sys/netinet/tcp_timer.c

   1 /*-
   2  * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1995
   3  *      The Regents of the University of California.  All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions
   7  * are met:
   8  * 1. Redistributions of source code must retain the above copyright
   9  *    notice, this list of conditions and the following disclaimer.
  10  * 2. Redistributions in binary form must reproduce the above copyright
  11  *    notice, this list of conditions and the following disclaimer in the
  12  *    documentation and/or other materials provided with the distribution.
  13  * 4. Neither the name of the University nor the names of its contributors
  14  *    may be used to endorse or promote products derived from this software
  15  *    without specific prior written permission.
  16  *
  17  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  18  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  19  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  20  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  21  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  22  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  23  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  24  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  25  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  26  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  27  * SUCH DAMAGE.
  28  *
  29  *      @(#)tcp_timer.c 8.2 (Berkeley) 5/24/95
  30  */
  31
  32 #include <sys/cdefs.h>
  33 __FBSDID("$FreeBSD$");
  34
  35 #include "opt_inet6.h"
  36 #include "opt_tcpdebug.h"
  37
  38 #include <sys/param.h>
  39 #include <sys/kernel.h>
  40 #include <sys/lock.h>
  41 #include <sys/mbuf.h>
  42 #include <sys/mutex.h>
  43 #include <sys/protosw.h>
  44 #include <sys/smp.h>
  45 #include <sys/socket.h>
  46 #include <sys/socketvar.h>
  47 #include <sys/sysctl.h>
  48 #include <sys/systm.h>
  49
  50 #include <net/if.h>
  51 #include <net/route.h>
  52 #include <net/vnet.h>
  53
  54 #include <netinet/cc.h>
  55 #include <netinet/in.h>
  56 #include <netinet/in_pcb.h>
  57 #include <netinet/in_systm.h>
  58 #ifdef INET6
  59 #include <netinet6/in6_pcb.h>
  60 #endif
  61 #include <netinet/ip_var.h>
  62 #include <netinet/tcp_fsm.h>
  63 #include <netinet/tcp_timer.h>
  64 #include <netinet/tcp_var.h>
  65 #include <netinet/tcpip.h>
  66 #ifdef TCPDEBUG
  67 #include <netinet/tcp_debug.h>
  68 #endif
  69
  70 int     tcp_keepinit;
  71 SYSCTL_PROC(_net_inet_tcp, TCPCTL_KEEPINIT, keepinit, CTLTYPE_INT|CTLFLAG_RW,
  72     &tcp_keepinit, 0, sysctl_msec_to_ticks, "I", "time to establish connection");
  73
  74 int     tcp_keepidle;
  75 SYSCTL_PROC(_net_inet_tcp, TCPCTL_KEEPIDLE, keepidle, CTLTYPE_INT|CTLFLAG_RW,
  76     &tcp_keepidle, 0, sysctl_msec_to_ticks, "I", "time before keepalive probes begin");
  77
  78 int     tcp_keepintvl;
  79 SYSCTL_PROC(_net_inet_tcp, TCPCTL_KEEPINTVL, keepintvl, CTLTYPE_INT|CTLFLAG_RW,
  80     &tcp_keepintvl, 0, sysctl_msec_to_ticks, "I", "time between keepalive probes");
  81
  82 int     tcp_delacktime;
