tcp_timer.c revision 157376
1/*- 2 * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1995 3 * The Regents of the University of California. All rights reserved. 4 * 5 * Redistribution and use in source and binary forms, with or without 6 * modification, are permitted provided that the following conditions 7 * are met: 8 * 1. Redistributions of source code must retain the above copyright 9 * notice, this list of conditions and the following disclaimer. 10 * 2. Redistributions in binary form must reproduce the above copyright 11 * notice, this list of conditions and the following disclaimer in the 12 * documentation and/or other materials provided with the distribution. 13 * 4. Neither the name of the University nor the names of its contributors 14 * may be used to endorse or promote products derived from this software 15 * without specific prior written permission. 16 * 17 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 18 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 19 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 20 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 21 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 22 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 23 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 24 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 25 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 26 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 27 * SUCH DAMAGE. 28 * 29 * @(#)tcp_timer.c 8.2 (Berkeley) 5/24/95 30 * $FreeBSD: head/sys/netinet/tcp_timer.c 157376 2006-04-01 16:36:36Z rwatson $ 31 */ 32 33#include "opt_inet6.h" 34#include "opt_tcpdebug.h" 35#include "opt_tcp_sack.h" 36 37#include <sys/param.h> 38#include <sys/kernel.h> 39#include <sys/lock.h> 40#include <sys/mbuf.h> 41#include <sys/mutex.h> 42#include <sys/protosw.h> 43#include <sys/socket.h> 44#include <sys/socketvar.h> 45#include <sys/sysctl.h> 46#include <sys/systm.h> 47 48#include <net/route.h> 49 50#include <netinet/in.h> 51#include <netinet/in_pcb.h> 52#include <netinet/in_systm.h> 53#ifdef INET6 54#include <netinet6/in6_pcb.h> 55#endif 56#include <netinet/ip_var.h> 57#include <netinet/tcp.h> 58#include <netinet/tcp_fsm.h> 59#include <netinet/tcp_timer.h> 60#include <netinet/tcp_var.h> 61#include <netinet/tcpip.h> 62#ifdef TCPDEBUG 63#include <netinet/tcp_debug.h> 64#endif 65 66int tcp_keepinit; 67SYSCTL_PROC(_net_inet_tcp, TCPCTL_KEEPINIT, keepinit, CTLTYPE_INT|CTLFLAG_RW, 68 &tcp_keepinit, 0, sysctl_msec_to_ticks, "I", ""); 69 70int tcp_keepidle; 71SYSCTL_PROC(_net_inet_tcp, TCPCTL_KEEPIDLE, keepidle, CTLTYPE_INT|CTLFLAG_RW, 72 &tcp_keepidle, 0, sysctl_msec_to_ticks, "I", ""); 73 74int tcp_keepintvl; 75SYSCTL_PROC(_net_inet_tcp, TCPCTL_KEEPINTVL, keepintvl, CTLTYPE_INT|CTLFLAG_RW, 76 &tcp_keepintvl, 0, sysctl_msec_to_ticks, "I", ""); 77 78int tcp_delacktime; 79SYSCTL_PROC(_net_inet_tcp, TCPCTL_DELACKTIME, delacktime, 80 CTLTYPE_INT|CTLFLAG_RW, &tcp_delacktime, 0, sysctl_msec_to_ticks, "I", 81 "Time before a delayed ACK is sent"); 82 83int tcp_msl; 84SYSCTL_PROC(_net_inet_tcp, OID_AUTO, msl, CTLTYPE_INT|CTLFLAG_RW, 