sys/netinet/tcp_timer.c

   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("$FreeBSD$");
  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,
  86     CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_NEEDGIANT,
  87     &tcp_persmin, 0, sysctl_msec_to_ticks, "I",
  88     "minimum persistence interval");
  89
  90 int    tcp_persmax;
  91 SYSCTL_PROC(_net_inet_tcp, OID_AUTO, persmax,
  92     CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_NEEDGIANT,
  93     &tcp_persmax, 0, sysctl_msec_to_ticks, "I",
  94     "maximum persistence interval");
  95
  96 int     tcp_keepinit;
  97 SYSCTL_PROC(_net_inet_tcp, TCPCTL_KEEPINIT, keepinit,
  98     CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_NEEDGIANT,
  99     &tcp_keepinit, 0, sysctl_msec_to_ticks, "I",
 100     "time to establish connection");
 101
 102 int     tcp_keepidle;
 103 SYSCTL_PROC(_net_inet_tcp, TCPCTL_KEEPIDLE, keepidle,
 104     CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_NEEDGIANT,
 105     &tcp_keepidle, 0, sysctl_msec_to_ticks, "I",
 106     "time before keepalive probes begin");
 107
 108 int     tcp_keepintvl;
 109 SYSCTL_PROC(_net_inet_tcp, TCPCTL_KEEPINTVL, keepintvl,
 110     CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_NEEDGIANT,
 111     &tcp_keepintvl, 0, sysctl_msec_to_ticks, "I",
 112     "time between keepalive probes");
 113
 114 int     tcp_delacktime;
 115 SYSCTL_PROC(_net_inet_tcp, TCPCTL_DELACKTIME, delacktime,
 116     CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_NEEDGIANT,
 117     &tcp_delacktime, 0, sysctl_msec_to_ticks, "I",
 118     "Time before a delayed ACK is sent");
 119
 120 int     tcp_msl;
 121 SYSCTL_PROC(_net_inet_tcp, OID_AUTO, msl,
 122     CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_NEEDGIANT,
 123     &tcp_msl, 0, sysctl_msec_to_ticks, "I",
 124     "Maximum segment lifetime");
 125
 126 int     tcp_rexmit_initial;
 127 SYSCTL_PROC(_net_inet_tcp, OID_AUTO, rexmit_initial,
 128    CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_NEEDGIANT,
 129     &tcp_rexmit_initial, 0, sysctl_msec_to_ticks, "I",
 130     "Initial Retransmission Timeout");
 131
 132 int     tcp_rexmit_min;
 133 SYSCTL_PROC(_net_inet_tcp, OID_AUTO, rexmit_min,
 134     CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_NEEDGIANT,
 135     &tcp_rexmit_min, 0, sysctl_msec_to_ticks, "I",
 136     "Minimum Retransmission Timeout");
 137
 138 int     tcp_rexmit_slop;
 139 SYSCTL_PROC(_net_inet_tcp, OID_AUTO, rexmit_slop,
 140     CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_NEEDGIANT,
 141     &tcp_rexmit_slop, 0, sysctl_msec_to_ticks, "I",
 142     "Retransmission Timer Slop");
 143
 144 VNET_DEFINE(int, tcp_always_keepalive) = 1;
 145 SYSCTL_INT(_net_inet_tcp, OID_AUTO, always_keepalive, CTLFLAG_VNET|CTLFLAG_RW,
 146     &VNET_NAME(tcp_always_keepalive) , 0,
 147     "Assume SO_KEEPALIVE on all TCP connections");
 148
 149 int    tcp_fast_finwait2_recycle = 0;
 150 SYSCTL_INT(_net_inet_tcp, OID_AUTO, fast_finwait2_recycle, CTLFLAG_RW,
 151     &tcp_fast_finwait2_recycle, 0,
 152     "Recycle closed FIN_WAIT_2 connections faster");
 153
 154 int    tcp_finwait2_timeout;
 155 SYSCTL_PROC(_net_inet_tcp, OID_AUTO, finwait2_timeout,
 156     CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_NEEDGIANT,
 157     &tcp_finwait2_timeout, 0, sysctl_msec_to_ticks, "I",
 158     "FIN-WAIT2 timeout");
 159
 160 int     tcp_keepcnt = TCPTV_KEEPCNT;
 161 SYSCTL_INT(_net_inet_tcp, OID_AUTO, keepcnt, CTLFLAG_RW, &tcp_keepcnt, 0,
 162     "Number of keepalive probes to send");
 163
 164         /* max idle probes */
 165 int     tcp_maxpersistidle;
 166
 167 int     tcp_rexmit_drop_options = 0;
 168 SYSCTL_INT(_net_inet_tcp, OID_AUTO, rexmit_drop_options, CTLFLAG_RW,
 169     &tcp_rexmit_drop_options, 0,
 170     "Drop TCP options from 3rd and later retransmitted SYN");
 171
 172 VNET_DEFINE(int, tcp_pmtud_blackhole_detect);
 173 SYSCTL_INT(_net_inet_tcp, OID_AUTO, pmtud_blackhole_detection,
 174     CTLFLAG_RW|CTLFLAG_VNET,
 175     &VNET_NAME(tcp_pmtud_blackhole_detect), 0,
 176     "Path MTU Discovery Black Hole Detection Enabled");
 177
 178 #ifdef INET
 179 VNET_DEFINE(int, tcp_pmtud_blackhole_mss) = 1200;
 180 SYSCTL_INT(_net_inet_tcp, OID_AUTO, pmtud_blackhole_mss,
 181     CTLFLAG_RW|CTLFLAG_VNET,
 182     &VNET_NAME(tcp_pmtud_blackhole_mss), 0,
 183     "Path MTU Discovery Black Hole Detection lowered MSS");
 184 #endif
 185
 186 #ifdef INET6
 187 VNET_DEFINE(int, tcp_v6pmtud_blackhole_mss) = 1220;
 188 SYSCTL_INT(_net_inet_tcp, OID_AUTO, v6pmtud_blackhole_mss,
 189     CTLFLAG_RW|CTLFLAG_VNET,
 190     &VNET_NAME(tcp_v6pmtud_blackhole_mss), 0,
 191     "Path MTU Discovery IPv6 Black Hole Detection lowered MSS");
 192 #endif
 193
 194 #ifdef  RSS
 195 static int      per_cpu_timers = 1;
 196 #else
 197 static int      per_cpu_timers = 0;
 198 #endif
 199 SYSCTL_INT(_net_inet_tcp, OID_AUTO, per_cpu_timers, CTLFLAG_RW,
 200     &per_cpu_timers , 0, "run tcp timers on all cpus");
 201
 202 /*
 203  * Map the given inp to a CPU id.