  83 SYSCTL_PROC(_net_inet_tcp, TCPCTL_DELACKTIME, delacktime, CTLTYPE_INT|CTLFLAG_RW,
  84     &tcp_delacktime, 0, sysctl_msec_to_ticks, "I",
  85     "Time before a delayed ACK is sent");
  86
  87 int     tcp_msl;
  88 SYSCTL_PROC(_net_inet_tcp, OID_AUTO, msl, CTLTYPE_INT|CTLFLAG_RW,
  89     &tcp_msl, 0, sysctl_msec_to_ticks, "I", "Maximum segment lifetime");
  90
  91 int     tcp_rexmit_min;
  92 SYSCTL_PROC(_net_inet_tcp, OID_AUTO, rexmit_min, CTLTYPE_INT|CTLFLAG_RW,
  93     &tcp_rexmit_min, 0, sysctl_msec_to_ticks, "I",
  94     "Minimum Retransmission Timeout");
  95
  96 int     tcp_rexmit_slop;
  97 SYSCTL_PROC(_net_inet_tcp, OID_AUTO, rexmit_slop, CTLTYPE_INT|CTLFLAG_RW,
  98     &tcp_rexmit_slop, 0, sysctl_msec_to_ticks, "I",
  99     "Retransmission Timer Slop");
 100
 101 static int      always_keepalive = 1;
 102 SYSCTL_INT(_net_inet_tcp, OID_AUTO, always_keepalive, CTLFLAG_RW,
 103     &always_keepalive , 0, "Assume SO_KEEPALIVE on all TCP connections");
 104
 105 int    tcp_fast_finwait2_recycle = 0;
 106 SYSCTL_INT(_net_inet_tcp, OID_AUTO, fast_finwait2_recycle, CTLFLAG_RW,
 107     &tcp_fast_finwait2_recycle, 0,
 108     "Recycle closed FIN_WAIT_2 connections faster");
 109
 110 int    tcp_finwait2_timeout;
 111 SYSCTL_PROC(_net_inet_tcp, OID_AUTO, finwait2_timeout, CTLTYPE_INT|CTLFLAG_RW,
 112     &tcp_finwait2_timeout, 0, sysctl_msec_to_ticks, "I", "FIN-WAIT2 timeout");
 113
 114 int     tcp_keepcnt = TCPTV_KEEPCNT;
 115 SYSCTL_INT(_net_inet_tcp, OID_AUTO, keepcnt, CTLFLAG_RW, &tcp_keepcnt, 0,
 116     "Number of keepalive probes to send");
 117
 118         /* max idle probes */
 119 int     tcp_maxpersistidle;
 120
 121 static int      per_cpu_timers = 0;
 122 SYSCTL_INT(_net_inet_tcp, OID_AUTO, per_cpu_timers, CTLFLAG_RW,
 123     &per_cpu_timers , 0, "run tcp timers on all cpus");
 124
 125 #define INP_CPU(inp)    (per_cpu_timers ? (!CPU_ABSENT(((inp)->inp_flowid % (mp_maxid+1))) ? \
 126                 ((inp)->inp_flowid % (mp_maxid+1)) : curcpu) : 0)
 127
 128 /*
 129  * Tcp protocol timeout routine called every 500 ms.
 130  * Updates timestamps used for TCP
 131  * causes finite state machine actions if timers expire.
 132  */
 133 void
 134 tcp_slowtimo(void)
 135 {
 136         VNET_ITERATOR_DECL(vnet_iter);
 137
 138         VNET_LIST_RLOCK_NOSLEEP();
 139         VNET_FOREACH(vnet_iter) {
 140                 CURVNET_SET(vnet_iter);
 141                 INP_INFO_WLOCK(&V_tcbinfo);
 142                 (void) tcp_tw_2msl_scan(0);
 143                 INP_INFO_WUNLOCK(&V_tcbinfo);
 144                 CURVNET_RESTORE();
 145         }
 146         VNET_LIST_RUNLOCK_NOSLEEP();
 147 }
 148
 149 int     tcp_syn_backoff[TCP_MAXRXTSHIFT + 1] =
 150     { 1, 1, 1, 1, 1, 2, 4, 8, 16, 32, 64, 64, 64 };
 151
 152 int     tcp_backoff[TCP_MAXRXTSHIFT + 1] =
 153     { 1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 512, 512, 512 };
 154
 155 static int tcp_totbackoff = 2559;       /* sum of tcp_backoff[] */
 156
 157 static int tcp_timer_race;
 158 SYSCTL_INT(_net_inet_tcp, OID_AUTO, timer_race, CTLFLAG_RD, &tcp_timer_race,
 159     0, "Count of t_inpcb races on tcp_discardcb");
 160
 161 /*
 162  * TCP timer processing.
