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
 115 static int      tcp_keepcnt = TCPTV_KEEPCNT;
 116         /* max idle probes */
 117 int     tcp_maxpersistidle;
 118         /* max idle time in persist */
 119 int     tcp_maxidle;
 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                 tcp_maxidle = tcp_keepcnt * tcp_keepintvl;
 142                 INP_INFO_WLOCK(&V_tcbinfo);
 143                 (void) tcp_tw_2msl_scan(0);
 144                 INP_INFO_WUNLOCK(&V_tcbinfo);
 145                 CURVNET_RESTORE();
 146         }
 147         VNET_LIST_RUNLOCK_NOSLEEP();
 148 }
 149
 150 int     tcp_syn_backoff[TCP_MAXRXTSHIFT + 1] =
 151     { 1, 1, 1, 1, 1, 2, 4, 8, 16, 32, 64, 64, 64 };
 152
 153 int     tcp_backoff[TCP_MAXRXTSHIFT + 1] =
 154     { 1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 512, 512, 512 };
 155
 156 static int tcp_totbackoff = 2559;       /* sum of tcp_backoff[] */
 157
 158 static int tcp_timer_race;
 159 SYSCTL_INT(_net_inet_tcp, OID_AUTO, timer_race, CTLFLAG_RD, &tcp_timer_race,
 160     0, "Count of t_inpcb races on tcp_discardcb");
 161
 162 /*
 163  * TCP timer processing.
 164  */
 165
 166 void
 167 tcp_timer_delack(void *xtp)
 168 {
 169         struct tcpcb *tp = xtp;
 170         struct inpcb *inp;
 171         CURVNET_SET(tp->t_vnet);
 172
 173         inp = tp->t_inpcb;
 174         /*
 175          * XXXRW: While this assert is in fact correct, bugs in the tcpcb
 176          * tear-down mean we need it as a work-around for races between
 177          * timers and tcp_discardcb().
 178          *
 179          * KASSERT(inp != NULL, ("tcp_timer_delack: inp == NULL"));
 180          */
 181         if (inp == NULL) {
 182                 tcp_timer_race++;
 183                 CURVNET_RESTORE();
 184                 return;
 185         }
 186         INP_WLOCK(inp);
 187         if ((inp->inp_flags & INP_DROPPED) || callout_pending(&tp->t_timers->tt_delack)
 188             || !callout_active(&tp->t_timers->tt_delack)) {
 189                 INP_WUNLOCK(inp);
 190                 CURVNET_RESTORE();
 191                 return;
 192         }
 193         callout_deactivate(&tp->t_timers->tt_delack);
 194
 195         tp->t_flags |= TF_ACKNOW;
 196         TCPSTAT_INC(tcps_delack);
 197         (void) tcp_output(tp);
 198         INP_WUNLOCK(inp);
 199         CURVNET_RESTORE();
 200 }
 201
 202 void
 203 tcp_timer_2msl(void *xtp)
 204 {
 205         struct tcpcb *tp = xtp;
 206         struct inpcb *inp;
 207         CURVNET_SET(tp->t_vnet);
 208 #ifdef TCPDEBUG
 209         int ostate;
 210
 211         ostate = tp->t_state;
 212 #endif
 213         /*
 214          * XXXRW: Does this actually happen?
 215          */
 216         INP_INFO_WLOCK(&V_tcbinfo);
 217         inp = tp->t_inpcb;
 218         /*
 219          * XXXRW: While this assert is in fact correct, bugs in the tcpcb
 220          * tear-down mean we need it as a work-around for races between
 221          * timers and tcp_discardcb().
