sys/netinet/tcp_timer.c

   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  * $FreeBSD$
  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
  66 int     tcp_keepinit;
  67 SYSCTL_PROC(_net_inet_tcp, TCPCTL_KEEPINIT, keepinit, CTLTYPE_INT|CTLFLAG_RW,
  68     &tcp_keepinit, 0, sysctl_msec_to_ticks, "I", "");
  69
  70 int     tcp_keepidle;
  71 SYSCTL_PROC(_net_inet_tcp, TCPCTL_KEEPIDLE, keepidle, CTLTYPE_INT|CTLFLAG_RW,
  72     &tcp_keepidle, 0, sysctl_msec_to_ticks, "I", "");
  73
  74 int     tcp_keepintvl;
  75 SYSCTL_PROC(_net_inet_tcp, TCPCTL_KEEPINTVL, keepintvl, CTLTYPE_INT|CTLFLAG_RW,
  76     &tcp_keepintvl, 0, sysctl_msec_to_ticks, "I", "");
  77
  78 int     tcp_delacktime;
  79 SYSCTL_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
  83 int     tcp_msl;
  84 SYSCTL_PROC(_net_inet_tcp, OID_AUTO, msl, CTLTYPE_INT|CTLFLAG_RW,
  85     &tcp_msl, 0, sysctl_msec_to_ticks, "I", "Maximum segment lifetime");
  86
  87 int     tcp_rexmit_min;
  88 SYSCTL_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
  91 int     tcp_rexmit_slop;
  92 SYSCTL_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
  95 static int      always_keepalive = 1;
  96 SYSCTL_INT(_net_inet_tcp, OID_AUTO, always_keepalive, CTLFLAG_RW,
  97     &always_keepalive , 0, "Assume SO_KEEPALIVE on all TCP connections");
  98
  99 static int      tcp_keepcnt = TCPTV_KEEPCNT;
 100         /* max idle probes */
 101 int     tcp_maxpersistidle;
 102         /* max idle time in persist */
 103 int     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  */
 110 void
 111 tcp_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
 120 int     tcp_syn_backoff[TCP_MAXRXTSHIFT + 1] =
 121     { 1, 1, 1, 1, 1, 2, 4, 8, 16, 32, 64, 64, 64 };
 122
 123 int     tcp_backoff[TCP_MAXRXTSHIFT + 1] =
 124     { 1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 512, 512, 512 };
 125
 126 static int tcp_totbackoff = 2559;       /* sum of tcp_backoff[] */
 127
 128 /*
 129  * TCP timer processing.
 130  */
 131
 132 void
 133 tcp_timer_delack(xtp)
 134         void *xtp;
 135 {
 136         struct tcpcb *tp = xtp;
 137         struct inpcb *inp;
 138
 139         INP_INFO_RLOCK(&tcbinfo);
 140         inp = tp->t_inpcb;
 141         if (inp == NULL) {
 142                 INP_INFO_RUNLOCK(&tcbinfo);
 143                 return;
 144         }
 145         INP_LOCK(inp);
 146         INP_INFO_RUNLOCK(&tcbinfo);
 147         if (callout_pending(tp->tt_delack) || !callout_active(tp->tt_delack)) {
 148                 INP_UNLOCK(inp);
 149                 return;
 150         }
 151         callout_deactivate(tp->tt_delack);
 152
 153         tp->t_flags |= TF_ACKNOW;
 154         tcpstat.tcps_delack++;
 155         (void) tcp_output(tp);
 156         INP_UNLOCK(inp);
 157 }
 158
 159 void
 160 tcp_timer_2msl(xtp)
 161         void *xtp;
 162 {
 163         struct tcpcb *tp = xtp;
 164         struct inpcb *inp;
 165 #ifdef TCPDEBUG
 166         int ostate;
 167
 168         ostate = tp->t_state;
 169 #endif
 170         INP_INFO_WLOCK(&tcbinfo);
 171         inp = tp->t_inpcb;
 172         if (inp == NULL) {
 173                 INP_INFO_WUNLOCK(&tcbinfo);
 174                 return;
 175         }
 176         INP_LOCK(inp);
 177         tcp_free_sackholes(tp);
 178         if (callout_pending(tp->tt_2msl) || !callout_active(tp->tt_2msl)) {
 179                 INP_UNLOCK(tp->t_inpcb);
 180                 INP_INFO_WUNLOCK(&tcbinfo);
 181                 return;
 182         }
 183         callout_deactivate(tp->tt_2msl);
 184         /*
 185          * 2 MSL timeout in shutdown went off.  If we're closed but
 186          * still waiting for peer to close and connection has been idle
 187          * too long, or if 2MSL time is up from TIME_WAIT, delete connection
 188          * control block.  Otherwise, check again in a bit.
