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/if.h> 51 #include <net/route.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 #include <netinet/vinet.h> 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 /* 122 * Tcp protocol timeout routine called every 500 ms. 123 * Updates timestamps used for TCP 124 * causes finite state machine actions if timers expire. 125 */ 126 void 127 tcp_slowtimo(void) 128 { 129 VNET_ITERATOR_DECL(vnet_iter); 130 131 VNET_LIST_RLOCK(); 132 VNET_FOREACH(vnet_iter) { 133 CURVNET_SET(vnet_iter); 134 INIT_VNET_INET(vnet_iter); 135 tcp_maxidle = tcp_keepcnt * tcp_keepintvl; 136 INP_INFO_WLOCK(&V_tcbinfo); 137 (void) tcp_tw_2msl_scan(0); 138 INP_INFO_WUNLOCK(&V_tcbinfo); 139 CURVNET_RESTORE(); 140 } 141 VNET_LIST_RUNLOCK(); 142 } 143 144 int tcp_syn_backoff[TCP_MAXRXTSHIFT + 1] = 145 { 1, 1, 1, 1, 1, 2, 4, 8, 16, 32, 64, 64, 64 }; 146 147 int tcp_backoff[TCP_MAXRXTSHIFT + 1] = 148 { 1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 512, 512, 512 }; 149 150 static int tcp_totbackoff = 2559; /* sum of tcp_backoff[] */ 151 152 static int tcp_timer_race; 153 SYSCTL_INT(_net_inet_tcp, OID_AUTO, timer_race, CTLFLAG_RD, &tcp_timer_race, 154 0, "Count of t_inpcb races on tcp_discardcb"); 155 156 /* 157 * TCP timer processing. 158 */ 159 160 void 161 tcp_timer_delack(void *xtp) 162 { 163 struct tcpcb *tp = xtp; 164 struct inpcb *inp; 165 CURVNET_SET(tp->t_vnet); 166 INIT_VNET_INET(tp->t_vnet); 167 168 INP_INFO_RLOCK(&V_tcbinfo); 169 inp = tp->t_inpcb; 170 /* 171 * XXXRW: While this assert is in fact correct, bugs in the tcpcb 172 * tear-down mean we need it as a work-around for races between 173 * timers and tcp_discardcb(). 174 * 175 * KASSERT(inp != NULL, ("tcp_timer_delack: inp == NULL")); 176 */ 177 if (inp == NULL) { 178 tcp_timer_race++; 179 INP_INFO_RUNLOCK(&V_tcbinfo); 180 CURVNET_RESTORE(); 181 return; 182 } 183 INP_WLOCK(inp); 184 INP_INFO_RUNLOCK(&V_tcbinfo); 185 if ((inp->inp_vflag & INP_DROPPED) || callout_pending(&tp->t_timers->tt_delack) 186 || !callout_active(&tp->t_timers->tt_delack)) { 187 INP_WUNLOCK(inp); 188 CURVNET_RESTORE(); 189 return; 190 } 191 callout_deactivate(&tp->t_timers->tt_delack); 192 193 tp->t_flags |= TF_ACKNOW; 194 V_tcpstat.tcps_delack++; 195 (void) tcp_output(tp); 196 INP_WUNLOCK(inp); 197 CURVNET_RESTORE(); 198 } 199 200 void 201 tcp_timer_2msl(void *xtp) 202 { 203 struct tcpcb *tp = xtp; 204 struct inpcb *inp; 205 CURVNET_SET(tp->t_vnet); 206 INIT_VNET_INET(tp->t_vnet); 207 #ifdef TCPDEBUG 208 int ostate; 209 210 ostate = tp->t_state; 211 #endif 212 /* 213 * XXXRW: Does this actually happen? 214 */ 215 INP_INFO_WLOCK(&V_tcbinfo); 216 inp = tp->t_inpcb; 217 /* 218 * XXXRW: While this assert is in fact correct, bugs in the tcpcb 219 * tear-down mean we need it as a work-around for races between 220 * timers and tcp_discardcb(). 221 * 222 * KASSERT(inp != NULL, ("tcp_timer_2msl: inp == NULL")); 223 */ 224 if (inp == NULL) { 225 tcp_timer_race++; 226 INP_INFO_WUNLOCK(&V_tcbinfo); 227 CURVNET_RESTORE(); 228 return; 229 } 230 INP_WLOCK(inp); 231 tcp_free_sackholes(tp); 232 if ((inp->inp_vflag & INP_DROPPED) || callout_pending(&tp->t_timers->tt_2msl) || 233 !callout_active(&tp->t_timers->tt_2msl)) { 234 INP_WUNLOCK(tp->t_inpcb); 235 INP_INFO_WUNLOCK(&V_tcbinfo); 236 CURVNET_RESTORE(); 237 return; 238 } 239 callout_deactivate(&tp->t_timers->tt_2msl); 240 /* 241 * 2 MSL timeout in shutdown went off. If we're closed but 242 * still waiting for peer to close and connection has been idle 243 * too long, or if 2MSL time is up from TIME_WAIT, delete connection 244 * control block. Otherwise, check again in a bit. 245 * 246 * If fastrecycle of FIN_WAIT_2, in FIN_WAIT_2 and receiver has closed, 247 * there's no point in hanging onto FIN_WAIT_2 socket. Just close it. 248 * Ignore fact that there were recent incoming segments. 