 204  *
 205  * This queries RSS if it's compiled in, else it defaults to the current
 206  * CPU ID.
 207  */
 208 inline int
 209 inp_to_cpuid(struct inpcb *inp)
 210 {
 211         u_int cpuid;
 212
 213 #ifdef  RSS
 214         if (per_cpu_timers) {
 215                 cpuid = rss_hash2cpuid(inp->inp_flowid, inp->inp_flowtype);
 216                 if (cpuid == NETISR_CPUID_NONE)
 217                         return (curcpu);        /* XXX */
 218                 else
 219                         return (cpuid);
 220         }
 221 #else
 222         /* Legacy, pre-RSS behaviour */
 223         if (per_cpu_timers) {
 224                 /*
 225                  * We don't have a flowid -> cpuid mapping, so cheat and
 226                  * just map unknown cpuids to curcpu.  Not the best, but
 227                  * apparently better than defaulting to swi 0.
 228                  */
 229                 cpuid = inp->inp_flowid % (mp_maxid + 1);
 230                 if (! CPU_ABSENT(cpuid))
 231                         return (cpuid);
 232                 return (curcpu);
 233         }
 234 #endif
 235         /* Default for RSS and non-RSS - cpuid 0 */
 236         else {
 237                 return (0);
 238         }
 239 }
 240
 241 /*
 242  * Tcp protocol timeout routine called every 500 ms.
 243  * Updates timestamps used for TCP
 244  * causes finite state machine actions if timers expire.
 245  */
 246 void
 247 tcp_slowtimo(void)
 248 {
 249         VNET_ITERATOR_DECL(vnet_iter);
 250
 251         VNET_LIST_RLOCK_NOSLEEP();
 252         VNET_FOREACH(vnet_iter) {
 253                 CURVNET_SET(vnet_iter);
 254                 (void) tcp_tw_2msl_scan(0);
 255                 CURVNET_RESTORE();
 256         }
 257         VNET_LIST_RUNLOCK_NOSLEEP();
 258 }
 259
 260 int     tcp_backoff[TCP_MAXRXTSHIFT + 1] =
 261     { 1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 512, 512, 512 };
 262
 263 int tcp_totbackoff = 2559;      /* sum of tcp_backoff[] */
 264
 265 /*
 266  * TCP timer processing.
 267  */
 268
 269 void
 270 tcp_timer_delack(void *xtp)
 271 {
 272         struct epoch_tracker et;
 273         struct tcpcb *tp = xtp;
 274         struct inpcb *inp;
 275         CURVNET_SET(tp->t_vnet);
 276
 277         inp = tp->t_inpcb;
 278         KASSERT(inp != NULL, ("%s: tp %p tp->t_inpcb == NULL", __func__, tp));
 279         INP_WLOCK(inp);
 280         if (callout_pending(&tp->t_timers->tt_delack) ||
 281             !callout_active(&tp->t_timers->tt_delack)) {
 282                 INP_WUNLOCK(inp);
 283                 CURVNET_RESTORE();
 284                 return;
 285         }
 286         callout_deactivate(&tp->t_timers->tt_delack);
 287         if ((inp->inp_flags & INP_DROPPED) != 0) {
 288                 INP_WUNLOCK(inp);
 289                 CURVNET_RESTORE();
 290                 return;
 291         }
 292         tp->t_flags |= TF_ACKNOW;
 293         TCPSTAT_INC(tcps_delack);
 294         NET_EPOCH_ENTER(et);
 295         (void) tp->t_fb->tfb_tcp_output(tp);
 296         INP_WUNLOCK(inp);
 297         NET_EPOCH_EXIT(et);
 298         CURVNET_RESTORE();
 299 }
 300
 301 void
 302 tcp_inpinfo_lock_del(struct inpcb *inp, struct tcpcb *tp)
 303 {
 304         if (inp && tp != NULL)
 305                 INP_WUNLOCK(inp);
 306 }
 307
 308 void
 309 tcp_timer_2msl(void *xtp)
 310 {
 311         struct tcpcb *tp = xtp;
 312         struct inpcb *inp;
 313         struct epoch_tracker et;
 314         CURVNET_SET(tp->t_vnet);
 315 #ifdef TCPDEBUG
 316         int ostate;
 317
 318         ostate = tp->t_state;
 319 #endif
 320         inp = tp->t_inpcb;
 321         KASSERT(inp != NULL, ("%s: tp %p tp->t_inpcb == NULL", __func__, tp));
 322         INP_WLOCK(inp);
 323         tcp_free_sackholes(tp);
 324         if (callout_pending(&tp->t_timers->tt_2msl) ||
 325             !callout_active(&tp->t_timers->tt_2msl)) {
 326                 INP_WUNLOCK(tp->t_inpcb);
 327                 CURVNET_RESTORE();
 328                 return;
 329         }
 330         callout_deactivate(&tp->t_timers->tt_2msl);
 331         if ((inp->inp_flags & INP_DROPPED) != 0) {
 332                 INP_WUNLOCK(inp);
 333                 CURVNET_RESTORE();
 334                 return;
 335         }
 336         KASSERT((tp->t_timers->tt_flags & TT_STOPPED) == 0,
 337                 ("%s: tp %p tcpcb can't be stopped here", __func__, tp));
 338         /*
 339          * 2 MSL timeout in shutdown went off.  If we're closed but
 340          * still waiting for peer to close and connection has been idle
 341          * too long delete connection control block.  Otherwise, check
 342          * again in a bit.
