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tcp_timer.c revision 1.63
      1 /*	$NetBSD: tcp_timer.c,v 1.63 2003/07/20 16:35:09 he Exp $	*/
      2 
      3 /*
      4  * Copyright (C) 1995, 1996, 1997, and 1998 WIDE Project.
      5  * All rights reserved.
      6  *
      7  * Redistribution and use in source and binary forms, with or without
      8  * modification, are permitted provided that the following conditions
      9  * are met:
     10  * 1. Redistributions of source code must retain the above copyright
     11  *    notice, this list of conditions and the following disclaimer.
     12  * 2. Redistributions in binary form must reproduce the above copyright
     13  *    notice, this list of conditions and the following disclaimer in the
     14  *    documentation and/or other materials provided with the distribution.
     15  * 3. Neither the name of the project nor the names of its contributors
     16  *    may be used to endorse or promote products derived from this software
     17  *    without specific prior written permission.
     18  *
     19  * THIS SOFTWARE IS PROVIDED BY THE PROJECT AND CONTRIBUTORS ``AS IS'' AND
     20  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     21  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     22  * ARE DISCLAIMED.  IN NO EVENT SHALL THE PROJECT OR CONTRIBUTORS BE LIABLE
     23  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     24  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     25  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     26  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     27  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     28  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     29  * SUCH DAMAGE.
     30  */
     31 
     32 /*-
     33  * Copyright (c) 1997, 1998, 2001 The NetBSD Foundation, Inc.
     34  * All rights reserved.
     35  *
     36  * This code is derived from software contributed to The NetBSD Foundation
     37  * by Jason R. Thorpe and Kevin M. Lahey of the Numerical Aerospace Simulation
     38  * Facility, NASA Ames Research Center.
     39  *
     40  * Redistribution and use in source and binary forms, with or without
     41  * modification, are permitted provided that the following conditions
     42  * are met:
     43  * 1. Redistributions of source code must retain the above copyright
     44  *    notice, this list of conditions and the following disclaimer.
     45  * 2. Redistributions in binary form must reproduce the above copyright
     46  *    notice, this list of conditions and the following disclaimer in the
     47  *    documentation and/or other materials provided with the distribution.
     48  * 3. All advertising materials mentioning features or use of this software
     49  *    must display the following acknowledgement:
     50  *	This product includes software developed by the NetBSD
     51  *	Foundation, Inc. and its contributors.
     52  * 4. Neither the name of The NetBSD Foundation nor the names of its
     53  *    contributors may be used to endorse or promote products derived
     54  *    from this software without specific prior written permission.
     55  *
     56  * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
     57  * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
     58  * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
     59  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
     60  * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
     61  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
     62  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
     63  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
     64  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
     65  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
     66  * POSSIBILITY OF SUCH DAMAGE.
     67  */
     68 
     69 /*
     70  * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1995
     71  *	The Regents of the University of California.  All rights reserved.
     72  *
     73  * Redistribution and use in source and binary forms, with or without
     74  * modification, are permitted provided that the following conditions
     75  * are met:
     76  * 1. Redistributions of source code must retain the above copyright
     77  *    notice, this list of conditions and the following disclaimer.
     78  * 2. Redistributions in binary form must reproduce the above copyright
     79  *    notice, this list of conditions and the following disclaimer in the
     80  *    documentation and/or other materials provided with the distribution.
     81  * 3. All advertising materials mentioning features or use of this software
     82  *    must display the following acknowledgement:
     83  *	This product includes software developed by the University of
     84  *	California, Berkeley and its contributors.
     85  * 4. Neither the name of the University nor the names of its contributors
     86  *    may be used to endorse or promote products derived from this software
     87  *    without specific prior written permission.
     88  *
     89  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
     90  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     91  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     92  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
     93  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     94  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     95  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     96  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     97  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     98  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     99  * SUCH DAMAGE.