 222          *
 223          * KASSERT(inp != NULL, ("tcp_timer_2msl: inp == NULL"));
 224          */
 225         if (inp == NULL) {
 226                 tcp_timer_race++;
 227                 INP_INFO_WUNLOCK(&V_tcbinfo);
 228                 CURVNET_RESTORE();
 229                 return;
 230         }
 231         INP_WLOCK(inp);
 232         tcp_free_sackholes(tp);
 233         if ((inp->inp_flags & INP_DROPPED) || callout_pending(&tp->t_timers->tt_2msl) ||
 234             !callout_active(&tp->t_timers->tt_2msl)) {
 235                 INP_WUNLOCK(tp->t_inpcb);
 236                 INP_INFO_WUNLOCK(&V_tcbinfo);
 237                 CURVNET_RESTORE();
 238                 return;
 239         }
 240         callout_deactivate(&tp->t_timers->tt_2msl);
 241         /*
 242          * 2 MSL timeout in shutdown went off.  If we're closed but
 243          * still waiting for peer to close and connection has been idle
 244          * too long, or if 2MSL time is up from TIME_WAIT, delete connection
 245          * control block.  Otherwise, check again in a bit.
 246          *
 247          * If fastrecycle of FIN_WAIT_2, in FIN_WAIT_2 and receiver has closed,
 248          * there's no point in hanging onto FIN_WAIT_2 socket. Just close it.
 249          * Ignore fact that there were recent incoming segments.
 250          */
 251         if (tcp_fast_finwait2_recycle && tp->t_state == TCPS_FIN_WAIT_2 &&
 252             tp->t_inpcb && tp->t_inpcb->inp_socket &&
 253             (tp->t_inpcb->inp_socket->so_rcv.sb_state & SBS_CANTRCVMORE)) {
 254                 TCPSTAT_INC(tcps_finwait2_drops);
 255                 tp = tcp_close(tp);
 256         } else {
 257                 if (tp->t_state != TCPS_TIME_WAIT &&
 258                    ticks - tp->t_rcvtime <= tcp_maxidle)
 259                        callout_reset_on(&tp->t_timers->tt_2msl, tcp_keepintvl,
 260                            tcp_timer_2msl, tp, INP_CPU(inp));
 261                else
 262                        tp = tcp_close(tp);
 263        }
 264
 265 #ifdef TCPDEBUG
 266         if (tp != NULL && (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
 267                 tcp_trace(TA_USER, ostate, tp, (void *)0, (struct tcphdr *)0,
 268                           PRU_SLOWTIMO);
 269 #endif
 270         if (tp != NULL)
 271                 INP_WUNLOCK(inp);
 272         INP_INFO_WUNLOCK(&V_tcbinfo);
 273         CURVNET_RESTORE();
 274 }
 275
 276 void
 277 tcp_timer_keep(void *xtp)
 278 {
 279         struct tcpcb *tp = xtp;
 280         struct tcptemp *t_template;
 281         struct inpcb *inp;
 282         CURVNET_SET(tp->t_vnet);
 283 #ifdef TCPDEBUG
 284         int ostate;
 285
 286         ostate = tp->t_state;
 287 #endif
 288         INP_INFO_WLOCK(&V_tcbinfo);
 289         inp = tp->t_inpcb;
 290         /*
 291          * XXXRW: While this assert is in fact correct, bugs in the tcpcb
 292          * tear-down mean we need it as a work-around for races between
 293          * timers and tcp_discardcb().
 294          *
 295          * KASSERT(inp != NULL, ("tcp_timer_keep: inp == NULL"));
 296          */
 297         if (inp == NULL) {
 298                 tcp_timer_race++;
 299                 INP_INFO_WUNLOCK(&V_tcbinfo);
 300                 CURVNET_RESTORE();
 301                 return;
 302         }
 303         INP_WLOCK(inp);
 304         if ((inp->inp_flags & INP_DROPPED) || callout_pending(&tp->t_timers->tt_keep)
 305             || !callout_active(&tp->t_timers->tt_keep)) {
 306                 INP_WUNLOCK(inp);
 307                 INP_INFO_WUNLOCK(&V_tcbinfo);
 308                 CURVNET_RESTORE();
 309                 return;
 310         }
 311         callout_deactivate(&tp->t_timers->tt_keep);
 312         /*
 313          * Keep-alive timer went off; send something
 314          * or drop connection if idle for too long.
