The Design and Implementation of the FreeBSD Operating System, Second Edition
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FreeBSD/Linux Kernel Cross Reference
sys/netinet/tcp_timer.c

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    1 /*-
    2  * SPDX-License-Identifier: BSD-3-Clause
    3  *
    4  * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1995
    5  *      The Regents of the University of California.  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 University 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 REGENTS 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 REGENTS 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  *      @(#)tcp_timer.c 8.2 (Berkeley) 5/24/95
   32  */
   33 
   34 #include <sys/cdefs.h>
   35 __FBSDID("$FreeBSD: releng/12.0/sys/netinet/tcp_timer.c 335924 2018-07-04 02:47:16Z mmacy $");
   36 
   37 #include "opt_inet.h"
   38 #include "opt_inet6.h"
   39 #include "opt_tcpdebug.h"
   40 #include "opt_rss.h"
   41 
   42 #include <sys/param.h>
   43 #include <sys/kernel.h>
   44 #include <sys/lock.h>
   45 #include <sys/mbuf.h>
   46 #include <sys/mutex.h>
   47 #include <sys/protosw.h>
   48 #include <sys/smp.h>
   49 #include <sys/socket.h>
   50 #include <sys/socketvar.h>
   51 #include <sys/sysctl.h>
   52 #include <sys/systm.h>
   53 
   54 #include <net/if.h>
   55 #include <net/route.h>
   56 #include <net/rss_config.h>
   57 #include <net/vnet.h>
   58 #include <net/netisr.h>
   59 
   60 #include <netinet/in.h>
   61 #include <netinet/in_kdtrace.h>
   62 #include <netinet/in_pcb.h>
   63 #include <netinet/in_rss.h>
   64 #include <netinet/in_systm.h>
   65 #ifdef INET6
   66 #include <netinet6/in6_pcb.h>
   67 #endif
   68 #include <netinet/ip_var.h>
   69 #include <netinet/tcp.h>
   70 #include <netinet/tcp_fsm.h>
   71 #include <netinet/tcp_log_buf.h>
   72 #include <netinet/tcp_timer.h>
   73 #include <netinet/tcp_var.h>
   74 #include <netinet/tcp_seq.h>
   75 #include <netinet/cc/cc.h>
   76 #ifdef INET6
   77 #include <netinet6/tcp6_var.h>
   78 #endif
   79 #include <netinet/tcpip.h>
   80 #ifdef TCPDEBUG
   81 #include <netinet/tcp_debug.h>
   82 #endif
   83 
   84 int    tcp_persmin;
   85 SYSCTL_PROC(_net_inet_tcp, OID_AUTO, persmin, CTLTYPE_INT|CTLFLAG_RW,
   86     &tcp_persmin, 0, sysctl_msec_to_ticks, "I", "minimum persistence interval");
   87 
   88 int    tcp_persmax;
   89 SYSCTL_PROC(_net_inet_tcp, OID_AUTO, persmax, CTLTYPE_INT|CTLFLAG_RW,
   90     &tcp_persmax, 0, sysctl_msec_to_ticks, "I", "maximum persistence interval");
   91 
   92 int     tcp_keepinit;
   93 SYSCTL_PROC(_net_inet_tcp, TCPCTL_KEEPINIT, keepinit, CTLTYPE_INT|CTLFLAG_RW,
   94     &tcp_keepinit, 0, sysctl_msec_to_ticks, "I", "time to establish connection");
   95 
   96 int     tcp_keepidle;
   97 SYSCTL_PROC(_net_inet_tcp, TCPCTL_KEEPIDLE, keepidle, CTLTYPE_INT|CTLFLAG_RW,
   98     &tcp_keepidle, 0, sysctl_msec_to_ticks, "I", "time before keepalive probes begin");
   99 
  100 int     tcp_keepintvl;
  101 SYSCTL_PROC(_net_inet_tcp, TCPCTL_KEEPINTVL, keepintvl, CTLTYPE_INT|CTLFLAG_RW,
  102     &tcp_keepintvl, 0, sysctl_msec_to_ticks, "I", "time between keepalive probes");
  103 
  104 int     tcp_delacktime;
  105 SYSCTL_PROC(_net_inet_tcp, TCPCTL_DELACKTIME, delacktime, CTLTYPE_INT|CTLFLAG_RW,
  106     &tcp_delacktime, 0, sysctl_msec_to_ticks, "I",
  107     "Time before a delayed ACK is sent");
  108 
  109 int     tcp_msl;
  110 SYSCTL_PROC(_net_inet_tcp, OID_AUTO, msl, CTLTYPE_INT|CTLFLAG_RW,
  111     &tcp_msl, 0, sysctl_msec_to_ticks, "I", "Maximum segment lifetime");
  112 
  113 int     tcp_rexmit_min;
  114 SYSCTL_PROC(_net_inet_tcp, OID_AUTO, rexmit_min, CTLTYPE_INT|CTLFLAG_RW,
  115     &tcp_rexmit_min, 0, sysctl_msec_to_ticks, "I",
  116     "Minimum Retransmission Timeout");
  117 
  118 int     tcp_rexmit_slop;
  119 SYSCTL_PROC(_net_inet_tcp, OID_AUTO, rexmit_slop, CTLTYPE_INT|CTLFLAG_RW,
  120     &tcp_rexmit_slop, 0, sysctl_msec_to_ticks, "I",
  121     "Retransmission Timer Slop");
  122 
  123 int     tcp_always_keepalive = 1;
  124 SYSCTL_INT(_net_inet_tcp, OID_AUTO, always_keepalive, CTLFLAG_RW,
  125     &tcp_always_keepalive , 0, "Assume SO_KEEPALIVE on all TCP connections");
  126 
  127 int    tcp_fast_finwait2_recycle = 0;