 163  */
 164
 165 void
 166 tcp_timer_delack(void *xtp)
 167 {
 168         struct tcpcb *tp = xtp;
 169         struct inpcb *inp;
 170         CURVNET_SET(tp->t_vnet);
 171
 172         inp = tp->t_inpcb;
 173         /*
 174          * XXXRW: While this assert is in fact correct, bugs in the tcpcb
 175          * tear-down mean we need it as a work-around for races between
 176          * timers and tcp_discardcb().
 177          *
 178          * KASSERT(inp != NULL, ("tcp_timer_delack: inp == NULL"));
 179          */
 180         if (inp == NULL) {
 181                 tcp_timer_race++;
 182                 CURVNET_RESTORE();
 183                 return;
 184         }
 185         INP_WLOCK(inp);
 186         if ((inp->inp_flags & INP_DROPPED) || callout_pending(&tp->t_timers->tt_delack)
 187             || !callout_active(&tp->t_timers->tt_delack)) {
 188                 INP_WUNLOCK(inp);
 189                 CURVNET_RESTORE();
 190                 return;
 191         }
 192         callout_deactivate(&tp->t_timers->tt_delack);
 193
 194         tp->t_flags |= TF_ACKNOW;
 195         TCPSTAT_INC(tcps_delack);
 196         (void) tcp_output(tp);
 197         INP_WUNLOCK(inp);
 198         CURVNET_RESTORE();
 199 }
 200
 201 void
 202 tcp_timer_2msl(void *xtp)
 203 {
 204         struct tcpcb *tp = xtp;
 205         struct inpcb *inp;
 206         CURVNET_SET(tp->t_vnet);
 207 #ifdef TCPDEBUG
 208         int ostate;
 209
 210         ostate = tp->t_state;
 211 #endif
 212         /*
 213          * XXXRW: Does this actually happen?
 214          */
 215         INP_INFO_WLOCK(&V_tcbinfo);
 216         inp = tp->t_inpcb;
 217         /*
 218          * XXXRW: While this assert is in fact correct, bugs in the tcpcb
 219          * tear-down mean we need it as a work-around for races between
 220          * timers and tcp_discardcb().
 221          *
 222          * KASSERT(inp != NULL, ("tcp_timer_2msl: inp == NULL"));
 223          */
 224         if (inp == NULL) {
 225                 tcp_timer_race++;
 226                 INP_INFO_WUNLOCK(&V_tcbinfo);
 227                 CURVNET_RESTORE();
 228                 return;
 229         }
 230         INP_WLOCK(inp);
 231         tcp_free_sackholes(tp);
 232         if ((inp->inp_flags & INP_DROPPED) || callout_pending(&tp->t_timers->tt_2msl) ||
 233             !callout_active(&tp->t_timers->tt_2msl)) {
 234                 INP_WUNLOCK(tp->t_inpcb);
 235                 INP_INFO_WUNLOCK(&V_tcbinfo);
 236                 CURVNET_RESTORE();
 237                 return;
 238         }
 239         callout_deactivate(&tp->t_timers->tt_2msl);
 240         /*
 241          * 2 MSL timeout in shutdown went off.  If we're closed but
 242          * still waiting for peer to close and connection has been idle
 243          * too long, or if 2MSL time is up from TIME_WAIT, delete connection
 244          * control block.  Otherwise, check again in a bit.
 245          *
 246          * If fastrecycle of FIN_WAIT_2, in FIN_WAIT_2 and receiver has closed,
 247          * there's no point in hanging onto FIN_WAIT_2 socket. Just close it.
 248          * Ignore fact that there were recent incoming segments.