 315          */
 316         TCPSTAT_INC(tcps_keeptimeo);
 317         if (tp->t_state < TCPS_ESTABLISHED)
 318                 goto dropit;
 319         if ((always_keepalive || inp->inp_socket->so_options & SO_KEEPALIVE) &&
 320             tp->t_state <= TCPS_CLOSING) {
 321                 if (ticks - tp->t_rcvtime >= tcp_keepidle + tcp_maxidle)
 322                         goto dropit;
 323                 /*
 324                  * Send a packet designed to force a response
 325                  * if the peer is up and reachable:
 326                  * either an ACK if the connection is still alive,
 327                  * or an RST if the peer has closed the connection
 328                  * due to timeout or reboot.
 329                  * Using sequence number tp->snd_una-1
 330                  * causes the transmitted zero-length segment
 331                  * to lie outside the receive window;
 332                  * by the protocol spec, this requires the
 333                  * correspondent TCP to respond.
 334                  */
 335                 TCPSTAT_INC(tcps_keepprobe);
 336                 t_template = tcpip_maketemplate(inp);
 337                 if (t_template) {
 338                         tcp_respond(tp, t_template->tt_ipgen,
 339                                     &t_template->tt_t, (struct mbuf *)NULL,
 340                                     tp->rcv_nxt, tp->snd_una - 1, 0);
 341                         free(t_template, M_TEMP);
 342                 }
 343                 callout_reset_on(&tp->t_timers->tt_keep, tcp_keepintvl, tcp_timer_keep, tp, INP_CPU(inp));
 344         } else
 345                 callout_reset_on(&tp->t_timers->tt_keep, tcp_keepidle, tcp_timer_keep, tp, INP_CPU(inp));
 346
 347 #ifdef TCPDEBUG
 348         if (inp->inp_socket->so_options & SO_DEBUG)
 349                 tcp_trace(TA_USER, ostate, tp, (void *)0, (struct tcphdr *)0,
 350                           PRU_SLOWTIMO);
 351 #endif
 352         INP_WUNLOCK(inp);
 353         INP_INFO_WUNLOCK(&V_tcbinfo);
 354         CURVNET_RESTORE();
 355         return;
 356
 357 dropit:
 358         TCPSTAT_INC(tcps_keepdrops);
 359         tp = tcp_drop(tp, ETIMEDOUT);
 360
 361 #ifdef TCPDEBUG
 362         if (tp != NULL && (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
 363                 tcp_trace(TA_USER, ostate, tp, (void *)0, (struct tcphdr *)0,
 364                           PRU_SLOWTIMO);
 365 #endif
 366         if (tp != NULL)
 367                 INP_WUNLOCK(tp->t_inpcb);
 368         INP_INFO_WUNLOCK(&V_tcbinfo);
 369         CURVNET_RESTORE();
 370 }
 371
 372 void
 373 tcp_timer_persist(void *xtp)
 374 {
 375         struct tcpcb *tp = xtp;
 376         struct inpcb *inp;
 377         CURVNET_SET(tp->t_vnet);
 378 #ifdef TCPDEBUG
 379         int ostate;
 380
 381         ostate = tp->t_state;
 382 #endif
 383         INP_INFO_WLOCK(&V_tcbinfo);
 384         inp = tp->t_inpcb;
 385         /*
 386          * XXXRW: While this assert is in fact correct, bugs in the tcpcb
 387          * tear-down mean we need it as a work-around for races between
 388          * timers and tcp_discardcb().
 389          *
 390          * KASSERT(inp != NULL, ("tcp_timer_persist: inp == NULL"));
 391          */
 392         if (inp == NULL) {
 393                 tcp_timer_race++;
 394                 INP_INFO_WUNLOCK(&V_tcbinfo);
 395                 CURVNET_RESTORE();
 396                 return;
 397         }
 398         INP_WLOCK(inp);
 399         if ((inp->inp_flags & INP_DROPPED) || callout_pending(&tp->t_timers->tt_persist)
 400             || !callout_active(&tp->t_timers->tt_persist)) {
 401                 INP_WUNLOCK(inp);
 402                 INP_INFO_WUNLOCK(&V_tcbinfo);
 403                 CURVNET_RESTORE();
 404                 return;
 405         }
 406         callout_deactivate(&tp->t_timers->tt_persist);
 407         /*
 408          * Persistance timer into zero window.
 409          * Force a byte to be output, if possible.
