Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)
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FreeBSD/Linux Kernel Cross Reference
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 * 3. All advertising materials mentioning features or use of this software 14 * must display the following acknowledgement: 15 * This product includes software developed by the University of 16 * California, Berkeley and its contributors. 17 * 4. Neither the name of the University nor the names of its contributors 18 * may be used to endorse or promote products derived from this software 19 * without specific prior written permission. 20 * 21 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 22 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 23 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 24 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 25 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 26 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 27 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 28 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 29 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 30 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 31 * SUCH DAMAGE. 32 * 33 * @(#)tcp_timer.c 8.2 (Berkeley) 5/24/95 34 * $FreeBSD: releng/5.0/sys/netinet/tcp_timer.c 108612 2003-01-03 20:35:59Z hsu $ 35 */ 36 37 #include "opt_inet6.h" 38 #include "opt_tcpdebug.h" 39 40 #include <sys/param.h> 41 #include <sys/kernel.h> 42 #include <sys/lock.h> 43 #include <sys/mbuf.h> 44 #include <sys/mutex.h> 45 #include <sys/protosw.h> 46 #include <sys/socket.h> 47 #include <sys/socketvar.h> 48 #include <sys/sysctl.h> 49 #include <sys/systm.h> 50 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 69 static int 70 sysctl_msec_to_ticks(SYSCTL_HANDLER_ARGS) 71 { 72 int error, s, tt; 73 74 tt = *(int *)oidp->oid_arg1; 75 s = (int)((int64_t)tt * 1000 / hz); 76 77 error = sysctl_handle_int(oidp, &s, 0, req); 78 if (error || !req->newptr) 79 return (error); 80 81 tt = (int)((int64_t)s * hz / 1000); 82 if (tt < 1) 83 return (EINVAL); 84 85 *(int *)oidp->oid_arg1 = tt; 86 return (0); 87 } 88 89 int tcp_keepinit; 90 SYSCTL_PROC(_net_inet_tcp, TCPCTL_KEEPINIT, keepinit, CTLTYPE_INT|CTLFLAG_RW, 91 &tcp_keepinit, 0, sysctl_msec_to_ticks, "I", ""); 92 93 int tcp_keepidle; 94 SYSCTL_PROC(_net_inet_tcp, TCPCTL_KEEPIDLE, keepidle, CTLTYPE_INT|CTLFLAG_RW, 95 &tcp_keepidle, 0, sysctl_msec_to_ticks, "I", ""); 96 97 int tcp_keepintvl; 98 SYSCTL_PROC(_net_inet_tcp, TCPCTL_KEEPINTVL, keepintvl, CTLTYPE_INT|CTLFLAG_RW, 99 &tcp_keepintvl, 0, sysctl_msec_to_ticks, "I", ""); 100 101 int tcp_delacktime; 102 SYSCTL_PROC(_net_inet_tcp, TCPCTL_DELACKTIME, delacktime, 103 CTLTYPE_INT|CTLFLAG_RW, &tcp_delacktime, 0, sysctl_msec_to_ticks, "I", 104 "Time before a delayed ACK is sent"); 105 106 int tcp_msl; 107 SYSCTL_PROC(_net_inet_tcp, OID_AUTO, msl, CTLTYPE_INT|CTLFLAG_RW, 108 &tcp_msl, 0, sysctl_msec_to_ticks, "I", "Maximum segment lifetime"); 109 110 int tcp_rexmit_min; 111 SYSCTL_PROC(_net_inet_tcp, OID_AUTO, rexmit_min, CTLTYPE_INT|CTLFLAG_RW, 112 &tcp_rexmit_min, 