    100  *
    101  *	@(#)tcp_timer.c	8.2 (Berkeley) 5/24/95
    102  */
    103 
    104 #include <sys/cdefs.h>
    105 __KERNEL_RCSID(0, "$NetBSD: tcp_timer.c,v 1.63 2003/07/20 16:35:09 he Exp $");
    106 
    107 #include "opt_inet.h"
    108 #include "opt_tcp_debug.h"
    109 
    110 #include <sys/param.h>
    111 #include <sys/systm.h>
    112 #include <sys/malloc.h>
    113 #include <sys/mbuf.h>
    114 #include <sys/socket.h>
    115 #include <sys/socketvar.h>
    116 #include <sys/protosw.h>
    117 #include <sys/errno.h>
    118 #include <sys/kernel.h>
    119 
    120 #include <net/if.h>
    121 #include <net/route.h>
    122 
    123 #include <netinet/in.h>
    124 #include <netinet/in_systm.h>
    125 #include <netinet/ip.h>
    126 #include <netinet/in_pcb.h>
    127 #include <netinet/ip_var.h>
    128 
    129 #ifdef INET6
    130 #ifndef INET
    131 #include <netinet/in.h>
    132 #endif
    133 #include <netinet/ip6.h>
    134 #include <netinet6/in6_pcb.h>
    135 #endif
    136 
    137 #include <netinet/tcp.h>
    138 #include <netinet/tcp_fsm.h>
    139 #include <netinet/tcp_seq.h>
    140 #include <netinet/tcp_timer.h>
    141 #include <netinet/tcp_var.h>
    142 #include <netinet/tcpip.h>
    143 #ifdef TCP_DEBUG
    144 #include <netinet/tcp_debug.h>
    145 #endif
    146 
    147 /*
    148  * Various tunable timer parameters.  These are initialized in tcp_init(),
    149  * unless they are patched.
    150  */
    151 int	tcp_keepidle = 0;
    152 int	tcp_keepintvl = 0;
    153 int	tcp_keepcnt = 0;		/* max idle probes */
    154 int	tcp_maxpersistidle = 0;		/* max idle time in persist */
    155 int	tcp_maxidle;			/* computed in tcp_slowtimo() */
    156 
    157 /*
    158  * Time to delay the ACK.  This is initialized in tcp_init(), unless
    159  * its patched.
    160  */
    161 int	tcp_delack_ticks = 0;
    162 
    163 void	tcp_timer_rexmt(void *);
    164 void	tcp_timer_persist(void *);
    165 void	tcp_timer_keep(void *);
    166 void	tcp_timer_2msl(void *);
    167 
    168 const tcp_timer_func_t tcp_timer_funcs[TCPT_NTIMERS] = {
    169 	tcp_timer_rexmt,
    170 	tcp_timer_persist,
    171 	tcp_timer_keep,
    172 	tcp_timer_2msl,
    173 };
    174 
    175 /*
    176  * Timer state initialization, called from tcp_init().
    177  */
    178 void
    179 tcp_timer_init(void)
    180 {
    181 
    182 	if (tcp_keepidle == 0)
    183 		tcp_keepidle = TCPTV_KEEP_IDLE;
    184 
    185 	if (tcp_keepintvl == 0)
    186 		tcp_keepintvl = TCPTV_KEEPINTVL;
    187 
    188 	if (tcp_keepcnt == 0)
    189 		tcp_keepcnt = TCPTV_KEEPCNT;
    190 
    191 	if (tcp_maxpersistidle == 0)
    192 		tcp_maxpersistidle = TCPTV_KEEP_IDLE;
    193 
    194 	if (tcp_delack_ticks == 0)
    195 		tcp_delack_ticks = TCP_DELACK_TICKS;
    196 }
    197 
    198 /*
    199  * Return how many timers are currently being invoked.
    200  */
    201 int
    202 tcp_timers_invoking(struct tcpcb *tp)
    203 {
    204 	int i;
    205 	int count = 0;
    206 
    207 	for (i = 0; i < TCPT_NTIMERS; i++)
    208 		if (callout_invoking(&tp->t_timer[i]))
    209 			count++;
    210 	if (callout_invoking(&tp->t_delack_ch))
    211 		count++;
    212 
    213 	return count;
    214 }
    215 
    216 /*
    217  * Callout to process delayed ACKs for a TCPCB.