 410          */
 411         TCPSTAT_INC(tcps_persisttimeo);
 412         /*
 413          * Hack: if the peer is dead/unreachable, we do not
 414          * time out if the window is closed.  After a full
 415          * backoff, drop the connection if the idle time
 416          * (no responses to probes) reaches the maximum
 417          * backoff that we would use if retransmitting.
 418          */
 419         if (tp->t_rxtshift == TCP_MAXRXTSHIFT &&
 420             (ticks - tp->t_rcvtime >= tcp_maxpersistidle ||
 421              ticks - tp->t_rcvtime >= TCP_REXMTVAL(tp) * tcp_totbackoff)) {
 422                 TCPSTAT_INC(tcps_persistdrop);
 423                 tp = tcp_drop(tp, ETIMEDOUT);
 424                 goto out;
 425         }
 426         tcp_setpersist(tp);
 427         tp->t_flags |= TF_FORCEDATA;
 428         (void) tcp_output(tp);
 429         tp->t_flags &= ~TF_FORCEDATA;
 430
 431 out:
 432 #ifdef TCPDEBUG
 433         if (tp != NULL && tp->t_inpcb->inp_socket->so_options & SO_DEBUG)
 434                 tcp_trace(TA_USER, ostate, tp, NULL, NULL, PRU_SLOWTIMO);
 435 #endif
 436         if (tp != NULL)
 437                 INP_WUNLOCK(inp);
 438         INP_INFO_WUNLOCK(&V_tcbinfo);
 439         CURVNET_RESTORE();
 440 }
 441
 442 void
 443 tcp_timer_rexmt(void * xtp)
 444 {
 445         struct tcpcb *tp = xtp;
 446         CURVNET_SET(tp->t_vnet);
 447         int rexmt;
 448         int headlocked;
 449         struct inpcb *inp;
 450 #ifdef TCPDEBUG
 451         int ostate;
 452
 453         ostate = tp->t_state;
 454 #endif
 455         INP_INFO_RLOCK(&V_tcbinfo);
 456         inp = tp->t_inpcb;
 457         /*
 458          * XXXRW: While this assert is in fact correct, bugs in the tcpcb
 459          * tear-down mean we need it as a work-around for races between
 460          * timers and tcp_discardcb().
 461          *
 462          * KASSERT(inp != NULL, ("tcp_timer_rexmt: inp == NULL"));
 463          */
 464         if (inp == NULL) {
 465                 tcp_timer_race++;
 466                 INP_INFO_RUNLOCK(&V_tcbinfo);
 467                 CURVNET_RESTORE();
 468                 return;
 469         }
 470         INP_WLOCK(inp);
 471         if ((inp->inp_flags & INP_DROPPED) || callout_pending(&tp->t_timers->tt_rexmt)
 472             || !callout_active(&tp->t_timers->tt_rexmt)) {
 473                 INP_WUNLOCK(inp);
 474                 INP_INFO_RUNLOCK(&V_tcbinfo);
 475                 CURVNET_RESTORE();
 476                 return;
 477         }
 478         callout_deactivate(&tp->t_timers->tt_rexmt);
 479         tcp_free_sackholes(tp);
 480         /*
 481          * Retransmission timer went off.  Message has not
 482          * been acked within retransmit interval.  Back off
 483          * to a longer retransmit interval and retransmit one segment.
 484          */
 485         if (++tp->t_rxtshift > TCP_MAXRXTSHIFT) {
 486                 tp->t_rxtshift = TCP_MAXRXTSHIFT;
 487                 TCPSTAT_INC(tcps_timeoutdrop);
 488                 in_pcbref(inp);
 489                 INP_INFO_RUNLOCK(&V_tcbinfo);
 490                 INP_WUNLOCK(inp);
 491                 INP_INFO_WLOCK(&V_tcbinfo);
 492                 INP_WLOCK(inp);
 493                 if (in_pcbrele_wlocked(inp)) {
 494                         INP_INFO_WUNLOCK(&V_tcbinfo);
 495                         CURVNET_RESTORE();
 496                         return;
 497                 }
 498                 if (inp->inp_flags & INP_DROPPED) {
 499                         INP_WUNLOCK(inp);
 500                         INP_INFO_WUNLOCK(&V_tcbinfo);
 501                         CURVNET_RESTORE();
 502                         return;
 503                 }
 504
 505                 tp = tcp_drop(tp, tp->t_softerror ?
