xref: /src/sys/netinet/tcp_timer.c

/*	$NetBSD: tcp_timer.c,v 1.96 2021/03/08 17:54:43 christos Exp $	*/

/*
 * Copyright (C) 1995, 1996, 1997, and 1998 WIDE Project.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the project nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE PROJECT AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE PROJECT OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

/*-
 * Copyright (c) 1997, 1998, 2001, 2005 The NetBSD Foundation, Inc.
 * All rights reserved.
 *
 * This code is derived from software contributed to The NetBSD Foundation
 * by Jason R. Thorpe and Kevin M. Lahey of the Numerical Aerospace Simulation
 * Facility, NASA Ames Research Center.
 * This code is derived from software contributed to The NetBSD Foundation
 * by Charles M. Hannum.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */

/*
 * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1995
 *	The Regents of the University of California.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *	@(#)tcp_timer.c	8.2 (Berkeley) 5/24/95
 */

#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: tcp_timer.c,v 1.96 2021/03/08 17:54:43 christos Exp $");

#ifdef _KERNEL_OPT
#include "opt_inet.h"
#include "opt_tcp_debug.h"
#include "opt_net_mpsafe.h"
#endif

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/mbuf.h>
#include <sys/socket.h>
#include <sys/socketvar.h>
#include <sys/protosw.h>
#include <sys/errno.h>
#include <sys/kernel.h>
#include <sys/callout.h>
#include <sys/workqueue.h>
#include <sys/cprng.h>

#include <net/if.h>

#include <netinet/in.h>
#include <netinet/in_systm.h>
#include <netinet/ip.h>
#include <netinet/in_pcb.h>
#include <netinet/ip_var.h>
#include <netinet/ip_icmp.h>

#ifdef INET6
#include <netinet/ip6.h>
#include <netinet6/in6_pcb.h>
#endif

#include <netinet/tcp.h>
#include <netinet/tcp_fsm.h>
#include <netinet/tcp_seq.h>
#include <netinet/tcp_timer.h>
#include <netinet/tcp_var.h>
#include <netinet/tcp_private.h>
#include <netinet/tcp_congctl.h>
#ifdef TCP_DEBUG
#include <netinet/tcp_debug.h>
#endif

/*
 * Various tunable timer parameters.  These are initialized in tcp_init(),
 * unless they are patched.
 */
u_int	tcp_keepinit = 0;
u_int	tcp_keepidle = 0;
u_int	tcp_keepintvl = 0;
u_int	tcp_keepcnt = 0;		/* max idle probes */

int	tcp_maxpersistidle = 0;		/* max idle time in persist */

static callout_t	tcp_slowtimo_ch;
#ifdef NET_MPSAFE
static struct workqueue	*tcp_slowtimo_wq;
static struct work	tcp_slowtimo_wk;
#endif

static void tcp_slowtimo_work(struct work *, void *);
static void tcp_slowtimo(void *);

/*
 * Time to delay the ACK.  This is initialized in tcp_init(), unless
 * its patched.
 */
int	tcp_delack_ticks = 0;

void	tcp_timer_rexmt(void *);
void	tcp_timer_persist(void *);
void	tcp_timer_keep(void *);
void	tcp_timer_2msl(void *);

const tcp_timer_func_t tcp_timer_funcs[TCPT_NTIMERS] = {
	tcp_timer_rexmt,
	tcp_timer_persist,
	tcp_timer_keep,
	tcp_timer_2msl,
};

/*
 * Timer state initialization, called from tcp_init().
 */
void
tcp_timer_init(void)
{

	if (tcp_keepinit == 0)
		tcp_keepinit = TCPTV_KEEP_INIT;

	if (tcp_keepidle == 0)
		tcp_keepidle = TCPTV_KEEP_IDLE;

	if (tcp_keepintvl == 0)
		tcp_keepintvl = TCPTV_KEEPINTVL;

	if (tcp_keepcnt == 0)
		tcp_keepcnt = TCPTV_KEEPCNT;

	if (tcp_maxpersistidle == 0)
		tcp_maxpersistidle = TCPTV_KEEP_IDLE;

