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/socket.h>
  45 #include <sys/socketvar.h>
  46 #include <sys/sysctl.h>
  47 #include <sys/systm.h>
  48
  49 #include <net/if.h>
  50 #include <net/route.h>
  51 #include <net/vnet.h>
  52
  53 #include <netinet/in.h>
  54 #include <netinet/in_pcb.h>
  55 #include <netinet/in_systm.h>
  56 #ifdef INET6
  57 #include <netinet6/in6_pcb.h>
  58 #endif
  59 #include <netinet/ip_var.h>
  60 #include <netinet/tcp.h>
  61 #include <netinet/tcp_fsm.h>
  62 #include <netinet/tcp_timer.h>
  63 #include <netinet/tcp_var.h>
  64 #include <netinet/tcpip.h>
  65 #ifdef TCPDEBUG
  66 #include <netinet/tcp_debug.h>
  67 #endif
  68
  69 int     tcp_keepinit;
  70 SYSCTL_PROC(_net_inet_tcp, TCPCTL_KEEPINIT, keepinit, CTLTYPE_INT|CTLFLAG_RW,
  71     &tcp_keepinit, 0, sysctl_msec_to_ticks, "I", "time to establish connection");
  72
  73 int     tcp_keepidle;
  74 SYSCTL_PROC(_net_inet_tcp, TCPCTL_KEEPIDLE, keepidle, CTLTYPE_INT|CTLFLAG_RW,
  75     &tcp_keepidle, 0, sysctl_msec_to_ticks, "I", "time before keepalive probes begin");
  76
  77 int     tcp_keepintvl;
  78 SYSCTL_PROC(_net_inet_tcp, TCPCTL_KEEPINTVL, keepintvl, CTLTYPE_INT|CTLFLAG_RW,
  79     &tcp_keepintvl, 0, sysctl_msec_to_ticks, "I", "time between keepalive probes");
  80
  81 int     tcp_delacktime;
  82 SYSCTL_PROC(_net_inet_tcp, TCPCTL_DELACKTIME, delacktime, CTLTYPE_INT|CTLFLAG_RW,
  83     &tcp_delacktime, 0, sysctl_msec_to_ticks, "I",
  84     "Time before a delayed ACK is sent");
  85
  86 int     tcp_msl;
  87 SYSCTL_PROC(_net_inet_tcp, OID_AUTO, msl, CTLTYPE_INT|CTLFLAG_RW,
  88     &tcp_msl, 0, sysctl_msec_to_ticks, "I", "Maximum segment lifetime");
  89
  90 int     tcp_rexmit_min;
  91 SYSCTL_PROC(_net_inet_tcp, OID_AUTO, rexmit_min, CTLTYPE_INT|CTLFLAG_RW,
  92     &tcp_rexmit_min, 0, sysctl_msec_to_ticks, "I",
  93     "Minimum Retransmission Timeout");
  94
  95 int     tcp_rexmit_slop;
  96 SYSCTL_PROC(_net_inet_tcp, OID_AUTO, rexmit_slop, CTLTYPE_INT|CTLFLAG_RW,
  97     &tcp_rexmit_slop, 0, sysctl_msec_to_ticks, "I",
  98     "Retransmission Timer Slop");
  99
 100 static int      always_keepalive = 1;
 101 SYSCTL_INT(_net_inet_tcp, OID_AUTO, always_keepalive, CTLFLAG_RW,
 102     &always_keepalive , 0, "Assume SO_KEEPALIVE on all TCP connections");
 103
 104 int    tcp_fast_finwait2_recycle = 0;
 105 SYSCTL_INT(_net_inet_tcp, OID_AUTO, fast_finwait2_recycle, CTLFLAG_RW,
 106     &tcp_fast_finwait2_recycle, 0,
 107     "Recycle closed FIN_WAIT_2 connections faster");
 108
 109 int    tcp_finwait2_timeout;
 110 SYSCTL_PROC(_net_inet_tcp, OID_AUTO, finwait2_timeout, CTLTYPE_INT|CTLFLAG_RW,
 111     &tcp_finwait2_timeout, 0, sysctl_msec_to_ticks, "I", "FIN-WAIT2 timeout");
 112
 113
 114 static int      tcp_keepcnt = TCPTV_KEEPCNT;
 115         /* max idle probes */
 116 int     tcp_maxpersistidle;
 117         /* max idle time in persist */
 118 int     tcp_maxidle;
 119
 120 /*
 121  * Tcp protocol timeout routine called every 500 ms.