 249          */
 250         if (tcp_fast_finwait2_recycle && tp->t_state == TCPS_FIN_WAIT_2 &&
 251             tp->t_inpcb && tp->t_inpcb->inp_socket &&
 252             (tp->t_inpcb->inp_socket->so_rcv.sb_state & SBS_CANTRCVMORE)) {
 253                 TCPSTAT_INC(tcps_finwait2_drops);
 254                 tp = tcp_close(tp);
 255         } else {
 256                 if (tp->t_state != TCPS_TIME_WAIT &&
 257                    ticks - tp->t_rcvtime <= TP_MAXIDLE(tp))
 258                        callout_reset_on(&tp->t_timers->tt_2msl,
 259                            TP_KEEPINTVL(tp), tcp_timer_2msl, tp, INP_CPU(inp));
 260                else
 261                        tp = tcp_close(tp);
 262        }
 263
 264 #ifdef TCPDEBUG
 265         if (tp != NULL && (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
 266                 tcp_trace(TA_USER, ostate, tp, (void *)0, (struct tcphdr *)0,
 267                           PRU_SLOWTIMO);
 268 #endif
 269         if (tp != NULL)
 270                 INP_WUNLOCK(inp);
 271         INP_INFO_WUNLOCK(&V_tcbinfo);
 272         CURVNET_RESTORE();
 273 }
 274
 275 void
 276 tcp_timer_keep(void *xtp)
 277 {
 278         struct tcpcb *tp = xtp;
 279         struct tcptemp *t_template;
 280         struct inpcb *inp;
 281         CURVNET_SET(tp->t_vnet);
 282 #ifdef TCPDEBUG
 283         int ostate;
 284
 285         ostate = tp->t_state;
 286 #endif
 287         INP_INFO_WLOCK(&V_tcbinfo);
 288         inp = tp->t_inpcb;
 289         /*
 290          * XXXRW: While this assert is in fact correct, bugs in the tcpcb
 291          * tear-down mean we need it as a work-around for races between
 292          * timers and tcp_discardcb().
 293          *
 294          * KASSERT(inp != NULL, ("tcp_timer_keep: inp == NULL"));
 295          */
 296         if (inp == NULL) {
 297                 tcp_timer_race++;
 298                 INP_INFO_WUNLOCK(&V_tcbinfo);
 299                 CURVNET_RESTORE();
 300                 return;
 301         }
 302         INP_WLOCK(inp);
 303         if ((inp->inp_flags & INP_DROPPED) || callout_pending(&tp->t_timers->tt_keep)
 304             || !callout_active(&tp->t_timers->tt_keep)) {
 305                 INP_WUNLOCK(inp);
 306                 INP_INFO_WUNLOCK(&V_tcbinfo);
 307                 CURVNET_RESTORE();
 308                 return;
 309         }
 310         callout_deactivate(&tp->t_timers->tt_keep);
 311         /*
 312          * Keep-alive timer went off; send something
 313          * or drop connection if idle for too long.
 314          */
 315         TCPSTAT_INC(tcps_keeptimeo);
 316         if (tp->t_state < TCPS_ESTABLISHED)
 317                 goto dropit;
 318         if ((always_keepalive || inp->inp_socket->so_options & SO_KEEPALIVE) &&
 319             tp->t_state <= TCPS_CLOSING) {
 320                 if (ticks - tp->t_rcvtime >= TP_KEEPIDLE(tp) + TP_MAXIDLE(tp))
 321                         goto dropit;
 322                 /*
 323                  * Send a packet designed to force a response
 324                  * if the peer is up and reachable:
 325                  * either an ACK if the connection is still alive,
 326                  * or an RST if the peer has closed the connection
 327                  * due to timeout or reboot.
 328                  * Using sequence number tp->snd_una-1
 329                  * causes the transmitted zero-length segment
 330                  * to lie outside the receive window;
 331                  * by the protocol spec, this requires the
 332                  * correspondent TCP to respond.