	if (tcp_delack_ticks == 0)
		tcp_delack_ticks = TCP_DELACK_TICKS;
}

void
tcp_slowtimo_init(void)
{
#ifdef NET_MPSAFE
	int error;

	error = workqueue_create(&tcp_slowtimo_wq, "tcp_slowtimo",
	    tcp_slowtimo_work, NULL, PRI_SOFTNET, IPL_SOFTNET, WQ_MPSAFE);
	if (error != 0)
		panic("%s: workqueue_create failed (%d)\n", __func__, error);
#endif
	callout_init(&tcp_slowtimo_ch, CALLOUT_MPSAFE);
	callout_reset(&tcp_slowtimo_ch, 1, tcp_slowtimo, NULL);
}

/*
 * Callout to process delayed ACKs for a TCPCB.
 */
void
tcp_delack(void *arg)
{
	struct tcpcb *tp = arg;

	/*
	 * If tcp_output() wasn't able to transmit the ACK
	 * for whatever reason, it will restart the delayed
	 * ACK callout.
	 */

	mutex_enter(softnet_lock);
	if ((tp->t_flags & (TF_DEAD | TF_DELACK)) != TF_DELACK) {
		mutex_exit(softnet_lock);
		return;
	}
	if (!callout_expired(&tp->t_delack_ch)) {
		mutex_exit(softnet_lock);
		return;
	}

	tp->t_flags |= TF_ACKNOW;
	KERNEL_LOCK(1, NULL);
	(void) tcp_output(tp);
	KERNEL_UNLOCK_ONE(NULL);
	mutex_exit(softnet_lock);
}

/*
 * Tcp protocol timeout routine called every 500 ms.
 * Updates the timers in all active tcb's and
 * causes finite state machine actions if timers expire.
 */
static void
tcp_slowtimo_work(struct work *wk, void *arg)
{

	mutex_enter(softnet_lock);
	tcp_iss_seq += TCP_ISSINCR + (TCP_ISS_RANDOM_MASK & cprng_fast32());
	tcp_now++;					/* for timestamps */
	mutex_exit(softnet_lock);

	callout_schedule(&tcp_slowtimo_ch, hz / PR_SLOWHZ);
}

static void
tcp_slowtimo(void *arg)
{

#ifdef NET_MPSAFE
	workqueue_enqueue(tcp_slowtimo_wq, &tcp_slowtimo_wk, NULL);
#else
	tcp_slowtimo_work(NULL, NULL);
#endif
}

/*
 * Cancel all timers for TCP tp.
 */
void
tcp_canceltimers(struct tcpcb *tp)
{
	int i;

	for (i = 0; i < TCPT_NTIMERS; i++)
		TCP_TIMER_DISARM(tp, i);
}

const int	tcp_backoff[TCP_MAXRXTSHIFT + 1] =
    { 1, 2, 4, 8, 16, 32, 64, 64, 64, 64, 64, 64, 64 };

const int	tcp_totbackoff = 511;	/* sum of tcp_backoff[] */

/*
 * TCP timer processing.
 */

void
tcp_timer_rexmt(void *arg)
{
	struct tcpcb *tp = arg;
	uint32_t rto;
#ifdef TCP_DEBUG
	struct socket *so = NULL;
	short ostate;
#endif

	mutex_enter(softnet_lock);
	if ((tp->t_flags & TF_DEAD) != 0) {
		mutex_exit(softnet_lock);
		return;
	}
	if (!callout_expired(&tp->t_timer[TCPT_REXMT])) {
		mutex_exit(softnet_lock);
		return;
	}

	KERNEL_LOCK(1, NULL);
	if ((tp->t_flags & TF_PMTUD_PEND) && tp->t_inpcb &&
	    SEQ_GEQ(tp->t_pmtud_th_seq, tp->snd_una) &&
	    SEQ_LT(tp->t_pmtud_th_seq, (int)(tp->snd_una + tp->t_ourmss))) {
		extern struct sockaddr_in icmpsrc;
		struct icmp icmp;

		tp->t_flags &= ~TF_PMTUD_PEND;

