2 * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1995
3 * The Regents of the University of California. All rights reserved.
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6 * modification, are permitted provided that the following conditions
8 * 1. Redistributions of source code must retain the above copyright
9 * notice, this list of conditions and the following disclaimer.
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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
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17 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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19 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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26 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
29 * @(#)tcp_timer.c 8.2 (Berkeley) 5/24/95
33 #include "opt_inet6.h"
34 #include "opt_tcpdebug.h"
36 #include <sys/param.h>
37 #include <sys/kernel.h>
40 #include <sys/limits.h>
42 #include <sys/mutex.h>
43 #include <sys/protosw.h>
44 #include <sys/socket.h>
45 #include <sys/socketvar.h>
46 #include <sys/sysctl.h>
47 #include <sys/systm.h>
49 #include <net/route.h>
51 #include <netinet/in.h>
52 #include <netinet/in_pcb.h>
53 #include <netinet/in_systm.h>
55 #include <netinet6/in6_pcb.h>
57 #include <netinet/ip_var.h>
58 #include <netinet/tcp.h>
59 #include <netinet/tcp_fsm.h>
60 #include <netinet/tcp_timer.h>
61 #include <netinet/tcp_var.h>
62 #include <netinet/tcpip.h>
64 #include <netinet/tcp_debug.h>
68 SYSCTL_PROC(_net_inet_tcp, TCPCTL_KEEPINIT, keepinit, CTLTYPE_INT|CTLFLAG_RW,
69 &tcp_keepinit, 0, sysctl_msec_to_ticks, "I", "");
72 SYSCTL_PROC(_net_inet_tcp, TCPCTL_KEEPIDLE, keepidle, CTLTYPE_INT|CTLFLAG_RW,
73 &tcp_keepidle, 0, sysctl_msec_to_ticks, "I", "");
76 SYSCTL_PROC(_net_inet_tcp, TCPCTL_KEEPINTVL, keepintvl, CTLTYPE_INT|CTLFLAG_RW,
77 &tcp_keepintvl, 0, sysctl_msec_to_ticks, "I", "");
80 SYSCTL_PROC(_net_inet_tcp, TCPCTL_DELACKTIME, delacktime, CTLTYPE_INT|CTLFLAG_RW,
81 &tcp_delacktime, 0, sysctl_msec_to_ticks, "I",
82 "Time before a delayed ACK is sent");
85 SYSCTL_PROC(_net_inet_tcp, OID_AUTO, msl, CTLTYPE_INT|CTLFLAG_RW,
86 &tcp_msl, 0, sysctl_msec_to_ticks, "I", "Maximum segment lifetime");
89 SYSCTL_PROC(_net_inet_tcp, OID_AUTO, rexmit_min, CTLTYPE_INT|CTLFLAG_RW,
90 &tcp_rexmit_min, 0, sysctl_msec_to_ticks, "I",
91 "Minimum Retransmission Timeout");
94 SYSCTL_PROC(_net_inet_tcp, OID_AUTO, rexmit_slop, CTLTYPE_INT|CTLFLAG_RW,
95 &tcp_rexmit_slop, 0, sysctl_msec_to_ticks, "I",
96 "Retransmission Timer Slop");
98 static int always_keepalive = 1;
99 SYSCTL_INT(_net_inet_tcp, OID_AUTO, always_keepalive, CTLFLAG_RW,
100 &always_keepalive , 0, "Assume SO_KEEPALIVE on all TCP connections");
102 int tcp_fast_finwait2_recycle = 0;
103 SYSCTL_INT(_net_inet_tcp, OID_AUTO, fast_finwait2_recycle, CTLFLAG_RW,
104 &tcp_fast_finwait2_recycle, 0,
105 "Recycle closed FIN_WAIT_2 connections faster");
107 int tcp_finwait2_timeout;
108 SYSCTL_PROC(_net_inet_tcp, OID_AUTO, finwait2_timeout, CTLTYPE_INT|CTLFLAG_RW,
109 &tcp_finwait2_timeout, 0, sysctl_msec_to_ticks, "I", "FIN-WAIT2 timeout");
112 static int tcp_keepcnt = TCPTV_KEEPCNT;
113 /* max idle probes */
114 int tcp_maxpersistidle;
115 /* max idle time in persist */
118 static void tcp_timer(void *);
119 static int tcp_timer_delack(struct tcpcb *, struct inpcb *);
120 static int tcp_timer_2msl(struct tcpcb *, struct inpcb *);
121 static int tcp_timer_keep(struct tcpcb *, struct inpcb *);
122 static int tcp_timer_persist(struct tcpcb *, struct inpcb *);
123 static int tcp_timer_rexmt(struct tcpcb *, struct inpcb *);
126 * Tcp protocol timeout routine called every 500 ms.
