEBUG(KERN_DEBUG pr_fmt("Peer %pI6:%u/%u unexpectedly shrunk window %u:%u (repaired)\n"), 343 &np->daddr, 344 ntohs(inet->inet_dport), inet->inet_num, 345 tp->snd_una, tp->snd_nxt); 346 } 347 #endif 348 if (tcp_time_stamp - tp->rcv_tstamp > TCP_RTO_MAX) { 349 tcp_write_err(sk); 350 goto out; 351 } 352 tcp_enter_loss(sk, 0); 353 tcp_retransmit_skb(sk, tcp_write_queue_head(sk)); 354 __sk_dst_reset(sk); 355 goto out_reset_timer; 356 } 357 358 if (tcp_write_timeout(sk)) 359 goto out; 360 361 if (icsk->icsk_retransmits == 0) { 362 int mib_idx; 363 364 if (icsk->icsk_ca_state == TCP_CA_Recovery) { 365 if (tcp_is_sack(tp)) 366 mib_idx = LINUX_MIB_TCPSACKRECOVERYFAIL; 367 else 368 mib_idx = LINUX_MIB_TCPRENORECOVERYFAIL; 369 } else if (icsk->icsk_ca_state == TCP_CA_Loss) { 370 mib_idx = LINUX_MIB_TCPLOSSFAILURES; 371 } else if ((icsk->icsk_ca_state == TCP_CA_Disorder) || 372 tp->sacked_out) { 373 if (tcp_is_sack(tp)) 374 mib_idx = LINUX_MIB_TCPSACKFAILURES; 375 else 376 mib_idx = LINUX_MIB_TCPRENOFAILURES; 377 } else { 378 mib_idx = LINUX_MIB_TCPTIMEOUTS; 379 } 380 NET_INC_STATS_BH(sock_net(sk), mib_idx); 381 } 382 383 if (tcp_use_frto(sk)) { 384 tcp_enter_frto(sk); 385 } else { 386 tcp_enter_loss(sk, 0); 387 } 388 389 if (tcp_retransmit_skb(sk, tcp_write_queue_head(sk)) > 0) { 390 /* Retransmission failed because of local congestion, 391 * do not backoff. 392 */ 393 if (!icsk->icsk_retransmits) 394 icsk->icsk_retransmits = 1; 395 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, 396 min(icsk->icsk_rto, TCP_RESOURCE_PROBE_INTERVAL), 397 TCP_RTO_MAX); 398 goto out; 399 } 400 401 /* Increase the timeout each time we retransmit. Note that 402 * we do not increase the rtt estimate. rto is initialized 403 * from rtt, but increases here. Jacobson (SIGCOMM 88) suggests 404 * that doubling rto each time is the least we can get away with. 405 * In KA9Q, Karn uses this for the first few times, and then 406 * goes to quadratic. netBSD doubles, but only goes up to *64, 407 * and clamps at 1 to 64 sec afterwards. Note that 120 sec is 408 * defined in the protocol as the maximum possible RTT. I guess 409 * we'll have to use something other than TCP to talk to the 410 * University of Mars. 411 * 412 * PAWS allows us longer timeouts and large windows, so once 413 * implemented ftp to mars will work nicely. We will have to fix 414 * the 120 second clamps though! 415 */ 416 icsk->icsk_backoff++; 417 icsk->icsk_retransmits++; 418 419 out_reset_timer: 420 /* If stream is thin, use linear timeouts. Since 'icsk_backoff' is 421 * used to reset timer, set to 0. Recalculate 'icsk_rto' as this 422 * might be increased if the stream oscillates between thin and thick, 423 * thus the old value might already be too high compared to the value 424 * set by 'tcp_set_rto' in tcp_input.c which resets the rto without 425 * backoff. Limit to TCP_THIN_LINEAR_RETRIES before initiating 426 * exponential backoff behaviour to avoid continue hammering 427 * linear-timeout retransmissions into a black hole 428 */ 429 if (sk->sk_state == TCP_ESTABLISHED && 430 (tp->thin_lto || sysctl_tcp_thin_linear_timeouts) && 431 tcp_stream_is_thin(tp) && 432 icsk->icsk_retransmits <= TCP_THIN_LINEAR_RETRIES) { 433 icsk->icsk_backoff = 0; 434 icsk->icsk_rto = min(__tcp_set_rto(tp), TCP_RTO_MAX); 435 } else { 436 /* Use normal (exponential) backoff */ 437 icsk->icsk_rto = min(icsk->icsk_rto << 1, TCP_RTO_MAX); 438 } 439 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, icsk->icsk_rto, TCP_RTO_MAX); 440 if (retransmits_timed_out(sk, sysctl_tcp_retries1 + 1, 0, 0)) 441 __sk_dst_reset(sk); 442 443 out:; 444 } 445 446 void tcp_write_timer_handler(struct sock *sk) 447 { 448 struct inet_connection_sock *icsk = inet_csk(sk); 449 int event; 450 451 if (sk->sk_state == TCP_CLOSE || !icsk->icsk_pending) 452 goto out; 453 454 if (time_after(icsk->icsk_timeout, jiffies)) { 455 sk_reset_timer(sk, &icsk->icsk_retransmit_timer, icsk->icsk_timeout); 456 goto out; 457 } 458 459 event = icsk->icsk_pending; 460 icsk->icsk_pending = 0; 461 462 switch (event) { 463 case ICSK_TIME_RETRANS: 464 tcp_retransmit_timer(sk); 465 break; 466 case ICSK_TIME_PROBE0: 467 tcp_probe_timer(sk); 468 break; 469 } 470 471 out: 472 sk_mem_reclaim(sk); 473 } 474 475 static void tcp_write_timer(unsigned long data) 476 { 477 struct sock *sk = (struct sock *)data; 478 479 bh_lock_sock(sk); 480 if (!sock_owned_by_user(sk)) { 481 tcp_write_timer_handler(sk); 482 } else { 483 /* deleguate our work to tcp_release_cb() */ 484 set_bit(TCP_WRITE_TIMER_DEFERRED, &tcp_sk(sk)->tsq_flags); 485 } 486 bh_unlock_sock(sk); 487 sock_put(sk); 488 } 489 490 /* 491 * Timer for listening sockets 492 */ 493 494 static void tcp_synack_timer(struct sock *sk) 495 { 496 inet_csk_reqsk_queue_prune(sk, TCP_SYNQ_INTERVAL, 497 TCP_TIMEOUT_INIT, TCP_RTO_MAX); 498 } 499 500 void tcp_syn_ack_timeout(struct sock *sk, struct request_sock *req) 501 { 502 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPTIMEOUTS); 503 } 504 EXPORT_SYMBOL(tcp_syn_ack_timeout); 505 506 void tcp_set_keepalive(struct sock *sk, int val) 507 { 508 if ((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN)) 509 return; 510 511 if (val && !sock_flag(sk, SOCK_KEEPOPEN)) 512 inet_csk_reset_keepalive_timer(sk, keepalive_time_when(tcp_sk(sk))); 513 else if (!val) 514 inet_csk_delete_keepalive_timer(sk); 515 } 516 517 518 static void tcp_keepalive_timer (unsigned long data) 519 { 520 struct sock *sk = (struct sock *) data; 521 struct inet_connection_sock *icsk = inet_csk(sk); 522 struct tcp_sock *tp = tcp_sk(sk); 523 u32 elapsed; 524 525 /* Only process if socket is not in use. */ 526 bh_lock_sock(sk); 527 if (sock_owned_by_user(sk)) { 528 /* Try again later. */ 529 inet_csk_reset_keepalive_timer (sk, HZ/20); 530 goto out; 531 } 532 533 if (sk->sk_state == TCP_LISTEN) { 534 tcp_synack_timer(sk); 535 goto out; 536 } 537 538 if (sk->sk_state == TCP_FIN_WAIT2 && sock_flag(sk, SOCK_DEAD)) { 539 if (tp->linger2 >= 0) { 540 const int tmo = tcp_fin_time(sk) - TCP_TIMEWAIT_LEN; 541 542 if (tmo > 0) { 543 tcp_time_wait(sk, TCP_FIN_WAIT2, tmo); 544 goto out; 545 } 546 } 547 tcp_send_active_reset(sk, GFP_ATOMIC); 548 goto death; 549 } 550 551 if (!sock_flag(sk, SOCK_KEEPOPEN) || sk->sk_state == TCP_CLOSE) 552 goto out; 553 554 elapsed = keepalive_time_when(tp); 555 556 /* It is alive without keepalive 8) */ 557 if (tp->packets_out || tcp_send_head(sk)) 558 goto resched; 559 560 elapsed = keepalive_time_elapsed(tp); 561 562 if (elapsed >= keepalive_time_when(tp)) { 563 /* If the TCP_USER_TIMEOUT option is enabled, use that 564 * to determine when to timeout instead. 565 */ 566 if ((icsk->icsk_user_timeout != 0 && 567 elapsed >= icsk->icsk_user_timeout && 568 icsk->icsk_probes_out > 0) || 569 (icsk->icsk_user_timeout == 0 && 570 icsk->icsk_probes_out >= keepalive_probes(tp))) { 571 tcp_send_active_reset(sk, GFP_ATOMIC); 572 tcp_write_err(sk); 573 goto out; 574 } 575 if (tcp_write_wakeup(sk) <= 0) { 576 icsk->icsk_probes_out++; 577 elapsed = keepalive_intvl_when(tp); 578 } else { 579 /* If keepalive was lost due to local congestion, 580 * try harder. 581 */ 582 elapsed = TCP_RESOURCE_PROBE_INTERVAL; 583 } 584 } else { 585 /* It is tp->rcv_tstamp + keepalive_time_when(tp) */ 586 elapsed = keepalive_time_when(tp) - elapsed; 587 } 588 589 sk_mem_reclaim(sk); 590 591 resched: 592 inet_csk_reset_keepalive_timer (sk, elapsed); 593 goto out; 594 595 death: 596 tcp_done(sk); 597 598 out: 599 bh_unlock_sock(sk); 600 sock_put(sk); 601 } 602 603 void tcp_init_xmit_timers(struct sock *sk) 604 { 605 inet_csk_init_xmit_timers(sk, &tcp_write_timer, &tcp_delack_timer, 606 &tcp_keepalive_timer); 607 } 608 EXPORT_SYMBOL(tcp_init_xmit_timers); 609