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 #include <sys/vimage.h>
  49
  50 #include <net/route.h>
  51
  52 #include <netinet/in.h>
  53 #include <netinet/in_pcb.h>
  54 #include <netinet/in_systm.h>
  55 #ifdef INET6
  56 #include <netinet6/in6_pcb.h>
  57 #endif
  58 #include <netinet/ip_var.h>
  59 #include <netinet/tcp.h>
  60 #include <netinet/tcp_fsm.h>
  61 #include <netinet/tcp_timer.h>
  62 #include <netinet/tcp_var.h>
  63 #include <netinet/tcpip.h>
  64 #ifdef TCPDEBUG
  65 #include <netinet/tcp_debug.h>
  66 #endif
  67
  68 int     tcp_keepinit;
  69 SYSCTL_PROC(_net_inet_tcp, TCPCTL_KEEPINIT, keepinit, CTLTYPE_INT|CTLFLAG_RW,
  70     &tcp_keepinit, 0, sysctl_msec_to_ticks, "I", "time to establish connection");
  71
  72 int     tcp_keepidle;
  73 SYSCTL_PROC(_net_inet_tcp, TCPCTL_KEEPIDLE, keepidle, CTLTYPE_INT|CTLFLAG_RW,
  74     &tcp_keepidle, 0, sysctl_msec_to_ticks, "I", "time before keepalive probes begin");
  75
  76 int     tcp_keepintvl;
  77 SYSCTL_PROC(_net_inet_tcp, TCPCTL_KEEPINTVL, keepintvl, CTLTYPE_INT|CTLFLAG_RW,
  78     &tcp_keepintvl, 0, sysctl_msec_to_ticks, "I", "time between keepalive probes");
  79
  80 int     tcp_delacktime;
  81 SYSCTL_PROC(_net_inet_tcp, TCPCTL_DELACKTIME, delacktime, CTLTYPE_INT|CTLFLAG_RW,
  82     &tcp_delacktime, 0, sysctl_msec_to_ticks, "I",
  83     "Time before a delayed ACK is sent");
  84
  85 int     tcp_msl;
  86 SYSCTL_PROC(_net_inet_tcp, OID_AUTO, msl, CTLTYPE_INT|CTLFLAG_RW,
  87     &tcp_msl, 0, sysctl_msec_to_ticks, "I", "Maximum segment lifetime");
  88
  89 int     tcp_rexmit_min;
  90 SYSCTL_PROC(_net_inet_tcp, OID_AUTO, rexmit_min, CTLTYPE_INT|CTLFLAG_RW,
  91     &tcp_rexmit_min, 0, sysctl_msec_to_ticks, "I",
  92     "Minimum Retransmission Timeout");
  93
  94 int     tcp_rexmit_slop;
  95 SYSCTL_PROC(_net_inet_tcp, OID_AUTO, rexmit_slop, CTLTYPE_INT|CTLFLAG_RW,
  96     &tcp_rexmit_slop, 0, sysctl_msec_to_ticks, "I",
  97     "Retransmission Timer Slop");
  98
  99 static int      always_keepalive = 1;
 100 SYSCTL_INT(_net_inet_tcp, OID_AUTO, always_keepalive, CTLFLAG_RW,
 101     &always_keepalive , 0, "Assume SO_KEEPALIVE on all TCP connections");
 102
 103 int    tcp_fast_finwait2_recycle = 0;
 104 SYSCTL_INT(_net_inet_tcp, OID_AUTO, fast_finwait2_recycle, CTLFLAG_RW,
 105     &tcp_fast_finwait2_recycle, 0,
 106     "Recycle closed FIN_WAIT_2 connections faster");
 107
 108 int    tcp_finwait2_timeout;
 109 SYSCTL_PROC(_net_inet_tcp, OID_AUTO, finwait2_timeout, CTLTYPE_INT|CTLFLAG_RW,
 110     &tcp_finwait2_timeout, 0, sysctl_msec_to_ticks, "I", "FIN-WAIT2 timeout");
 111
 112
 113 static int      tcp_keepcnt = TCPTV_KEEPCNT;
 114         /* max idle probes */
 115 int     tcp_maxpersistidle;
 116         /* max idle time in persist */
 117 int     tcp_maxidle;
 118
 119 /*
 120  * Tcp protocol timeout routine called every 500 ms.
 121  * Updates timestamps used for TCP
 122  * causes finite state machine actions if timers expire.