0, sysctl_msec_to_ticks, "I", "Minimum Retransmission Timeout"); 113 114 int tcp_rexmit_slop; 115 SYSCTL_PROC(_net_inet_tcp, OID_AUTO, rexmit_slop, CTLTYPE_INT|CTLFLAG_RW, 116 &tcp_rexmit_slop, 0, sysctl_msec_to_ticks, "I", "Retransmission Timer Slop"); 117 118 static int always_keepalive = 1; 119 SYSCTL_INT(_net_inet_tcp, OID_AUTO, always_keepalive, CTLFLAG_RW, 120 &always_keepalive , 0, "Assume SO_KEEPALIVE on all TCP connections"); 121 122 static int tcp_keepcnt = TCPTV_KEEPCNT; 123 /* max idle probes */ 124 int tcp_maxpersistidle; 125 /* max idle time in persist */ 126 int tcp_maxidle; 127 128 /* 129 * Tcp protocol timeout routine called every 500 ms. 130 * Updates timestamps used for TCP 131 * causes finite state machine actions if timers expire. 132 */ 133 void 134 tcp_slowtimo() 135 { 136 int s; 137 138 s = splnet(); 139 140 tcp_maxidle = tcp_keepcnt * tcp_keepintvl; 141 142 splx(s); 143 } 144 145 /* 146 * Cancel all timers for TCP tp. 147 */ 148 void 149 tcp_canceltimers(tp) 150 struct tcpcb *tp; 151 { 152 callout_stop(tp->tt_2msl); 153 callout_stop(tp->tt_persist); 154 callout_stop(tp->tt_keep); 155 callout_stop(tp->tt_rexmt); 156 } 157 158 int tcp_syn_backoff[TCP_MAXRXTSHIFT + 1] = 159 { 1, 1, 1, 1, 1, 2, 4, 8, 16, 32, 64, 64, 64 }; 160 161 int tcp_backoff[TCP_MAXRXTSHIFT + 1] = 162 { 1, 2, 4, 8, 16, 32, 64, 64, 64, 64, 64, 64, 64 }; 163 164 static int tcp_totbackoff = 511; /* sum of tcp_backoff[] */ 165 166 /* 167 * TCP timer processing. 168 */ 169 170 void 171 tcp_timer_delack(xtp) 172 void *xtp; 173 { 174 struct tcpcb *tp = xtp; 175 int s; 176 struct inpcb *inp; 177 178 s = splnet(); 179 INP_INFO_RLOCK(&tcbinfo); 180 inp = tp->t_inpcb; 181 if (!inp) { 182 INP_INFO_RUNLOCK(&tcbinfo); 183 splx(s); 184 return; 185 } 186 INP_LOCK(inp); 187 INP_INFO_RUNLOCK(&tcbinfo); 188 if (callout_pending(tp->tt_delack) || !callout_active(tp->tt_delack)) { 189 INP_UNLOCK(inp); 190 splx(s); 191 return; 192 } 193 callout_deactivate(tp->tt_delack); 194 195 tp->t_flags |= TF_ACKNOW; 196 tcpstat.tcps_delack++; 197 (void) tcp_output(tp); 198 INP_UNLOCK(inp); 199 splx(s); 200 } 201 202 void 203 tcp_timer_2msl(xtp) 204 void *xtp; 205 { 206 struct tcpcb *tp = xtp; 207 int s; 208 struct inpcb *inp; 209 #ifdef TCPDEBUG 210 int ostate; 211 212 ostate = tp->t_state; 213 #endif 214 s = splnet(); 215 INP_INFO_WLOCK(&tcbinfo); 216 inp = tp->t_inpcb; 217 if (!inp) { 218 INP_INFO_WUNLOCK(&tcbinfo); 219 splx(s); 220 return; 221 } 222 INP_LOCK(inp); 223 if (callout_pending(tp->tt_2msl) || !callout_active(tp->tt_2msl)) { 224 INP_UNLOCK(tp->t_inpcb); 225 INP_INFO_WUNLOCK(&tcbinfo); 226 splx(s); 227 return; 228 } 229 callout_deactivate(tp->tt_2msl); 230 /* 231 * 2 MSL timeout in shutdown went off. If we're closed but 232 * still waiting for peer to close and connection has been idle 233 * too long, or if 2MSL time is up from TIME_WAIT, delete connection 234 * control block. Otherwise, check again in a bit. 235 */ 236 if (tp->t_state != TCPS_TIME_WAIT && 237 (ticks - tp->t_rcvtime) <= tcp_maxidle) 238 callout_reset(tp->tt_2msl, tcp_keepintvl, 239 tcp_timer_2msl, tp); 240 else 241 tp = tcp_close(tp); 242 243 #ifdef TCPDEBUG 244 if (tp && (tp->t_inpcb->inp_socket->so_options & SO_DEBUG)) 245 tcp_trace(TA_USER, ostate, tp, (void *)0, (struct tcphdr *)0, 246 PRU_SLOWTIMO); 247 #endif 248 if (tp) 249 INP_UNLOCK(inp); 250 INP_INFO_WUNLOCK(&tcbinfo); 251 splx(s); 252 } 253 254 void 255 tcp_timer_keep(xtp) 256 void *xtp; 257 { 258 struct tcpcb *tp = xtp; 259 struct tcptemp *t_template; 260 int s; 261 struct inpcb *inp; 262 #ifdef TCPDEBUG 263 int ostate; 264 265 ostate = tp->t_state; 266 #endif 267 s = splnet(); 268 INP_INFO_WLOCK(&tcbinfo); 269 inp = tp->t_inpcb; 270 if (!inp) { 271 INP_INFO_WUNLOCK(&tcbinfo); 272 splx(s); 273 return; 274 } 275 INP_LOCK(inp); 276 if (callout_pending(tp->tt_keep) || !callout_active(tp->tt_keep)) { 277 INP_UNLOCK(inp); 278 INP_INFO_WUNLOCK(&tcbinfo); 279 splx(s); 280 return; 281 } 282 callout_deactivate(tp->tt_keep); 283 /* 284 * Keep-alive timer went off; send something 285 * or drop connection if idle for too long. 286 */ 287 tcpstat.tcps_keeptimeo++; 288 if (tp->t_state < TCPS_ESTABLISHED) 289 goto dropit; 290 if ((always_keepalive || 291 tp->t_inpcb->inp_socket->so_options & SO_KEEPALIVE) && 292 tp->t_state <= TCPS_CLOSING) { 293 if ((ticks - tp->t_rcvtime) >= tcp_keepidle + tcp_maxidle) 294 goto dropit; 295 /* 296 * Send a packet designed to force a response 297 * if the peer is up and reachable: 298 * either an ACK if the connection is still alive, 299 * or an RST if the peer has closed the connection 300 * due to timeout or reboot. 301 * Using sequence number tp->snd_una-1 302 * causes the transmitted zero-length segment 303 * to lie outside the receive window; 304 * by the protocol spec, this requires the 305 * correspondent TCP to respond. 306 */ 307 tcpstat.tcps_keepprobe++; 308 t_template = tcp_maketemplate(tp); 309 if (t_template) { 310 tcp_respond(tp, t_template->tt_ipgen, 311 &t_template->tt_t, (struct mbuf *)NULL, 312 tp->rcv_nxt, tp->snd_una - 1, 0); 313 (void) m_free(dtom(t_template)); 314 } 315 callout_reset(tp->tt_keep, tcp_keepintvl, tcp_timer_keep, tp); 316 } else 317 callout_reset(tp->tt_keep, tcp_keepidle, tcp_timer_keep, tp); 318 319 #ifdef TCPDEBUG 320 if (tp->t_inpcb->inp_socket->so_options & SO_DEBUG) 321 tcp_trace(TA_USER, ostate, tp, (void *)0, (struct tcphdr *)0, 322 PRU_SLOWTIMO); 323 #endif 324 INP_UNLOCK(inp); 325 INP_INFO_WUNLOCK(&tcbinfo); 326 splx(s); 327 return; 328 329 dropit: 330 tcpstat.tcps_keepdrops++; 331 tp = tcp_drop(tp, ETIMEDOUT); 332 333 #ifdef TCPDEBUG 334 if (tp && (tp->t_inpcb->inp_socket->so_options & SO_DEBUG)) 335 tcp_trace(TA_USER, ostate, tp, (void *)0, (struct tcphdr *)0, 336 PRU_SLOWTIMO); 337 #endif 338 if (tp) 339 INP_UNLOCK(tp->t_inpcb); 340 INP_INFO_WUNLOCK(&tcbinfo); 341 splx(s); 342 } 343 344 void 345 tcp_timer_persist(xtp) 346 void *xtp; 347 { 348 struct tcpcb *tp = xtp; 349 int s; 350 struct inpcb *inp; 351 #ifdef TCPDEBUG 352 int ostate; 353 354 ostate = tp->t_state; 355 #endif 356 s = splnet(); 357 INP_INFO_WLOCK(&tcbinfo); 358 inp = tp->t_inpcb; 359 if (!inp) { 360 INP_INFO_WUNLOCK(&tcbinfo); 361 splx(s); 362 return; 363 } 364 INP_LOCK(inp); 365 if (callout_pending(tp->tt_persist) || !callout_active(tp->tt_persist)){ 366 INP_UNLOCK(inp); 367 INP_INFO_WUNLOCK(&tcbinfo); 368 splx(s); 369 return; 370 } 371 callout_deactivate(tp->tt_persist); 372 /* 373 * Persistance timer into zero window. 