85 &tcp_msl, 0, sysctl_msec_to_ticks, "I", "Maximum segment lifetime"); 86 87int tcp_rexmit_min; 88SYSCTL_PROC(_net_inet_tcp, OID_AUTO, rexmit_min, CTLTYPE_INT|CTLFLAG_RW, 89 &tcp_rexmit_min, 0, sysctl_msec_to_ticks, "I", "Minimum Retransmission Timeout"); 90 91int tcp_rexmit_slop; 92SYSCTL_PROC(_net_inet_tcp, OID_AUTO, rexmit_slop, CTLTYPE_INT|CTLFLAG_RW, 93 &tcp_rexmit_slop, 0, sysctl_msec_to_ticks, "I", "Retransmission Timer Slop"); 94 95static int always_keepalive = 1; 96SYSCTL_INT(_net_inet_tcp, OID_AUTO, always_keepalive, CTLFLAG_RW, 97 &always_keepalive , 0, "Assume SO_KEEPALIVE on all TCP connections"); 98 99static int tcp_keepcnt = TCPTV_KEEPCNT; 100 /* max idle probes */ 101int tcp_maxpersistidle; 102 /* max idle time in persist */ 103int tcp_maxidle; 104 105/* 106 * Tcp protocol timeout routine called every 500 ms. 107 * Updates timestamps used for TCP 108 * causes finite state machine actions if timers expire. 109 */ 110void 111tcp_slowtimo() 112{ 113 114 tcp_maxidle = tcp_keepcnt * tcp_keepintvl; 115 INP_INFO_WLOCK(&tcbinfo); 116 (void) tcp_timer_2msl_tw(0); 117 INP_INFO_WUNLOCK(&tcbinfo); 118} 119 120int tcp_syn_backoff[TCP_MAXRXTSHIFT + 1] = 121 { 1, 1, 1, 1, 1, 2, 4, 8, 16, 32, 64, 64, 64 }; 122 123int tcp_backoff[TCP_MAXRXTSHIFT + 1] = 124 { 1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 512, 512, 512 }; 125 126static int tcp_totbackoff = 2559; /* sum of tcp_backoff[] */ 127 128static int tcp_timer_race; 129SYSCTL_INT(_net_inet_tcp, OID_AUTO, timer_race, CTLFLAG_RD, &tcp_timer_race, 130 0, "Count of t_inpcb races on tcp_discardcb"); 131 132/* 133 * TCP timer processing. 134 */ 135 136void 137tcp_timer_delack(xtp) 138 void *xtp; 139{ 140 struct tcpcb *tp = xtp; 141 struct inpcb *inp; 142 143 INP_INFO_RLOCK(&tcbinfo); 144 inp = tp->t_inpcb; 145 /* 146 * XXXRW: While this assert is in fact correct, bugs in the tcpcb 147 * tear-down mean we need it as a work-around for races between 148 * timers and tcp_discardcb(). 149 * 150 * KASSERT(inp != NULL, ("tcp_timer_delack: inp == NULL")); 151 */ 152 if (inp == NULL) { 153 tcp_timer_race++; 154 INP_INFO_RUNLOCK(&tcbinfo); 155 return; 156 } 157 INP_LOCK(inp); 158 INP_INFO_RUNLOCK(&tcbinfo); 159 if (callout_pending(tp->tt_delack) || !callout_active(tp->tt_delack)) { 160 INP_UNLOCK(inp); 161 return; 162 } 163 callout_deactivate(tp->tt_delack); 164 165 tp->t_flags |= TF_ACKNOW; 166 tcpstat.tcps_delack++; 167 (void) tcp_output(tp); 168 INP_UNLOCK(inp); 169} 170 171void 172tcp_timer_2msl(xtp) 173 void *xtp; 174{ 175 struct tcpcb *tp = xtp; 176 struct inpcb *inp; 177#ifdef TCPDEBUG 178 int ostate; 179 180 ostate = tp->t_state; 181#endif 182 /* 183 * XXXRW: Does this actually happen? 184 */ 185 INP_INFO_WLOCK(&tcbinfo); 186 inp = tp->t_inpcb; 187 /* 188 * XXXRW: While this assert is in fact correct, bugs in the tcpcb 189 * tear-down mean we need it as a work-around for races between 190 * timers and tcp_discardcb(). 