 123  */
 124 void
 125 tcp_slowtimo(void)
 126 {
 127
 128         tcp_maxidle = tcp_keepcnt * tcp_keepintvl;
 129         INP_INFO_WLOCK(&V_tcbinfo);
 130         (void) tcp_tw_2msl_scan(0);
 131         INP_INFO_WUNLOCK(&V_tcbinfo);
 132 }
 133
 134 int     tcp_syn_backoff[TCP_MAXRXTSHIFT + 1] =
 135     { 1, 1, 1, 1, 1, 2, 4, 8, 16, 32, 64, 64, 64 };
 136
 137 int     tcp_backoff[TCP_MAXRXTSHIFT + 1] =
 138     { 1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 512, 512, 512 };
 139
 140 static int tcp_totbackoff = 2559;       /* sum of tcp_backoff[] */
 141
 142 static int tcp_timer_race;
 143 SYSCTL_INT(_net_inet_tcp, OID_AUTO, timer_race, CTLFLAG_RD, &tcp_timer_race,
 144     0, "Count of t_inpcb races on tcp_discardcb");
 145
 146 /*
 147  * TCP timer processing.
 148  */
 149
 150 void
 151 tcp_timer_delack(void *xtp)
 152 {
 153         struct tcpcb *tp = xtp;
 154         struct inpcb *inp;
 155
 156         INP_INFO_RLOCK(&V_tcbinfo);
 157         inp = tp->t_inpcb;
 158         /*
 159          * XXXRW: While this assert is in fact correct, bugs in the tcpcb
 160          * tear-down mean we need it as a work-around for races between
 161          * timers and tcp_discardcb().
 162          *
 163          * KASSERT(inp != NULL, ("tcp_timer_delack: inp == NULL"));
 164          */
 165         if (inp == NULL) {
 166                 tcp_timer_race++;
 167                 INP_INFO_RUNLOCK(&V_tcbinfo);
 168                 return;
 169         }
 170         INP_WLOCK(inp);
 171         INP_INFO_RUNLOCK(&V_tcbinfo);
 172         if ((inp->inp_vflag & INP_DROPPED) || callout_pending(&tp->t_timers->tt_delack)
 173             || !callout_active(&tp->t_timers->tt_delack)) {
 174                 INP_WUNLOCK(inp);
 175                 return;
 176         }
 177         callout_deactivate(&tp->t_timers->tt_delack);
 178
 179         tp->t_flags |= TF_ACKNOW;
 180         V_tcpstat.tcps_delack++;
 181         (void) tcp_output(tp);
 182         INP_WUNLOCK(inp);
 183 }
 184
 185 void
 186 tcp_timer_2msl(void *xtp)
 187 {
 188         struct tcpcb *tp = xtp;
 189         struct inpcb *inp;
 190 #ifdef TCPDEBUG
 191         int ostate;
 192
 193         ostate = tp->t_state;
 194 #endif
 195         /*
 196          * XXXRW: Does this actually happen?
 197          */
 198         INP_INFO_WLOCK(&V_tcbinfo);
 199         inp = tp->t_inpcb;
 200         /*
 201          * XXXRW: While this assert is in fact correct, bugs in the tcpcb
 202          * tear-down mean we need it as a work-around for races between
 203          * timers and tcp_discardcb().
 204          *
 205          * KASSERT(inp != NULL, ("tcp_timer_2msl: inp == NULL"));
 206          */
 207         if (inp == NULL) {
 208                 tcp_timer_race++;
 209                 INP_INFO_WUNLOCK(&V_tcbinfo);
 210                 return;
 211         }
 212         INP_WLOCK(inp);
 213         tcp_free_sackholes(tp);
 214         if ((inp->inp_vflag & INP_DROPPED) || callout_pending(&tp->t_timers->tt_2msl) ||
 215             !callout_active(&tp->t_timers->tt_2msl)) {
 216                 INP_WUNLOCK(tp->t_inpcb);
 217                 INP_INFO_WUNLOCK(&V_tcbinfo);
 218                 return;
 219         }
 220         callout_deactivate(&tp->t_timers->tt_2msl);
 221         /*
 222          * 2 MSL timeout in shutdown went off.  If we're closed but
 223          * still waiting for peer to close and connection has been idle
 224          * too long, or if 2MSL time is up from TIME_WAIT, delete connection
 225          * control block.  Otherwise, check again in a bit.
 226          *
 227          * If fastrecycle of FIN_WAIT_2, in FIN_WAIT_2 and receiver has closed,
 228          * there's no point in hanging onto FIN_WAIT_2 socket. Just close it.
