Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)
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sys/netinet/tcp_timer.c
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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: releng/8.0/sys/netinet/tcp_timer.c 196019 2009-08-01 19:26:27Z rwatson $"); 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 }
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