 333                  */
 334                 TCPSTAT_INC(tcps_keepprobe);
 335                 t_template = tcpip_maketemplate(inp);
 336                 if (t_template) {
 337                         tcp_respond(tp, t_template->tt_ipgen,
 338                                     &t_template->tt_t, (struct mbuf *)NULL,
 339                                     tp->rcv_nxt, tp->snd_una - 1, 0);
 340                         free(t_template, M_TEMP);
 341                 }
 342                 callout_reset_on(&tp->t_timers->tt_keep, TP_KEEPINTVL(tp),
 343                     tcp_timer_keep, tp, INP_CPU(inp));
 344         } else
 345                 callout_reset_on(&tp->t_timers->tt_keep, TP_KEEPIDLE(tp),
 346                     tcp_timer_keep, tp, INP_CPU(inp));
 347
 348 #ifdef TCPDEBUG
 349         if (inp->inp_socket->so_options & SO_DEBUG)
 350                 tcp_trace(TA_USER, ostate, tp, (void *)0, (struct tcphdr *)0,
 351                           PRU_SLOWTIMO);
 352 #endif
 353         INP_WUNLOCK(inp);
 354         INP_INFO_WUNLOCK(&V_tcbinfo);
 355         CURVNET_RESTORE();
 356         return;
 357
 358 dropit:
 359         TCPSTAT_INC(tcps_keepdrops);
 360         tp = tcp_drop(tp, ETIMEDOUT);
 361
 362 #ifdef TCPDEBUG
 363         if (tp != NULL && (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
 364                 tcp_trace(TA_USER, ostate, tp, (void *)0, (struct tcphdr *)0,
 365                           PRU_SLOWTIMO);
 366 #endif
 367         if (tp != NULL)
 368                 INP_WUNLOCK(tp->t_inpcb);
 369         INP_INFO_WUNLOCK(&V_tcbinfo);
 370         CURVNET_RESTORE();
 371 }
 372
 373 void
 374 tcp_timer_persist(void *xtp)
 375 {
 376         struct tcpcb *tp = xtp;
 377         struct inpcb *inp;
 378         CURVNET_SET(tp->t_vnet);
 379 #ifdef TCPDEBUG
 380         int ostate;
 381
 382         ostate = tp->t_state;
 383 #endif
 384         INP_INFO_WLOCK(&V_tcbinfo);
 385         inp = tp->t_inpcb;
 386         /*
 387          * XXXRW: While this assert is in fact correct, bugs in the tcpcb
 388          * tear-down mean we need it as a work-around for races between
 389          * timers and tcp_discardcb().
 390          *
 391          * KASSERT(inp != NULL, ("tcp_timer_persist: inp == NULL"));
 392          */
 393         if (inp == NULL) {
 394                 tcp_timer_race++;
 395                 INP_INFO_WUNLOCK(&V_tcbinfo);
 396                 CURVNET_RESTORE();
 397                 return;
 398         }
 399         INP_WLOCK(inp);
 400         if ((inp->inp_flags & INP_DROPPED) || callout_pending(&tp->t_timers->tt_persist)
 401             || !callout_active(&tp->t_timers->tt_persist)) {
 402                 INP_WUNLOCK(inp);
 403                 INP_INFO_WUNLOCK(&V_tcbinfo);
 404                 CURVNET_RESTORE();
 405                 return;
 406         }
 407         callout_deactivate(&tp->t_timers->tt_persist);
 408         /*
 409          * Persistance timer into zero window.
 410          * Force a byte to be output, if possible.
 411          */
 412         TCPSTAT_INC(tcps_persisttimeo);
 413         /*
 414          * Hack: if the peer is dead/unreachable, we do not
 415          * time out if the window is closed.  After a full
 416          * backoff, drop the connection if the idle time
 417          * (no responses to probes) reaches the maximum
 418          * backoff that we would use if retransmitting.