 122  * Updates timestamps used for TCP
 123  * causes finite state machine actions if timers expire.
 124  */
 125 void
 126 tcp_slowtimo(void)
 127 {
 128         VNET_ITERATOR_DECL(vnet_iter);
 129
 130         VNET_LIST_RLOCK_NOSLEEP();
 131         VNET_FOREACH(vnet_iter) {
 132                 CURVNET_SET(vnet_iter);
 133                 tcp_maxidle = tcp_keepcnt * tcp_keepintvl;
 134                 INP_INFO_WLOCK(&V_tcbinfo);
 135                 (void) tcp_tw_2msl_scan(0);
 136                 INP_INFO_WUNLOCK(&V_tcbinfo);
 137                 CURVNET_RESTORE();
 138         }
 139         VNET_LIST_RUNLOCK_NOSLEEP();
 140 }
 141
 142 int     tcp_syn_backoff[TCP_MAXRXTSHIFT + 1] =
 143     { 1, 1, 1, 1, 1, 2, 4, 8, 16, 32, 64, 64, 64 };
 144
 145 int     tcp_backoff[TCP_MAXRXTSHIFT + 1] =
 146     { 1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 512, 512, 512 };
 147
 148 static int tcp_totbackoff = 2559;       /* sum of tcp_backoff[] */
 149
 150 static int tcp_timer_race;
 151 SYSCTL_INT(_net_inet_tcp, OID_AUTO, timer_race, CTLFLAG_RD, &tcp_timer_race,
 152     0, "Count of t_inpcb races on tcp_discardcb");
 153
 154 /*
 155  * TCP timer processing.
 156  */
 157
 158 void
 159 tcp_timer_delack(void *xtp)
 160 {
 161         struct tcpcb *tp = xtp;
 162         struct inpcb *inp;
 163         CURVNET_SET(tp->t_vnet);
 164
 165         INP_INFO_RLOCK(&V_tcbinfo);
 166         inp = tp->t_inpcb;
 167         /*
 168          * XXXRW: While this assert is in fact correct, bugs in the tcpcb
 169          * tear-down mean we need it as a work-around for races between
 170          * timers and tcp_discardcb().
 171          *
 172          * KASSERT(inp != NULL, ("tcp_timer_delack: inp == NULL"));
 173          */
 174         if (inp == NULL) {
 175                 tcp_timer_race++;
 176                 INP_INFO_RUNLOCK(&V_tcbinfo);
 177                 CURVNET_RESTORE();
 178                 return;
 179         }
 180         INP_WLOCK(inp);
 181         INP_INFO_RUNLOCK(&V_tcbinfo);
 182         if ((inp->inp_flags & INP_DROPPED) || callout_pending(&tp->t_timers->tt_delack)
 183             || !callout_active(&tp->t_timers->tt_delack)) {
 184                 INP_WUNLOCK(inp);
 185                 CURVNET_RESTORE();
 186                 return;
 187         }
 188         callout_deactivate(&tp->t_timers->tt_delack);
 189
 190         tp->t_flags |= TF_ACKNOW;
 191         TCPSTAT_INC(tcps_delack);
 192         (void) tcp_output(tp);
 193         INP_WUNLOCK(inp);
 194         CURVNET_RESTORE();
 195 }
 196
 197 void
 198 tcp_timer_2msl(void *xtp)
 199 {
 200         struct tcpcb *tp = xtp;
 201         struct inpcb *inp;
 202         CURVNET_SET(tp->t_vnet);
 203 #ifdef TCPDEBUG
 204         int ostate;
 205
 206         ostate = tp->t_state;
 207 #endif
 208         /*
 209          * XXXRW: Does this actually happen?
 210          */
 211         INP_INFO_WLOCK(&V_tcbinfo);
 212         inp = tp->t_inpcb;
 213         /*
 214          * XXXRW: While this assert is in fact correct, bugs in the tcpcb
 215          * tear-down mean we need it as a work-around for races between
 216          * timers and tcp_discardcb().