 189          */
 190         if (tp->t_state != TCPS_TIME_WAIT &&
 191             (ticks - tp->t_rcvtime) <= tcp_maxidle)
 192                 callout_reset(tp->tt_2msl, tcp_keepintvl,
 193                               tcp_timer_2msl, tp);
 194         else
 195                 tp = tcp_close(tp);
 196
 197 #ifdef TCPDEBUG
 198         if (tp != NULL && (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
 199                 tcp_trace(TA_USER, ostate, tp, (void *)0, (struct tcphdr *)0,
 200                           PRU_SLOWTIMO);
 201 #endif
 202         if (tp != NULL)
 203                 INP_UNLOCK(inp);
 204         INP_INFO_WUNLOCK(&tcbinfo);
 205 }
 206
 207 /*
 208  * The timed wait lists contain references to each of the TCP sessions
 209  * currently TIME_WAIT state.  The list pointers, including the list pointers
 210  * in each tcptw structure, are protected using the global tcbinfo lock,
 211  * which must be held over list iteration and modification.
 212  */
 213 struct twlist {
 214         LIST_HEAD(, tcptw)      tw_list;
 215         struct tcptw    tw_tail;
 216 };
 217 #define TWLIST_NLISTS   2
 218 static struct twlist twl_2msl[TWLIST_NLISTS];
 219 static struct twlist *tw_2msl_list[] = { &twl_2msl[0], &twl_2msl[1], NULL };
 220
 221 void
 222 tcp_timer_init(void)
 223 {
 224         int i;
 225         struct twlist *twl;
 226
 227         for (i = 0; i < TWLIST_NLISTS; i++) {
 228                 twl = &twl_2msl[i];
 229                 LIST_INIT(&twl->tw_list);
 230                 LIST_INSERT_HEAD(&twl->tw_list, &twl->tw_tail, tw_2msl);
 231         }
 232 }
 233
 234 void
 235 tcp_timer_2msl_reset(struct tcptw *tw, int timeo)
 236 {
 237         int i;
 238         struct tcptw *tw_tail;
 239
 240         INP_INFO_WLOCK_ASSERT(&tcbinfo);
 241         INP_LOCK_ASSERT(tw->tw_inpcb);
 242         if (tw->tw_time != 0)
 243                 LIST_REMOVE(tw, tw_2msl);
 244         tw->tw_time = timeo + ticks;
 245         i = timeo > tcp_msl ? 1 : 0;
 246         tw_tail = &twl_2msl[i].tw_tail;
 247         LIST_INSERT_BEFORE(tw_tail, tw, tw_2msl);
 248 }
 249
 250 void
 251 tcp_timer_2msl_stop(struct tcptw *tw)
 252 {
 253
 254         INP_INFO_WLOCK_ASSERT(&tcbinfo);
 255         if (tw->tw_time != 0)
 256                 LIST_REMOVE(tw, tw_2msl);
 257 }
 258
 259 struct tcptw *
 260 tcp_timer_2msl_tw(int reuse)
 261 {
 262         struct tcptw *tw, *tw_tail;
 263         struct twlist *twl;
 264         int i;
 265
 266         INP_INFO_WLOCK_ASSERT(&tcbinfo);
 267         for (i = 0; i < 2; i++) {
 268                 twl = tw_2msl_list[i];
 269                 tw_tail = &twl->tw_tail;
 270                 for (;;) {
 271                         tw = LIST_FIRST(&twl->tw_list);
 272                         if (tw == tw_tail || (!reuse && tw->tw_time > ticks))
 273                                 break;
 274                         INP_LOCK(tw->tw_inpcb);
 275                         if (tcp_twclose(tw, reuse) != NULL)
 276                                 return (tw);
 277                 }
 278         }
 279         return (NULL);
 280 }
 281
 282 void
 283 tcp_timer_keep(xtp)
 284         void *xtp;
 285 {
 286         struct tcpcb *tp = xtp;
 287         struct tcptemp *t_template;
 288         struct inpcb *inp;
 289 #ifdef TCPDEBUG
 290         int ostate;
 291
 292         ostate = tp->t_state;
 293 #endif
 294         INP_INFO_WLOCK(&tcbinfo);
 295         inp = tp->t_inpcb;
 296         if (!inp) {
 297                 INP_INFO_WUNLOCK(&tcbinfo);
 298                 return;
 299         }
 300         INP_LOCK(inp);
 301         if (callout_pending(tp->tt_keep) || !callout_active(tp->tt_keep)) {
 302                 INP_UNLOCK(inp);
 303                 INP_INFO_WUNLOCK(&tcbinfo);
 304                 return;
 305         }
 306         callout_deactivate(tp->tt_keep);
 307         /*
 308          * Keep-alive timer went off; send something
 309          * or drop connection if idle for too long.