  128 SYSCTL_INT(_net_inet_tcp, OID_AUTO, fast_finwait2_recycle, CTLFLAG_RW, 
  129     &tcp_fast_finwait2_recycle, 0,
  130     "Recycle closed FIN_WAIT_2 connections faster");
  131 
  132 int    tcp_finwait2_timeout;
  133 SYSCTL_PROC(_net_inet_tcp, OID_AUTO, finwait2_timeout, CTLTYPE_INT|CTLFLAG_RW,
  134     &tcp_finwait2_timeout, 0, sysctl_msec_to_ticks, "I", "FIN-WAIT2 timeout");
  135 
  136 int     tcp_keepcnt = TCPTV_KEEPCNT;
  137 SYSCTL_INT(_net_inet_tcp, OID_AUTO, keepcnt, CTLFLAG_RW, &tcp_keepcnt, 0,
  138     "Number of keepalive probes to send");
  139 
  140         /* max idle probes */
  141 int     tcp_maxpersistidle;
  142 
  143 int     tcp_rexmit_drop_options = 0;
  144 SYSCTL_INT(_net_inet_tcp, OID_AUTO, rexmit_drop_options, CTLFLAG_RW,
  145     &tcp_rexmit_drop_options, 0,
  146     "Drop TCP options from 3rd and later retransmitted SYN");
  147 
  148 VNET_DEFINE(int, tcp_pmtud_blackhole_detect);
  149 SYSCTL_INT(_net_inet_tcp, OID_AUTO, pmtud_blackhole_detection,
  150     CTLFLAG_RW|CTLFLAG_VNET,
  151     &VNET_NAME(tcp_pmtud_blackhole_detect), 0,
  152     "Path MTU Discovery Black Hole Detection Enabled");
  153 
  154 #ifdef INET
  155 VNET_DEFINE(int, tcp_pmtud_blackhole_mss) = 1200;
  156 SYSCTL_INT(_net_inet_tcp, OID_AUTO, pmtud_blackhole_mss,
  157     CTLFLAG_RW|CTLFLAG_VNET,
  158     &VNET_NAME(tcp_pmtud_blackhole_mss), 0,
  159     "Path MTU Discovery Black Hole Detection lowered MSS");
  160 #endif
  161 
  162 #ifdef INET6
  163 VNET_DEFINE(int, tcp_v6pmtud_blackhole_mss) = 1220;
  164 SYSCTL_INT(_net_inet_tcp, OID_AUTO, v6pmtud_blackhole_mss,
  165     CTLFLAG_RW|CTLFLAG_VNET,
  166     &VNET_NAME(tcp_v6pmtud_blackhole_mss), 0,
  167     "Path MTU Discovery IPv6 Black Hole Detection lowered MSS");
  168 #endif
  169 
  170 #ifdef  RSS
  171 static int      per_cpu_timers = 1;
  172 #else
  173 static int      per_cpu_timers = 0;
  174 #endif
  175 SYSCTL_INT(_net_inet_tcp, OID_AUTO, per_cpu_timers, CTLFLAG_RW,
  176     &per_cpu_timers , 0, "run tcp timers on all cpus");
  177 
  178 /*
  179  * Map the given inp to a CPU id.
  180  *
  181  * This queries RSS if it's compiled in, else it defaults to the current
  182  * CPU ID.
  183  */
  184 inline int
  185 inp_to_cpuid(struct inpcb *inp)
  186 {
  187         u_int cpuid;
  188 
  189 #ifdef  RSS
  190         if (per_cpu_timers) {
  191                 cpuid = rss_hash2cpuid(inp->inp_flowid, inp->inp_flowtype);
  192                 if (cpuid == NETISR_CPUID_NONE)
  193                         return (curcpu);        /* XXX */
  194                 else
  195                         return (cpuid);
  196         }
  197 #else
  198         /* Legacy, pre-RSS behaviour */
  199         if (per_cpu_timers) {
  200                 /*
  201                  * We don't have a flowid -> cpuid mapping, so cheat and
  202                  * just map unknown cpuids to curcpu.  Not the best, but
  203                  * apparently better than defaulting to swi 0.
  204                  */
  205                 cpuid = inp->inp_flowid % (mp_maxid + 1);
  206                 if (! CPU_ABSENT(cpuid))
  207                         return (cpuid);
  208                 return (curcpu);
  209         }
  210 #endif
  211         /* Default for RSS and non-RSS - cpuid 0 */
  212         else {
  213                 return (0);
  214         }
  215 }
  216 
  217 /*
  218  * Tcp protocol timeout routine called every 500 ms.
  219  * Updates timestamps used for TCP
  220  * causes finite state machine actions if timers expire.
  221  */
  222 void
  223 tcp_slowtimo(void)
  224 {
  225         VNET_ITERATOR_DECL(vnet_iter);
  226 
  227         VNET_LIST_RLOCK_NOSLEEP();
  228         VNET_FOREACH(vnet_iter) {
  229                 CURVNET_SET(vnet_iter);
  230                 (void) tcp_tw_2msl_scan(0);
  231                 CURVNET_RESTORE();
  232         }
  233         VNET_LIST_RUNLOCK_NOSLEEP();
  234 }
  235 
  236 int     tcp_syn_backoff[TCP_MAXRXTSHIFT + 1] =
  237     { 1, 1, 1, 1, 1, 2, 4, 8, 16, 32, 64, 64, 64 };
  238 
  239 int     tcp_backoff[TCP_MAXRXTSHIFT + 1] =
  240     { 1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 512, 512, 512 };
  241 
  242 int tcp_totbackoff = 2559;      /* sum of tcp_backoff[] */
  243 
  244 /*
  245  * TCP timer processing.