 217          *
 218          * KASSERT(inp != NULL, ("tcp_timer_2msl: inp == NULL"));
 219          */
 220         if (inp == NULL) {
 221                 tcp_timer_race++;
 222                 INP_INFO_WUNLOCK(&V_tcbinfo);
 223                 CURVNET_RESTORE();
 224                 return;
 225         }
 226         INP_WLOCK(inp);
 227         tcp_free_sackholes(tp);
 228         if ((inp->inp_flags & INP_DROPPED) || callout_pending(&tp->t_timers->tt_2msl) ||
 229             !callout_active(&tp->t_timers->tt_2msl)) {
 230                 INP_WUNLOCK(tp->t_inpcb);
 231                 INP_INFO_WUNLOCK(&V_tcbinfo);
 232                 CURVNET_RESTORE();
 233                 return;
 234         }
 235         callout_deactivate(&tp->t_timers->tt_2msl);
 236         /*
 237          * 2 MSL timeout in shutdown went off.  If we're closed but
 238          * still waiting for peer to close and connection has been idle
 239          * too long, or if 2MSL time is up from TIME_WAIT, delete connection
 240          * control block.  Otherwise, check again in a bit.
 241          *
 242          * If fastrecycle of FIN_WAIT_2, in FIN_WAIT_2 and receiver has closed,
 243          * there's no point in hanging onto FIN_WAIT_2 socket. Just close it.
 244          * Ignore fact that there were recent incoming segments.
 245          */
 246         if (tcp_fast_finwait2_recycle && tp->t_state == TCPS_FIN_WAIT_2 &&
 247             tp->t_inpcb && tp->t_inpcb->inp_socket &&
 248             (tp->t_inpcb->inp_socket->so_rcv.sb_state & SBS_CANTRCVMORE)) {
 249                 TCPSTAT_INC(tcps_finwait2_drops);
 250                 tp = tcp_close(tp);
 251         } else {
 252                 if (tp->t_state != TCPS_TIME_WAIT &&
 253                    ticks - tp->t_rcvtime <= tcp_maxidle)
 254                        callout_reset(&tp->t_timers->tt_2msl, tcp_keepintvl,
 255                                      tcp_timer_2msl, tp);
 256                else
 257                        tp = tcp_close(tp);
 258        }
 259
 260 #ifdef TCPDEBUG
 261         if (tp != NULL && (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
 262                 tcp_trace(TA_USER, ostate, tp, (void *)0, (struct tcphdr *)0,
 263                           PRU_SLOWTIMO);
 264 #endif
 265         if (tp != NULL)
 266                 INP_WUNLOCK(inp);
 267         INP_INFO_WUNLOCK(&V_tcbinfo);
 268         CURVNET_RESTORE();
 269 }
 270
 271 void
 272 tcp_timer_keep(void *xtp)
 273 {
 274         struct tcpcb *tp = xtp;
 275         struct tcptemp *t_template;
 276         struct inpcb *inp;
 277         CURVNET_SET(tp->t_vnet);
 278 #ifdef TCPDEBUG
 279         int ostate;
 280
 281         ostate = tp->t_state;
 282 #endif
 283         INP_INFO_WLOCK(&V_tcbinfo);
 284         inp = tp->t_inpcb;
 285         /*
 286          * XXXRW: While this assert is in fact correct, bugs in the tcpcb
 287          * tear-down mean we need it as a work-around for races between
 288          * timers and tcp_discardcb().
 289          *
 290          * KASSERT(inp != NULL, ("tcp_timer_keep: inp == NULL"));
 291          */
 292         if (inp == NULL) {
 293                 tcp_timer_race++;
 294                 INP_INFO_WUNLOCK(&V_tcbinfo);
 295                 CURVNET_RESTORE();
 296                 return;
 297         }
 298         INP_WLOCK(inp);
 299         if ((inp->inp_flags & INP_DROPPED) || callout_pending(&tp->t_timers->tt_keep)
 300             || !callout_active(&tp->t_timers->tt_keep)) {
 301                 INP_WUNLOCK(inp);
 302                 INP_INFO_WUNLOCK(&V_tcbinfo);
 303                 CURVNET_RESTORE();
 304                 return;
 305         }
 306         callout_deactivate(&tp->t_timers->tt_keep);
 307         /*
 308          * Keep-alive timer went off; send something
 309          * or drop connection if idle for too long.
 310          */
 311         TCPSTAT_INC(tcps_keeptimeo);
 312         if (tp->t_state < TCPS_ESTABLISHED)
 313                 goto dropit;
 314         if ((always_keepalive || inp->inp_socket->so_options & SO_KEEPALIVE) &&
 315             tp->t_state <= TCPS_CLOSING) {
 316                 if (ticks - tp->t_rcvtime >= tcp_keepidle + tcp_maxidle)
 317                         goto dropit;
 318                 /*
 319                  * Send a packet designed to force a response
 320                  * if the peer is up and reachable:
 321                  * either an ACK if the connection is still alive,
 322                  * or an RST if the peer has closed the connection
 323                  * due to timeout or reboot.