127 * Updates timestamps used for TCP
128 * causes finite state machine actions if timers expire.
134 tcp_maxidle = tcp_keepcnt * tcp_keepintvl;
135 INP_INFO_WLOCK(&tcbinfo);
136 (void) tcp_timer_2msl_tw(0);
137 INP_INFO_WUNLOCK(&tcbinfo);
140 int tcp_syn_backoff[TCP_MAXRXTSHIFT + 1] =
141 { 1, 1, 1, 1, 1, 2, 4, 8, 16, 32, 64, 64, 64 };
143 int tcp_backoff[TCP_MAXRXTSHIFT + 1] =
144 { 1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 512, 512, 512 };
146 static int tcp_totbackoff = 2559; /* sum of tcp_backoff[] */
148 static int tcp_timer_race;
149 SYSCTL_INT(_net_inet_tcp, OID_AUTO, timer_race, CTLFLAG_RD, &tcp_timer_race,
150 0, "Count of t_inpcb races on tcp_discardcb");
154 tcp_timer_activate(struct tcpcb *tp, int timer_type, u_int delta)
156 struct inpcb *inp = tp->t_inpcb;
157 struct tcp_timer *tt = tp->t_timers;
158 int tick = ticks; /* Stable time base. */
159 int next = delta ? tick + delta : 0;
161 INP_LOCK_ASSERT(inp);
163 CTR6(KTR_NET, "%p %s inp %p active %x delta %i nextc %i",
164 tp, __func__, inp, tt->tt_active, delta, tt->tt_nextc);
166 /* Set new value for timer. */
169 CTR4(KTR_NET, "%p %s TT_DELACK old %i new %i",
170 tp, __func__, tt->tt_delack, next);
171 tt->tt_delack = next;
174 CTR4(KTR_NET, "%p %s TT_REXMT old %i new %i",
175 tp, __func__, tt->tt_rexmt, next);
179 CTR4(KTR_NET, "%p %s TT_PERSIST old %i new %i",
180 tp, __func__, tt->tt_persist, next);
181 tt->tt_persist = next;
184 CTR4(KTR_NET, "%p %s TT_KEEP old %i new %i",
185 tp, __func__, tt->tt_keep, next);
189 CTR4(KTR_NET, "%p %s TT_2MSL old %i new %i",
190 tp, __func__, tt->tt_2msl, next);
193 case 0: /* Dummy for timer rescan. */
194 CTR3(KTR_NET, "%p %s timer rescan new %i", tp, __func__, next);
198 /* If some other timer is active and is schedules sooner just return. */
199 if (tt->tt_active != timer_type && tt->tt_nextc < next &&
200 callout_active(&tt->tt_timer))
203 /* Select next timer to schedule. */
204 tt->tt_nextc = INT_MAX;
206 if (tt->tt_delack && tt->tt_delack < tt->tt_nextc) {
207 tt->tt_nextc = tt->tt_delack;
208 tt->tt_active = TT_DELACK;
210 if (tt->tt_rexmt && tt->tt_rexmt < tt->tt_nextc) {
211 tt->tt_nextc = tt->tt_rexmt;
212 tt->tt_active = TT_REXMT;
214 if (tt->tt_persist && tt->tt_persist < tt->tt_nextc) {
215 tt->tt_nextc = tt->tt_persist;
216 tt->tt_active = TT_PERSIST;
218 if (tt->tt_keep && tt->tt_keep < tt->tt_nextc) {
219 tt->tt_nextc = tt->tt_keep;
220 tt->tt_active = TT_KEEP;
222 if (tt->tt_2msl && tt->tt_2msl < tt->tt_nextc) {
223 tt->tt_nextc = tt->tt_2msl;
224 tt->tt_active = TT_2MSL;