  246  */
  247 
  248 void
  249 tcp_timer_delack(void *xtp)
  250 {
  251         struct tcpcb *tp = xtp;
  252         struct inpcb *inp;
  253         CURVNET_SET(tp->t_vnet);
  254 
  255         inp = tp->t_inpcb;
  256         KASSERT(inp != NULL, ("%s: tp %p tp->t_inpcb == NULL", __func__, tp));
  257         INP_WLOCK(inp);
  258         if (callout_pending(&tp->t_timers->tt_delack) ||
  259             !callout_active(&tp->t_timers->tt_delack)) {
  260                 INP_WUNLOCK(inp);
  261                 CURVNET_RESTORE();
  262                 return;
  263         }
  264         callout_deactivate(&tp->t_timers->tt_delack);
  265         if ((inp->inp_flags & INP_DROPPED) != 0) {
  266                 INP_WUNLOCK(inp);
  267                 CURVNET_RESTORE();
  268                 return;
  269         }
  270         tp->t_flags |= TF_ACKNOW;
  271         TCPSTAT_INC(tcps_delack);
  272         (void) tp->t_fb->tfb_tcp_output(tp);
  273         INP_WUNLOCK(inp);
  274         CURVNET_RESTORE();
  275 }
  276 
  277 void
  278 tcp_inpinfo_lock_del(struct inpcb *inp, struct tcpcb *tp)
  279 {
  280         if (inp && tp != NULL)
  281                 INP_WUNLOCK(inp);
  282 }
  283 
  284 void
  285 tcp_timer_2msl(void *xtp)
  286 {
  287         struct tcpcb *tp = xtp;
  288         struct inpcb *inp;
  289         struct epoch_tracker et;
  290         CURVNET_SET(tp->t_vnet);
  291 #ifdef TCPDEBUG
  292         int ostate;
  293 
  294         ostate = tp->t_state;
  295 #endif
  296         inp = tp->t_inpcb;
  297         KASSERT(inp != NULL, ("%s: tp %p tp->t_inpcb == NULL", __func__, tp));
  298         INP_WLOCK(inp);
  299         tcp_free_sackholes(tp);
  300         if (callout_pending(&tp->t_timers->tt_2msl) ||
  301             !callout_active(&tp->t_timers->tt_2msl)) {
  302                 INP_WUNLOCK(tp->t_inpcb);
  303                 CURVNET_RESTORE();
  304                 return;
  305         }
  306         callout_deactivate(&tp->t_timers->tt_2msl);
  307         if ((inp->inp_flags & INP_DROPPED) != 0) {
  308                 INP_WUNLOCK(inp);
  309                 CURVNET_RESTORE();
  310                 return;
  311         }
  312         KASSERT((tp->t_timers->tt_flags & TT_STOPPED) == 0,
  313                 ("%s: tp %p tcpcb can't be stopped here", __func__, tp));
  314         /*
  315          * 2 MSL timeout in shutdown went off.  If we're closed but
  316          * still waiting for peer to close and connection has been idle
  317          * too long delete connection control block.  Otherwise, check
  318          * again in a bit.
  319          *
  320          * If in TIME_WAIT state just ignore as this timeout is handled in
  321          * tcp_tw_2msl_scan().
  322          *
  323          * If fastrecycle of FIN_WAIT_2, in FIN_WAIT_2 and receiver has closed, 
  324          * there's no point in hanging onto FIN_WAIT_2 socket. Just close it. 
  325          * Ignore fact that there were recent incoming segments.
  326          */
  327         if ((inp->inp_flags & INP_TIMEWAIT) != 0) {
  328                 INP_WUNLOCK(inp);
  329                 CURVNET_RESTORE();
  330                 return;
  331         }
  332         if (tcp_fast_finwait2_recycle && tp->t_state == TCPS_FIN_WAIT_2 &&
  333             tp->t_inpcb && tp->t_inpcb->inp_socket && 
  334             (tp->t_inpcb->inp_socket->so_rcv.sb_state & SBS_CANTRCVMORE)) {
  335                 TCPSTAT_INC(tcps_finwait2_drops);
  336                 if (inp->inp_flags & (INP_TIMEWAIT | INP_DROPPED)) {
  337                         tcp_inpinfo_lock_del(inp, tp);
  338                         goto out;
  339                 }
  340                 INP_INFO_RLOCK_ET(&V_tcbinfo, et);
  341                 tp = tcp_close(tp);             
  342                 INP_INFO_RUNLOCK_ET(&V_tcbinfo, et);
  343                 tcp_inpinfo_lock_del(inp, tp);
  344                 goto out;
  345         } else {
  346                 if (ticks - tp->t_rcvtime <= TP_MAXIDLE(tp)) {
  347                         callout_reset(&tp->t_timers->tt_2msl,
  348                                       TP_KEEPINTVL(tp), tcp_timer_2msl, tp);
  349                 } else {
  350                         if (inp->inp_flags & (INP_TIMEWAIT | INP_DROPPED)) {
  351                                 tcp_inpinfo_lock_del(inp, tp);
  352                                 goto out;
  353                         }
  354                         INP_INFO_RLOCK_ET(&V_tcbinfo, et);
  355                         tp = tcp_close(tp);
  356                         INP_INFO_RUNLOCK_ET(&V_tcbinfo, et);
  357                         tcp_inpinfo_lock_del(inp, tp);
  358                         goto out;
  359                 }
  360         }
  361 
  362 #ifdef TCPDEBUG
  363         if (tp != NULL && (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
  364                 tcp_trace(TA_USER, ostate, tp, (void *)0, (struct tcphdr *)0,
  365                           PRU_SLOWTIMO);
  366 #endif
  367         TCP_PROBE2(debug__user, tp, PRU_SLOWTIMO);
  368 
  369         if (tp != NULL)
  370                 INP_WUNLOCK(inp);
  371 out:
  372         CURVNET_RESTORE();
  373 }
  374 
  375 void
  376 tcp_timer_keep(void *xtp)
  377 {
  378         struct tcpcb *tp = xtp;
  379         struct tcptemp *t_template;
  380         struct inpcb *inp;
  381         struct epoch_tracker et;
  382         CURVNET_SET(tp->t_vnet);
  383 #ifdef TCPDEBUG
  384         int ostate;
  385 
  386         ostate = tp->t_state;
  387 #endif
  388         inp = tp->t_inpcb;
  389         KASSERT(inp != NULL, ("%s: tp %p tp->t_inpcb == NULL", __func__, tp));
  390         INP_WLOCK(inp);
  391         if (callout_pending(&tp->t_timers->tt_keep) ||
  392             !callout_active(&tp->t_timers->tt_keep)) {
  393                 INP_WUNLOCK(inp);
  394                 CURVNET_RESTORE();
  395                 return;
  396         }
  397         callout_deactivate(&tp->t_timers->tt_keep);
  398         if ((inp->inp_flags & INP_DROPPED) != 0) {
  399                 INP_WUNLOCK(inp);
  400                 CURVNET_RESTORE();
  401                 return;
  402         }
  403         KASSERT((tp->t_timers->tt_flags & TT_STOPPED) == 0,
  404                 ("%s: tp %p tcpcb can't be stopped here", __func__, tp));
  405 
  406         /*
  407          * Because we don't regularly reset the keepalive callout in
  408          * the ESTABLISHED state, it may be that we don't actually need
  409          * to send a keepalive yet. If that occurs, schedule another
  410          * call for the next time the keepalive timer might expire.