191 * 192 * KASSERT(inp != NULL, ("tcp_timer_2msl: inp == NULL")); 193 */ 194 if (inp == NULL) { 195 tcp_timer_race++; 196 INP_INFO_RUNLOCK(&tcbinfo); 197 return; 198 } 199 INP_LOCK(inp); 200 tcp_free_sackholes(tp); 201 if (callout_pending(tp->tt_2msl) || !callout_active(tp->tt_2msl)) { 202 INP_UNLOCK(tp->t_inpcb); 203 INP_INFO_WUNLOCK(&tcbinfo); 204 return; 205 } 206 callout_deactivate(tp->tt_2msl); 207 /* 208 * 2 MSL timeout in shutdown went off. If we're closed but 209 * still waiting for peer to close and connection has been idle 210 * too long, or if 2MSL time is up from TIME_WAIT, delete connection 211 * control block. Otherwise, check again in a bit. 212 */ 213 if (tp->t_state != TCPS_TIME_WAIT && 214 (ticks - tp->t_rcvtime) <= tcp_maxidle) 215 callout_reset(tp->tt_2msl, tcp_keepintvl, 216 tcp_timer_2msl, tp); 217 else 218 tp = tcp_close(tp); 219 220#ifdef TCPDEBUG 221 if (tp != NULL && (tp->t_inpcb->inp_socket->so_options & SO_DEBUG)) 222 tcp_trace(TA_USER, ostate, tp, (void *)0, (struct tcphdr *)0, 223 PRU_SLOWTIMO); 224#endif 225 if (tp != NULL) 226 INP_UNLOCK(inp); 227 INP_INFO_WUNLOCK(&tcbinfo); 228} 229 230/* 231 * The timed wait lists contain references to each of the TCP sessions 232 * currently TIME_WAIT state. The list pointers, including the list pointers 233 * in each tcptw structure, are protected using the global tcbinfo lock, 234 * which must be held over list iteration and modification. 235 */ 236struct twlist { 237 LIST_HEAD(, tcptw) tw_list; 238 struct tcptw tw_tail; 239}; 240#define TWLIST_NLISTS 2 241static struct twlist twl_2msl[TWLIST_NLISTS]; 242static struct twlist *tw_2msl_list[] = { &twl_2msl[0], &twl_2msl[1], NULL }; 243 244void 245tcp_timer_init(void) 246{ 247 int i; 248 struct twlist *twl; 249 250 for (i = 0; i < TWLIST_NLISTS; i++) { 251 twl = &twl_2msl[i]; 252 LIST_INIT(&twl->tw_list); 253 LIST_INSERT_HEAD(&twl->tw_list, &twl->tw_tail, tw_2msl); 254 } 255} 256 257void 258tcp_timer_2msl_reset(struct tcptw *tw, int timeo) 259{ 260 int i; 261 struct tcptw *tw_tail; 262 263 INP_INFO_WLOCK_ASSERT(&tcbinfo); 264 INP_LOCK_ASSERT(tw->tw_inpcb); 265 if (tw->tw_time != 0) 266 LIST_REMOVE(tw, tw_2msl); 267 tw->tw_time = timeo + ticks; 268 i = timeo > tcp_msl ? 1 : 0; 269 tw_tail = &twl_2msl[i].tw_tail; 270 LIST_INSERT_BEFORE(tw_tail, tw, tw_2msl); 271} 272 273void 274tcp_timer_2msl_stop(struct tcptw *tw) 275{ 276 277 INP_INFO_WLOCK_ASSERT(&tcbinfo); 278 if (tw->tw_time != 0) 279 LIST_REMOVE(tw, tw_2msl); 280} 281 282struct tcptw * 283tcp_timer_2msl_tw(int reuse) 284{ 285 struct tcptw *tw, *tw_tail; 286 struct twlist *twl; 287 int i; 288 289 INP_INFO_WLOCK_ASSERT(&tcbinfo); 290 for (i = 0; i < 2; i++) { 291 twl = tw_2msl_list[i]; 292 tw_tail = &twl->tw_tail; 293 tw = LIST_FIRST(&twl->tw_list); 294 if (tw == tw_tail || (!reuse && tw->tw_time > ticks)) 295 continue; 296 INP_LOCK(tw->tw_inpcb); 297 tcp_twclose(tw, reuse); 298 return (tw); 299 } 300 return (NULL); 301} 302 303void 304tcp_timer_keep(xtp) 305 void *xtp; 306{ 307 struct tcpcb *tp = xtp; 308 struct tcptemp *t_template; 309 struct inpcb *inp; 310#ifdef TCPDEBUG 311 int ostate; 312 313 ostate = tp->t_state; 314#endif 315 INP_INFO_WLOCK(&tcbinfo); 316 inp = tp->t_inpcb; 317 /* 318 * XXXRW: While this assert is in fact correct, bugs in the tcpcb 319 * tear-down mean we need it as a work-around for races between 320 * timers and tcp_discardcb(). 