 310          */
 311         tcpstat.tcps_keeptimeo++;
 312         if (tp->t_state < TCPS_ESTABLISHED)
 313                 goto dropit;
 314         if ((always_keepalive || inp->inp_socket->so_options & SO_KEEPALIVE) &&
 315             tp->t_state <= TCPS_CLOSING) {
 316                 if ((ticks - tp->t_rcvtime) >= tcp_keepidle + tcp_maxidle)
 317                         goto dropit;
 318                 /*
 319                  * Send a packet designed to force a response
 320                  * if the peer is up and reachable:
 321                  * either an ACK if the connection is still alive,
 322                  * or an RST if the peer has closed the connection
 323                  * due to timeout or reboot.
 324                  * Using sequence number tp->snd_una-1
 325                  * causes the transmitted zero-length segment
 326                  * to lie outside the receive window;
 327                  * by the protocol spec, this requires the
 328                  * correspondent TCP to respond.
 329                  */
 330                 tcpstat.tcps_keepprobe++;
 331                 t_template = tcpip_maketemplate(inp);
 332                 if (t_template) {
 333                         tcp_respond(tp, t_template->tt_ipgen,
 334                                     &t_template->tt_t, (struct mbuf *)NULL,
 335                                     tp->rcv_nxt, tp->snd_una - 1, 0);
 336                         (void) m_free(dtom(t_template));
 337                 }
 338                 callout_reset(tp->tt_keep, tcp_keepintvl, tcp_timer_keep, tp);
 339         } else
 340                 callout_reset(tp->tt_keep, tcp_keepidle, tcp_timer_keep, tp);
 341
 342 #ifdef TCPDEBUG
 343         if (inp->inp_socket->so_options & SO_DEBUG)
 344                 tcp_trace(TA_USER, ostate, tp, (void *)0, (struct tcphdr *)0,
 345                           PRU_SLOWTIMO);
 346 #endif
 347         INP_UNLOCK(inp);
 348         INP_INFO_WUNLOCK(&tcbinfo);
 349         return;
 350
 351 dropit:
 352         tcpstat.tcps_keepdrops++;
 353         tp = tcp_drop(tp, ETIMEDOUT);
 354
 355 #ifdef TCPDEBUG
 356         if (tp != NULL && (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
 357                 tcp_trace(TA_USER, ostate, tp, (void *)0, (struct tcphdr *)0,
 358                           PRU_SLOWTIMO);
 359 #endif
 360         if (tp != NULL)
 361                 INP_UNLOCK(tp->t_inpcb);
 362         INP_INFO_WUNLOCK(&tcbinfo);
 363 }
 364
 365 void
 366 tcp_timer_persist(xtp)
 367         void *xtp;
 368 {
 369         struct tcpcb *tp = xtp;
 370         struct inpcb *inp;
 371 #ifdef TCPDEBUG
 372         int ostate;
 373
 374         ostate = tp->t_state;
 375 #endif
 376         INP_INFO_WLOCK(&tcbinfo);
 377         inp = tp->t_inpcb;
 378         if (!inp) {
 379                 INP_INFO_WUNLOCK(&tcbinfo);
 380                 return;
 381         }
 382         INP_LOCK(inp);
 383         if (callout_pending(tp->tt_persist) || !callout_active(tp->tt_persist)){
 384                 INP_UNLOCK(inp);
 385                 INP_INFO_WUNLOCK(&tcbinfo);
 386                 return;
 387         }
 388         callout_deactivate(tp->tt_persist);
 389         /*
 390          * Persistance timer into zero window.