 343          *
 344          * If in TIME_WAIT state just ignore as this timeout is handled in
 345          * tcp_tw_2msl_scan().
 346          *
 347          * If fastrecycle of FIN_WAIT_2, in FIN_WAIT_2 and receiver has closed,
 348          * there's no point in hanging onto FIN_WAIT_2 socket. Just close it.
 349          * Ignore fact that there were recent incoming segments.
 350          */
 351         if ((inp->inp_flags & INP_TIMEWAIT) != 0) {
 352                 INP_WUNLOCK(inp);
 353                 CURVNET_RESTORE();
 354                 return;
 355         }
 356         if (tcp_fast_finwait2_recycle && tp->t_state == TCPS_FIN_WAIT_2 &&
 357             tp->t_inpcb && tp->t_inpcb->inp_socket &&
 358             (tp->t_inpcb->inp_socket->so_rcv.sb_state & SBS_CANTRCVMORE)) {
 359                 TCPSTAT_INC(tcps_finwait2_drops);
 360                 if (inp->inp_flags & (INP_TIMEWAIT | INP_DROPPED)) {
 361                         tcp_inpinfo_lock_del(inp, tp);
 362                         goto out;
 363                 }
 364                 NET_EPOCH_ENTER(et);
 365                 tp = tcp_close(tp);
 366                 NET_EPOCH_EXIT(et);
 367                 tcp_inpinfo_lock_del(inp, tp);
 368                 goto out;
 369         } else {
 370                 if (ticks - tp->t_rcvtime <= TP_MAXIDLE(tp)) {
 371                         callout_reset(&tp->t_timers->tt_2msl,
 372                                       TP_KEEPINTVL(tp), tcp_timer_2msl, tp);
 373                 } else {
 374                         if (inp->inp_flags & (INP_TIMEWAIT | INP_DROPPED)) {
 375                                 tcp_inpinfo_lock_del(inp, tp);
 376                                 goto out;
 377                         }
 378                         NET_EPOCH_ENTER(et);
 379                         tp = tcp_close(tp);
 380                         NET_EPOCH_EXIT(et);
 381                         tcp_inpinfo_lock_del(inp, tp);
 382                         goto out;
 383                 }
 384         }
 385
 386 #ifdef TCPDEBUG
 387         if (tp != NULL && (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
 388                 tcp_trace(TA_USER, ostate, tp, (void *)0, (struct tcphdr *)0,
 389                           PRU_SLOWTIMO);
 390 #endif
 391         TCP_PROBE2(debug__user, tp, PRU_SLOWTIMO);
 392
 393         if (tp != NULL)
 394                 INP_WUNLOCK(inp);
 395 out:
 396         CURVNET_RESTORE();
 397 }
 398
 399 void
 400 tcp_timer_keep(void *xtp)
 401 {
 402         struct tcpcb *tp = xtp;
 403         struct tcptemp *t_template;
 404         struct inpcb *inp;
 405         struct epoch_tracker et;
 406         CURVNET_SET(tp->t_vnet);
 407 #ifdef TCPDEBUG
 408         int ostate;
 409
 410         ostate = tp->t_state;
 411 #endif
 412         inp = tp->t_inpcb;
 413         KASSERT(inp != NULL, ("%s: tp %p tp->t_inpcb == NULL", __func__, tp));
 414         INP_WLOCK(inp);
 415         if (callout_pending(&tp->t_timers->tt_keep) ||
 416             !callout_active(&tp->t_timers->tt_keep)) {
 417                 INP_WUNLOCK(inp);
 418                 CURVNET_RESTORE();
 419                 return;
 420         }
 421         callout_deactivate(&tp->t_timers->tt_keep);
 422         if ((inp->inp_flags & INP_DROPPED) != 0) {
 423                 INP_WUNLOCK(inp);
 424                 CURVNET_RESTORE();
 425                 return;
 426         }
 427         KASSERT((tp->t_timers->tt_flags & TT_STOPPED) == 0,
 428                 ("%s: tp %p tcpcb can't be stopped here", __func__, tp));
 429
 430         /*
 431          * Because we don't regularly reset the keepalive callout in
 432          * the ESTABLISHED state, it may be that we don't actually need
 433          * to send a keepalive yet. If that occurs, schedule another
 434          * call for the next time the keepalive timer might expire.
 435          */
 436         if (TCPS_HAVEESTABLISHED(tp->t_state)) {
 437                 u_int idletime;
 438
 439                 idletime = ticks - tp->t_rcvtime;
 440                 if (idletime < TP_KEEPIDLE(tp)) {
 441                         callout_reset(&tp->t_timers->tt_keep,
 442                             TP_KEEPIDLE(tp) - idletime, tcp_timer_keep, tp);
 443                         INP_WUNLOCK(inp);
 444                         CURVNET_RESTORE();
 445                         return;
 446                 }
 447         }
 448
 449         /*
 450          * Keep-alive timer went off; send something
 451          * or drop connection if idle for too long.
 452          */
 453         TCPSTAT_INC(tcps_keeptimeo);
 454         if (tp->t_state < TCPS_ESTABLISHED)
 455                 goto dropit;
 456         if ((V_tcp_always_keepalive ||
 457             inp->inp_socket->so_options & SO_KEEPALIVE) &&
 458             tp->t_state <= TCPS_CLOSING) {
 459                 if (ticks - tp->t_rcvtime >= TP_KEEPIDLE(tp) + TP_MAXIDLE(tp))
 460                         goto dropit;
 461                 /*
 462                  * Send a packet designed to force a response
 463                  * if the peer is up and reachable:
 464                  * either an ACK if the connection is still alive,
 465                  * or an RST if the peer has closed the connection
 466                  * due to timeout or reboot.