249 */ 250 if (tcp_fast_finwait2_recycle && tp->t_state == TCPS_FIN_WAIT_2 && 251 tp->t_inpcb && tp->t_inpcb->inp_socket && 252 (tp->t_inpcb->inp_socket->so_rcv.sb_state & SBS_CANTRCVMORE)) { 253 V_tcpstat.tcps_finwait2_drops++; 254 tp = tcp_close(tp); 255 } else { 256 if (tp->t_state != TCPS_TIME_WAIT && 257 (ticks - tp->t_rcvtime) <= tcp_maxidle) 258 callout_reset(&tp->t_timers->tt_2msl, tcp_keepintvl, 259 tcp_timer_2msl, tp); 260 else 261 tp = tcp_close(tp); 262 } 263 264 #ifdef TCPDEBUG 265 if (tp != NULL && (tp->t_inpcb->inp_socket->so_options & SO_DEBUG)) 266 tcp_trace(TA_USER, ostate, tp, (void *)0, (struct tcphdr *)0, 267 PRU_SLOWTIMO); 268 #endif 269 if (tp != NULL) 270 INP_WUNLOCK(inp); 271 INP_INFO_WUNLOCK(&V_tcbinfo); 272 CURVNET_RESTORE(); 273 } 274 275 void 276 tcp_timer_keep(void *xtp) 277 { 278 struct tcpcb *tp = xtp; 279 struct tcptemp *t_template; 280 struct inpcb *inp; 281 CURVNET_SET(tp->t_vnet); 282 INIT_VNET_INET(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_vflag & 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 V_tcpstat.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 V_tcpstat.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(&tp->t_timers->tt_keep, tcp_keepintvl, tcp_timer_keep, tp); 344 } else 345 callout_reset(&tp->t_timers->tt_keep, tcp_keepidle, tcp_timer_keep, tp); 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 V_tcpstat.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 INIT_VNET_INET(tp->t_vnet); 379 #ifdef TCPDEBUG 380 int ostate; 381 382 ostate = tp->t_state; 383 #endif 384 INP_INFO_WLOCK(&V_tcbinfo); 385 inp = tp->t_inpcb; 386 /* 387 * XXXRW: While this assert is in fact correct, bugs in the tcpcb 388 * tear-down mean we need it as a work-around for races between 389 * timers and tcp_discardcb(). 390 * 391 * KASSERT(inp != NULL, ("tcp_timer_persist: inp == NULL")); 392 */ 393 if (inp == NULL) { 394 tcp_timer_race++; 395 INP_INFO_WUNLOCK(&V_tcbinfo); 396 CURVNET_RESTORE(); 397 return; 398 } 399 INP_WLOCK(inp); 400 if ((inp->inp_vflag & INP_DROPPED) || callout_pending(&tp->t_timers->tt_persist) 401 || !callout_active(&tp->t_timers->tt_persist)) { 402 INP_WUNLOCK(inp); 403 INP_INFO_WUNLOCK(&V_tcbinfo); 404 CURVNET_RESTORE(); 405 return; 406 } 407 callout_deactivate(&tp->t_timers->tt_persist); 408 /* 409 * Persistance timer into zero window. 410 * Force a byte to be output, if possible. 411 */ 412 V_tcpstat.tcps_persisttimeo++; 413 /* 414 * Hack: if the peer is dead/unreachable, we do not 415 * time out if the window is closed. After a full 416 * backoff, drop the connection if the idle time 417 * (no responses to probes) reaches the maximum 418 * backoff that we would use if retransmitting. 