  411          */
  412         if (TCPS_HAVEESTABLISHED(tp->t_state)) {
  413                 u_int idletime;
  414 
  415                 idletime = ticks - tp->t_rcvtime;
  416                 if (idletime < TP_KEEPIDLE(tp)) {
  417                         callout_reset(&tp->t_timers->tt_keep,
  418                             TP_KEEPIDLE(tp) - idletime, tcp_timer_keep, tp);
  419                         INP_WUNLOCK(inp);
  420                         CURVNET_RESTORE();
  421                         return;
  422                 }
  423         }
  424 
  425         /*
  426          * Keep-alive timer went off; send something
  427          * or drop connection if idle for too long.
  428          */
  429         TCPSTAT_INC(tcps_keeptimeo);
  430         if (tp->t_state < TCPS_ESTABLISHED)
  431                 goto dropit;
  432         if ((tcp_always_keepalive ||
  433             inp->inp_socket->so_options & SO_KEEPALIVE) &&
  434             tp->t_state <= TCPS_CLOSING) {
  435                 if (ticks - tp->t_rcvtime >= TP_KEEPIDLE(tp) + TP_MAXIDLE(tp))
  436                         goto dropit;
  437                 /*
  438                  * Send a packet designed to force a response
  439                  * if the peer is up and reachable:
  440                  * either an ACK if the connection is still alive,
  441                  * or an RST if the peer has closed the connection
  442                  * due to timeout or reboot.
  443                  * Using sequence number tp->snd_una-1
  444                  * causes the transmitted zero-length segment
  445                  * to lie outside the receive window;
  446                  * by the protocol spec, this requires the
  447                  * correspondent TCP to respond.
  448                  */
  449                 TCPSTAT_INC(tcps_keepprobe);
  450                 t_template = tcpip_maketemplate(inp);
  451                 if (t_template) {
  452                         tcp_respond(tp, t_template->tt_ipgen,
  453                                     &t_template->tt_t, (struct mbuf *)NULL,
  454                                     tp->rcv_nxt, tp->snd_una - 1, 0);
  455                         free(t_template, M_TEMP);
  456                 }
  457                 callout_reset(&tp->t_timers->tt_keep, TP_KEEPINTVL(tp),
  458                               tcp_timer_keep, tp);
  459         } else
  460                 callout_reset(&tp->t_timers->tt_keep, TP_KEEPIDLE(tp),
  461                               tcp_timer_keep, tp);
  462 
  463 #ifdef TCPDEBUG
  464         if (inp->inp_socket->so_options & SO_DEBUG)
  465                 tcp_trace(TA_USER, ostate, tp, (void *)0, (struct tcphdr *)0,
  466                           PRU_SLOWTIMO);
  467 #endif
  468         TCP_PROBE2(debug__user, tp, PRU_SLOWTIMO);
  469         INP_WUNLOCK(inp);
  470         CURVNET_RESTORE();
  471         return;
  472 
  473 dropit:
  474         TCPSTAT_INC(tcps_keepdrops);
  475         if (inp->inp_flags & (INP_TIMEWAIT | INP_DROPPED)) {
  476                 tcp_inpinfo_lock_del(inp, tp);
  477                 goto out;
  478         }
  479         INP_INFO_RLOCK_ET(&V_tcbinfo, et);
  480         tp = tcp_drop(tp, ETIMEDOUT);
  481 
  482 #ifdef TCPDEBUG
  483         if (tp != NULL && (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
  484                 tcp_trace(TA_USER, ostate, tp, (void *)0, (struct tcphdr *)0,
  485                           PRU_SLOWTIMO);
  486 #endif
  487         TCP_PROBE2(debug__user, tp, PRU_SLOWTIMO);
  488         INP_INFO_RUNLOCK_ET(&V_tcbinfo, et);
  489         tcp_inpinfo_lock_del(inp, tp);
  490  out:
  491         CURVNET_RESTORE();
  492 }
  493 
  494 void
  495 tcp_timer_persist(void *xtp)
  496 {
  497         struct tcpcb *tp = xtp;
  498         struct inpcb *inp;
  499         struct epoch_tracker et;
  500         CURVNET_SET(tp->t_vnet);
  501 #ifdef TCPDEBUG
  502         int ostate;
  503 
  504         ostate = tp->t_state;
  505 #endif
  506         inp = tp->t_inpcb;
  507         KASSERT(inp != NULL, ("%s: tp %p tp->t_inpcb == NULL", __func__, tp));
  508         INP_WLOCK(inp);
  509         if (callout_pending(&tp->t_timers->tt_persist) ||
  510             !callout_active(&tp->t_timers->tt_persist)) {
  511                 INP_WUNLOCK(inp);
  512                 CURVNET_RESTORE();
  513                 return;
  514         }
  515         callout_deactivate(&tp->t_timers->tt_persist);
  516         if ((inp->inp_flags & INP_DROPPED) != 0) {
  517                 INP_WUNLOCK(inp);
  518                 CURVNET_RESTORE();
  519                 return;
  520         }
  521         KASSERT((tp->t_timers->tt_flags & TT_STOPPED) == 0,
  522                 ("%s: tp %p tcpcb can't be stopped here", __func__, tp));
  523         /*
  524          * Persistence timer into zero window.
  525          * Force a byte to be output, if possible.
  526          */
  527         TCPSTAT_INC(tcps_persisttimeo);
  528         /*
  529          * Hack: if the peer is dead/unreachable, we do not
  530          * time out if the window is closed.  After a full
  531          * backoff, drop the connection if the idle time
  532          * (no responses to probes) reaches the maximum
  533          * backoff that we would use if retransmitting.