 419          */
 420         if (tp->t_rxtshift == TCP_MAXRXTSHIFT &&
 421             (ticks - tp->t_rcvtime >= tcp_maxpersistidle ||
 422              ticks - tp->t_rcvtime >= TCP_REXMTVAL(tp) * tcp_totbackoff)) {
 423                 TCPSTAT_INC(tcps_persistdrop);
 424                 tp = tcp_drop(tp, ETIMEDOUT);
 425                 goto out;
 426         }
 427         tcp_setpersist(tp);
 428         tp->t_flags |= TF_FORCEDATA;
 429         (void) tcp_output(tp);
 430         tp->t_flags &= ~TF_FORCEDATA;
 431
 432 out:
 433 #ifdef TCPDEBUG
 434         if (tp != NULL && tp->t_inpcb->inp_socket->so_options & SO_DEBUG)
 435                 tcp_trace(TA_USER, ostate, tp, NULL, NULL, PRU_SLOWTIMO);
 436 #endif
 437         if (tp != NULL)
 438                 INP_WUNLOCK(inp);
 439         INP_INFO_WUNLOCK(&V_tcbinfo);
 440         CURVNET_RESTORE();
 441 }
 442
 443 void
 444 tcp_timer_rexmt(void * xtp)
 445 {
 446         struct tcpcb *tp = xtp;
 447         CURVNET_SET(tp->t_vnet);
 448         int rexmt;
 449         int headlocked;
 450         struct inpcb *inp;
 451 #ifdef TCPDEBUG
 452         int ostate;
 453
 454         ostate = tp->t_state;
 455 #endif
 456         INP_INFO_RLOCK(&V_tcbinfo);
 457         inp = tp->t_inpcb;
 458         /*
 459          * XXXRW: While this assert is in fact correct, bugs in the tcpcb
 460          * tear-down mean we need it as a work-around for races between
 461          * timers and tcp_discardcb().
 462          *
 463          * KASSERT(inp != NULL, ("tcp_timer_rexmt: inp == NULL"));
 464          */
 465         if (inp == NULL) {
 466                 tcp_timer_race++;
 467                 INP_INFO_RUNLOCK(&V_tcbinfo);
 468                 CURVNET_RESTORE();
 469                 return;
 470         }
 471         INP_WLOCK(inp);
 472         if ((inp->inp_flags & INP_DROPPED) || callout_pending(&tp->t_timers->tt_rexmt)
 473             || !callout_active(&tp->t_timers->tt_rexmt)) {
 474                 INP_WUNLOCK(inp);
 475                 INP_INFO_RUNLOCK(&V_tcbinfo);
 476                 CURVNET_RESTORE();
 477                 return;
 478         }
 479         callout_deactivate(&tp->t_timers->tt_rexmt);
 480         tcp_free_sackholes(tp);
 481         /*
 482          * Retransmission timer went off.  Message has not
 483          * been acked within retransmit interval.  Back off
 484          * to a longer retransmit interval and retransmit one segment.
 485          */
 486         if (++tp->t_rxtshift > TCP_MAXRXTSHIFT) {
 487                 tp->t_rxtshift = TCP_MAXRXTSHIFT;
 488                 TCPSTAT_INC(tcps_timeoutdrop);
 489                 in_pcbref(inp);
 490                 INP_INFO_RUNLOCK(&V_tcbinfo);
 491                 INP_WUNLOCK(inp);
 492                 INP_INFO_WLOCK(&V_tcbinfo);
 493                 INP_WLOCK(inp);
 494                 if (in_pcbrele_wlocked(inp)) {
 495                         INP_INFO_WUNLOCK(&V_tcbinfo);
 496                         CURVNET_RESTORE();
 497                         return;
 498                 }
 499                 if (inp->inp_flags & INP_DROPPED) {
 500                         INP_WUNLOCK(inp);
 501                         INP_INFO_WUNLOCK(&V_tcbinfo);
 502                         CURVNET_RESTORE();
 503                         return;
 504                 }
 505
 506                 tp = tcp_drop(tp, tp->t_softerror ?