 467                  * Using sequence number tp->snd_una-1
 468                  * causes the transmitted zero-length segment
 469                  * to lie outside the receive window;
 470                  * by the protocol spec, this requires the
 471                  * correspondent TCP to respond.
 472                  */
 473                 TCPSTAT_INC(tcps_keepprobe);
 474                 t_template = tcpip_maketemplate(inp);
 475                 if (t_template) {
 476                         NET_EPOCH_ENTER(et);
 477                         tcp_respond(tp, t_template->tt_ipgen,
 478                                     &t_template->tt_t, (struct mbuf *)NULL,
 479                                     tp->rcv_nxt, tp->snd_una - 1, 0);
 480                         NET_EPOCH_EXIT(et);
 481                         free(t_template, M_TEMP);
 482                 }
 483                 callout_reset(&tp->t_timers->tt_keep, TP_KEEPINTVL(tp),
 484                               tcp_timer_keep, tp);
 485         } else
 486                 callout_reset(&tp->t_timers->tt_keep, TP_KEEPIDLE(tp),
 487                               tcp_timer_keep, tp);
 488
 489 #ifdef TCPDEBUG
 490         if (inp->inp_socket->so_options & SO_DEBUG)
 491                 tcp_trace(TA_USER, ostate, tp, (void *)0, (struct tcphdr *)0,
 492                           PRU_SLOWTIMO);
 493 #endif
 494         TCP_PROBE2(debug__user, tp, PRU_SLOWTIMO);
 495         INP_WUNLOCK(inp);
 496         CURVNET_RESTORE();
 497         return;
 498
 499 dropit:
 500         TCPSTAT_INC(tcps_keepdrops);
 501         if (inp->inp_flags & (INP_TIMEWAIT | INP_DROPPED)) {
 502                 tcp_inpinfo_lock_del(inp, tp);
 503                 goto out;
 504         }
 505         NET_EPOCH_ENTER(et);
 506         tp = tcp_drop(tp, ETIMEDOUT);
 507
 508 #ifdef TCPDEBUG
 509         if (tp != NULL && (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
 510                 tcp_trace(TA_USER, ostate, tp, (void *)0, (struct tcphdr *)0,
 511                           PRU_SLOWTIMO);
 512 #endif
 513         TCP_PROBE2(debug__user, tp, PRU_SLOWTIMO);
 514         NET_EPOCH_EXIT(et);
 515         tcp_inpinfo_lock_del(inp, tp);
 516  out:
 517         CURVNET_RESTORE();
 518 }
 519
 520 void
 521 tcp_timer_persist(void *xtp)
 522 {
 523         struct tcpcb *tp = xtp;
 524         struct inpcb *inp;
 525         struct epoch_tracker et;
 526         CURVNET_SET(tp->t_vnet);
 527 #ifdef TCPDEBUG
 528         int ostate;
 529
 530         ostate = tp->t_state;
 531 #endif
 532         inp = tp->t_inpcb;
 533         KASSERT(inp != NULL, ("%s: tp %p tp->t_inpcb == NULL", __func__, tp));
 534         INP_WLOCK(inp);
 535         if (callout_pending(&tp->t_timers->tt_persist) ||
 536             !callout_active(&tp->t_timers->tt_persist)) {
 537                 INP_WUNLOCK(inp);
 538                 CURVNET_RESTORE();
 539                 return;
 540         }
 541         callout_deactivate(&tp->t_timers->tt_persist);
 542         if ((inp->inp_flags & INP_DROPPED) != 0) {
 543                 INP_WUNLOCK(inp);
 544                 CURVNET_RESTORE();
 545                 return;
 546         }
 547         KASSERT((tp->t_timers->tt_flags & TT_STOPPED) == 0,
 548                 ("%s: tp %p tcpcb can't be stopped here", __func__, tp));
 549         /*
 550          * Persistence timer into zero window.
 551          * Force a byte to be output, if possible.
 552          */
 553         TCPSTAT_INC(tcps_persisttimeo);
 554         /*
 555          * Hack: if the peer is dead/unreachable, we do not
 556          * time out if the window is closed.  After a full
 557          * backoff, drop the connection if the idle time
 558          * (no responses to probes) reaches the maximum
 559          * backoff that we would use if retransmitting.
 560          */
 561         if (tp->t_rxtshift == TCP_MAXRXTSHIFT &&
 562             (ticks - tp->t_rcvtime >= tcp_maxpersistidle ||
 563              ticks - tp->t_rcvtime >= TCP_REXMTVAL(tp) * tcp_totbackoff)) {
 564                 TCPSTAT_INC(tcps_persistdrop);
 565                 if (inp->inp_flags & (INP_TIMEWAIT | INP_DROPPED)) {
 566                         tcp_inpinfo_lock_del(inp, tp);
 567                         goto out;
 568                 }
 569                 NET_EPOCH_ENTER(et);
 570                 tp = tcp_drop(tp, ETIMEDOUT);
 571                 NET_EPOCH_EXIT(et);
 572                 tcp_inpinfo_lock_del(inp, tp);
 573                 goto out;
 574         }
 575         /*
 576          * If the user has closed the socket then drop a persisting
 577          * connection after a much reduced timeout.