  534          */
  535         if (tp->t_rxtshift == TCP_MAXRXTSHIFT &&
  536             (ticks - tp->t_rcvtime >= tcp_maxpersistidle ||
  537              ticks - tp->t_rcvtime >= TCP_REXMTVAL(tp) * tcp_totbackoff)) {
  538                 TCPSTAT_INC(tcps_persistdrop);
  539                 if (inp->inp_flags & (INP_TIMEWAIT | INP_DROPPED)) {
  540                         tcp_inpinfo_lock_del(inp, tp);
  541                         goto out;
  542                 }
  543                 INP_INFO_RLOCK_ET(&V_tcbinfo, et);
  544                 tp = tcp_drop(tp, ETIMEDOUT);
  545                 INP_INFO_RUNLOCK_ET(&V_tcbinfo, et);
  546                 tcp_inpinfo_lock_del(inp, tp);
  547                 goto out;
  548         }
  549         /*
  550          * If the user has closed the socket then drop a persisting
  551          * connection after a much reduced timeout.
  552          */
  553         if (tp->t_state > TCPS_CLOSE_WAIT &&
  554             (ticks - tp->t_rcvtime) >= TCPTV_PERSMAX) {
  555                 TCPSTAT_INC(tcps_persistdrop);
  556                 if (inp->inp_flags & (INP_TIMEWAIT | INP_DROPPED)) {
  557                         tcp_inpinfo_lock_del(inp, tp);
  558                         goto out;
  559                 }
  560                 INP_INFO_RLOCK_ET(&V_tcbinfo, et);
  561                 tp = tcp_drop(tp, ETIMEDOUT);
  562                 INP_INFO_RUNLOCK_ET(&V_tcbinfo, et);
  563                 tcp_inpinfo_lock_del(inp, tp);
  564                 goto out;
  565         }
  566         tcp_setpersist(tp);
  567         tp->t_flags |= TF_FORCEDATA;
  568         (void) tp->t_fb->tfb_tcp_output(tp);
  569         tp->t_flags &= ~TF_FORCEDATA;
  570 
  571 #ifdef TCPDEBUG
  572         if (tp != NULL && tp->t_inpcb->inp_socket->so_options & SO_DEBUG)
  573                 tcp_trace(TA_USER, ostate, tp, NULL, NULL, PRU_SLOWTIMO);
  574 #endif
  575         TCP_PROBE2(debug__user, tp, PRU_SLOWTIMO);
  576         INP_WUNLOCK(inp);
  577 out:
  578         CURVNET_RESTORE();
  579 }
  580 
  581 void
  582 tcp_timer_rexmt(void * xtp)
  583 {
  584         struct tcpcb *tp = xtp;
  585         CURVNET_SET(tp->t_vnet);
  586         int rexmt;
  587         struct inpcb *inp;
  588         struct epoch_tracker et;
  589 #ifdef TCPDEBUG
  590         int ostate;
  591 
  592         ostate = tp->t_state;
  593 #endif
  594         inp = tp->t_inpcb;
  595         KASSERT(inp != NULL, ("%s: tp %p tp->t_inpcb == NULL", __func__, tp));
  596         INP_WLOCK(inp);
  597         if (callout_pending(&tp->t_timers->tt_rexmt) ||
  598             !callout_active(&tp->t_timers->tt_rexmt)) {
  599                 INP_WUNLOCK(inp);
  600                 CURVNET_RESTORE();
  601                 return;
  602         }
  603         callout_deactivate(&tp->t_timers->tt_rexmt);
  604         if ((inp->inp_flags & INP_DROPPED) != 0) {
  605                 INP_WUNLOCK(inp);
  606                 CURVNET_RESTORE();
  607                 return;
  608         }
  609         KASSERT((tp->t_timers->tt_flags & TT_STOPPED) == 0,
  610                 ("%s: tp %p tcpcb can't be stopped here", __func__, tp));
  611         tcp_free_sackholes(tp);
  612         TCP_LOG_EVENT(tp, NULL, NULL, NULL, TCP_LOG_RTO, 0, 0, NULL, false);
  613         if (tp->t_fb->tfb_tcp_rexmit_tmr) {
  614                 /* The stack has a timer action too. */
  615                 (*tp->t_fb->tfb_tcp_rexmit_tmr)(tp);
  616         }
  617         /*
  618          * Retransmission timer went off.  Message has not
  619          * been acked within retransmit interval.  Back off
  620          * to a longer retransmit interval and retransmit one segment.
  621          */
  622         if (++tp->t_rxtshift > TCP_MAXRXTSHIFT) {
  623                 tp->t_rxtshift = TCP_MAXRXTSHIFT;
  624                 TCPSTAT_INC(tcps_timeoutdrop);
  625                 if (inp->inp_flags & (INP_TIMEWAIT | INP_DROPPED)) {
  626                         tcp_inpinfo_lock_del(inp, tp);
  627                         goto out;
  628                 }
  629                 INP_INFO_RLOCK_ET(&V_tcbinfo, et);
  630                 tp = tcp_drop(tp, ETIMEDOUT);
  631                 INP_INFO_RUNLOCK_ET(&V_tcbinfo, et);
  632                 tcp_inpinfo_lock_del(inp, tp);
  633                 goto out;
  634         }
  635         if (tp->t_state == TCPS_SYN_SENT) {
  636                 /*
  637                  * If the SYN was retransmitted, indicate CWND to be
  638                  * limited to 1 segment in cc_conn_init().
  639                  */
  640                 tp->snd_cwnd = 1;
  641         } else if (tp->t_rxtshift == 1) {
  642                 /*
  643                  * first retransmit; record ssthresh and cwnd so they can
  644                  * be recovered if this turns out to be a "bad" retransmit.
  645                  * A retransmit is considered "bad" if an ACK for this
  646                  * segment is received within RTT/2 interval; the assumption
  647                  * here is that the ACK was already in flight.  See
  648                  * "On Estimating End-to-End Network Path Properties" by
  649                  * Allman and Paxson for more details.