 507                               tp->t_softerror : ETIMEDOUT);
 508                 headlocked = 1;
 509                 goto out;
 510         }
 511         INP_INFO_RUNLOCK(&V_tcbinfo);
 512         headlocked = 0;
 513         if (tp->t_rxtshift == 1) {
 514                 /*
 515                  * first retransmit; record ssthresh and cwnd so they can
 516                  * be recovered if this turns out to be a "bad" retransmit.
 517                  * A retransmit is considered "bad" if an ACK for this
 518                  * segment is received within RTT/2 interval; the assumption
 519                  * here is that the ACK was already in flight.  See
 520                  * "On Estimating End-to-End Network Path Properties" by
 521                  * Allman and Paxson for more details.
 522                  */
 523                 tp->snd_cwnd_prev = tp->snd_cwnd;
 524                 tp->snd_ssthresh_prev = tp->snd_ssthresh;
 525                 tp->snd_recover_prev = tp->snd_recover;
 526                 if (IN_FASTRECOVERY(tp->t_flags))
 527                         tp->t_flags |= TF_WASFRECOVERY;
 528                 else
 529                         tp->t_flags &= ~TF_WASFRECOVERY;
 530                 if (IN_CONGRECOVERY(tp->t_flags))
 531                         tp->t_flags |= TF_WASCRECOVERY;
 532                 else
 533                         tp->t_flags &= ~TF_WASCRECOVERY;
 534                 tp->t_badrxtwin = ticks + (tp->t_srtt >> (TCP_RTT_SHIFT + 1));
 535                 tp->t_flags |= TF_PREVVALID;
 536         } else
 537                 tp->t_flags &= ~TF_PREVVALID;
 538         TCPSTAT_INC(tcps_rexmttimeo);
 539         if (tp->t_state == TCPS_SYN_SENT)
 540                 rexmt = TCP_REXMTVAL(tp) * tcp_syn_backoff[tp->t_rxtshift];
 541         else
 542                 rexmt = TCP_REXMTVAL(tp) * tcp_backoff[tp->t_rxtshift];
 543         TCPT_RANGESET(tp->t_rxtcur, rexmt,
 544                       tp->t_rttmin, TCPTV_REXMTMAX);
 545         /*
 546          * Disable rfc1323 if we haven't got any response to
 547          * our third SYN to work-around some broken terminal servers
 548          * (most of which have hopefully been retired) that have bad VJ
 549          * header compression code which trashes TCP segments containing
 550          * unknown-to-them TCP options.
 551          */
 552         if ((tp->t_state == TCPS_SYN_SENT) && (tp->t_rxtshift == 3))
 553                 tp->t_flags &= ~(TF_REQ_SCALE|TF_REQ_TSTMP);
 554         /*
 555          * If we backed off this far, our srtt estimate is probably bogus.
 556          * Clobber it so we'll take the next rtt measurement as our srtt;
 557          * move the current srtt into rttvar to keep the current
 558          * retransmit times until then.
 559          */
 560         if (tp->t_rxtshift > TCP_MAXRXTSHIFT / 4) {
 561 #ifdef INET6
 562                 if ((tp->t_inpcb->inp_vflag & INP_IPV6) != 0)
 563                         in6_losing(tp->t_inpcb);
 564                 else
 565 #endif
 566                 tp->t_rttvar += (tp->t_srtt >> TCP_RTT_SHIFT);
 567                 tp->t_srtt = 0;
 568         }
 569         tp->snd_nxt = tp->snd_una;
 570         tp->snd_recover = tp->snd_max;
 571         /*
 572          * Force a segment to be sent.
 573          */
 574         tp->t_flags |= TF_ACKNOW;
 575         /*
 576          * If timing a segment in this window, stop the timer.
