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