374 * Force a byte to be output, if possible. 375 */ 376 tcpstat.tcps_persisttimeo++; 377 /* 378 * Hack: if the peer is dead/unreachable, we do not 379 * time out if the window is closed. After a full 380 * backoff, drop the connection if the idle time 381 * (no responses to probes) reaches the maximum 382 * backoff that we would use if retransmitting. 383 */ 384 if (tp->t_rxtshift == TCP_MAXRXTSHIFT && 385 ((ticks - tp->t_rcvtime) >= tcp_maxpersistidle || 386 (ticks - tp->t_rcvtime) >= TCP_REXMTVAL(tp) * tcp_totbackoff)) { 387 tcpstat.tcps_persistdrop++; 388 tp = tcp_drop(tp, ETIMEDOUT); 389 goto out; 390 } 391 tcp_setpersist(tp); 392 tp->t_force = 1; 393 (void) tcp_output(tp); 394 tp->t_force = 0; 395 396 out: 397 #ifdef TCPDEBUG 398 if (tp && tp->t_inpcb->inp_socket->so_options & SO_DEBUG) 399 tcp_trace(TA_USER, ostate, tp, (void *)0, (struct tcphdr *)0, 400 PRU_SLOWTIMO); 401 #endif 402 if (tp) 403 INP_UNLOCK(inp); 404 INP_INFO_WUNLOCK(&tcbinfo); 405 splx(s); 406 } 407 408 void 409 tcp_timer_rexmt(xtp) 410 void *xtp; 411 { 412 struct tcpcb *tp = xtp; 413 int s; 414 int rexmt; 415 int headlocked; 416 struct inpcb *inp; 417 #ifdef TCPDEBUG 418 int ostate; 419 420 ostate = tp->t_state; 421 #endif 422 s = splnet(); 423 INP_INFO_WLOCK(&tcbinfo); 424 headlocked = 1; 425 inp = tp->t_inpcb; 426 if (!inp) { 427 INP_INFO_WUNLOCK(&tcbinfo); 428 splx(s); 429 return; 430 } 431 INP_LOCK(inp); 432 if (callout_pending(tp->tt_rexmt) || !callout_active(tp->tt_rexmt)) { 433 INP_UNLOCK(inp); 434 INP_INFO_WUNLOCK(&tcbinfo); 435 splx(s); 436 return; 437 } 438 callout_deactivate(tp->tt_rexmt); 439 /* 440 * Retransmission timer went off. Message has not 441 * been acked within retransmit interval. Back off 442 * to a longer retransmit interval and retransmit one segment. 443 */ 444 if (++tp->t_rxtshift > TCP_MAXRXTSHIFT) { 445 tp->t_rxtshift = TCP_MAXRXTSHIFT; 446 tcpstat.tcps_timeoutdrop++; 447 tp = tcp_drop(tp, tp->t_softerror ? 448 tp->t_softerror : ETIMEDOUT); 449 goto out; 450 } 451 INP_INFO_WUNLOCK(&tcbinfo); 452 headlocked = 0; 453 if (tp->t_rxtshift == 1) { 454 /* 455 * first retransmit; record ssthresh and cwnd so they can 456 * be recovered if this turns out to be a "bad" retransmit. 457 * A retransmit is considered "bad" if an ACK for this 458 * segment is received within RTT/2 interval; the assumption 459 * here is that the ACK was already in flight. See 460 * "On Estimating End-to-End Network Path Properties" by 461 * Allman and Paxson for more details. 462 */ 463 tp->snd_cwnd_prev = tp->snd_cwnd; 464 tp->snd_ssthresh_prev = tp->snd_ssthresh; 465 tp->t_badrxtwin = ticks + (tp->t_srtt >> (TCP_RTT_SHIFT + 1)); 466 } 467 tcpstat.tcps_rexmttimeo++; 468 if (tp->t_state == TCPS_SYN_SENT) 469 rexmt = TCP_REXMTVAL(tp) * tcp_syn_backoff[tp->t_rxtshift]; 470 else 471 rexmt = TCP_REXMTVAL(tp) * tcp_backoff[tp->t_rxtshift]; 472 TCPT_RANGESET(tp->t_rxtcur, rexmt, 473 tp->t_rttmin, TCPTV_REXMTMAX); 474 /* 475 * Disable rfc1323 and rfc1644 if we havn't got any response to 476 * our third SYN to work-around some broken terminal servers 477 * (most of which have hopefully been retired) that have bad VJ 478 * header compression code which trashes TCP segments containing 479 * unknown-to-them TCP options. 