 229          * Ignore fact that there were recent incoming segments.
 230          */
 231         if (tcp_fast_finwait2_recycle && tp->t_state == TCPS_FIN_WAIT_2 &&
 232             tp->t_inpcb && tp->t_inpcb->inp_socket &&
 233             (tp->t_inpcb->inp_socket->so_rcv.sb_state & SBS_CANTRCVMORE)) {
 234                 V_tcpstat.tcps_finwait2_drops++;
 235                 tp = tcp_close(tp);
 236         } else {
 237                 if (tp->t_state != TCPS_TIME_WAIT &&
 238                    (ticks - tp->t_rcvtime) <= tcp_maxidle)
 239                        callout_reset(&tp->t_timers->tt_2msl, tcp_keepintvl,
 240                                      tcp_timer_2msl, tp);
 241                else
 242                        tp = tcp_close(tp);
 243        }
 244
 245 #ifdef TCPDEBUG
 246         if (tp != NULL && (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
 247                 tcp_trace(TA_USER, ostate, tp, (void *)0, (struct tcphdr *)0,
 248                           PRU_SLOWTIMO);
 249 #endif
 250         if (tp != NULL)
 251                 INP_WUNLOCK(inp);
 252         INP_INFO_WUNLOCK(&V_tcbinfo);
 253 }
 254
 255 void
 256 tcp_timer_keep(void *xtp)
 257 {
 258         struct tcpcb *tp = xtp;
 259         struct tcptemp *t_template;
 260         struct inpcb *inp;
 261 #ifdef TCPDEBUG
 262         int ostate;
 263
 264         ostate = tp->t_state;
 265 #endif
 266         INP_INFO_WLOCK(&V_tcbinfo);
 267         inp = tp->t_inpcb;
 268         /*
 269          * XXXRW: While this assert is in fact correct, bugs in the tcpcb
 270          * tear-down mean we need it as a work-around for races between
 271          * timers and tcp_discardcb().
 272          *
 273          * KASSERT(inp != NULL, ("tcp_timer_keep: inp == NULL"));
 274          */
 275         if (inp == NULL) {
 276                 tcp_timer_race++;
 277                 INP_INFO_WUNLOCK(&V_tcbinfo);
 278                 return;
 279         }
 280         INP_WLOCK(inp);
 281         if ((inp->inp_vflag & INP_DROPPED) || callout_pending(&tp->t_timers->tt_keep)
 282             || !callout_active(&tp->t_timers->tt_keep)) {
 283                 INP_WUNLOCK(inp);
 284                 INP_INFO_WUNLOCK(&V_tcbinfo);
 285                 return;
 286         }
 287         callout_deactivate(&tp->t_timers->tt_keep);
 288         /*
 289          * Keep-alive timer went off; send something
 290          * or drop connection if idle for too long.
 291          */
 292         V_tcpstat.tcps_keeptimeo++;
 293         if (tp->t_state < TCPS_ESTABLISHED)
 294                 goto dropit;
 295         if ((always_keepalive || inp->inp_socket->so_options & SO_KEEPALIVE) &&
 296             tp->t_state <= TCPS_CLOSING) {
 297                 if ((ticks - tp->t_rcvtime) >= tcp_keepidle + tcp_maxidle)
 298                         goto dropit;
 299                 /*
 300                  * Send a packet designed to force a response
 301                  * if the peer is up and reachable:
 302                  * either an ACK if the connection is still alive,
 303                  * or an RST if the peer has closed the connection
 304                  * due to timeout or reboot.
 305                  * Using sequence number tp->snd_una-1
 306                  * causes the transmitted zero-length segment
 307                  * to lie outside the receive window;
 308                  * by the protocol spec, this requires the
 309                  * correspondent TCP to respond.