227 /* Rearm callout with new timer if we found one. */
229 CTR4(KTR_NET, "%p %s callout_reset active %x nextc in %i",
230 tp, __func__, tt->tt_active, tt->tt_nextc - tick);
231 callout_reset(&tt->tt_timer,
232 tt->tt_nextc - tick, tcp_timer, (void *)inp);
234 CTR2(KTR_NET, "%p %s callout_stop", tp, __func__);
235 callout_stop(&tt->tt_timer);
243 tcp_timer_active(struct tcpcb *tp, int timer_type)
246 switch (timer_type) {
248 CTR3(KTR_NET, "%p %s TT_DELACK %i",
249 tp, __func__, tp->t_timers->tt_delack);
250 return (tp->t_timers->tt_delack ? 1 : 0);
253 CTR3(KTR_NET, "%p %s TT_REXMT %i",
254 tp, __func__, tp->t_timers->tt_rexmt);
255 return (tp->t_timers->tt_rexmt ? 1 : 0);
258 CTR3(KTR_NET, "%p %s TT_PERSIST %i",
259 tp, __func__, tp->t_timers->tt_persist);
260 return (tp->t_timers->tt_persist ? 1 : 0);
263 CTR3(KTR_NET, "%p %s TT_KEEP %i",
264 tp, __func__, tp->t_timers->tt_keep);
265 return (tp->t_timers->tt_keep ? 1 : 0);
268 CTR3(KTR_NET, "%p %s TT_2MSL %i",
269 tp, __func__, tp->t_timers->tt_2msl);
270 return (tp->t_timers->tt_2msl ? 1 : 0);
277 tcp_timer(void *xinp)
279 struct inpcb *inp = (struct inpcb *)xinp;
280 struct tcpcb *tp = intotcpcb(inp);
281 struct tcp_timer *tt;
285 /* INP lock was obtained by callout. */
286 INP_LOCK_ASSERT(inp);
289 * We've got a couple of race conditions here:
290 * - The tcpcb was converted into a compressed TW pcb. All our
291 * timers have been stopped while this callout already tried
292 * to obtain the inpcb lock. TW pcbs have their own timers
293 * and we just return.
295 if (inp->inp_vflag & INP_TIMEWAIT)
298 * - The tcpcb was discarded. All our timers have been stopped
299 * while this callout already tried to obtain the inpcb lock
300 * and we just return.
305 tt = tp->t_timers; /* Initialize. */
306 CTR6(KTR_NET, "%p %s inp %p active %x tick %i nextc %i",
307 tp, __func__, inp, tt->tt_active, tick, tt->tt_nextc);
310 * - We may have been waiting on the lock while the tcpcb has
311 * been scheduled for destruction. In this case no active
312 * timers remain and we just return.
314 if (tt->tt_active == 0)
318 * - The timer was rescheduled while this callout was already
319 * waiting on the lock. This may happen when a packet just
320 * came in. Rescan and reschedule the the timer in case we
321 * just turned it off.
323 if (tick < tt->tt_nextc)
327 * Mark as done. The active bit in struct callout is not
328 * automatically cleared. See callout(9) for more info.
329 * In tcp_discardcb() we depend on the correctly cleared
330 * active bit for faster processing.