321 * 322 * KASSERT(inp != NULL, ("tcp_timer_keep: inp == NULL")); 323 */ 324 if (inp == NULL) { 325 tcp_timer_race++; 326 INP_INFO_RUNLOCK(&tcbinfo); 327 return; 328 } 329 INP_LOCK(inp); 330 if (callout_pending(tp->tt_keep) || !callout_active(tp->tt_keep)) { 331 INP_UNLOCK(inp); 332 INP_INFO_WUNLOCK(&tcbinfo); 333 return; 334 } 335 callout_deactivate(tp->tt_keep); 336 /* 337 * Keep-alive timer went off; send something 338 * or drop connection if idle for too long. 339 */ 340 tcpstat.tcps_keeptimeo++; 341 if (tp->t_state < TCPS_ESTABLISHED) 342 goto dropit; 343 if ((always_keepalive || inp->inp_socket->so_options & SO_KEEPALIVE) && 344 tp->t_state <= TCPS_CLOSING) { 345 if ((ticks - tp->t_rcvtime) >= tcp_keepidle + tcp_maxidle) 346 goto dropit; 347 /* 348 * Send a packet designed to force a response 349 * if the peer is up and reachable: 350 * either an ACK if the connection is still alive, 351 * or an RST if the peer has closed the connection 352 * due to timeout or reboot. 353 * Using sequence number tp->snd_una-1 354 * causes the transmitted zero-length segment 355 * to lie outside the receive window; 356 * by the protocol spec, this requires the 357 * correspondent TCP to respond. 358 */ 359 tcpstat.tcps_keepprobe++; 360 t_template = tcpip_maketemplate(inp); 361 if (t_template) { 362 tcp_respond(tp, t_template->tt_ipgen, 363 &t_template->tt_t, (struct mbuf *)NULL, 364 tp->rcv_nxt, tp->snd_una - 1, 0); 365 (void) m_free(dtom(t_template)); 366 } 367 callout_reset(tp->tt_keep, tcp_keepintvl, tcp_timer_keep, tp); 368 } else 369 callout_reset(tp->tt_keep, tcp_keepidle, tcp_timer_keep, tp); 370 371#ifdef TCPDEBUG 372 if (inp->inp_socket->so_options & SO_DEBUG) 373 tcp_trace(TA_USER, ostate, tp, (void *)0, (struct tcphdr *)0, 374 PRU_SLOWTIMO); 375#endif 376 INP_UNLOCK(inp); 377 INP_INFO_WUNLOCK(&tcbinfo); 378 return; 379 380dropit: 381 tcpstat.tcps_keepdrops++; 382 tp = tcp_drop(tp, ETIMEDOUT); 383 384#ifdef TCPDEBUG 385 if (tp != NULL && (tp->t_inpcb->inp_socket->so_options & SO_DEBUG)) 386 tcp_trace(TA_USER, ostate, tp, (void *)0, (struct tcphdr *)0, 387 PRU_SLOWTIMO); 388#endif 389 if (tp != NULL) 390 INP_UNLOCK(tp->t_inpcb); 391 INP_INFO_WUNLOCK(&tcbinfo); 392} 393 394void 395tcp_timer_persist(xtp) 396 void *xtp; 397{ 398 struct tcpcb *tp = xtp; 399 struct inpcb *inp; 400#ifdef TCPDEBUG 401 int ostate; 402 403 ostate = tp->t_state; 404#endif 405 INP_INFO_WLOCK(&tcbinfo); 406 inp = tp->t_inpcb; 407 /* 408 * XXXRW: While this assert is in fact correct, bugs in the tcpcb 409 * tear-down mean we need it as a work-around for races between 410 * timers and tcp_discardcb(). 411 * 412 * KASSERT(inp != NULL, ("tcp_timer_persist: inp == NULL")); 413 */ 414 if (inp == NULL) { 415 tcp_timer_race++; 416 INP_INFO_RUNLOCK(&tcbinfo); 417 return; 418 } 419 INP_LOCK(inp); 420 if (callout_pending(tp->tt_persist) || !callout_active(tp->tt_persist)){ 421 INP_UNLOCK(inp); 422 INP_INFO_WUNLOCK(&tcbinfo); 423 return; 424 } 425 callout_deactivate(tp->tt_persist); 426 /* 427 * Persistance timer into zero window. 