 310                  */
 311                 V_tcpstat.tcps_keepprobe++;
 312                 t_template = tcpip_maketemplate(inp);
 313                 if (t_template) {
 314                         tcp_respond(tp, t_template->tt_ipgen,
 315                                     &t_template->tt_t, (struct mbuf *)NULL,
 316                                     tp->rcv_nxt, tp->snd_una - 1, 0);
 317                         free(t_template, M_TEMP);
 318                 }
 319                 callout_reset(&tp->t_timers->tt_keep, tcp_keepintvl, tcp_timer_keep, tp);
 320         } else
 321                 callout_reset(&tp->t_timers->tt_keep, tcp_keepidle, tcp_timer_keep, tp);
 322
 323 #ifdef TCPDEBUG
 324         if (inp->inp_socket->so_options & SO_DEBUG)
 325                 tcp_trace(TA_USER, ostate, tp, (void *)0, (struct tcphdr *)0,
 326                           PRU_SLOWTIMO);
 327 #endif
 328         INP_WUNLOCK(inp);
 329         INP_INFO_WUNLOCK(&V_tcbinfo);
 330         return;
 331
 332 dropit:
 333         V_tcpstat.tcps_keepdrops++;
 334         tp = tcp_drop(tp, ETIMEDOUT);
 335
 336 #ifdef TCPDEBUG
 337         if (tp != NULL && (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
 338                 tcp_trace(TA_USER, ostate, tp, (void *)0, (struct tcphdr *)0,
 339                           PRU_SLOWTIMO);
 340 #endif
 341         if (tp != NULL)
 342                 INP_WUNLOCK(tp->t_inpcb);
 343         INP_INFO_WUNLOCK(&V_tcbinfo);
 344 }
 345
 346 void
 347 tcp_timer_persist(void *xtp)
 348 {
 349         struct tcpcb *tp = xtp;
 350         struct inpcb *inp;
 351 #ifdef TCPDEBUG
 352         int ostate;
 353
 354         ostate = tp->t_state;
 355 #endif
 356         INP_INFO_WLOCK(&V_tcbinfo);
 357         inp = tp->t_inpcb;
 358         /*
 359          * XXXRW: While this assert is in fact correct, bugs in the tcpcb
 360          * tear-down mean we need it as a work-around for races between
 361          * timers and tcp_discardcb().
 362          *
 363          * KASSERT(inp != NULL, ("tcp_timer_persist: inp == NULL"));
 364          */
 365         if (inp == NULL) {
 366                 tcp_timer_race++;
 367                 INP_INFO_WUNLOCK(&V_tcbinfo);
 368                 return;
 369         }
 370         INP_WLOCK(inp);
 371         if ((inp->inp_vflag & INP_DROPPED) || callout_pending(&tp->t_timers->tt_persist)
 372             || !callout_active(&tp->t_timers->tt_persist)) {
 373                 INP_WUNLOCK(inp);
 374                 INP_INFO_WUNLOCK(&V_tcbinfo);
 375                 return;
 376         }
 377         callout_deactivate(&tp->t_timers->tt_persist);
 378         /*
 379          * Persistance timer into zero window.
 380          * Force a byte to be output, if possible.
 381          */
 382         V_tcpstat.tcps_persisttimeo++;
 383         /*
 384          * Hack: if the peer is dead/unreachable, we do not
 385          * time out if the window is closed.  After a full
 386          * backoff, drop the connection if the idle time
 387          * (no responses to probes) reaches the maximum
 388          * backoff that we would use if retransmitting.
 389          */
 390         if (tp->t_rxtshift == TCP_MAXRXTSHIFT &&
 391             ((ticks - tp->t_rcvtime) >= tcp_maxpersistidle ||
 392              (ticks - tp->t_rcvtime) >= TCP_REXMTVAL(tp) * tcp_totbackoff)) {
 393                 V_tcpstat.tcps_persistdrop++;
 394                 tp = tcp_drop(tp, ETIMEDOUT);
 395                 goto out;
 396         }
 397         tcp_setpersist(tp);
 398         tp->t_flags |= TF_FORCEDATA;
 399         (void) tcp_output(tp);
 400         tp->t_flags &= ~TF_FORCEDATA;
 401
 402 out:
 403 #ifdef TCPDEBUG
 404         if (tp != NULL && tp->t_inpcb->inp_socket->so_options & SO_DEBUG)
 405                 tcp_trace(TA_USER, ostate, tp, NULL, NULL, PRU_SLOWTIMO);
 406 #endif
 407         if (tp != NULL)
 408                 INP_WUNLOCK(inp);
 409         INP_INFO_WUNLOCK(&V_tcbinfo);
 410 }
 411
 412 void
 413 tcp_timer_rexmt(void * xtp)
 414 {
 415         struct tcpcb *tp = xtp;
 416         int rexmt;
 417         int headlocked;
 418         struct inpcb *inp;
 419 #ifdef TCPDEBUG
 420         int ostate;
 421
 422         ostate = tp->t_state;
 423 #endif
 424         INP_INFO_WLOCK(&V_tcbinfo);
 425         headlocked = 1;
 426         inp = tp->t_inpcb;
 427         /*
 428          * XXXRW: While this assert is in fact correct, bugs in the tcpcb
 429          * tear-down mean we need it as a work-around for races between
 430          * timers and tcp_discardcb().