  650                  */
  651                 tp->snd_cwnd_prev = tp->snd_cwnd;
  652                 tp->snd_ssthresh_prev = tp->snd_ssthresh;
  653                 tp->snd_recover_prev = tp->snd_recover;
  654                 if (IN_FASTRECOVERY(tp->t_flags))
  655                         tp->t_flags |= TF_WASFRECOVERY;
  656                 else
  657                         tp->t_flags &= ~TF_WASFRECOVERY;
  658                 if (IN_CONGRECOVERY(tp->t_flags))
  659                         tp->t_flags |= TF_WASCRECOVERY;
  660                 else
  661                         tp->t_flags &= ~TF_WASCRECOVERY;
  662                 if ((tp->t_flags & TF_RCVD_TSTMP) == 0)
  663                         tp->t_badrxtwin = ticks + (tp->t_srtt >> (TCP_RTT_SHIFT + 1));
  664                 /* In the event that we've negotiated timestamps
  665                  * badrxtwin will be set to the value that we set
  666                  * the retransmitted packet's to_tsval to by tcp_output
  667                  */
  668                 tp->t_flags |= TF_PREVVALID;
  669         } else
  670                 tp->t_flags &= ~TF_PREVVALID;
  671         TCPSTAT_INC(tcps_rexmttimeo);
  672         if ((tp->t_state == TCPS_SYN_SENT) ||
  673             (tp->t_state == TCPS_SYN_RECEIVED))
  674                 rexmt = TCPTV_RTOBASE * tcp_syn_backoff[tp->t_rxtshift];
  675         else
  676                 rexmt = TCP_REXMTVAL(tp) * tcp_backoff[tp->t_rxtshift];
  677         TCPT_RANGESET(tp->t_rxtcur, rexmt,
  678                       tp->t_rttmin, TCPTV_REXMTMAX);
  679 
  680         /*
  681          * We enter the path for PLMTUD if connection is established or, if
  682          * connection is FIN_WAIT_1 status, reason for the last is that if
  683          * amount of data we send is very small, we could send it in couple of
  684          * packets and process straight to FIN. In that case we won't catch
  685          * ESTABLISHED state.
  686          */
  687         if (V_tcp_pmtud_blackhole_detect && (((tp->t_state == TCPS_ESTABLISHED))
  688             || (tp->t_state == TCPS_FIN_WAIT_1))) {
  689 #ifdef INET6
  690                 int isipv6;
  691 #endif
  692 
  693                 /*
  694                  * Idea here is that at each stage of mtu probe (usually, 1448
  695                  * -> 1188 -> 524) should be given 2 chances to recover before
  696                  *  further clamping down. 'tp->t_rxtshift % 2 == 0' should
  697                  *  take care of that.
  698                  */
  699                 if (((tp->t_flags2 & (TF2_PLPMTU_PMTUD|TF2_PLPMTU_MAXSEGSNT)) ==
  700                     (TF2_PLPMTU_PMTUD|TF2_PLPMTU_MAXSEGSNT)) &&
  701                     (tp->t_rxtshift >= 2 && tp->t_rxtshift < 6 &&
  702                     tp->t_rxtshift % 2 == 0)) {
  703                         /*
  704                          * Enter Path MTU Black-hole Detection mechanism:
  705                          * - Disable Path MTU Discovery (IP "DF" bit).
  706                          * - Reduce MTU to lower value than what we
  707                          *   negotiated with peer.
  708                          */
  709                         if ((tp->t_flags2 & TF2_PLPMTU_BLACKHOLE) == 0) {
  710                                 /* Record that we may have found a black hole. */
  711                                 tp->t_flags2 |= TF2_PLPMTU_BLACKHOLE;
  712                                 /* Keep track of previous MSS. */
  713                                 tp->t_pmtud_saved_maxseg = tp->t_maxseg;
  714                         }
  715 
  716                         /* 
  717                          * Reduce the MSS to blackhole value or to the default
  718                          * in an attempt to retransmit.
  719                          */
  720 #ifdef INET6
  721                         isipv6 = (tp->t_inpcb->inp_vflag & INP_IPV6) ? 1 : 0;
  722                         if (isipv6 &&
  723                             tp->t_maxseg > V_tcp_v6pmtud_blackhole_mss) {
  724                                 /* Use the sysctl tuneable blackhole MSS. */
  725                                 tp->t_maxseg = V_tcp_v6pmtud_blackhole_mss;
  726                                 TCPSTAT_INC(tcps_pmtud_blackhole_activated);
  727                         } else if (isipv6) {
  728                                 /* Use the default MSS. */
  729                                 tp->t_maxseg = V_tcp_v6mssdflt;
  730                                 /*
  731                                  * Disable Path MTU Discovery when we switch to
  732                                  * minmss.
  733                                  */
  734                                 tp->t_flags2 &= ~TF2_PLPMTU_PMTUD;
  735                                 TCPSTAT_INC(tcps_pmtud_blackhole_activated_min_mss);
  736                         }
  737 #endif
  738 #if defined(INET6) && defined(INET)
  739                         else
  740 #endif
  741 #ifdef INET
  742                         if (tp->t_maxseg > V_tcp_pmtud_blackhole_mss) {
  743                                 /* Use the sysctl tuneable blackhole MSS. */
  744                                 tp->t_maxseg = V_tcp_pmtud_blackhole_mss;
  745                                 TCPSTAT_INC(tcps_pmtud_blackhole_activated);
  746                         } else {
  747                                 /* Use the default MSS. */
  748                                 tp->t_maxseg = V_tcp_mssdflt;
  749                                 /*
  750                                  * Disable Path MTU Discovery when we switch to
  751                                  * minmss.
  752                                  */
  753                                 tp->t_flags2 &= ~TF2_PLPMTU_PMTUD;
  754                                 TCPSTAT_INC(tcps_pmtud_blackhole_activated_min_mss);
  755                         }
  756 #endif
  757                         /*
  758                          * Reset the slow-start flight size
  759                          * as it may depend on the new MSS.
  760                          */
  761                         if (CC_ALGO(tp)->conn_init != NULL)
  762                                 CC_ALGO(tp)->conn_init(tp->ccv);
  763                 } else {
  764                         /*
  765                          * If further retransmissions are still unsuccessful
  766                          * with a lowered MTU, maybe this isn't a blackhole and
  767                          * we restore the previous MSS and blackhole detection
  768                          * flags.
  769                          * The limit '6' is determined by giving each probe
  770                          * stage (1448, 1188, 524) 2 chances to recover.