428 * Force a byte to be output, if possible. 429 */ 430 tcpstat.tcps_persisttimeo++; 431 /* 432 * Hack: if the peer is dead/unreachable, we do not 433 * time out if the window is closed. After a full 434 * backoff, drop the connection if the idle time 435 * (no responses to probes) reaches the maximum 436 * backoff that we would use if retransmitting. 437 */ 438 if (tp->t_rxtshift == TCP_MAXRXTSHIFT && 439 ((ticks - tp->t_rcvtime) >= tcp_maxpersistidle || 440 (ticks - tp->t_rcvtime) >= TCP_REXMTVAL(tp) * tcp_totbackoff)) { 441 tcpstat.tcps_persistdrop++; 442 tp = tcp_drop(tp, ETIMEDOUT); 443 goto out; 444 } 445 tcp_setpersist(tp); 446 tp->t_flags |= TF_FORCEDATA; 447 (void) tcp_output(tp); 448 tp->t_flags &= ~TF_FORCEDATA; 449 450out: 451#ifdef TCPDEBUG 452 if (tp->t_inpcb->inp_socket->so_options & SO_DEBUG) 453 tcp_trace(TA_USER, ostate, tp, (void *)0, (struct tcphdr *)0, 454 PRU_SLOWTIMO); 455#endif 456 if (tp != NULL) 457 INP_UNLOCK(inp); 458 INP_INFO_WUNLOCK(&tcbinfo); 459} 460 461void 462tcp_timer_rexmt(xtp) 463 void *xtp; 464{ 465 struct tcpcb *tp = xtp; 466 int rexmt; 467 int headlocked; 468 struct inpcb *inp; 469#ifdef TCPDEBUG 470 int ostate; 471 472 ostate = tp->t_state; 473#endif 474 INP_INFO_WLOCK(&tcbinfo); 475 headlocked = 1; 476 inp = tp->t_inpcb; 477 /* 478 * XXXRW: While this assert is in fact correct, bugs in the tcpcb 479 * tear-down mean we need it as a work-around for races between 480 * timers and tcp_discardcb(). 481 * 482 * KASSERT(inp != NULL, ("tcp_timer_rexmt: inp == NULL")); 483 */ 484 if (inp == NULL) { 485 tcp_timer_race++; 486 INP_INFO_RUNLOCK(&tcbinfo); 487 return; 488 } 489 INP_LOCK(inp); 490 if (callout_pending(tp->tt_rexmt) || !callout_active(tp->tt_rexmt)) { 491 INP_UNLOCK(inp); 492 INP_INFO_WUNLOCK(&tcbinfo); 493 return; 494 } 495 callout_deactivate(tp->tt_rexmt); 496 tcp_free_sackholes(tp); 497 /* 498 * Retransmission timer went off. Message has not 499 * been acked within retransmit interval. Back off 500 * to a longer retransmit interval and retransmit one segment. 501 */ 502 if (++tp->t_rxtshift > TCP_MAXRXTSHIFT) { 503 tp->t_rxtshift = TCP_MAXRXTSHIFT; 504 tcpstat.tcps_timeoutdrop++; 505 tp = tcp_drop(tp, tp->t_softerror ? 506 tp->t_softerror : ETIMEDOUT); 507 goto out; 508 } 509 INP_INFO_WUNLOCK(&tcbinfo); 510 headlocked = 0; 511 if (tp->t_rxtshift == 1) { 512 /* 513 * first retransmit; record ssthresh and cwnd so they can 514 * be recovered if this turns out to be a "bad" retransmit. 515 * A retransmit is considered "bad" if an ACK for this 516 * segment is received within RTT/2 interval; the assumption 517 * here is that the ACK was already in flight. See 518 * "On Estimating End-to-End Network Path Properties" by 519 * Allman and Paxson for more details. 