 431          *
 432          * KASSERT(inp != NULL, ("tcp_timer_rexmt: inp == NULL"));
 433          */
 434         if (inp == NULL) {
 435                 tcp_timer_race++;
 436                 INP_INFO_WUNLOCK(&V_tcbinfo);
 437                 return;
 438         }
 439         INP_WLOCK(inp);
 440         if ((inp->inp_vflag & INP_DROPPED) || callout_pending(&tp->t_timers->tt_rexmt)
 441             || !callout_active(&tp->t_timers->tt_rexmt)) {
 442                 INP_WUNLOCK(inp);
 443                 INP_INFO_WUNLOCK(&V_tcbinfo);
 444                 return;
 445         }
 446         callout_deactivate(&tp->t_timers->tt_rexmt);
 447         tcp_free_sackholes(tp);
 448         /*
 449          * Retransmission timer went off.  Message has not
 450          * been acked within retransmit interval.  Back off
 451          * to a longer retransmit interval and retransmit one segment.
 452          */
 453         if (++tp->t_rxtshift > TCP_MAXRXTSHIFT) {
 454                 tp->t_rxtshift = TCP_MAXRXTSHIFT;
 455                 V_tcpstat.tcps_timeoutdrop++;
 456                 tp = tcp_drop(tp, tp->t_softerror ?
 457                               tp->t_softerror : ETIMEDOUT);
 458                 goto out;
 459         }
 460         INP_INFO_WUNLOCK(&V_tcbinfo);
 461         headlocked = 0;
 462         if (tp->t_rxtshift == 1) {
 463                 /*
 464                  * first retransmit; record ssthresh and cwnd so they can
 465                  * be recovered if this turns out to be a "bad" retransmit.
 466                  * A retransmit is considered "bad" if an ACK for this
 467                  * segment is received within RTT/2 interval; the assumption
 468                  * here is that the ACK was already in flight.  See
 469                  * "On Estimating End-to-End Network Path Properties" by
 470                  * Allman and Paxson for more details.
 471                  */
 472                 tp->snd_cwnd_prev = tp->snd_cwnd;
 473                 tp->snd_ssthresh_prev = tp->snd_ssthresh;
 474                 tp->snd_recover_prev = tp->snd_recover;
 475                 if (IN_FASTRECOVERY(tp))
 476                   tp->t_flags |= TF_WASFRECOVERY;
 477                 else
 478                   tp->t_flags &= ~TF_WASFRECOVERY;
 479                 tp->t_badrxtwin = ticks + (tp->t_srtt >> (TCP_RTT_SHIFT + 1));
 480         }
 481         V_tcpstat.tcps_rexmttimeo++;
 482         if (tp->t_state == TCPS_SYN_SENT)
 483                 rexmt = TCP_REXMTVAL(tp) * tcp_syn_backoff[tp->t_rxtshift];
 484         else
 485                 rexmt = TCP_REXMTVAL(tp) * tcp_backoff[tp->t_rxtshift];
 486         TCPT_RANGESET(tp->t_rxtcur, rexmt,
 487                       tp->t_rttmin, TCPTV_REXMTMAX);
 488         /*
 489          * Disable rfc1323 if we havn't got any response to
 490          * our third SYN to work-around some broken terminal servers
 491          * (most of which have hopefully been retired) that have bad VJ
 492          * header compression code which trashes TCP segments containing
 493          * unknown-to-them TCP options.
 494          */
 495         if ((tp->t_state == TCPS_SYN_SENT) && (tp->t_rxtshift == 3))
 496                 tp->t_flags &= ~(TF_REQ_SCALE|TF_REQ_TSTMP);
 497         /*
 498          * If we backed off this far, our srtt estimate is probably bogus.
 499          * Clobber it so we'll take the next rtt measurement as our srtt;
 500          * move the current srtt into rttvar to keep the current
 501          * retransmit times until then.
 502          */
 503         if (tp->t_rxtshift > TCP_MAXRXTSHIFT / 4) {
 504 #ifdef INET6
 505                 if ((tp->t_inpcb->inp_vflag & INP_IPV6) != 0)
 506                         in6_losing(tp->t_inpcb);
 507                 else
 508 #endif
 509                 tp->t_rttvar += (tp->t_srtt >> TCP_RTT_SHIFT);
 510                 tp->t_srtt = 0;
 511         }
 512         tp->snd_nxt = tp->snd_una;
 513         tp->snd_recover = tp->snd_max;
 514         /*
 515          * Force a segment to be sent.