332 callout_deactivate(&tt->tt_timer);
334 /* Check which timer has fired and remove this timer activation. */
335 timer = tt->tt_active;
341 CTR2(KTR_NET, "%p %s running TT_DELACK", tp, __func__);
343 down = tcp_timer_delack(tp, inp); /* down == 0 */
346 CTR2(KTR_NET, "%p %s running TT_REXMT", tp, __func__);
348 down = tcp_timer_rexmt(tp, inp);
351 CTR2(KTR_NET, "%p %s running TT_PERSIST", tp, __func__);
353 down = tcp_timer_persist(tp, inp);
356 CTR2(KTR_NET, "%p %s running TT_KEEP", tp, __func__);
358 down = tcp_timer_keep(tp, inp);
361 CTR2(KTR_NET, "%p %s running TT_2MSL", tp, __func__);
363 down = tcp_timer_2msl(tp, inp);
366 CTR2(KTR_NET, "%p %s running nothing", tp, __func__);
370 CTR4(KTR_NET, "%p %s down %i active %x",
371 tp, __func__, down, tt->tt_active);
372 /* Do we still exist? */
377 /* Rescan if no timer was reactivated above. */
378 if (tt->tt_active == 0)
379 tcp_timer_activate(tp, 0, 0);
382 INP_UNLOCK(inp); /* CALLOUT_RETURNUNLOCKED */
386 INP_UNLOCK(inp); /* Prevent LOR at expense of race. */
387 INP_INFO_WLOCK(&tcbinfo);
390 /* When tp is gone we've lost the race. */
391 if (inp->inp_ppcb == NULL) {
392 CTR3(KTR_NET, "%p %s inp %p lost shutdown race",
395 INP_UNLOCK(inp); /* CALLOUT_RETURNUNLOCKED */
396 INP_INFO_WUNLOCK(&tcbinfo);
399 KASSERT(tp == inp->inp_ppcb, ("%s: tp changed", __func__));
401 /* Shutdown the connection. */
408 tp->t_softerror ? tp->t_softerror : ETIMEDOUT);
411 CTR3(KTR_NET, "%p %s inp %p after shutdown", tp, __func__, inp);
414 INP_UNLOCK(inp); /* CALLOUT_RETURNUNLOCKED */
416 INP_INFO_WUNLOCK(&tcbinfo);
422 * TCP timer processing.
425 tcp_timer_delack(struct tcpcb *tp, struct inpcb *inp)
428 tp->t_flags |= TF_ACKNOW;
429 tcpstat.tcps_delack++;
430 (void) tcp_output(tp);
435 tcp_timer_2msl(struct tcpcb *tp, struct inpcb *inp)
440 ostate = tp->t_state;
443 * 2 MSL timeout in shutdown went off. If we're closed but
444 * still waiting for peer to close and connection has been idle
445 * too long, or if 2MSL time is up from TIME_WAIT, delete connection
446 * control block. Otherwise, check again in a bit.
448 * If fastrecycle of FIN_WAIT_2, in FIN_WAIT_2 and receiver has closed,
449 * there's no point in hanging onto FIN_WAIT_2 socket. Just close it.
450 * Ignore fact that there were recent incoming segments.
452 if (tcp_fast_finwait2_recycle && tp->t_state == TCPS_FIN_WAIT_2 &&
453 tp->t_inpcb->inp_socket &&
454 (tp->t_inpcb->inp_socket->so_rcv.sb_state & SBS_CANTRCVMORE)) {
455 tcpstat.tcps_finwait2_drops++;
456 return (1); /* tcp_close */
458 if (tp->t_state != TCPS_TIME_WAIT &&
459 (ticks - tp->t_rcvtime) <= tcp_maxidle)
460 tcp_timer_activate(tp, TT_2MSL, tcp_keepintvl);
462 return (1); /* tcp_close */
466 if (tp != NULL && (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
467 tcp_trace(TA_USER, ostate, tp, (void *)0, (struct tcphdr *)0,
474 * The timed wait queue contains references to each of the TCP sessions
475 * currently in the TIME_WAIT state. The queue pointers, including the
476 * queue pointers in each tcptw structure, are protected using the global
477 * tcbinfo lock, which must be held over queue iteration and modification.