 578          */
 579         if (tp->t_state > TCPS_CLOSE_WAIT &&
 580             (ticks - tp->t_rcvtime) >= TCPTV_PERSMAX) {
 581                 TCPSTAT_INC(tcps_persistdrop);
 582                 if (inp->inp_flags & (INP_TIMEWAIT | INP_DROPPED)) {
 583                         tcp_inpinfo_lock_del(inp, tp);
 584                         goto out;
 585                 }
 586                 NET_EPOCH_ENTER(et);
 587                 tp = tcp_drop(tp, ETIMEDOUT);
 588                 NET_EPOCH_EXIT(et);
 589                 tcp_inpinfo_lock_del(inp, tp);
 590                 goto out;
 591         }
 592         tcp_setpersist(tp);
 593         tp->t_flags |= TF_FORCEDATA;
 594         NET_EPOCH_ENTER(et);
 595         (void) tp->t_fb->tfb_tcp_output(tp);
 596         NET_EPOCH_EXIT(et);
 597         tp->t_flags &= ~TF_FORCEDATA;
 598
 599 #ifdef TCPDEBUG
 600         if (tp != NULL && tp->t_inpcb->inp_socket->so_options & SO_DEBUG)
 601                 tcp_trace(TA_USER, ostate, tp, NULL, NULL, PRU_SLOWTIMO);
 602 #endif
 603         TCP_PROBE2(debug__user, tp, PRU_SLOWTIMO);
 604         INP_WUNLOCK(inp);
 605 out:
 606         CURVNET_RESTORE();
 607 }
 608
 609 void
 610 tcp_timer_rexmt(void * xtp)
 611 {
 612         struct tcpcb *tp = xtp;
 613         CURVNET_SET(tp->t_vnet);
 614         int rexmt;
 615         struct inpcb *inp;
 616         struct epoch_tracker et;
 617 #ifdef TCPDEBUG
 618         int ostate;
 619
 620         ostate = tp->t_state;
 621 #endif
 622         inp = tp->t_inpcb;
 623         KASSERT(inp != NULL, ("%s: tp %p tp->t_inpcb == NULL", __func__, tp));
 624         INP_WLOCK(inp);
 625         if (callout_pending(&tp->t_timers->tt_rexmt) ||
 626             !callout_active(&tp->t_timers->tt_rexmt)) {
 627                 INP_WUNLOCK(inp);
 628                 CURVNET_RESTORE();
 629                 return;
 630         }
 631         callout_deactivate(&tp->t_timers->tt_rexmt);
 632         if ((inp->inp_flags & INP_DROPPED) != 0) {
 633                 INP_WUNLOCK(inp);
 634                 CURVNET_RESTORE();
 635                 return;
 636         }
 637         KASSERT((tp->t_timers->tt_flags & TT_STOPPED) == 0,
 638                 ("%s: tp %p tcpcb can't be stopped here", __func__, tp));
 639         tcp_free_sackholes(tp);
 640         TCP_LOG_EVENT(tp, NULL, NULL, NULL, TCP_LOG_RTO, 0, 0, NULL, false);
 641         if (tp->t_fb->tfb_tcp_rexmit_tmr) {
 642                 /* The stack has a timer action too. */
 643                 (*tp->t_fb->tfb_tcp_rexmit_tmr)(tp);
 644         }
 645         /*
 646          * Retransmission timer went off.  Message has not
 647          * been acked within retransmit interval.  Back off
 648          * to a longer retransmit interval and retransmit one segment.
 649          */
 650         if (++tp->t_rxtshift > TCP_MAXRXTSHIFT) {
 651                 tp->t_rxtshift = TCP_MAXRXTSHIFT;
 652                 TCPSTAT_INC(tcps_timeoutdrop);
 653                 if (inp->inp_flags & (INP_TIMEWAIT | INP_DROPPED)) {
 654                         tcp_inpinfo_lock_del(inp, tp);
 655                         goto out;
 656                 }
 657                 NET_EPOCH_ENTER(et);
 658                 tp = tcp_drop(tp, ETIMEDOUT);
 659                 NET_EPOCH_EXIT(et);
 660                 tcp_inpinfo_lock_del(inp, tp);
 661                 goto out;
 662         }
 663         if (tp->t_state == TCPS_SYN_SENT) {
 664                 /*
 665                  * If the SYN was retransmitted, indicate CWND to be
 666                  * limited to 1 segment in cc_conn_init().
 667                  */
 668                 tp->snd_cwnd = 1;
 669         } else if (tp->t_rxtshift == 1) {
 670                 /*
 671                  * first retransmit; record ssthresh and cwnd so they can
 672                  * be recovered if this turns out to be a "bad" retransmit.
 673                  * A retransmit is considered "bad" if an ACK for this
 674                  * segment is received within RTT/2 interval; the assumption
 675                  * here is that the ACK was already in flight.  See
 676                  * "On Estimating End-to-End Network Path Properties" by
 677                  * Allman and Paxson for more details.
 678                  */
 679                 tp->snd_cwnd_prev = tp->snd_cwnd;
 680                 tp->snd_ssthresh_prev = tp->snd_ssthresh;
 681                 tp->snd_recover_prev = tp->snd_recover;
 682                 if (IN_FASTRECOVERY(tp->t_flags))
 683                         tp->t_flags |= TF_WASFRECOVERY;
 684                 else
 685                         tp->t_flags &= ~TF_WASFRECOVERY;
 686                 if (IN_CONGRECOVERY(tp->t_flags))
 687                         tp->t_flags |= TF_WASCRECOVERY;
 688                 else
 689                         tp->t_flags &= ~TF_WASCRECOVERY;
 690                 if ((tp->t_flags & TF_RCVD_TSTMP) == 0)
 691                         tp->t_badrxtwin = ticks + (tp->t_srtt >> (TCP_RTT_SHIFT + 1));
 692                 /* In the event that we've negotiated timestamps
 693                  * badrxtwin will be set to the value that we set
 694                  * the retransmitted packet's to_tsval to by tcp_output
 695                  */
 696                 tp->t_flags |= TF_PREVVALID;
 697         } else
 698                 tp->t_flags &= ~TF_PREVVALID;
 699         TCPSTAT_INC(tcps_rexmttimeo);
 700         if ((tp->t_state == TCPS_SYN_SENT) ||
 701             (tp->t_state == TCPS_SYN_RECEIVED))
 702                 rexmt = tcp_rexmit_initial * tcp_backoff[tp->t_rxtshift];
 703         else
 704                 rexmt = TCP_REXMTVAL(tp) * tcp_backoff[tp->t_rxtshift];
 705         TCPT_RANGESET(tp->t_rxtcur, rexmt,
 706                       tp->t_rttmin, TCPTV_REXMTMAX);
 707
 708         /*
 709          * We enter the path for PLMTUD if connection is established or, if
 710          * connection is FIN_WAIT_1 status, reason for the last is that if
 711          * amount of data we send is very small, we could send it in couple of
 712          * packets and process straight to FIN. In that case we won't catch
 713          * ESTABLISHED state.