    218  */
    219 void
    220 tcp_delack(void *arg)
    221 {
    222 	struct tcpcb *tp = arg;
    223 	int s;
    224 
    225 	/*
    226 	 * If tcp_output() wasn't able to transmit the ACK
    227 	 * for whatever reason, it will restart the delayed
    228 	 * ACK callout.
    229 	 */
    230 
    231 	s = splsoftnet();
    232 	callout_ack(&tp->t_delack_ch);
    233 	if (tcp_isdead(tp)) {
    234 		splx(s);
    235 		return;
    236 	}
    237 
    238 	tp->t_flags |= TF_ACKNOW;
    239 	(void) tcp_output(tp);
    240 	splx(s);
    241 }
    242 
    243 /*
    244  * Tcp protocol timeout routine called every 500 ms.
    245  * Updates the timers in all active tcb's and
    246  * causes finite state machine actions if timers expire.
    247  */
    248 void
    249 tcp_slowtimo()
    250 {
    251 	int s;
    252 
    253 	s = splsoftnet();
    254 	tcp_maxidle = tcp_keepcnt * tcp_keepintvl;
    255 	tcp_iss_seq += TCP_ISSINCR;			/* increment iss */
    256 	tcp_now++;					/* for timestamps */
    257 	splx(s);
    258 }
    259 
    260 /*
    261  * Cancel all timers for TCP tp.
    262  */
    263 void
    264 tcp_canceltimers(tp)
    265 	struct tcpcb *tp;
    266 {
    267 	int i;
    268 
    269 	for (i = 0; i < TCPT_NTIMERS; i++)
    270 		TCP_TIMER_DISARM(tp, i);
    271 }
    272 
    273 const int	tcp_backoff[TCP_MAXRXTSHIFT + 1] =
    274     { 1, 2, 4, 8, 16, 32, 64, 64, 64, 64, 64, 64, 64 };
    275 
    276 const int	tcp_totbackoff = 511;	/* sum of tcp_backoff[] */
    277 
    278 /*
    279  * TCP timer processing.
    280  */
    281 
    282 void
    283 tcp_timer_rexmt(void *arg)
    284 {
    285 	struct tcpcb *tp = arg;
    286 	uint32_t rto;
    287 	int s;
    288 #ifdef TCP_DEBUG
    289 	struct socket *so;
    290 	short ostate;
    291 #endif
    292 
    293 	s = splsoftnet();
    294 	callout_ack(&tp->t_timer[TCPT_KEEP]);
    295 	if (tcp_isdead(tp)) {
    296 		splx(s);
    297 		return;
    298 	}
    299 
    300 #ifdef TCP_DEBUG
    301 #ifdef INET
    302 	if (tp->t_inpcb)
    303 		so = tp->t_inpcb->inp_socket;
    304 #endif
    305 #ifdef INET6
    306 	if (tp->t_in6pcb)
    307 		so = tp->t_in6pcb->in6p_socket;
    308 #endif
    309 	ostate = tp->t_state;
    310 #endif /* TCP_DEBUG */
    311 
    312 	/*
    313 	 * Retransmission timer went off.  Message has not
    314 	 * been acked within retransmit interval.  Back off
    315 	 * to a longer retransmit interval and retransmit one segment.
    316 	 */
    317 
    318 	if (++tp->t_rxtshift > TCP_MAXRXTSHIFT) {
    319 		tp->t_rxtshift = TCP_MAXRXTSHIFT;
    320 		tcpstat.tcps_timeoutdrop++;
    321 		tp = tcp_drop(tp, tp->t_softerror ?
    322 		    tp->t_softerror : ETIMEDOUT);
    323 		goto out;
    324 	}
    325 	tcpstat.tcps_rexmttimeo++;
    326 	rto = TCP_REXMTVAL(tp);
    327 	if (rto < tp->t_rttmin)
    328 		rto = tp->t_rttmin;
    329 	TCPT_RANGESET(tp->t_rxtcur, rto * tcp_backoff[tp->t_rxtshift],
    330 	    tp->t_rttmin, TCPTV_REXMTMAX);
    331 	TCP_TIMER_ARM(tp, TCPT_REXMT, tp->t_rxtcur);
    332 
    333 	/*
    334 	 * If we are losing and we are trying path MTU discovery,
    335 	 * try turning it off.  This will avoid black holes in
    336 	 * the network which suppress or fail to send "packet
    337 	 * too big" ICMP messages.  We should ideally do
    338 	 * lots more sophisticated searching to find the right
    339 	 * value here...