479 static TAILQ_HEAD(, tcptw) twq_2msl;
485 TAILQ_INIT(&twq_2msl);
489 tcp_timer_2msl_reset(struct tcptw *tw, int rearm)
492 INP_INFO_WLOCK_ASSERT(&tcbinfo);
493 INP_LOCK_ASSERT(tw->tw_inpcb);
495 TAILQ_REMOVE(&twq_2msl, tw, tw_2msl);
496 tw->tw_time = ticks + 2 * tcp_msl;
497 TAILQ_INSERT_TAIL(&twq_2msl, tw, tw_2msl);
501 tcp_timer_2msl_stop(struct tcptw *tw)
504 INP_INFO_WLOCK_ASSERT(&tcbinfo);
505 TAILQ_REMOVE(&twq_2msl, tw, tw_2msl);
509 tcp_timer_2msl_tw(int reuse)
513 INP_INFO_WLOCK_ASSERT(&tcbinfo);
515 tw = TAILQ_FIRST(&twq_2msl);
516 if (tw == NULL || (!reuse && tw->tw_time > ticks))
518 INP_LOCK(tw->tw_inpcb);
519 tcp_twclose(tw, reuse);
527 tcp_timer_keep(struct tcpcb *tp, struct inpcb *inp)
529 struct tcptemp *t_template;
533 ostate = tp->t_state;
536 * Keep-alive timer went off; send something
537 * or drop connection if idle for too long.
539 tcpstat.tcps_keeptimeo++;
540 if (tp->t_state < TCPS_ESTABLISHED)
542 if ((always_keepalive || inp->inp_socket->so_options & SO_KEEPALIVE) &&
543 tp->t_state <= TCPS_CLOSING) {
544 if ((ticks - tp->t_rcvtime) >= tcp_keepidle + tcp_maxidle)
547 * Send a packet designed to force a response
548 * if the peer is up and reachable:
549 * either an ACK if the connection is still alive,
550 * or an RST if the peer has closed the connection
551 * due to timeout or reboot.
552 * Using sequence number tp->snd_una-1
553 * causes the transmitted zero-length segment
554 * to lie outside the receive window;
555 * by the protocol spec, this requires the
556 * correspondent TCP to respond.
558 tcpstat.tcps_keepprobe++;
559 t_template = tcpip_maketemplate(inp);
561 tcp_respond(tp, t_template->tt_ipgen,
562 &t_template->tt_t, (struct mbuf *)NULL,
563 tp->rcv_nxt, tp->snd_una - 1, 0);
564 (void) m_free(dtom(t_template));
566 tcp_timer_activate(tp, TT_KEEP, tcp_keepintvl);
568 tcp_timer_activate(tp, TT_KEEP, tcp_keepidle);
571 if (inp->inp_socket->so_options & SO_DEBUG)
572 tcp_trace(TA_USER, ostate, tp, (void *)0, (struct tcphdr *)0,
578 tcpstat.tcps_keepdrops++;
579 return (2); /* tcp_drop() */
583 tcp_timer_persist(struct tcpcb *tp, struct inpcb *inp)
588 ostate = tp->t_state;
591 * Persistance timer into zero window.
592 * Force a byte to be output, if possible.
594 tcpstat.tcps_persisttimeo++;
596 * Hack: if the peer is dead/unreachable, we do not
597 * time out if the window is closed. After a full
598 * backoff, drop the connection if the idle time
599 * (no responses to probes) reaches the maximum
600 * backoff that we would use if retransmitting.
602 if (tp->t_rxtshift == TCP_MAXRXTSHIFT &&
603 ((ticks - tp->t_rcvtime) >= tcp_maxpersistidle ||
604 (ticks - tp->t_rcvtime) >= TCP_REXMTVAL(tp) * tcp_totbackoff)) {
605 tcpstat.tcps_persistdrop++;
606 return (2); /* tcp_drop() */
609 tp->t_flags |= TF_FORCEDATA;
610 (void) tcp_output(tp);
611 tp->t_flags &= ~TF_FORCEDATA;
614 if (tp != NULL && tp->t_inpcb->inp_socket->so_options & SO_DEBUG)
615 tcp_trace(TA_USER, ostate, tp, NULL, NULL, PRU_SLOWTIMO);
621 tcp_timer_rexmt(struct tcpcb *tp, struct inpcb *inp)
627 ostate = tp->t_state;
629 tcp_free_sackholes(tp);
631 * Retransmission timer went off. Message has not
632 * been acked within retransmit interval. Back off
633 * to a longer retransmit interval and retransmit one segment.