 714          */
 715         if (V_tcp_pmtud_blackhole_detect && (((tp->t_state == TCPS_ESTABLISHED))
 716             || (tp->t_state == TCPS_FIN_WAIT_1))) {
 717 #ifdef INET6
 718                 int isipv6;
 719 #endif
 720
 721                 /*
 722                  * Idea here is that at each stage of mtu probe (usually, 1448
 723                  * -> 1188 -> 524) should be given 2 chances to recover before
 724                  *  further clamping down. 'tp->t_rxtshift % 2 == 0' should
 725                  *  take care of that.
 726                  */
 727                 if (((tp->t_flags2 & (TF2_PLPMTU_PMTUD|TF2_PLPMTU_MAXSEGSNT)) ==
 728                     (TF2_PLPMTU_PMTUD|TF2_PLPMTU_MAXSEGSNT)) &&
 729                     (tp->t_rxtshift >= 2 && tp->t_rxtshift < 6 &&
 730                     tp->t_rxtshift % 2 == 0)) {
 731                         /*
 732                          * Enter Path MTU Black-hole Detection mechanism:
 733                          * - Disable Path MTU Discovery (IP "DF" bit).
 734                          * - Reduce MTU to lower value than what we
 735                          *   negotiated with peer.
 736                          */
 737                         if ((tp->t_flags2 & TF2_PLPMTU_BLACKHOLE) == 0) {
 738                                 /* Record that we may have found a black hole. */
 739                                 tp->t_flags2 |= TF2_PLPMTU_BLACKHOLE;
 740                                 /* Keep track of previous MSS. */
 741                                 tp->t_pmtud_saved_maxseg = tp->t_maxseg;
 742                         }
 743
 744                         /*
 745                          * Reduce the MSS to blackhole value or to the default
 746                          * in an attempt to retransmit.
 747                          */
 748 #ifdef INET6
 749                         isipv6 = (tp->t_inpcb->inp_vflag & INP_IPV6) ? 1 : 0;
 750                         if (isipv6 &&
 751                             tp->t_maxseg > V_tcp_v6pmtud_blackhole_mss) {
 752                                 /* Use the sysctl tuneable blackhole MSS. */
 753                                 tp->t_maxseg = V_tcp_v6pmtud_blackhole_mss;
 754                                 TCPSTAT_INC(tcps_pmtud_blackhole_activated);
 755                         } else if (isipv6) {
 756                                 /* Use the default MSS. */
 757                                 tp->t_maxseg = V_tcp_v6mssdflt;
 758                                 /*
 759                                  * Disable Path MTU Discovery when we switch to
 760                                  * minmss.
 761                                  */
 762                                 tp->t_flags2 &= ~TF2_PLPMTU_PMTUD;
 763                                 TCPSTAT_INC(tcps_pmtud_blackhole_activated_min_mss);
 764                         }
 765 #endif
 766 #if defined(INET6) && defined(INET)
 767                         else
 768 #endif
 769 #ifdef INET
 770                         if (tp->t_maxseg > V_tcp_pmtud_blackhole_mss) {
 771                                 /* Use the sysctl tuneable blackhole MSS. */
 772                                 tp->t_maxseg = V_tcp_pmtud_blackhole_mss;
 773                                 TCPSTAT_INC(tcps_pmtud_blackhole_activated);
 774                         } else {
 775                                 /* Use the default MSS. */
 776                                 tp->t_maxseg = V_tcp_mssdflt;
 777                                 /*
 778                                  * Disable Path MTU Discovery when we switch to
 779                                  * minmss.
 780                                  */
 781                                 tp->t_flags2 &= ~TF2_PLPMTU_PMTUD;
 782                                 TCPSTAT_INC(tcps_pmtud_blackhole_activated_min_mss);
 783                         }
 784 #endif
 785                         /*
 786                          * Reset the slow-start flight size
 787                          * as it may depend on the new MSS.
 788                          */
 789                         if (CC_ALGO(tp)->conn_init != NULL)
 790                                 CC_ALGO(tp)->conn_init(tp->ccv);
 791                 } else {
 792                         /*
 793                          * If further retransmissions are still unsuccessful
 794                          * with a lowered MTU, maybe this isn't a blackhole and
 795                          * we restore the previous MSS and blackhole detection
 796                          * flags.
 797                          * The limit '6' is determined by giving each probe
 798                          * stage (1448, 1188, 524) 2 chances to recover.
 799                          */
 800                         if ((tp->t_flags2 & TF2_PLPMTU_BLACKHOLE) &&
 801                             (tp->t_rxtshift >= 6)) {
 802                                 tp->t_flags2 |= TF2_PLPMTU_PMTUD;
 803                                 tp->t_flags2 &= ~TF2_PLPMTU_BLACKHOLE;
 804                                 tp->t_maxseg = tp->t_pmtud_saved_maxseg;
 805                                 TCPSTAT_INC(tcps_pmtud_blackhole_failed);
 806                                 /*
 807                                  * Reset the slow-start flight size as it
 808                                  * may depend on the new MSS.