 324                  * Using sequence number tp->snd_una-1
 325                  * causes the transmitted zero-length segment
 326                  * to lie outside the receive window;
 327                  * by the protocol spec, this requires the
 328                  * correspondent TCP to respond.
 329                  */
 330                 TCPSTAT_INC(tcps_keepprobe);
 331                 t_template = tcpip_maketemplate(inp);
 332                 if (t_template) {
 333                         tcp_respond(tp, t_template->tt_ipgen,
 334                                     &t_template->tt_t, (struct mbuf *)NULL,
 335                                     tp->rcv_nxt, tp->snd_una - 1, 0);
 336                         free(t_template, M_TEMP);
 337                 }
 338                 callout_reset(&tp->t_timers->tt_keep, tcp_keepintvl, tcp_timer_keep, tp);
 339         } else
 340                 callout_reset(&tp->t_timers->tt_keep, tcp_keepidle, tcp_timer_keep, tp);
 341
 342 #ifdef TCPDEBUG
 343         if (inp->inp_socket->so_options & SO_DEBUG)
 344                 tcp_trace(TA_USER, ostate, tp, (void *)0, (struct tcphdr *)0,
 345                           PRU_SLOWTIMO);
 346 #endif
 347         INP_WUNLOCK(inp);
 348         INP_INFO_WUNLOCK(&V_tcbinfo);
 349         CURVNET_RESTORE();
 350         return;
 351
 352 dropit:
 353         TCPSTAT_INC(tcps_keepdrops);
 354         tp = tcp_drop(tp, ETIMEDOUT);
 355
 356 #ifdef TCPDEBUG
 357         if (tp != NULL && (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
 358                 tcp_trace(TA_USER, ostate, tp, (void *)0, (struct tcphdr *)0,
 359                           PRU_SLOWTIMO);
 360 #endif
 361         if (tp != NULL)
 362                 INP_WUNLOCK(tp->t_inpcb);
 363         INP_INFO_WUNLOCK(&V_tcbinfo);
 364         CURVNET_RESTORE();
 365 }
 366
 367 void
 368 tcp_timer_persist(void *xtp)
 369 {
 370         struct tcpcb *tp = xtp;
 371         struct inpcb *inp;
 372         CURVNET_SET(tp->t_vnet);
 373 #ifdef TCPDEBUG
 374         int ostate;
 375
 376         ostate = tp->t_state;
 377 #endif
 378         INP_INFO_WLOCK(&V_tcbinfo);
 379         inp = tp->t_inpcb;
 380         /*
 381          * XXXRW: While this assert is in fact correct, bugs in the tcpcb
 382          * tear-down mean we need it as a work-around for races between
 383          * timers and tcp_discardcb().
 384          *
 385          * KASSERT(inp != NULL, ("tcp_timer_persist: inp == NULL"));
 386          */
 387         if (inp == NULL) {
 388                 tcp_timer_race++;
 389                 INP_INFO_WUNLOCK(&V_tcbinfo);
 390                 CURVNET_RESTORE();
 391                 return;
 392         }
 393         INP_WLOCK(inp);
 394         if ((inp->inp_flags & INP_DROPPED) || callout_pending(&tp->t_timers->tt_persist)
 395             || !callout_active(&tp->t_timers->tt_persist)) {
 396                 INP_WUNLOCK(inp);
 397                 INP_INFO_WUNLOCK(&V_tcbinfo);
 398                 CURVNET_RESTORE();
 399                 return;
 400         }
 401         callout_deactivate(&tp->t_timers->tt_persist);
 402         /*
 403          * Persistance timer into zero window.
 404          * Force a byte to be output, if possible.
 405          */
 406         TCPSTAT_INC(tcps_persisttimeo);
 407         /*
 408          * Hack: if the peer is dead/unreachable, we do not
 409          * time out if the window is closed.  After a full
 410          * backoff, drop the connection if the idle time
 411          * (no responses to probes) reaches the maximum
 412          * backoff that we would use if retransmitting.