    340 	 */
    341 	if (tp->t_mtudisc && tp->t_rxtshift > TCP_MAXRXTSHIFT / 6) {
    342 		tcpstat.tcps_pmtublackhole++;
    343 
    344 #ifdef INET
    345 		/* try turning PMTUD off */
    346 		if (tp->t_inpcb)
    347 			tp->t_mtudisc = 0;
    348 #endif
    349 #ifdef INET6
    350 		/* try using IPv6 minimum MTU */
    351 		if (tp->t_in6pcb)
    352 			tp->t_mtudisc = 0;
    353 #endif
    354 
    355 		/* XXX: more sophisticated Black hole recovery code? */
    356 	}
    357 
    358 	/*
    359 	 * If losing, let the lower level know and try for
    360 	 * a better route.  Also, if we backed off this far,
    361 	 * our srtt estimate is probably bogus.  Clobber it
    362 	 * so we'll take the next rtt measurement as our srtt;
    363 	 * move the current srtt into rttvar to keep the current
    364 	 * retransmit times until then.
    365 	 */
    366 	if (tp->t_rxtshift > TCP_MAXRXTSHIFT / 4) {
    367 #ifdef INET
    368 		if (tp->t_inpcb)
    369 			in_losing(tp->t_inpcb);
    370 #endif
    371 #ifdef INET6
    372 		if (tp->t_in6pcb)
    373 			in6_losing(tp->t_in6pcb);
    374 #endif
    375 		tp->t_rttvar += (tp->t_srtt >> TCP_RTT_SHIFT);
    376 		tp->t_srtt = 0;
    377 	}
    378 	tp->snd_nxt = tp->snd_una;
    379 	/*
    380 	 * If timing a segment in this window, stop the timer.
    381 	 */
    382 	tp->t_rtttime = 0;
    383 	/*
    384 	 * Remember if we are retransmitting a SYN, because if
    385 	 * we do, set the initial congestion window must be set
    386 	 * to 1 segment.
    387 	 */
    388 	if (tp->t_state == TCPS_SYN_SENT)
    389 		tp->t_flags |= TF_SYN_REXMT;
    390 	/*
    391 	 * Close the congestion window down to one segment
    392 	 * (we'll open it by one segment for each ack we get).
    393 	 * Since we probably have a window's worth of unacked
    394 	 * data accumulated, this "slow start" keeps us from
    395 	 * dumping all that data as back-to-back packets (which
    396 	 * might overwhelm an intermediate gateway).
    397 	 *
    398 	 * There are two phases to the opening: Initially we
    399 	 * open by one mss on each ack.  This makes the window
    400 	 * size increase exponentially with time.  If the
    401 	 * window is larger than the path can handle, this
    402 	 * exponential growth results in dropped packet(s)
    403 	 * almost immediately.  To get more time between
    404 	 * drops but still "push" the network to take advantage
    405 	 * of improving conditions, we switch from exponential
    406 	 * to linear window opening at some threshhold size.
    407 	 * For a threshhold, we use half the current window
    408 	 * size, truncated to a multiple of the mss.
    409 	 *
    410 	 * (the minimum cwnd that will give us exponential
    411 	 * growth is 2 mss.  We don't allow the threshhold
    412 	 * to go below this.)