  771                          */
  772                         if ((tp->t_flags2 & TF2_PLPMTU_BLACKHOLE) &&
  773                             (tp->t_rxtshift >= 6)) {
  774                                 tp->t_flags2 |= TF2_PLPMTU_PMTUD;
  775                                 tp->t_flags2 &= ~TF2_PLPMTU_BLACKHOLE;
  776                                 tp->t_maxseg = tp->t_pmtud_saved_maxseg;
  777                                 TCPSTAT_INC(tcps_pmtud_blackhole_failed);
  778                                 /*
  779                                  * Reset the slow-start flight size as it
  780                                  * may depend on the new MSS.
  781                                  */
  782                                 if (CC_ALGO(tp)->conn_init != NULL)
  783                                         CC_ALGO(tp)->conn_init(tp->ccv);
  784                         }
  785                 }
  786         }
  787 
  788         /*
  789          * Disable RFC1323 and SACK if we haven't got any response to
  790          * our third SYN to work-around some broken terminal servers
  791          * (most of which have hopefully been retired) that have bad VJ
  792          * header compression code which trashes TCP segments containing
  793          * unknown-to-them TCP options.
  794          */
  795         if (tcp_rexmit_drop_options && (tp->t_state == TCPS_SYN_SENT) &&
  796             (tp->t_rxtshift == 3))
  797                 tp->t_flags &= ~(TF_REQ_SCALE|TF_REQ_TSTMP|TF_SACK_PERMIT);
  798         /*
  799          * If we backed off this far, notify the L3 protocol that we're having
  800          * connection problems.
  801          */
  802         if (tp->t_rxtshift > TCP_RTT_INVALIDATE) {
  803 #ifdef INET6
  804                 if ((tp->t_inpcb->inp_vflag & INP_IPV6) != 0)
  805                         in6_losing(tp->t_inpcb);
  806                 else
  807 #endif
  808                         in_losing(tp->t_inpcb);
  809         }
  810         tp->snd_nxt = tp->snd_una;
  811         tp->snd_recover = tp->snd_max;
  812         /*
  813          * Force a segment to be sent.
  814          */
  815         tp->t_flags |= TF_ACKNOW;
  816         /*
  817          * If timing a segment in this window, stop the timer.
  818          */
  819         tp->t_rtttime = 0;
  820 
  821         cc_cong_signal(tp, NULL, CC_RTO);
  822 
  823         (void) tp->t_fb->tfb_tcp_output(tp);
  824 
  825 #ifdef TCPDEBUG
  826         if (tp != NULL && (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
  827                 tcp_trace(TA_USER, ostate, tp, (void *)0, (struct tcphdr *)0,
  828                           PRU_SLOWTIMO);
  829 #endif
  830         TCP_PROBE2(debug__user, tp, PRU_SLOWTIMO);
  831         INP_WUNLOCK(inp);
  832 out:
  833         CURVNET_RESTORE();
  834 }
  835 
  836 void
  837 tcp_timer_activate(struct tcpcb *tp, uint32_t timer_type, u_int delta)
  838 {
  839         struct callout *t_callout;
  840         timeout_t *f_callout;
  841         struct inpcb *inp = tp->t_inpcb;
  842         int cpu = inp_to_cpuid(inp);
  843 
  844 #ifdef TCP_OFFLOAD
  845         if (tp->t_flags & TF_TOE)
  846                 return;
  847 #endif
  848 
  849         if (tp->t_timers->tt_flags & TT_STOPPED)
  850                 return;
  851 
  852         switch (timer_type) {
  853                 case TT_DELACK:
  854                         t_callout = &tp->t_timers->tt_delack;
  855                         f_callout = tcp_timer_delack;
  856                         break;
  857                 case TT_REXMT:
  858                         t_callout = &tp->t_timers->tt_rexmt;
  859                         f_callout = tcp_timer_rexmt;
  860                         break;
  861                 case TT_PERSIST:
  862                         t_callout = &tp->t_timers->tt_persist;
  863                         f_callout = tcp_timer_persist;
  864                         break;
  865                 case TT_KEEP:
  866                         t_callout = &tp->t_timers->tt_keep;
  867                         f_callout = tcp_timer_keep;
  868                         break;
  869                 case TT_2MSL:
  870                         t_callout = &tp->t_timers->tt_2msl;
  871                         f_callout = tcp_timer_2msl;
  872                         break;
  873                 default:
  874                         if (tp->t_fb->tfb_tcp_timer_activate) {
  875                                 tp->t_fb->tfb_tcp_timer_activate(tp, timer_type, delta);
  876                                 return;
  877                         }
  878                         panic("tp %p bad timer_type %#x", tp, timer_type);
  879                 }
  880         if (delta == 0) {
  881                 callout_stop(t_callout);
  882         } else {
  883                 callout_reset_on(t_callout, delta, f_callout, tp, cpu);
  884         }
  885 }
  886 
  887 int
  888 tcp_timer_active(struct tcpcb *tp, uint32_t timer_type)
  889 {
  890         struct callout *t_callout;
  891 
  892         switch (timer_type) {
  893                 case TT_DELACK:
  894                         t_callout = &tp->t_timers->tt_delack;
  895                         break;
  896                 case TT_REXMT:
  897                         t_callout = &tp->t_timers->tt_rexmt;
  898                         break;
  899                 case TT_PERSIST:
  900                         t_callout = &tp->t_timers->tt_persist;
  901                         break;
  902                 case TT_KEEP:
  903                         t_callout = &tp->t_timers->tt_keep;
  904                         break;
  905                 case TT_2MSL:
  906                         t_callout = &tp->t_timers->tt_2msl;
  907                         break;
  908                 default:
  909                         if (tp->t_fb->tfb_tcp_timer_active) {
  910                                 return(tp->t_fb->tfb_tcp_timer_active(tp, timer_type));
  911                         }
  912                         panic("tp %p bad timer_type %#x", tp, timer_type);
  913                 }
  914         return callout_active(t_callout);
  915 }
  916 
  917 /*
  918  * Stop the timer from running, and apply a flag
  919  * against the timer_flags that will force the
  920  * timer never to run. The flag is needed to assure
  921  * a race does not leave it running and cause
  922  * the timer to possibly restart itself (keep and persist
  923  * especially do this). 