		/* XXX create fake icmp message with relevant entries */
		icmp.icmp_nextmtu = tp->t_pmtud_nextmtu;
		icmp.icmp_ip.ip_len = tp->t_pmtud_ip_len;
		icmp.icmp_ip.ip_hl = tp->t_pmtud_ip_hl;
		icmpsrc.sin_addr = tp->t_inpcb->inp_faddr;
		icmp_mtudisc(&icmp, icmpsrc.sin_addr);

		/*
		 * Notify all connections to the same peer about
		 * new mss and trigger retransmit.
		 */
		in_pcbnotifyall(&tcbtable, icmpsrc.sin_addr, EMSGSIZE,
		    tcp_mtudisc);
		KERNEL_UNLOCK_ONE(NULL);
		mutex_exit(softnet_lock);
 		return;
 	}
#ifdef TCP_DEBUG
	if (tp->t_inpcb)
		so = tp->t_inpcb->inp_socket;
#ifdef INET6
	if (tp->t_in6pcb)
		so = tp->t_in6pcb->in6p_socket;
#endif
	ostate = tp->t_state;
#endif /* TCP_DEBUG */

	/*
	 * Clear the SACK scoreboard, reset FACK estimate.
	 */
	tcp_free_sackholes(tp);
	tp->snd_fack = tp->snd_una;

	/*
	 * Retransmission timer went off.  Message has not
	 * been acked within retransmit interval.  Back off
	 * to a longer retransmit interval and retransmit one segment.
	 */

	if (++tp->t_rxtshift > TCP_MAXRXTSHIFT) {
		tp->t_rxtshift = TCP_MAXRXTSHIFT;
		TCP_STATINC(TCP_STAT_TIMEOUTDROP);
		tp = tcp_drop(tp, tp->t_softerror ?
		    tp->t_softerror : ETIMEDOUT);
		goto out;
	}
	TCP_STATINC(TCP_STAT_REXMTTIMEO);
	rto = TCP_REXMTVAL(tp);
	if (rto < tp->t_rttmin)
		rto = tp->t_rttmin;
	TCPT_RANGESET(tp->t_rxtcur, rto * tcp_backoff[tp->t_rxtshift],
	    tp->t_rttmin, TCPTV_REXMTMAX);
	TCP_TIMER_ARM(tp, TCPT_REXMT, tp->t_rxtcur);

	/*
	 * If we are losing and we are trying path MTU discovery,
	 * try turning it off.  This will avoid black holes in
	 * the network which suppress or fail to send "packet
	 * too big" ICMP messages.  We should ideally do
	 * lots more sophisticated searching to find the right
	 * value here...
	 */
	if (tp->t_mtudisc && tp->t_rxtshift > TCP_MAXRXTSHIFT / 6) {
		TCP_STATINC(TCP_STAT_PMTUBLACKHOLE);

		/* try turning PMTUD off */
		if (tp->t_inpcb)
			tp->t_mtudisc = 0;
#ifdef INET6
		/* try using IPv6 minimum MTU */
		if (tp->t_in6pcb)
			tp->t_mtudisc = 0;
#endif

		/* XXX: more sophisticated Black hole recovery code? */
	}

	/*
	 * If losing, let the lower level know and try for
	 * a better route.  Also, if we backed off this far,
	 * our srtt estimate is probably bogus.  Clobber it
	 * so we'll take the next rtt measurement as our srtt;
	 * move the current srtt into rttvar to keep the current
	 * retransmit times until then.
	 */
	if (tp->t_rxtshift > TCP_MAXRXTSHIFT / 4) {
		if (tp->t_inpcb)
			in_losing(tp->t_inpcb);
#ifdef INET6
		if (tp->t_in6pcb)
			in6_losing(tp->t_in6pcb);
#endif
		/*
		 * This operation is not described in RFC2988.  The
		 * point is to keep srtt+4*rttvar constant, so we
		 * should shift right 2 bits to divide by 4, and then
		 * shift right one bit because the storage
		 * representation of rttvar is 1/16s vs 1/32s for
		 * srtt.
		 */
		tp->t_rttvar += (tp->t_srtt >> TCP_RTT_SHIFT);
		tp->t_srtt = 0;
	}
	tp->snd_nxt = tp->snd_una;
	tp->snd_high = tp->snd_max;
	/*
	 * If timing a segment in this window, stop the timer.
	 */
	tp->t_rtttime = 0;
	/*
	 * Remember if we are retransmitting a SYN, because if
	 * we do, set the initial congestion window must be set
	 * to 1 segment.
	 */
	if (tp->t_state == TCPS_SYN_SENT)
		tp->t_flags |= TF_SYN_REXMT;