 391          * Force a byte to be output, if possible.
 392          */
 393         tcpstat.tcps_persisttimeo++;
 394         /*
 395          * Hack: if the peer is dead/unreachable, we do not
 396          * time out if the window is closed.  After a full
 397          * backoff, drop the connection if the idle time
 398          * (no responses to probes) reaches the maximum
 399          * backoff that we would use if retransmitting.
 400          */
 401         if (tp->t_rxtshift == TCP_MAXRXTSHIFT &&
 402             ((ticks - tp->t_rcvtime) >= tcp_maxpersistidle ||
 403              (ticks - tp->t_rcvtime) >= TCP_REXMTVAL(tp) * tcp_totbackoff)) {
 404                 tcpstat.tcps_persistdrop++;
 405                 tp = tcp_drop(tp, ETIMEDOUT);
 406                 goto out;
 407         }
 408         tcp_setpersist(tp);
 409         tp->t_flags |= TF_FORCEDATA;
 410         (void) tcp_output(tp);
 411         tp->t_flags &= ~TF_FORCEDATA;
 412
 413 out:
 414 #ifdef TCPDEBUG
 415         if (tp != NULL && tp->t_inpcb->inp_socket->so_options & SO_DEBUG)
 416                 tcp_trace(TA_USER, ostate, tp, (void *)0, (struct tcphdr *)0,
 417                           PRU_SLOWTIMO);
 418 #endif
 419         if (tp != NULL)
 420                 INP_UNLOCK(inp);
 421         INP_INFO_WUNLOCK(&tcbinfo);
 422 }
 423
 424 void
 425 tcp_timer_rexmt(xtp)
 426         void *xtp;
 427 {
 428         struct tcpcb *tp = xtp;
 429         int rexmt;
 430         int headlocked;
 431         struct inpcb *inp;
 432 #ifdef TCPDEBUG
 433         int ostate;
 434
 435         ostate = tp->t_state;
 436 #endif
 437         INP_INFO_WLOCK(&tcbinfo);
 438         headlocked = 1;
 439         inp = tp->t_inpcb;
 440         if (!inp) {
 441                 INP_INFO_WUNLOCK(&tcbinfo);
 442                 return;
 443         }
 444         INP_LOCK(inp);
 445         if (callout_pending(tp->tt_rexmt) || !callout_active(tp->tt_rexmt)) {
 446                 INP_UNLOCK(inp);
 447                 INP_INFO_WUNLOCK(&tcbinfo);
 448                 return;
 449         }
 450         callout_deactivate(tp->tt_rexmt);
 451         tcp_free_sackholes(tp);
 452         /*
 453          * Retransmission timer went off.  Message has not
 454          * been acked within retransmit interval.  Back off
 455          * to a longer retransmit interval and retransmit one segment.
 456          */
 457         if (++tp->t_rxtshift > TCP_MAXRXTSHIFT) {
 458                 tp->t_rxtshift = TCP_MAXRXTSHIFT;
 459                 tcpstat.tcps_timeoutdrop++;
 460                 tp = tcp_drop(tp, tp->t_softerror ?
 461                               tp->t_softerror : ETIMEDOUT);
 462                 goto out;
 463         }
 464         INP_INFO_WUNLOCK(&tcbinfo);
 465         headlocked = 0;
 466         if (tp->t_rxtshift == 1) {
 467                 /*
 468                  * first retransmit; record ssthresh and cwnd so they can
 469                  * be recovered if this turns out to be a "bad" retransmit.
 470                  * A retransmit is considered "bad" if an ACK for this
 471                  * segment is received within RTT/2 interval; the assumption
 472                  * here is that the ACK was already in flight.  See
 473                  * "On Estimating End-to-End Network Path Properties" by
 474                  * Allman and Paxson for more details.