 506                               tp->t_softerror : ETIMEDOUT);
 507                 headlocked = 1;
 508                 goto out;
 509         }
 510         INP_INFO_RUNLOCK(&V_tcbinfo);
 511         headlocked = 0;
 512         if (tp->t_rxtshift == 1) {
 513                 /*
 514                  * first retransmit; record ssthresh and cwnd so they can
 515                  * be recovered if this turns out to be a "bad" retransmit.
 516                  * A retransmit is considered "bad" if an ACK for this
 517                  * segment is received within RTT/2 interval; the assumption
 518                  * here is that the ACK was already in flight.  See
 519                  * "On Estimating End-to-End Network Path Properties" by
 520                  * Allman and Paxson for more details.
 521                  */
 522                 tp->snd_cwnd_prev = tp->snd_cwnd;
 523                 tp->snd_ssthresh_prev = tp->snd_ssthresh;
 524                 tp->snd_recover_prev = tp->snd_recover;
 525                 if (IN_FASTRECOVERY(tp->t_flags))
 526                         tp->t_flags |= TF_WASFRECOVERY;
 527                 else
 528                         tp->t_flags &= ~TF_WASFRECOVERY;
 529                 if (IN_CONGRECOVERY(tp->t_flags))
 530                         tp->t_flags |= TF_WASCRECOVERY;
 531                 else
 532                         tp->t_flags &= ~TF_WASCRECOVERY;
 533                 tp->t_badrxtwin = ticks + (tp->t_srtt >> (TCP_RTT_SHIFT + 1));
 534                 tp->t_flags |= TF_PREVVALID;
 535         } else
 536                 tp->t_flags &= ~TF_PREVVALID;
 537         TCPSTAT_INC(tcps_rexmttimeo);
 538         if (tp->t_state == TCPS_SYN_SENT)
 539                 rexmt = TCP_REXMTVAL(tp) * tcp_syn_backoff[tp->t_rxtshift];
 540         else
 541                 rexmt = TCP_REXMTVAL(tp) * tcp_backoff[tp->t_rxtshift];
 542         TCPT_RANGESET(tp->t_rxtcur, rexmt,
 543                       tp->t_rttmin, TCPTV_REXMTMAX);
 544         /*
 545          * Disable rfc1323 if we haven't got any response to
 546          * our third SYN to work-around some broken terminal servers
 547          * (most of which have hopefully been retired) that have bad VJ
 548          * header compression code which trashes TCP segments containing
 549          * unknown-to-them TCP options.
 550          */
 551         if ((tp->t_state == TCPS_SYN_SENT) && (tp->t_rxtshift == 3))
 552                 tp->t_flags &= ~(TF_REQ_SCALE|TF_REQ_TSTMP);
 553         /*
 554          * If we backed off this far, our srtt estimate is probably bogus.
 555          * Clobber it so we'll take the next rtt measurement as our srtt;
 556          * move the current srtt into rttvar to keep the current
 557          * retransmit times until then.
 558          */
 559         if (tp->t_rxtshift > TCP_MAXRXTSHIFT / 4) {
 560 #ifdef INET6
 561                 if ((tp->t_inpcb->inp_vflag & INP_IPV6) != 0)
 562                         in6_losing(tp->t_inpcb);
 563                 else
 564 #endif
 565                 tp->t_rttvar += (tp->t_srtt >> TCP_RTT_SHIFT);
 566                 tp->t_srtt = 0;
 567         }
 568         tp->snd_nxt = tp->snd_una;
 569         tp->snd_recover = tp->snd_max;
 570         /*
 571          * Force a segment to be sent.
 572          */
 573         tp->t_flags |= TF_ACKNOW;
 574         /*
 575          * If timing a segment in this window, stop the timer.