	/*
	 * Adjust congestion control parameters.
	 */
	tp->t_congctl->slow_retransmit(tp);

	(void) tcp_output(tp);

 out:
#ifdef TCP_DEBUG
	if (tp && so->so_options & SO_DEBUG)
		tcp_trace(TA_USER, ostate, tp, NULL,
		    PRU_SLOWTIMO | (TCPT_REXMT << 8));
#endif
	KERNEL_UNLOCK_ONE(NULL);
	mutex_exit(softnet_lock);
}

void
tcp_timer_persist(void *arg)
{
	struct tcpcb *tp = arg;
	uint32_t rto;
#ifdef TCP_DEBUG
	struct socket *so = NULL;
	short ostate;
#endif

	mutex_enter(softnet_lock);
	if ((tp->t_flags & TF_DEAD) != 0) {
		mutex_exit(softnet_lock);
		return;
	}
	if (!callout_expired(&tp->t_timer[TCPT_PERSIST])) {
		mutex_exit(softnet_lock);
		return;
	}

	KERNEL_LOCK(1, NULL);
#ifdef TCP_DEBUG
	if (tp->t_inpcb)
		so = tp->t_inpcb->inp_socket;
#ifdef INET6
	if (tp->t_in6pcb)
		so = tp->t_in6pcb->in6p_socket;
#endif

	ostate = tp->t_state;
#endif /* TCP_DEBUG */

	/*
	 * Persistance timer into zero window.
	 * Force a byte to be output, if possible.
	 */

	/*
	 * Hack: if the peer is dead/unreachable, we do not
	 * time out if the window is closed.  After a full
	 * backoff, drop the connection if the idle time
	 * (no responses to probes) reaches the maximum
	 * backoff that we would use if retransmitting.
	 */
	rto = TCP_REXMTVAL(tp);
	if (rto < tp->t_rttmin)
		rto = tp->t_rttmin;
	if (tp->t_rxtshift == TCP_MAXRXTSHIFT &&
	    ((tcp_now - tp->t_rcvtime) >= tcp_maxpersistidle ||
	    (tcp_now - tp->t_rcvtime) >= rto * tcp_totbackoff)) {
		TCP_STATINC(TCP_STAT_PERSISTDROPS);
		tp = tcp_drop(tp, ETIMEDOUT);
		goto out;
	}
	TCP_STATINC(TCP_STAT_PERSISTTIMEO);
	tcp_setpersist(tp);
	tp->t_force = 1;
	(void) tcp_output(tp);
	tp->t_force = 0;

 out:
#ifdef TCP_DEBUG
	if (tp && so->so_options & SO_DEBUG)
		tcp_trace(TA_USER, ostate, tp, NULL,
		    PRU_SLOWTIMO | (TCPT_PERSIST << 8));
#endif
	KERNEL_UNLOCK_ONE(NULL);
	mutex_exit(softnet_lock);
}

void
tcp_timer_keep(void *arg)
{
	struct tcpcb *tp = arg;
	struct socket *so = NULL;	/* Quell compiler warning */
#ifdef TCP_DEBUG
	short ostate;
#endif

	mutex_enter(softnet_lock);
	if ((tp->t_flags & TF_DEAD) != 0) {
		mutex_exit(softnet_lock);
		return;
	}
	if (!callout_expired(&tp->t_timer[TCPT_KEEP])) {
		mutex_exit(softnet_lock);
		return;
	}

	KERNEL_LOCK(1, NULL);

#ifdef TCP_DEBUG
	ostate = tp->t_state;
#endif /* TCP_DEBUG */

	/*
	 * Keep-alive timer went off; send something
	 * or drop connection if idle for too long.
	 */