    413 	 */
    414 	{
    415 	u_int win = min(tp->snd_wnd, tp->snd_cwnd) / 2 / tp->t_segsz;
    416 	if (win < 2)
    417 		win = 2;
    418 	/* Loss Window MUST be one segment. */
    419 	tp->snd_cwnd = tp->t_segsz;
    420 	tp->snd_ssthresh = win * tp->t_segsz;
    421 	tp->t_dupacks = 0;
    422 	}
    423 	(void) tcp_output(tp);
    424 
    425  out:
    426 #ifdef TCP_DEBUG
    427 	if (tp && so->so_options & SO_DEBUG)
    428 		tcp_trace(TA_USER, ostate, tp, NULL,
    429 		    PRU_SLOWTIMO | (TCPT_REXMT << 8));
    430 #endif
    431 	splx(s);
    432 }
    433 
    434 void
    435 tcp_timer_persist(void *arg)
    436 {
    437 	struct tcpcb *tp = arg;
    438 	uint32_t rto;
    439 	int s;
    440 #ifdef TCP_DEBUG
    441 	struct socket *so;
    442 	short ostate;
    443 #endif
    444 
    445 	s = splsoftnet();
    446 	callout_ack(&tp->t_timer[TCPT_PERSIST]);
    447 	if (tcp_isdead(tp)) {
    448 		splx(s);
    449 		return;
    450 	}
    451 
    452 #ifdef TCP_DEBUG
    453 #ifdef INET
    454 	if (tp->t_inpcb)
    455 		so = tp->t_inpcb->inp_socket;
    456 #endif
    457 #ifdef INET6
    458 	if (tp->t_in6pcb)
    459 		so = tp->t_in6pcb->in6p_socket;
    460 #endif
    461 
    462 	ostate = tp->t_state;
    463 #endif /* TCP_DEBUG */
    464 
    465 	/*
    466 	 * Persistance timer into zero window.
    467 	 * Force a byte to be output, if possible.
    468 	 */
    469 
    470 	/*
    471 	 * Hack: if the peer is dead/unreachable, we do not
    472 	 * time out if the window is closed.  After a full
    473 	 * backoff, drop the connection if the idle time
    474 	 * (no responses to probes) reaches the maximum
    475 	 * backoff that we would use if retransmitting.
    476 	 */
    477 	rto = TCP_REXMTVAL(tp);
    478 	if (rto < tp->t_rttmin)
    479 		rto = tp->t_rttmin;
    480 	if (tp->t_rxtshift == TCP_MAXRXTSHIFT &&
    481 	    ((tcp_now - tp->t_rcvtime) >= tcp_maxpersistidle ||
    482 	    (tcp_now - tp->t_rcvtime) >= rto * tcp_totbackoff)) {
    483 		tcpstat.tcps_persistdrops++;
    484 		tp = tcp_drop(tp, ETIMEDOUT);
    485 		goto out;
    486 	}
    487 	tcpstat.tcps_persisttimeo++;
    488 	tcp_setpersist(tp);
    489 	tp->t_force = 1;
    490 	(void) tcp_output(tp);
    491 	tp->t_force = 0;
    492 
    493  out:
    494 #ifdef TCP_DEBUG
    495 	if (tp && so->so_options & SO_DEBUG)
    496 		tcp_trace(TA_USER, ostate, tp, NULL,
    497 		    PRU_SLOWTIMO | (TCPT_PERSIST << 8));
    498 #endif
    499 	splx(s);
    500 }
    501 
    502 void
    503 tcp_timer_keep(void *arg)
    504 {
    505 	struct tcpcb *tp = arg;
    506 	struct socket *so = NULL;	/* Quell compiler warning */
    507 	int s;
    508 #ifdef TCP_DEBUG
    509 	short ostate;
    510 #endif
    511 
    512 	s = splsoftnet();
    513 	callout_ack(&tp->t_timer[TCPT_KEEP]);
    514 	if (tcp_isdead(tp)) {
    515 		splx(s);
    516 		return;
    517 	}
    518 
    519 #ifdef TCP_DEBUG
    520 	ostate = tp->t_state;
    521 #endif /* TCP_DEBUG */
    522 
    523 	/*
    524 	 * Keep-alive timer went off; send something
    525 	 * or drop connection if idle for too long.
    526 	 */
    527 
    528 	tcpstat.tcps_keeptimeo++;
    529 	if (TCPS_HAVEESTABLISHED(tp->t_state) == 0)
    530 		goto dropit;
    531 #ifdef INET
    532 	if (tp->t_inpcb)
    533 		so = tp->t_inpcb->inp_socket;
    534 #endif
    535 #ifdef INET6
    536 	if (tp->t_in6pcb)
    537 		so = tp->t_in6pcb->in6p_socket;
    538 #endif
    539 	if (so->so_options & SO_KEEPALIVE &&
    540 	    tp->t_state <= TCPS_CLOSE_WAIT) {
    541 	    	if ((tcp_maxidle > 0) &&
    542 		    ((tcp_now - tp->t_rcvtime) >=
    543 		     tcp_keepidle + tcp_maxidle))
    544 			goto dropit;
    545 		/*
    546 		 * Send a packet designed to force a response
    547 		 * if the peer is up and reachable:
    548 		 * either an ACK if the connection is still alive,
    549 		 * or an RST if the peer has closed the connection
    550 		 * due to timeout or reboot.