  924  */
  925 int
  926 tcp_timer_suspend(struct tcpcb *tp, uint32_t timer_type)
  927 {
  928         struct callout *t_callout;
  929         uint32_t t_flags;
  930 
  931         switch (timer_type) {
  932                 case TT_DELACK:
  933                         t_flags = TT_DELACK_SUS;
  934                         t_callout = &tp->t_timers->tt_delack;
  935                         break;
  936                 case TT_REXMT:
  937                         t_flags = TT_REXMT_SUS;
  938                         t_callout = &tp->t_timers->tt_rexmt;
  939                         break;
  940                 case TT_PERSIST:
  941                         t_flags = TT_PERSIST_SUS;
  942                         t_callout = &tp->t_timers->tt_persist;
  943                         break;
  944                 case TT_KEEP:
  945                         t_flags = TT_KEEP_SUS;
  946                         t_callout = &tp->t_timers->tt_keep;
  947                         break;
  948                 case TT_2MSL:
  949                         t_flags = TT_2MSL_SUS;
  950                         t_callout = &tp->t_timers->tt_2msl;
  951                         break;
  952                 default:
  953                         panic("tp:%p bad timer_type 0x%x", tp, timer_type);
  954         }
  955         tp->t_timers->tt_flags |= t_flags;
  956         return (callout_stop(t_callout));
  957 }
  958 
  959 void
  960 tcp_timers_unsuspend(struct tcpcb *tp, uint32_t timer_type)
  961 {
  962         switch (timer_type) {
  963                 case TT_DELACK:
  964                         if (tp->t_timers->tt_flags & TT_DELACK_SUS) {
  965                                 tp->t_timers->tt_flags &= ~TT_DELACK_SUS;
  966                                 if (tp->t_flags & TF_DELACK) {
  967                                         /* Delayed ack timer should be up activate a timer */
  968                                         tp->t_flags &= ~TF_DELACK;
  969                                         tcp_timer_activate(tp, TT_DELACK,
  970                                             tcp_delacktime);
  971                                 }
  972                         }
  973                         break;
  974                 case TT_REXMT:
  975                         if (tp->t_timers->tt_flags & TT_REXMT_SUS) {
  976                                 tp->t_timers->tt_flags &= ~TT_REXMT_SUS;
  977                                 if (SEQ_GT(tp->snd_max, tp->snd_una) &&
  978                                     (tcp_timer_active((tp), TT_PERSIST) == 0) &&
  979                                     tp->snd_wnd) {
  980                                         /* We have outstanding data activate a timer */
  981                                         tcp_timer_activate(tp, TT_REXMT, 
  982                                             tp->t_rxtcur);
  983                                 }
  984                         }
  985                         break;
  986                 case TT_PERSIST:
  987                         if (tp->t_timers->tt_flags & TT_PERSIST_SUS) {
  988                                 tp->t_timers->tt_flags &= ~TT_PERSIST_SUS;
  989                                 if (tp->snd_wnd == 0) {
  990                                         /* Activate the persists timer */
  991                                         tp->t_rxtshift = 0;
  992                                         tcp_setpersist(tp);
  993                                 }
  994                         }
  995                         break;
  996                 case TT_KEEP:
  997                         if (tp->t_timers->tt_flags & TT_KEEP_SUS) {
  998                                 tp->t_timers->tt_flags &= ~TT_KEEP_SUS;
  999                                 tcp_timer_activate(tp, TT_KEEP,
 1000                                             TCPS_HAVEESTABLISHED(tp->t_state) ?
 1001                                             TP_KEEPIDLE(tp) : TP_KEEPINIT(tp));
 1002                         }
 1003                         break;
 1004                 case TT_2MSL:
 1005                         if (tp->t_timers->tt_flags &= TT_2MSL_SUS) {
 1006                                 tp->t_timers->tt_flags &= ~TT_2MSL_SUS;
 1007                                 if ((tp->t_state == TCPS_FIN_WAIT_2) &&
 1008                                     ((tp->t_inpcb->inp_socket == NULL) ||
 1009                                      (tp->t_inpcb->inp_socket->so_rcv.sb_state & SBS_CANTRCVMORE))) {
 1010                                         /* Star the 2MSL timer */
 1011                                         tcp_timer_activate(tp, TT_2MSL,
 1012                                             (tcp_fast_finwait2_recycle) ?
 1013                                             tcp_finwait2_timeout : TP_MAXIDLE(tp));
 1014                                 }
 1015                         }
 1016                         break;
 1017                 default:
 1018                         panic("tp:%p bad timer_type 0x%x", tp, timer_type);
 1019         }
 1020 }
 1021 
 1022 void
 1023 tcp_timer_stop(struct tcpcb *tp, uint32_t timer_type)
 1024 {
 1025         struct callout *t_callout;
 1026 
 1027         tp->t_timers->tt_flags |= TT_STOPPED;
 1028         switch (timer_type) {
 1029                 case TT_DELACK:
 1030                         t_callout = &tp->t_timers->tt_delack;
 1031                         break;
 1032                 case TT_REXMT:
 1033                         t_callout = &tp->t_timers->tt_rexmt;
 1034                         break;
 1035                 case TT_PERSIST:
 1036                         t_callout = &tp->t_timers->tt_persist;
 1037                         break;
 1038                 case TT_KEEP:
 1039                         t_callout = &tp->t_timers->tt_keep;
 1040                         break;
 1041                 case TT_2MSL:
 1042                         t_callout = &tp->t_timers->tt_2msl;
 1043                         break;
 1044                 default:
 1045                         if (tp->t_fb->tfb_tcp_timer_stop) {
 1046                                 /* 
 1047                                  * XXXrrs we need to look at this with the
 1048                                  * stop case below (flags).
 1049                                  */
 1050                                 tp->t_fb->tfb_tcp_timer_stop(tp, timer_type);
 1051                                 return;
 1052                         }
 1053                         panic("tp %p bad timer_type %#x", tp, timer_type);
 1054                 }
 1055 
 1056         if (callout_async_drain(t_callout, tcp_timer_discard) == 0) {
 1057                 /*
 1058                  * Can't stop the callout, defer tcpcb actual deletion
 1059                  * to the last one. We do this using the async drain
 1060                  * function and incrementing the count in 
 1061                  */
 1062                 tp->t_timers->tt_draincnt++;
 1063         }
 1064 }

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