 809                                  */
 810                                 if (CC_ALGO(tp)->conn_init != NULL)
 811                                         CC_ALGO(tp)->conn_init(tp->ccv);
 812                         }
 813                 }
 814         }
 815
 816         /*
 817          * Disable RFC1323 and SACK if we haven't got any response to
 818          * our third SYN to work-around some broken terminal servers
 819          * (most of which have hopefully been retired) that have bad VJ
 820          * header compression code which trashes TCP segments containing
 821          * unknown-to-them TCP options.
 822          */
 823         if (tcp_rexmit_drop_options && (tp->t_state == TCPS_SYN_SENT) &&
 824             (tp->t_rxtshift == 3))
 825                 tp->t_flags &= ~(TF_REQ_SCALE|TF_REQ_TSTMP|TF_SACK_PERMIT);
 826         /*
 827          * If we backed off this far, notify the L3 protocol that we're having
 828          * connection problems.
 829          */
 830         if (tp->t_rxtshift > TCP_RTT_INVALIDATE) {
 831 #ifdef INET6
 832                 if ((tp->t_inpcb->inp_vflag & INP_IPV6) != 0)
 833                         in6_losing(tp->t_inpcb);
 834                 else
 835 #endif
 836                         in_losing(tp->t_inpcb);
 837         }
 838         tp->snd_nxt = tp->snd_una;
 839         tp->snd_recover = tp->snd_max;
 840         /*
 841          * Force a segment to be sent.
 842          */
 843         tp->t_flags |= TF_ACKNOW;
 844         /*
 845          * If timing a segment in this window, stop the timer.
 846          */
 847         tp->t_rtttime = 0;
 848
 849         cc_cong_signal(tp, NULL, CC_RTO);
 850         NET_EPOCH_ENTER(et);
 851         (void) tp->t_fb->tfb_tcp_output(tp);
 852         NET_EPOCH_EXIT(et);
 853 #ifdef TCPDEBUG
 854         if (tp != NULL && (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
 855                 tcp_trace(TA_USER, ostate, tp, (void *)0, (struct tcphdr *)0,
 856                           PRU_SLOWTIMO);
 857 #endif
 858         TCP_PROBE2(debug__user, tp, PRU_SLOWTIMO);
 859         INP_WUNLOCK(inp);
 860 out:
 861         CURVNET_RESTORE();
 862 }
 863
 864 void
 865 tcp_timer_activate(struct tcpcb *tp, uint32_t timer_type, u_int delta)
 866 {
 867         struct callout *t_callout;
 868         callout_func_t *f_callout;
 869         struct inpcb *inp = tp->t_inpcb;
 870         int cpu = inp_to_cpuid(inp);
 871
 872 #ifdef TCP_OFFLOAD
 873         if (tp->t_flags & TF_TOE)
 874                 return;
 875 #endif
 876
 877         if (tp->t_timers->tt_flags & TT_STOPPED)
 878                 return;
 879
 880         switch (timer_type) {
 881                 case TT_DELACK:
 882                         t_callout = &tp->t_timers->tt_delack;
 883                         f_callout = tcp_timer_delack;
 884                         break;
 885                 case TT_REXMT:
 886                         t_callout = &tp->t_timers->tt_rexmt;
 887                         f_callout = tcp_timer_rexmt;
 888                         break;
 889                 case TT_PERSIST:
 890                         t_callout = &tp->t_timers->tt_persist;
 891                         f_callout = tcp_timer_persist;
 892                         break;
 893                 case TT_KEEP:
 894                         t_callout = &tp->t_timers->tt_keep;
 895                         f_callout = tcp_timer_keep;
 896                         break;
 897                 case TT_2MSL:
 898                         t_callout = &tp->t_timers->tt_2msl;
 899                         f_callout = tcp_timer_2msl;
 900                         break;
 901                 default:
 902                         if (tp->t_fb->tfb_tcp_timer_activate) {
 903                                 tp->t_fb->tfb_tcp_timer_activate(tp, timer_type, delta);
 904                                 return;
 905                         }
 906                         panic("tp %p bad timer_type %#x", tp, timer_type);
 907                 }
 908         if (delta == 0) {
 909                 callout_stop(t_callout);
 910         } else {
 911                 callout_reset_on(t_callout, delta, f_callout, tp, cpu);
 912         }
 913 }
 914
 915 int
 916 tcp_timer_active(struct tcpcb *tp, uint32_t timer_type)
 917 {
 918         struct callout *t_callout;
 919
 920         switch (timer_type) {
 921                 case TT_DELACK:
 922                         t_callout = &tp->t_timers->tt_delack;
 923                         break;
 924                 case TT_REXMT:
 925                         t_callout = &tp->t_timers->tt_rexmt;
 926                         break;
 927                 case TT_PERSIST:
 928                         t_callout = &tp->t_timers->tt_persist;
 929                         break;
 930                 case TT_KEEP:
 931                         t_callout = &tp->t_timers->tt_keep;
 932                         break;
 933                 case TT_2MSL:
 934                         t_callout = &tp->t_timers->tt_2msl;
 935                         break;
 936                 default:
 937                         if (tp->t_fb->tfb_tcp_timer_active) {
 938                                 return(tp->t_fb->tfb_tcp_timer_active(tp, timer_type));
 939                         }
 940                         panic("tp %p bad timer_type %#x", tp, timer_type);
 941                 }
 942         return callout_active(t_callout);
 943 }
 944
 945 /*
 946  * Stop the timer from running, and apply a flag
 947  * against the timer_flags that will force the
 948  * timer never to run. The flag is needed to assure
 949  * a race does not leave it running and cause
 950  * the timer to possibly restart itself (keep and persist
 951  * especially do this).