    551 		 * Using sequence number tp->snd_una-1
    552 		 * causes the transmitted zero-length segment
    553 		 * to lie outside the receive window;
    554 		 * by the protocol spec, this requires the
    555 		 * correspondent TCP to respond.
    556 		 */
    557 		tcpstat.tcps_keepprobe++;
    558 		if (tcp_compat_42) {
    559 			/*
    560 			 * The keepalive packet must have nonzero
    561 			 * length to get a 4.2 host to respond.
    562 			 */
    563 			(void)tcp_respond(tp, tp->t_template,
    564 			    (struct mbuf *)NULL, NULL, tp->rcv_nxt - 1,
    565 			    tp->snd_una - 1, 0);
    566 		} else {
    567 			(void)tcp_respond(tp, tp->t_template,
    568 			    (struct mbuf *)NULL, NULL, tp->rcv_nxt,
    569 			    tp->snd_una - 1, 0);
    570 		}
    571 		TCP_TIMER_ARM(tp, TCPT_KEEP, tcp_keepintvl);
    572 	} else
    573 		TCP_TIMER_ARM(tp, TCPT_KEEP, tcp_keepidle);
    574 
    575 #ifdef TCP_DEBUG
    576 	if (tp && so->so_options & SO_DEBUG)
    577 		tcp_trace(TA_USER, ostate, tp, NULL,
    578 		    PRU_SLOWTIMO | (TCPT_KEEP << 8));
    579 #endif
    580 	splx(s);
    581 	return;
    582 
    583  dropit:
    584 	tcpstat.tcps_keepdrops++;
    585 	(void) tcp_drop(tp, ETIMEDOUT);
    586 	splx(s);
    587 }
    588 
    589 void
    590 tcp_timer_2msl(void *arg)
    591 {
    592 	struct tcpcb *tp = arg;
    593 	int s;
    594 #ifdef TCP_DEBUG
    595 	struct socket *so;
    596 	short ostate;
    597 #endif
    598 
    599 	s = splsoftnet();
    600 	callout_ack(&tp->t_timer[TCPT_2MSL]);
    601 	if (tcp_isdead(tp)) {
    602 		splx(s);
    603 		return;
    604 	}
    605 
    606 #ifdef TCP_DEBUG
    607 #ifdef INET
    608 	if (tp->t_inpcb)
    609 		so = tp->t_inpcb->inp_socket;
    610 #endif
    611 #ifdef INET6
    612 	if (tp->t_in6pcb)
    613 		so = tp->t_in6pcb->in6p_socket;
    614 #endif
    615 
    616 	ostate = tp->t_state;
    617 #endif /* TCP_DEBUG */
    618 
    619 	/*
    620 	 * 2 MSL timeout in shutdown went off.  If we're closed but
    621 	 * still waiting for peer to close and connection has been idle
    622 	 * too long, or if 2MSL time is up from TIME_WAIT, delete connection
    623 	 * control block.  Otherwise, check again in a bit.
    624 	 */
    625 	if (tp->t_state != TCPS_TIME_WAIT &&
    626 	    ((tcp_maxidle == 0) || ((tcp_now - tp->t_rcvtime) <= tcp_maxidle)))
    627 		TCP_TIMER_ARM(tp, TCPT_2MSL, tcp_keepintvl);
    628 	else
    629 		tp = tcp_close(tp);
    630 
    631 #ifdef TCP_DEBUG
    632 	if (tp && so->so_options & SO_DEBUG)
    633 		tcp_trace(TA_USER, ostate, tp, NULL,
    634 		    PRU_SLOWTIMO | (TCPT_2MSL << 8));
    635 #endif
    636 	splx(s);
    637 }
    638