 576          */
 577         tp->t_rtttime = 0;
 578
 579         cc_cong_signal(tp, NULL, CC_RTO);
 580
 581         (void) tcp_output(tp);
 582
 583 out:
 584 #ifdef TCPDEBUG
 585         if (tp != NULL && (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
 586                 tcp_trace(TA_USER, ostate, tp, (void *)0, (struct tcphdr *)0,
 587                           PRU_SLOWTIMO);
 588 #endif
 589         if (tp != NULL)
 590                 INP_WUNLOCK(inp);
 591         if (headlocked)
 592                 INP_INFO_WUNLOCK(&V_tcbinfo);
 593         CURVNET_RESTORE();
 594 }
 595
 596 void
 597 tcp_timer_activate(struct tcpcb *tp, int timer_type, u_int delta)
 598 {
 599         struct callout *t_callout;
 600         void *f_callout;
 601         struct inpcb *inp = tp->t_inpcb;
 602         int cpu = INP_CPU(inp);
 603
 604         switch (timer_type) {
 605                 case TT_DELACK:
 606                         t_callout = &tp->t_timers->tt_delack;
 607                         f_callout = tcp_timer_delack;
 608                         break;
 609                 case TT_REXMT:
 610                         t_callout = &tp->t_timers->tt_rexmt;
 611                         f_callout = tcp_timer_rexmt;
 612                         break;
 613                 case TT_PERSIST:
 614                         t_callout = &tp->t_timers->tt_persist;
 615                         f_callout = tcp_timer_persist;
 616                         break;
 617                 case TT_KEEP:
 618                         t_callout = &tp->t_timers->tt_keep;
 619                         f_callout = tcp_timer_keep;
 620                         break;
 621                 case TT_2MSL:
 622                         t_callout = &tp->t_timers->tt_2msl;
 623                         f_callout = tcp_timer_2msl;
 624                         break;
 625                 default:
 626                         panic("bad timer_type");
 627                 }
 628         if (delta == 0) {
 629                 callout_stop(t_callout);
 630         } else {
 631                 callout_reset_on(t_callout, delta, f_callout, tp, cpu);
 632         }
 633 }
 634
 635 int
 636 tcp_timer_active(struct tcpcb *tp, int timer_type)
 637 {
 638         struct callout *t_callout;
 639
 640         switch (timer_type) {
 641                 case TT_DELACK:
 642                         t_callout = &tp->t_timers->tt_delack;
 643                         break;
 644                 case TT_REXMT:
 645                         t_callout = &tp->t_timers->tt_rexmt;
 646                         break;
 647                 case TT_PERSIST:
 648                         t_callout = &tp->t_timers->tt_persist;
 649                         break;
 650                 case TT_KEEP:
 651                         t_callout = &tp->t_timers->tt_keep;
 652                         break;
 653                 case TT_2MSL:
 654                         t_callout = &tp->t_timers->tt_2msl;
 655                         break;
 656                 default:
 657                         panic("bad timer_type");
 658                 }
 659         return callout_active(t_callout);
 660 }
 661
 662 #define ticks_to_msecs(t)       (1000*(t) / hz)
 663
 664 void
 665 tcp_timer_to_xtimer(struct tcpcb *tp, struct tcp_timer *timer, struct xtcp_timer *xtimer)
 666 {
 667         bzero(xtimer, sizeof(struct xtcp_timer));
 668         if (timer == NULL)
 669                 return;
 670         if (callout_active(&timer->tt_delack))
 671                 xtimer->tt_delack = ticks_to_msecs(timer->tt_delack.c_time - ticks);
 672         if (callout_active(&timer->tt_rexmt))
 673                 xtimer->tt_rexmt = ticks_to_msecs(timer->tt_rexmt.c_time - ticks);
 674         if (callout_active(&timer->tt_persist))
 675                 xtimer->tt_persist = ticks_to_msecs(timer->tt_persist.c_time - ticks);
 676         if (callout_active(&timer->tt_keep))
 677                 xtimer->tt_keep = ticks_to_msecs(timer->tt_keep.c_time - ticks);
 678         if (callout_active(&timer->tt_2msl))
 679                 xtimer->tt_2msl = ticks_to_msecs(timer->tt_2msl.c_time - ticks);
 680         xtimer->t_rcvtime = ticks_to_msecs(ticks - tp->t_rcvtime);
 681 }