419 */ 420 if (tp->t_rxtshift == TCP_MAXRXTSHIFT && 421 ((ticks - tp->t_rcvtime) >= tcp_maxpersistidle || 422 (ticks - tp->t_rcvtime) >= TCP_REXMTVAL(tp) * tcp_totbackoff)) { 423 V_tcpstat.tcps_persistdrop++; 424 tp = tcp_drop(tp, ETIMEDOUT); 425 goto out; 426 } 427 tcp_setpersist(tp); 428 tp->t_flags |= TF_FORCEDATA; 429 (void) tcp_output(tp); 430 tp->t_flags &= ~TF_FORCEDATA; 431 432 out: 433 #ifdef TCPDEBUG 434 if (tp != NULL && tp->t_inpcb->inp_socket->so_options & SO_DEBUG) 435 tcp_trace(TA_USER, ostate, tp, NULL, NULL, PRU_SLOWTIMO); 436 #endif 437 if (tp != NULL) 438 INP_WUNLOCK(inp); 439 INP_INFO_WUNLOCK(&V_tcbinfo); 440 CURVNET_RESTORE(); 441 } 442 443 void 444 tcp_timer_rexmt(void * xtp) 445 { 446 struct tcpcb *tp = xtp; 447 CURVNET_SET(tp->t_vnet); 448 INIT_VNET_INET(tp->t_vnet); 449 int rexmt; 450 int headlocked; 451 struct inpcb *inp; 452 #ifdef TCPDEBUG 453 int ostate; 454 455 ostate = tp->t_state; 456 #endif 457 INP_INFO_WLOCK(&V_tcbinfo); 458 headlocked = 1; 459 inp = tp->t_inpcb; 460 /* 461 * XXXRW: While this assert is in fact correct, bugs in the tcpcb 462 * tear-down mean we need it as a work-around for races between 463 * timers and tcp_discardcb(). 464 * 465 * KASSERT(inp != NULL, ("tcp_timer_rexmt: inp == NULL")); 466 */ 467 if (inp == NULL) { 468 tcp_timer_race++; 469 INP_INFO_WUNLOCK(&V_tcbinfo); 470 CURVNET_RESTORE(); 471 return; 472 } 473 INP_WLOCK(inp); 474 if ((inp->inp_vflag & INP_DROPPED) || callout_pending(&tp->t_timers->tt_rexmt) 475 || !callout_active(&tp->t_timers->tt_rexmt)) { 476 INP_WUNLOCK(inp); 477 INP_INFO_WUNLOCK(&V_tcbinfo); 478 CURVNET_RESTORE(); 479 return; 480 } 481 callout_deactivate(&tp->t_timers->tt_rexmt); 482 tcp_free_sackholes(tp); 483 /* 484 * Retransmission timer went off. Message has not 485 * been acked within retransmit interval. Back off 486 * to a longer retransmit interval and retransmit one segment. 487 */ 488 if (++tp->t_rxtshift > TCP_MAXRXTSHIFT) { 489 tp->t_rxtshift = TCP_MAXRXTSHIFT; 490 V_tcpstat.tcps_timeoutdrop++; 491 tp = tcp_drop(tp, tp->t_softerror ? 492 tp->t_softerror : ETIMEDOUT); 493 goto out; 494 } 495 INP_INFO_WUNLOCK(&V_tcbinfo); 496 headlocked = 0; 497 if (tp->t_rxtshift == 1) { 498 /* 499 * first retransmit; record ssthresh and cwnd so they can 500 * be recovered if this turns out to be a "bad" retransmit. 501 * A retransmit is considered "bad" if an ACK for this 502 * segment is received within RTT/2 interval; the assumption 503 * here is that the ACK was already in flight. See 504 * "On Estimating End-to-End Network Path Properties" by 505 * Allman and Paxson for more details. 506 */ 507 tp->snd_cwnd_prev = tp->snd_cwnd; 508 tp->snd_ssthresh_prev = tp->snd_ssthresh; 509 tp->snd_recover_prev = tp->snd_recover; 510 if (IN_FASTRECOVERY(tp)) 511 tp->t_flags |= TF_WASFRECOVERY; 512 else 513 tp->t_flags &= ~TF_WASFRECOVERY; 514 tp->t_badrxtwin = ticks + (tp->t_srtt >> (TCP_RTT_SHIFT + 1)); 515 } 516 V_tcpstat.tcps_rexmttimeo++; 517 if (tp->t_state == TCPS_SYN_SENT) 518 rexmt = TCP_REXMTVAL(tp) * tcp_syn_backoff[tp->t_rxtshift]; 519 else 520 rexmt = TCP_REXMTVAL(tp) * tcp_backoff[tp->t_rxtshift]; 521 TCPT_RANGESET(tp->t_rxtcur, rexmt, 522 tp->t_rttmin, TCPTV_REXMTMAX); 523 /* 524 * Disable rfc1323 if we havn't got any response to 525 * our third SYN to work-around some broken terminal servers 526 * (most of which have hopefully been retired) that have bad VJ 527 * header compression code which trashes TCP segments containing 528 * unknown-to-them TCP options. 529 */ 530 if ((tp->t_state == TCPS_SYN_SENT) && (tp->t_rxtshift == 3)) 531 tp->t_flags &= ~(TF_REQ_SCALE|TF_REQ_TSTMP); 532 /* 533 * If we backed off this far, our srtt estimate is probably bogus. 