635 if (++tp->t_rxtshift > TCP_MAXRXTSHIFT) {
636 tp->t_rxtshift = TCP_MAXRXTSHIFT;
637 tcpstat.tcps_timeoutdrop++;
638 return (2); /* tcp_drop() */
640 if (tp->t_rxtshift == 1) {
642 * first retransmit; record ssthresh and cwnd so they can
643 * be recovered if this turns out to be a "bad" retransmit.
644 * A retransmit is considered "bad" if an ACK for this
645 * segment is received within RTT/2 interval; the assumption
646 * here is that the ACK was already in flight. See
647 * "On Estimating End-to-End Network Path Properties" by
648 * Allman and Paxson for more details.
650 tp->snd_cwnd_prev = tp->snd_cwnd;
651 tp->snd_ssthresh_prev = tp->snd_ssthresh;
652 tp->snd_recover_prev = tp->snd_recover;
653 if (IN_FASTRECOVERY(tp))
654 tp->t_flags |= TF_WASFRECOVERY;
656 tp->t_flags &= ~TF_WASFRECOVERY;
657 tp->t_badrxtwin = ticks + (tp->t_srtt >> (TCP_RTT_SHIFT + 1));
659 tcpstat.tcps_rexmttimeo++;
660 if (tp->t_state == TCPS_SYN_SENT)
661 rexmt = TCP_REXMTVAL(tp) * tcp_syn_backoff[tp->t_rxtshift];
663 rexmt = TCP_REXMTVAL(tp) * tcp_backoff[tp->t_rxtshift];
664 TCPT_RANGESET(tp->t_rxtcur, rexmt,
665 tp->t_rttmin, TCPTV_REXMTMAX);
667 * Disable rfc1323 if we havn't got any response to
668 * our third SYN to work-around some broken terminal servers
669 * (most of which have hopefully been retired) that have bad VJ
670 * header compression code which trashes TCP segments containing
671 * unknown-to-them TCP options.
673 if ((tp->t_state == TCPS_SYN_SENT) && (tp->t_rxtshift == 3))
674 tp->t_flags &= ~(TF_REQ_SCALE|TF_REQ_TSTMP);
676 * If we backed off this far, our srtt estimate is probably bogus.
677 * Clobber it so we'll take the next rtt measurement as our srtt;
678 * move the current srtt into rttvar to keep the current
679 * retransmit times until then.
681 if (tp->t_rxtshift > TCP_MAXRXTSHIFT / 4) {
683 if ((tp->t_inpcb->inp_vflag & INP_IPV6) != 0)
684 in6_losing(tp->t_inpcb);
687 tp->t_rttvar += (tp->t_srtt >> TCP_RTT_SHIFT);
690 tp->snd_nxt = tp->snd_una;
691 tp->snd_recover = tp->snd_max;
693 * Force a segment to be sent.
695 tp->t_flags |= TF_ACKNOW;
697 * If timing a segment in this window, stop the timer.
701 * Close the congestion window down to one segment
702 * (we'll open it by one segment for each ack we get).
703 * Since we probably have a window's worth of unacked
704 * data accumulated, this "slow start" keeps us from
705 * dumping all that data as back-to-back packets (which
706 * might overwhelm an intermediate gateway).
708 * There are two phases to the opening: Initially we
709 * open by one mss on each ack. This makes the window
710 * size increase exponentially with time. If the
711 * window is larger than the path can handle, this
712 * exponential growth results in dropped packet(s)
713 * almost immediately. To get more time between
714 * drops but still "push" the network to take advantage
715 * of improving conditions, we switch from exponential
716 * to linear window opening at some threshhold size.
717 * For a threshhold, we use half the current window
718 * size, truncated to a multiple of the mss.
720 * (the minimum cwnd that will give us exponential
721 * growth is 2 mss. We don't allow the threshhold
725 u_int win = min(tp->snd_wnd, tp->snd_cwnd) / 2 / tp->t_maxseg;
728 tp->snd_cwnd = tp->t_maxseg;
729 tp->snd_ssthresh = win * tp->t_maxseg;
732 EXIT_FASTRECOVERY(tp);
733 (void) tcp_output(tp);
736 if (tp != NULL && (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
737 tcp_trace(TA_USER, ostate, tp, (void *)0, (struct tcphdr *)0,