 413          */
 414         if (tp->t_rxtshift == TCP_MAXRXTSHIFT &&
 415             (ticks - tp->t_rcvtime >= tcp_maxpersistidle ||
 416              ticks - tp->t_rcvtime >= TCP_REXMTVAL(tp) * tcp_totbackoff)) {
 417                 TCPSTAT_INC(tcps_persistdrop);
 418                 tp = tcp_drop(tp, ETIMEDOUT);
 419                 goto out;
 420         }
 421         tcp_setpersist(tp);
 422         tp->t_flags |= TF_FORCEDATA;
 423         (void) tcp_output(tp);
 424         tp->t_flags &= ~TF_FORCEDATA;
 425
 426 out:
 427 #ifdef TCPDEBUG
 428         if (tp != NULL && tp->t_inpcb->inp_socket->so_options & SO_DEBUG)
 429                 tcp_trace(TA_USER, ostate, tp, NULL, NULL, PRU_SLOWTIMO);
 430 #endif
 431         if (tp != NULL)
 432                 INP_WUNLOCK(inp);
 433         INP_INFO_WUNLOCK(&V_tcbinfo);
 434         CURVNET_RESTORE();
 435 }
 436
 437 void
 438 tcp_timer_rexmt(void * xtp)
 439 {
 440         struct tcpcb *tp = xtp;
 441         CURVNET_SET(tp->t_vnet);
 442         int rexmt;
 443         int headlocked;
 444         struct inpcb *inp;
 445 #ifdef TCPDEBUG
 446         int ostate;
 447
 448         ostate = tp->t_state;
 449 #endif
 450         INP_INFO_WLOCK(&V_tcbinfo);
 451         headlocked = 1;
 452         inp = tp->t_inpcb;
 453         /*
 454          * XXXRW: While this assert is in fact correct, bugs in the tcpcb
 455          * tear-down mean we need it as a work-around for races between
 456          * timers and tcp_discardcb().
 457          *
 458          * KASSERT(inp != NULL, ("tcp_timer_rexmt: inp == NULL"));
 459          */
 460         if (inp == NULL) {
 461                 tcp_timer_race++;
 462                 INP_INFO_WUNLOCK(&V_tcbinfo);
 463                 CURVNET_RESTORE();
 464                 return;
 465         }
 466         INP_WLOCK(inp);
 467         if ((inp->inp_flags & INP_DROPPED) || callout_pending(&tp->t_timers->tt_rexmt)
 468             || !callout_active(&tp->t_timers->tt_rexmt)) {
 469                 INP_WUNLOCK(inp);
 470                 INP_INFO_WUNLOCK(&V_tcbinfo);
 471                 CURVNET_RESTORE();
 472                 return;
 473         }
 474         callout_deactivate(&tp->t_timers->tt_rexmt);
 475         tcp_free_sackholes(tp);
 476         /*
 477          * Retransmission timer went off.  Message has not
 478          * been acked within retransmit interval.  Back off
 479          * to a longer retransmit interval and retransmit one segment.
 480          */
 481         if (++tp->t_rxtshift > TCP_MAXRXTSHIFT) {
 482                 tp->t_rxtshift = TCP_MAXRXTSHIFT;
 483                 TCPSTAT_INC(tcps_timeoutdrop);
 484                 tp = tcp_drop(tp, tp->t_softerror ?
 485                               tp->t_softerror : ETIMEDOUT);
 486                 goto out;
 487         }
 488         INP_INFO_WUNLOCK(&V_tcbinfo);
 489         headlocked = 0;
 490         if (tp->t_rxtshift == 1) {
 491                 /*
 492                  * first retransmit; record ssthresh and cwnd so they can
 493                  * be recovered if this turns out to be a "bad" retransmit.
 494                  * A retransmit is considered "bad" if an ACK for this
 495                  * segment is received within RTT/2 interval; the assumption
 496                  * here is that the ACK was already in flight.  See
 497                  * "On Estimating End-to-End Network Path Properties" by
 498                  * Allman and Paxson for more details.