534 * Clobber it so we'll take the next rtt measurement as our srtt; 535 * move the current srtt into rttvar to keep the current 536 * retransmit times until then. 537 */ 538 if (tp->t_rxtshift > TCP_MAXRXTSHIFT / 4) { 539 #ifdef INET6 540 if ((tp->t_inpcb->inp_vflag & INP_IPV6) != 0) 541 in6_losing(tp->t_inpcb); 542 else 543 #endif 544 tp->t_rttvar += (tp->t_srtt >> TCP_RTT_SHIFT); 545 tp->t_srtt = 0; 546 } 547 tp->snd_nxt = tp->snd_una; 548 tp->snd_recover = tp->snd_max; 549 /* 550 * Force a segment to be sent. 551 */ 552 tp->t_flags |= TF_ACKNOW; 553 /* 554 * If timing a segment in this window, stop the timer. 555 */ 556 tp->t_rtttime = 0; 557 /* 558 * Close the congestion window down to one segment 559 * (we'll open it by one segment for each ack we get). 560 * Since we probably have a window's worth of unacked 561 * data accumulated, this "slow start" keeps us from 562 * dumping all that data as back-to-back packets (which 563 * might overwhelm an intermediate gateway). 564 * 565 * There are two phases to the opening: Initially we 566 * open by one mss on each ack. This makes the window 567 * size increase exponentially with time. If the 568 * window is larger than the path can handle, this 569 * exponential growth results in dropped packet(s) 570 * almost immediately. To get more time between 571 * drops but still "push" the network to take advantage 572 * of improving conditions, we switch from exponential 573 * to linear window opening at some threshhold size. 574 * For a threshhold, we use half the current window 575 * size, truncated to a multiple of the mss. 576 * 577 * (the minimum cwnd that will give us exponential 578 * growth is 2 mss. We don't allow the threshhold 579 * to go below this.) 580 */ 581 { 582 u_int win = min(tp->snd_wnd, tp->snd_cwnd) / 2 / tp->t_maxseg; 583 if (win < 2) 584 win = 2; 585 tp->snd_cwnd = tp->t_maxseg; 586 tp->snd_ssthresh = win * tp->t_maxseg; 587 tp->t_dupacks = 0; 588 } 589 EXIT_FASTRECOVERY(tp); 590 tp->t_bytes_acked = 0; 591 (void) tcp_output(tp); 592 593 out: 594 #ifdef TCPDEBUG 595 if (tp != NULL && (tp->t_inpcb->inp_socket->so_options & SO_DEBUG)) 596 tcp_trace(TA_USER, ostate, tp, (void *)0, (struct tcphdr *)0, 597 PRU_SLOWTIMO); 598 #endif 599 if (tp != NULL) 600 INP_WUNLOCK(inp); 601 if (headlocked) 602 INP_INFO_WUNLOCK(&V_tcbinfo); 603 CURVNET_RESTORE(); 604 } 605 606 void 607 tcp_timer_activate(struct tcpcb *tp, int timer_type, u_int delta) 608 { 609 struct callout *t_callout; 610 void *f_callout; 611 612 switch (timer_type) { 613 case TT_DELACK: 614 t_callout = &tp->t_timers->tt_delack; 615 f_callout = tcp_timer_delack; 616 break; 617 case TT_REXMT: 618 t_callout = &tp->t_timers->tt_rexmt; 619 f_callout = tcp_timer_rexmt; 620 break; 621 case TT_PERSIST: 622 t_callout = &tp->t_timers->tt_persist; 623 f_callout = tcp_timer_persist; 624 break; 625 case TT_KEEP: 626 t_callout = &tp->t_timers->tt_keep; 627 f_callout = tcp_timer_keep; 628 break; 629 case TT_2MSL: 630 t_callout = &tp->t_timers->tt_2msl; 631 f_callout = tcp_timer_2msl; 632 break; 633 default: 634 panic("bad timer_type"); 635 } 636 if (delta == 0) { 637 callout_stop(t_callout); 638 } else { 639 callout_reset(t_callout, delta, f_callout, tp); 640 } 641 } 642 643 int 644 tcp_timer_active(struct tcpcb *tp, int timer_type) 645 { 646 struct callout *t_callout; 647 648 switch (timer_type) { 649 case TT_DELACK: 650 t_callout = &tp->t_timers->tt_delack; 651 break; 652 case TT_REXMT: 653 t_callout = &tp->t_timers->tt_rexmt; 654 break; 655 case TT_PERSIST: 656 t_callout = &tp->t_timers->tt_persist; 657 break; 658 case TT_KEEP: 659 t_callout = &tp->t_timers->tt_keep; 660 break; 661 case TT_2MSL: 662 t_callout = &tp->t_timers->tt_2msl; 663 break; 664 default: 665 panic("bad timer_type"); 666 } 667 return callout_active(t_callout); 668 } 669