 516          */
 517         tp->t_flags |= TF_ACKNOW;
 518         /*
 519          * If timing a segment in this window, stop the timer.
 520          */
 521         tp->t_rtttime = 0;
 522         /*
 523          * Close the congestion window down to one segment
 524          * (we'll open it by one segment for each ack we get).
 525          * Since we probably have a window's worth of unacked
 526          * data accumulated, this "slow start" keeps us from
 527          * dumping all that data as back-to-back packets (which
 528          * might overwhelm an intermediate gateway).
 529          *
 530          * There are two phases to the opening: Initially we
 531          * open by one mss on each ack.  This makes the window
 532          * size increase exponentially with time.  If the
 533          * window is larger than the path can handle, this
 534          * exponential growth results in dropped packet(s)
 535          * almost immediately.  To get more time between
 536          * drops but still "push" the network to take advantage
 537          * of improving conditions, we switch from exponential
 538          * to linear window opening at some threshhold size.
 539          * For a threshhold, we use half the current window
 540          * size, truncated to a multiple of the mss.
 541          *
 542          * (the minimum cwnd that will give us exponential
 543          * growth is 2 mss.  We don't allow the threshhold
 544          * to go below this.)
 545          */
 546         {
 547                 u_int win = min(tp->snd_wnd, tp->snd_cwnd) / 2 / tp->t_maxseg;
 548                 if (win < 2)
 549                         win = 2;
 550                 tp->snd_cwnd = tp->t_maxseg;
 551                 tp->snd_ssthresh = win * tp->t_maxseg;
 552                 tp->t_dupacks = 0;
 553         }
 554         EXIT_FASTRECOVERY(tp);
 555         (void) tcp_output(tp);
 556
 557 out:
 558 #ifdef TCPDEBUG
 559         if (tp != NULL && (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
 560                 tcp_trace(TA_USER, ostate, tp, (void *)0, (struct tcphdr *)0,
 561                           PRU_SLOWTIMO);
 562 #endif
 563         if (tp != NULL)
 564                 INP_WUNLOCK(inp);
 565         if (headlocked)
 566                 INP_INFO_WUNLOCK(&V_tcbinfo);
 567 }
 568
 569 void
 570 tcp_timer_activate(struct tcpcb *tp, int timer_type, u_int delta)
 571 {
 572         struct callout *t_callout;
 573         void *f_callout;
 574
 575         switch (timer_type) {
 576                 case TT_DELACK:
 577                         t_callout = &tp->t_timers->tt_delack;
 578                         f_callout = tcp_timer_delack;
 579                         break;
 580                 case TT_REXMT:
 581                         t_callout = &tp->t_timers->tt_rexmt;
 582                         f_callout = tcp_timer_rexmt;
 583                         break;
 584                 case TT_PERSIST:
 585                         t_callout = &tp->t_timers->tt_persist;
 586                         f_callout = tcp_timer_persist;
 587                         break;
 588                 case TT_KEEP:
 589                         t_callout = &tp->t_timers->tt_keep;
 590                         f_callout = tcp_timer_keep;
 591                         break;
 592                 case TT_2MSL:
 593                         t_callout = &tp->t_timers->tt_2msl;
 594                         f_callout = tcp_timer_2msl;
 595                         break;
 596                 default:
 597                         panic("bad timer_type");
 598                 }
 599         if (delta == 0) {
 600                 callout_stop(t_callout);
 601         } else {
 602                 callout_reset(t_callout, delta, f_callout, tp);
 603         }
 604 }
 605
 606 int
 607 tcp_timer_active(struct tcpcb *tp, int timer_type)
 608 {
 609         struct callout *t_callout;
 610
 611         switch (timer_type) {
 612                 case TT_DELACK:
 613                         t_callout = &tp->t_timers->tt_delack;
 614                         break;
 615                 case TT_REXMT:
 616                         t_callout = &tp->t_timers->tt_rexmt;
 617                         break;
 618                 case TT_PERSIST:
 619                         t_callout = &tp->t_timers->tt_persist;
 620                         break;
 621                 case TT_KEEP:
 622                         t_callout = &tp->t_timers->tt_keep;
 623                         break;
 624                 case TT_2MSL:
 625                         t_callout = &tp->t_timers->tt_2msl;
 626                         break;
 627                 default:
 628                         panic("bad timer_type");
 629                 }
 630         return callout_active(t_callout);
 631 }