 475                  */
 476                 tp->snd_cwnd_prev = tp->snd_cwnd;
 477                 tp->snd_ssthresh_prev = tp->snd_ssthresh;
 478                 tp->snd_recover_prev = tp->snd_recover;
 479                 if (IN_FASTRECOVERY(tp))
 480                   tp->t_flags |= TF_WASFRECOVERY;
 481                 else
 482                   tp->t_flags &= ~TF_WASFRECOVERY;
 483                 tp->t_badrxtwin = ticks + (tp->t_srtt >> (TCP_RTT_SHIFT + 1));
 484         }
 485         tcpstat.tcps_rexmttimeo++;
 486         if (tp->t_state == TCPS_SYN_SENT)
 487                 rexmt = TCP_REXMTVAL(tp) * tcp_syn_backoff[tp->t_rxtshift];
 488         else
 489                 rexmt = TCP_REXMTVAL(tp) * tcp_backoff[tp->t_rxtshift];
 490         TCPT_RANGESET(tp->t_rxtcur, rexmt,
 491                       tp->t_rttmin, TCPTV_REXMTMAX);
 492         /*
 493          * Disable rfc1323 if we havn't got any response to
 494          * our third SYN to work-around some broken terminal servers
 495          * (most of which have hopefully been retired) that have bad VJ
 496          * header compression code which trashes TCP segments containing
 497          * unknown-to-them TCP options.
 498          */
 499         if ((tp->t_state == TCPS_SYN_SENT) && (tp->t_rxtshift == 3))
 500                 tp->t_flags &= ~(TF_REQ_SCALE|TF_REQ_TSTMP);
 501         /*
 502          * If we backed off this far, our srtt estimate is probably bogus.
 503          * Clobber it so we'll take the next rtt measurement as our srtt;
 504          * move the current srtt into rttvar to keep the current
 505          * retransmit times until then.
 506          */
 507         if (tp->t_rxtshift > TCP_MAXRXTSHIFT / 4) {
 508 #ifdef INET6
 509                 if ((tp->t_inpcb->inp_vflag & INP_IPV6) != 0)
 510                         in6_losing(tp->t_inpcb);
 511                 else
 512 #endif
 513                 tp->t_rttvar += (tp->t_srtt >> TCP_RTT_SHIFT);
 514                 tp->t_srtt = 0;
 515         }
 516         tp->snd_nxt = tp->snd_una;
 517         tp->snd_recover = tp->snd_max;
 518         /*
 519          * Force a segment to be sent.
 520          */
 521         tp->t_flags |= TF_ACKNOW;
 522         /*
 523          * If timing a segment in this window, stop the timer.
 524          */
 525         tp->t_rtttime = 0;
 526         /*
 527          * Close the congestion window down to one segment
 528          * (we'll open it by one segment for each ack we get).
 529          * Since we probably have a window's worth of unacked
 530          * data accumulated, this "slow start" keeps us from
 531          * dumping all that data as back-to-back packets (which
 532          * might overwhelm an intermediate gateway).
 533          *
 534          * There are two phases to the opening: Initially we
 535          * open by one mss on each ack.  This makes the window
 536          * size increase exponentially with time.  If the
 537          * window is larger than the path can handle, this
 538          * exponential growth results in dropped packet(s)
 539          * almost immediately.  To get more time between
 540          * drops but still "push" the network to take advantage
 541          * of improving conditions, we switch from exponential
 542          * to linear window opening at some threshhold size.
 543          * For a threshhold, we use half the current window
 544          * size, truncated to a multiple of the mss.
 545          *
 546          * (the minimum cwnd that will give us exponential
 547          * growth is 2 mss.  We don't allow the threshhold
 548          * to go below this.)
 549          */
 550         {
 551                 u_int win = min(tp->snd_wnd, tp->snd_cwnd) / 2 / tp->t_maxseg;
 552                 if (win < 2)
 553                         win = 2;
 554                 tp->snd_cwnd = tp->t_maxseg;
 555                 tp->snd_ssthresh = win * tp->t_maxseg;
 556                 tp->t_dupacks = 0;
 557         }
 558         EXIT_FASTRECOVERY(tp);
 559         (void) tcp_output(tp);
 560
 561 out:
 562 #ifdef TCPDEBUG
 563         if (tp != NULL && (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
 564                 tcp_trace(TA_USER, ostate, tp, (void *)0, (struct tcphdr *)0,
 565                           PRU_SLOWTIMO);
 566 #endif
 567         if (tp != NULL)
 568                 INP_UNLOCK(inp);
 569         if (headlocked)
 570                 INP_INFO_WUNLOCK(&tcbinfo);
 571 }