520 */ 521 tp->snd_cwnd_prev = tp->snd_cwnd; 522 tp->snd_ssthresh_prev = tp->snd_ssthresh; 523 tp->snd_recover_prev = tp->snd_recover; 524 if (IN_FASTRECOVERY(tp)) 525 tp->t_flags |= TF_WASFRECOVERY; 526 else 527 tp->t_flags &= ~TF_WASFRECOVERY; 528 tp->t_badrxtwin = ticks + (tp->t_srtt >> (TCP_RTT_SHIFT + 1)); 529 } 530 tcpstat.tcps_rexmttimeo++; 531 if (tp->t_state == TCPS_SYN_SENT) 532 rexmt = TCP_REXMTVAL(tp) * tcp_syn_backoff[tp->t_rxtshift]; 533 else 534 rexmt = TCP_REXMTVAL(tp) * tcp_backoff[tp->t_rxtshift]; 535 TCPT_RANGESET(tp->t_rxtcur, rexmt, 536 tp->t_rttmin, TCPTV_REXMTMAX); 537 /* 538 * Disable rfc1323 if we havn't got any response to 539 * our third SYN to work-around some broken terminal servers 540 * (most of which have hopefully been retired) that have bad VJ 541 * header compression code which trashes TCP segments containing 542 * unknown-to-them TCP options. 543 */ 544 if ((tp->t_state == TCPS_SYN_SENT) && (tp->t_rxtshift == 3)) 545 tp->t_flags &= ~(TF_REQ_SCALE|TF_REQ_TSTMP); 546 /* 547 * If we backed off this far, our srtt estimate is probably bogus. 548 * Clobber it so we'll take the next rtt measurement as our srtt; 549 * move the current srtt into rttvar to keep the current 550 * retransmit times until then. 551 */ 552 if (tp->t_rxtshift > TCP_MAXRXTSHIFT / 4) { 553#ifdef INET6 554 if ((tp->t_inpcb->inp_vflag & INP_IPV6) != 0) 555 in6_losing(tp->t_inpcb); 556 else 557#endif 558 tp->t_rttvar += (tp->t_srtt >> TCP_RTT_SHIFT); 559 tp->t_srtt = 0; 560 } 561 tp->snd_nxt = tp->snd_una; 562 tp->snd_recover = tp->snd_max; 563 /* 564 * Force a segment to be sent. 565 */ 566 tp->t_flags |= TF_ACKNOW; 567 /* 568 * If timing a segment in this window, stop the timer. 569 */ 570 tp->t_rtttime = 0; 571 /* 572 * Close the congestion window down to one segment 573 * (we'll open it by one segment for each ack we get). 574 * Since we probably have a window's worth of unacked 575 * data accumulated, this "slow start" keeps us from 576 * dumping all that data as back-to-back packets (which 577 * might overwhelm an intermediate gateway). 578 * 579 * There are two phases to the opening: Initially we 580 * open by one mss on each ack. This makes the window 581 * size increase exponentially with time. If the 582 * window is larger than the path can handle, this 583 * exponential growth results in dropped packet(s) 584 * almost immediately. To get more time between 585 * drops but still "push" the network to take advantage 586 * of improving conditions, we switch from exponential 587 * to linear window opening at some threshhold size. 588 * For a threshhold, we use half the current window 589 * size, truncated to a multiple of the mss. 590 * 591 * (the minimum cwnd that will give us exponential 592 * growth is 2 mss. We don't allow the threshhold 593 * to go below this.) 594 */ 595 { 596 u_int win = min(tp->snd_wnd, tp->snd_cwnd) / 2 / tp->t_maxseg; 597 if (win < 2) 598 win = 2; 599 tp->snd_cwnd = tp->t_maxseg; 600 tp->snd_ssthresh = win * tp->t_maxseg; 601 tp->t_dupacks = 0; 602 } 603 EXIT_FASTRECOVERY(tp); 604 (void) tcp_output(tp); 605 606out: 607#ifdef TCPDEBUG 608 if (tp != NULL && (tp->t_inpcb->inp_socket->so_options & SO_DEBUG)) 609 tcp_trace(TA_USER, ostate, tp, (void *)0, (struct tcphdr *)0, 610 PRU_SLOWTIMO); 611#endif 612 if (tp != NULL) 613 INP_UNLOCK(inp); 614 if (headlocked) 615 INP_INFO_WUNLOCK(&tcbinfo); 616} 617