 577          */
 578         tp->t_rtttime = 0;
 579
 580         cc_cong_signal(tp, NULL, CC_RTO);
 581
 582         (void) tcp_output(tp);
 583
 584 out:
 585 #ifdef TCPDEBUG
 586         if (tp != NULL && (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
 587                 tcp_trace(TA_USER, ostate, tp, (void *)0, (struct tcphdr *)0,
 588                           PRU_SLOWTIMO);
 589 #endif
 590         if (tp != NULL)
 591                 INP_WUNLOCK(inp);
 592         if (headlocked)
 593                 INP_INFO_WUNLOCK(&V_tcbinfo);
 594         CURVNET_RESTORE();
 595 }
 596
 597 void
 598 tcp_timer_activate(struct tcpcb *tp, int timer_type, u_int delta)
 599 {
 600         struct callout *t_callout;
 601         void *f_callout;
 602         struct inpcb *inp = tp->t_inpcb;
 603         int cpu = INP_CPU(inp);
 604
 605         switch (timer_type) {
 606                 case TT_DELACK:
 607                         t_callout = &tp->t_timers->tt_delack;
 608                         f_callout = tcp_timer_delack;
 609                         break;
 610                 case TT_REXMT:
 611                         t_callout = &tp->t_timers->tt_rexmt;
 612                         f_callout = tcp_timer_rexmt;
 613                         break;
 614                 case TT_PERSIST:
 615                         t_callout = &tp->t_timers->tt_persist;
 616                         f_callout = tcp_timer_persist;
 617                         break;
 618                 case TT_KEEP:
 619                         t_callout = &tp->t_timers->tt_keep;
 620                         f_callout = tcp_timer_keep;
 621                         break;
 622                 case TT_2MSL:
 623                         t_callout = &tp->t_timers->tt_2msl;
 624                         f_callout = tcp_timer_2msl;
 625                         break;
 626                 default:
 627                         panic("bad timer_type");
 628                 }
 629         if (delta == 0) {
 630                 callout_stop(t_callout);
 631         } else {
 632                 callout_reset_on(t_callout, delta, f_callout, tp, cpu);
 633         }
 634 }
 635
 636 int
 637 tcp_timer_active(struct tcpcb *tp, int timer_type)
 638 {
 639         struct callout *t_callout;
 640
 641         switch (timer_type) {
 642                 case TT_DELACK:
 643                         t_callout = &tp->t_timers->tt_delack;
 644                         break;
 645                 case TT_REXMT:
 646                         t_callout = &tp->t_timers->tt_rexmt;
 647                         break;
 648                 case TT_PERSIST:
 649                         t_callout = &tp->t_timers->tt_persist;
 650                         break;
 651                 case TT_KEEP:
 652                         t_callout = &tp->t_timers->tt_keep;
 653                         break;
 654                 case TT_2MSL:
 655                         t_callout = &tp->t_timers->tt_2msl;
 656                         break;
 657                 default:
 658                         panic("bad timer_type");
 659                 }
 660         return callout_active(t_callout);
 661 }
 662
 663 #define ticks_to_msecs(t)       (1000*(t) / hz)
 664
 665 void
 666 tcp_timer_to_xtimer(struct tcpcb *tp, struct tcp_timer *timer, struct xtcp_timer *xtimer)
 667 {
 668         bzero(xtimer, sizeof(struct xtcp_timer));
 669         if (timer == NULL)
 670                 return;
 671         if (callout_active(&timer->tt_delack))
 672                 xtimer->tt_delack = ticks_to_msecs(timer->tt_delack.c_time - ticks);
 673         if (callout_active(&timer->tt_rexmt))
 674                 xtimer->tt_rexmt = ticks_to_msecs(timer->tt_rexmt.c_time - ticks);
 675         if (callout_active(&timer->tt_persist))
 676                 xtimer->tt_persist = ticks_to_msecs(timer->tt_persist.c_time - ticks);
 677         if (callout_active(&timer->tt_keep))
 678                 xtimer->tt_keep = ticks_to_msecs(timer->tt_keep.c_time - ticks);
 679         if (callout_active(&timer->tt_2msl))
 680                 xtimer->tt_2msl = ticks_to_msecs(timer->tt_2msl.c_time - ticks);
 681         xtimer->t_rcvtime = ticks_to_msecs(ticks - tp->t_rcvtime);
 682 }