480 */ 481 if ((tp->t_state == TCPS_SYN_SENT) && (tp->t_rxtshift == 3)) 482 tp->t_flags &= ~(TF_REQ_SCALE|TF_REQ_TSTMP|TF_REQ_CC); 483 /* 484 * If losing, let the lower level know and try for 485 * a better route. Also, if we backed off this far, 486 * our srtt estimate is probably bogus. Clobber it 487 * so we'll take the next rtt measurement as our srtt; 488 * move the current srtt into rttvar to keep the current 489 * retransmit times until then. 490 */ 491 if (tp->t_rxtshift > TCP_MAXRXTSHIFT / 4) { 492 #ifdef INET6 493 if ((tp->t_inpcb->inp_vflag & INP_IPV6) != 0) 494 in6_losing(tp->t_inpcb); 495 else 496 #endif 497 in_losing(tp->t_inpcb); 498 tp->t_rttvar += (tp->t_srtt >> TCP_RTT_SHIFT); 499 tp->t_srtt = 0; 500 } 501 tp->snd_nxt = tp->snd_una; 502 /* 503 * Note: We overload snd_recover to function also as the 504 * snd_last variable described in RFC 2582 505 */ 506 tp->snd_recover = tp->snd_max; 507 /* 508 * Force a segment to be sent. 509 */ 510 tp->t_flags |= TF_ACKNOW; 511 /* 512 * If timing a segment in this window, stop the timer. 513 */ 514 tp->t_rtttime = 0; 515 /* 516 * Close the congestion window down to one segment 517 * (we'll open it by one segment for each ack we get). 518 * Since we probably have a window's worth of unacked 519 * data accumulated, this "slow start" keeps us from 520 * dumping all that data as back-to-back packets (which 521 * might overwhelm an intermediate gateway). 522 * 523 * There are two phases to the opening: Initially we 524 * open by one mss on each ack. This makes the window 525 * size increase exponentially with time. If the 526 * window is larger than the path can handle, this 527 * exponential growth results in dropped packet(s) 528 * almost immediately. To get more time between 529 * drops but still "push" the network to take advantage 530 * of improving conditions, we switch from exponential 531 * to linear window opening at some threshhold size. 532 * For a threshhold, we use half the current window 533 * size, truncated to a multiple of the mss. 534 * 535 * (the minimum cwnd that will give us exponential 536 * growth is 2 mss. We don't allow the threshhold 537 * to go below this.) 538 */ 539 { 540 u_int win = min(tp->snd_wnd, tp->snd_cwnd) / 2 / tp->t_maxseg; 541 if (win < 2) 542 win = 2; 543 tp->snd_cwnd = tp->t_maxseg; 544 tp->snd_ssthresh = win * tp->t_maxseg; 545 tp->t_dupacks = 0; 546 } 547 (void) tcp_output(tp); 548 549 out: 550 #ifdef TCPDEBUG 551 if (tp && (tp->t_inpcb->inp_socket->so_options & SO_DEBUG)) 552 tcp_trace(TA_USER, ostate, tp, (void *)0, (struct tcphdr *)0, 553 PRU_SLOWTIMO); 554 #endif 555 if (tp) 556 INP_UNLOCK(inp); 557 if (headlocked) 558 INP_INFO_WUNLOCK(&tcbinfo); 559 splx(s); 560 }
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