 499                  */
 500                 tp->snd_cwnd_prev = tp->snd_cwnd;
 501                 tp->snd_ssthresh_prev = tp->snd_ssthresh;
 502                 tp->snd_recover_prev = tp->snd_recover;
 503                 if (IN_FASTRECOVERY(tp))
 504                   tp->t_flags |= TF_WASFRECOVERY;
 505                 else
 506                   tp->t_flags &= ~TF_WASFRECOVERY;
 507                 tp->t_badrxtwin = ticks + (tp->t_srtt >> (TCP_RTT_SHIFT + 1));
 508         }
 509         TCPSTAT_INC(tcps_rexmttimeo);
 510         if (tp->t_state == TCPS_SYN_SENT)
 511                 rexmt = TCP_REXMTVAL(tp) * tcp_syn_backoff[tp->t_rxtshift];
 512         else
 513                 rexmt = TCP_REXMTVAL(tp) * tcp_backoff[tp->t_rxtshift];
 514         TCPT_RANGESET(tp->t_rxtcur, rexmt,
 515                       tp->t_rttmin, TCPTV_REXMTMAX);
 516         /*
 517          * Disable rfc1323 if we havn't got any response to
 518          * our third SYN to work-around some broken terminal servers
 519          * (most of which have hopefully been retired) that have bad VJ
 520          * header compression code which trashes TCP segments containing
 521          * unknown-to-them TCP options.
 522          */
 523         if ((tp->t_state == TCPS_SYN_SENT) && (tp->t_rxtshift == 3))
 524                 tp->t_flags &= ~(TF_REQ_SCALE|TF_REQ_TSTMP);
 525         /*
 526          * If we backed off this far, our srtt estimate is probably bogus.
 527          * Clobber it so we'll take the next rtt measurement as our srtt;
 528          * move the current srtt into rttvar to keep the current
 529          * retransmit times until then.
 530          */
 531         if (tp->t_rxtshift > TCP_MAXRXTSHIFT / 4) {
 532 #ifdef INET6
 533                 if ((tp->t_inpcb->inp_vflag & INP_IPV6) != 0)
 534                         in6_losing(tp->t_inpcb);
 535                 else
 536 #endif
 537                 tp->t_rttvar += (tp->t_srtt >> TCP_RTT_SHIFT);
 538                 tp->t_srtt = 0;
 539         }
 540         tp->snd_nxt = tp->snd_una;
 541         tp->snd_recover = tp->snd_max;
 542         /*
 543          * Force a segment to be sent.
 544          */
 545         tp->t_flags |= TF_ACKNOW;
 546         /*
 547          * If timing a segment in this window, stop the timer.
 548          */
 549         tp->t_rtttime = 0;
 550         /*
 551          * Close the congestion window down to one segment
 552          * (we'll open it by one segment for each ack we get).
 553          * Since we probably have a window's worth of unacked
 554          * data accumulated, this "slow start" keeps us from
 555          * dumping all that data as back-to-back packets (which
 556          * might overwhelm an intermediate gateway).
 557          *
 558          * There are two phases to the opening: Initially we
 559          * open by one mss on each ack.  This makes the window
 560          * size increase exponentially with time.  If the
 561          * window is larger than the path can handle, this
 562          * exponential growth results in dropped packet(s)
 563          * almost immediately.  To get more time between
 564          * drops but still "push" the network to take advantage
 565          * of improving conditions, we switch from exponential
 566          * to linear window opening at some threshhold size.
 567          * For a threshhold, we use half the current window
 568          * size, truncated to a multiple of the mss.
 569          *
 570          * (the minimum cwnd that will give us exponential
 571          * growth is 2 mss.  We don't allow the threshhold
 572          * to go below this.)
 573          */
 574         {
 575                 u_int win = min(tp->snd_wnd, tp->snd_cwnd) / 2 / tp->t_maxseg;
 576                 if (win < 2)
 577                         win = 2;
 578                 tp->snd_cwnd = tp->t_maxseg;
 579                 tp->snd_ssthresh = win * tp->t_maxseg;
 580                 tp->t_dupacks = 0;
 581         }
 582         EXIT_FASTRECOVERY(tp);
 583         tp->t_bytes_acked = 0;
 584         (void) tcp_output(tp);
 585
 586 out:
 587 #ifdef TCPDEBUG
 588         if (tp != NULL && (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
 589                 tcp_trace(TA_USER, ostate, tp, (void *)0, (struct tcphdr *)0,
 590                           PRU_SLOWTIMO);
 591 #endif
 592         if (tp != NULL)
 593                 INP_WUNLOCK(inp);
 594         if (headlocked)
 595                 INP_INFO_WUNLOCK(&V_tcbinfo);
 596         CURVNET_RESTORE();
 597 }
 598
 599 void
 600 tcp_timer_activate(struct tcpcb *tp, int timer_type, u_int delta)
 601 {
 602         struct callout *t_callout;
 603         void *f_callout;
 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(t_callout, delta, f_callout, tp);
 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 }