 952  */
 953 int
 954 tcp_timer_suspend(struct tcpcb *tp, uint32_t timer_type)
 955 {
 956         struct callout *t_callout;
 957         uint32_t t_flags;
 958
 959         switch (timer_type) {
 960                 case TT_DELACK:
 961                         t_flags = TT_DELACK_SUS;
 962                         t_callout = &tp->t_timers->tt_delack;
 963                         break;
 964                 case TT_REXMT:
 965                         t_flags = TT_REXMT_SUS;
 966                         t_callout = &tp->t_timers->tt_rexmt;
 967                         break;
 968                 case TT_PERSIST:
 969                         t_flags = TT_PERSIST_SUS;
 970                         t_callout = &tp->t_timers->tt_persist;
 971                         break;
 972                 case TT_KEEP:
 973                         t_flags = TT_KEEP_SUS;
 974                         t_callout = &tp->t_timers->tt_keep;
 975                         break;
 976                 case TT_2MSL:
 977                         t_flags = TT_2MSL_SUS;
 978                         t_callout = &tp->t_timers->tt_2msl;
 979                         break;
 980                 default:
 981                         panic("tp:%p bad timer_type 0x%x", tp, timer_type);
 982         }
 983         tp->t_timers->tt_flags |= t_flags;
 984         return (callout_stop(t_callout));
 985 }
 986
 987 void
 988 tcp_timers_unsuspend(struct tcpcb *tp, uint32_t timer_type)
 989 {
 990         switch (timer_type) {
 991                 case TT_DELACK:
 992                         if (tp->t_timers->tt_flags & TT_DELACK_SUS) {
 993                                 tp->t_timers->tt_flags &= ~TT_DELACK_SUS;
 994                                 if (tp->t_flags & TF_DELACK) {
 995                                         /* Delayed ack timer should be up activate a timer */
 996                                         tp->t_flags &= ~TF_DELACK;
 997                                         tcp_timer_activate(tp, TT_DELACK,
 998                                             tcp_delacktime);
 999                                 }
1000                         }
1001                         break;
1002                 case TT_REXMT:
1003                         if (tp->t_timers->tt_flags & TT_REXMT_SUS) {
1004                                 tp->t_timers->tt_flags &= ~TT_REXMT_SUS;
1005                                 if (SEQ_GT(tp->snd_max, tp->snd_una) &&
1006                                     (tcp_timer_active((tp), TT_PERSIST) == 0) &&
1007                                     tp->snd_wnd) {
1008                                         /* We have outstanding data activate a timer */
1009                                         tcp_timer_activate(tp, TT_REXMT,
1010                                             tp->t_rxtcur);
1011                                 }
1012                         }
1013                         break;
1014                 case TT_PERSIST:
1015                         if (tp->t_timers->tt_flags & TT_PERSIST_SUS) {
1016                                 tp->t_timers->tt_flags &= ~TT_PERSIST_SUS;
1017                                 if (tp->snd_wnd == 0) {
1018                                         /* Activate the persists timer */
1019                                         tp->t_rxtshift = 0;
1020                                         tcp_setpersist(tp);
1021                                 }
1022                         }
1023                         break;
1024                 case TT_KEEP:
1025                         if (tp->t_timers->tt_flags & TT_KEEP_SUS) {
1026                                 tp->t_timers->tt_flags &= ~TT_KEEP_SUS;
1027                                 tcp_timer_activate(tp, TT_KEEP,
1028                                             TCPS_HAVEESTABLISHED(tp->t_state) ?
1029                                             TP_KEEPIDLE(tp) : TP_KEEPINIT(tp));
1030                         }
1031                         break;
1032                 case TT_2MSL:
1033                         if (tp->t_timers->tt_flags &= TT_2MSL_SUS) {
1034                                 tp->t_timers->tt_flags &= ~TT_2MSL_SUS;
1035                                 if ((tp->t_state == TCPS_FIN_WAIT_2) &&
1036                                     ((tp->t_inpcb->inp_socket == NULL) ||
1037                                      (tp->t_inpcb->inp_socket->so_rcv.sb_state & SBS_CANTRCVMORE))) {
1038                                         /* Star the 2MSL timer */
1039                                         tcp_timer_activate(tp, TT_2MSL,
1040                                             (tcp_fast_finwait2_recycle) ?
1041                                             tcp_finwait2_timeout : TP_MAXIDLE(tp));
1042                                 }
1043                         }
1044                         break;
1045                 default:
1046                         panic("tp:%p bad timer_type 0x%x", tp, timer_type);
1047         }
1048 }
1049
1050 void
1051 tcp_timer_stop(struct tcpcb *tp, uint32_t timer_type)
1052 {
1053         struct callout *t_callout;
1054
1055         tp->t_timers->tt_flags |= TT_STOPPED;
1056         switch (timer_type) {
1057                 case TT_DELACK:
1058                         t_callout = &tp->t_timers->tt_delack;
1059                         break;
1060                 case TT_REXMT:
1061                         t_callout = &tp->t_timers->tt_rexmt;
1062                         break;
1063                 case TT_PERSIST:
1064                         t_callout = &tp->t_timers->tt_persist;
1065                         break;
1066                 case TT_KEEP:
1067                         t_callout = &tp->t_timers->tt_keep;
1068                         break;
1069                 case TT_2MSL:
1070                         t_callout = &tp->t_timers->tt_2msl;
1071                         break;
1072                 default:
1073                         if (tp->t_fb->tfb_tcp_timer_stop) {
1074                                 /*
1075                                  * XXXrrs we need to look at this with the
1076                                  * stop case below (flags).
1077                                  */
1078                                 tp->t_fb->tfb_tcp_timer_stop(tp, timer_type);
1079                                 return;
1080                         }
1081                         panic("tp %p bad timer_type %#x", tp, timer_type);
1082                 }
1083
1084         if (callout_async_drain(t_callout, tcp_timer_discard) == 0) {
1085                 /*
1086                  * Can't stop the callout, defer tcpcb actual deletion
1087                  * to the last one. We do this using the async drain
1088                  * function and incrementing the count in
1089                  */
1090                 tp->t_timers->tt_draincnt++;
1091         }
1092 }