	TCP_STATINC(TCP_STAT_KEEPTIMEO);
	if (TCPS_HAVEESTABLISHED(tp->t_state) == 0)
		goto dropit;
	if (tp->t_inpcb)
		so = tp->t_inpcb->inp_socket;
#ifdef INET6
	if (tp->t_in6pcb)
		so = tp->t_in6pcb->in6p_socket;
#endif
	KASSERT(so != NULL);
	if (so->so_options & SO_KEEPALIVE &&
	    tp->t_state <= TCPS_CLOSE_WAIT) {
	    	if ((tp->t_maxidle > 0) &&
		    ((tcp_now - tp->t_rcvtime) >=
		     tp->t_keepidle + tp->t_maxidle))
			goto dropit;
		/*
		 * Send a packet designed to force a response
		 * if the peer is up and reachable:
		 * either an ACK if the connection is still alive,
		 * or an RST if the peer has closed the connection
		 * due to timeout or reboot.
		 * Using sequence number tp->snd_una-1
		 * causes the transmitted zero-length segment
		 * to lie outside the receive window;
		 * by the protocol spec, this requires the
		 * correspondent TCP to respond.
		 */
		TCP_STATINC(TCP_STAT_KEEPPROBE);

		(void)tcp_respond(tp, tp->t_template,
		    NULL, NULL, tp->rcv_nxt,
		    tp->snd_una - 1, 0);

		TCP_TIMER_ARM(tp, TCPT_KEEP, tp->t_keepintvl);
	} else
		TCP_TIMER_ARM(tp, TCPT_KEEP, tp->t_keepidle);

#ifdef TCP_DEBUG
	if (tp && so->so_options & SO_DEBUG)
		tcp_trace(TA_USER, ostate, tp, NULL,
		    PRU_SLOWTIMO | (TCPT_KEEP << 8));
#endif
	KERNEL_UNLOCK_ONE(NULL);
	mutex_exit(softnet_lock);
	return;

 dropit:
	TCP_STATINC(TCP_STAT_KEEPDROPS);
	(void) tcp_drop(tp, ETIMEDOUT);
	KERNEL_UNLOCK_ONE(NULL);
	mutex_exit(softnet_lock);
}

void
tcp_timer_2msl(void *arg)
{
	struct tcpcb *tp = arg;
#ifdef TCP_DEBUG
	struct socket *so = NULL;
	short ostate;
#endif

	mutex_enter(softnet_lock);
	if ((tp->t_flags & TF_DEAD) != 0) {
		mutex_exit(softnet_lock);
		return;
	}
	if (!callout_expired(&tp->t_timer[TCPT_2MSL])) {
		mutex_exit(softnet_lock);
		return;
	}

	/*
	 * 2 MSL timeout went off, clear the SACK scoreboard, reset
	 * the FACK estimate.
	 */
	KERNEL_LOCK(1, NULL);
	tcp_free_sackholes(tp);
	tp->snd_fack = tp->snd_una;

#ifdef TCP_DEBUG
	if (tp->t_inpcb)
		so = tp->t_inpcb->inp_socket;
#ifdef INET6
	if (tp->t_in6pcb)
		so = tp->t_in6pcb->in6p_socket;
#endif

	ostate = tp->t_state;
#endif /* TCP_DEBUG */

	/*
	 * 2 MSL timeout in shutdown went off.  If we're closed but
	 * still waiting for peer to close and connection has been idle
	 * too long, or if 2MSL time is up from TIME_WAIT, delete connection
	 * control block.  Otherwise, check again in a bit.
	 */
	if (tp->t_state != TCPS_TIME_WAIT &&
	    ((tp->t_maxidle == 0) ||
	    ((tcp_now - tp->t_rcvtime) <= tp->t_maxidle)))
	    TCP_TIMER_ARM(tp, TCPT_2MSL, tp->t_keepintvl);
	else
		tp = tcp_close(tp);

#ifdef TCP_DEBUG
	if (tp && so->so_options & SO_DEBUG)
		tcp_trace(TA_USER, ostate, tp, NULL,
		    PRU_SLOWTIMO | (TCPT_2MSL << 8));
#endif
	KERNEL_UNLOCK_ONE(NULL);
	mutex_exit(softnet_lock);
}