1 /* $OpenBSD: tcp_timer.c,v 1.53 2016/12/19 08:36:49 mpi Exp $ */ 2 /* $NetBSD: tcp_timer.c,v 1.14 1996/02/13 23:44:09 christos Exp $ */ 3 4 /* 5 * Copyright (c) 1982, 1986, 1988, 1990, 1993 6 * The Regents of the University of California. All rights reserved. 7 * 8 * Redistribution and use in source and binary forms, with or without 9 * modification, are permitted provided that the following conditions 10 * are met: 11 * 1. Redistributions of source code must retain the above copyright 12 * notice, this list of conditions and the following disclaimer. 13 * 2. Redistributions in binary form must reproduce the above copyright 14 * notice, this list of conditions and the following disclaimer in the 15 * documentation and/or other materials provided with the distribution. 16 * 3. Neither the name of the University nor the names of its contributors 17 * may be used to endorse or promote products derived from this software 18 * without specific prior written permission. 19 * 20 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 21 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 24 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30 * SUCH DAMAGE. 31 * 32 * @(#)tcp_timer.c 8.1 (Berkeley) 6/10/93 33 */ 34 35 #include <sys/param.h> 36 #include <sys/systm.h> 37 #include <sys/mbuf.h> 38 #include <sys/socket.h> 39 #include <sys/socketvar.h> 40 #include <sys/protosw.h> 41 #include <sys/kernel.h> 42 #include <sys/pool.h> 43 44 #include <net/route.h> 45 46 #include <netinet/in.h> 47 #include <netinet/ip.h> 48 #include <netinet/in_pcb.h> 49 #include <netinet/ip_var.h> 50 #include <netinet/tcp.h> 51 #include <netinet/tcp_fsm.h> 52 #include <netinet/tcp_timer.h> 53 #include <netinet/tcp_var.h> 54 #include <netinet/ip_icmp.h> 55 #include <netinet/tcp_seq.h> 56 57 int tcp_always_keepalive; 58 int tcp_keepidle; 59 int tcp_keepintvl; 60 int tcp_maxpersistidle; /* max idle time in persist */ 61 int tcp_maxidle; 62 63 /* 64 * Time to delay the ACK. This is initialized in tcp_init(), unless 65 * its patched. 66 */ 67 int tcp_delack_ticks; 68 69 void tcp_timer_rexmt(void *); 70 void tcp_timer_persist(void *); 71 void tcp_timer_keep(void *); 72 void tcp_timer_2msl(void *); 73 74 const tcp_timer_func_t tcp_timer_funcs[TCPT_NTIMERS] = { 75 tcp_timer_rexmt, 76 tcp_timer_persist, 77 tcp_timer_keep, 78 tcp_timer_2msl, 79 }; 80 81 /* 82 * Timer state initialization, called from tcp_init(). 83 */ 84 void 85 tcp_timer_init(void) 86 { 87 88 if (tcp_keepidle == 0) 89 tcp_keepidle = TCPTV_KEEP_IDLE; 90 91 if (tcp_keepintvl == 0) 92 tcp_keepintvl = TCPTV_KEEPINTVL; 93 94 if (tcp_maxpersistidle == 0) 95 tcp_maxpersistidle = TCPTV_KEEP_IDLE; 96 97 if (tcp_delack_ticks == 0) 98 tcp_delack_ticks = TCP_DELACK_TICKS; 99 } 100 101 /* 102 * Callout to process delayed ACKs for a TCPCB. 103 */ 104 void 105 tcp_delack(void *arg) 106 { 107 struct tcpcb *tp = arg; 108 int s; 109 110 /* 111 * If tcp_output() wasn't able to transmit the ACK 112 * for whatever reason, it will restart the delayed 113 * ACK callout. 114 */ 115 NET_LOCK(s); 116 if (tp->t_flags & TF_DEAD) 117 goto out; 118 tp->t_flags |= TF_ACKNOW; 119 (void) tcp_output(tp); 120 out: 121 NET_UNLOCK(s); 122 } 123 124 /* 125 * Tcp protocol timeout routine called every 500 ms. 126 * Updates the timers in all active tcb's and 127 * causes finite state machine actions if timers expire. 128 */ 129 void 130 tcp_slowtimo(void) 131 { 132 splsoftassert(IPL_SOFTNET); 133 134 tcp_maxidle = TCPTV_KEEPCNT * tcp_keepintvl; 135 tcp_iss += TCP_ISSINCR2/PR_SLOWHZ; /* increment iss */ 136 tcp_now++; /* for timestamps */ 137 } 138 139 /* 140 * Cancel all timers for TCP tp. 141 */ 142 void 143 tcp_canceltimers(struct tcpcb *tp) 144 { 145 int i; 146 147 for (i = 0; i < TCPT_NTIMERS; i++) 148 TCP_TIMER_DISARM(tp, i); 149 } 150 151 int tcp_backoff[TCP_MAXRXTSHIFT + 1] = 152 { 1, 2, 4, 8, 16, 32, 64, 64, 64, 64, 64, 64, 64 }; 153 154 int tcp_totbackoff = 511; /* sum of tcp_backoff[] */ 155 156 /* 157 * TCP timer processing. 158 */ 159 160 #ifdef TCP_SACK 161 void tcp_timer_freesack(struct tcpcb *); 162 163 void 164 tcp_timer_freesack(struct tcpcb *tp) 165 { 166 struct sackhole *p, *q; 167 /* 168 * Free SACK holes for 2MSL and REXMT timers. 169 */ 170 q = tp->snd_holes; 171 while (q != NULL) { 172 p = q; 173 q = q->next; 174 pool_put(&sackhl_pool, p); 175 } 176 tp->snd_holes = 0; 177 #ifdef TCP_FACK 178 tp->snd_fack = tp->snd_una; 179 tp->retran_data = 0; 180 tp->snd_awnd = 0; 181 #endif /* TCP_FACK */ 182 } 183 #endif /* TCP_SACK */ 184 185 void 186 tcp_timer_rexmt(void *arg) 187 { 188 struct tcpcb *tp = arg; 189 uint32_t rto; 190 int s; 191 192 NET_LOCK(s); 193 if (tp->t_flags & TF_DEAD) 194 goto out; 195 196 if ((tp->t_flags & TF_PMTUD_PEND) && tp->t_inpcb && 197 SEQ_GEQ(tp->t_pmtud_th_seq, tp->snd_una) && 198 SEQ_LT(tp->t_pmtud_th_seq, (int)(tp->snd_una + tp->t_maxseg))) { 199 struct sockaddr_in sin; 200 struct icmp icmp; 201 202 tp->t_flags &= ~TF_PMTUD_PEND; 203 204 /* XXX create fake icmp message with relevant entries */ 205 icmp.icmp_nextmtu = tp->t_pmtud_nextmtu; 206 icmp.icmp_ip.ip_len = tp->t_pmtud_ip_len; 207 icmp.icmp_ip.ip_hl = tp->t_pmtud_ip_hl; 208 icmp.icmp_ip.ip_dst = tp->t_inpcb->inp_faddr; 209 icmp_mtudisc(&icmp, tp->t_inpcb->inp_rtableid); 210 211 /* 212 * Notify all connections to the same peer about 213 * new mss and trigger retransmit. 214 */ 215 bzero(&sin, sizeof(sin)); 216 sin.sin_len = sizeof(sin); 217 sin.sin_family = AF_INET; 218 sin.sin_addr = tp->t_inpcb->inp_faddr; 219 in_pcbnotifyall(&tcbtable, sintosa(&sin), 220 tp->t_inpcb->inp_rtableid, EMSGSIZE, tcp_mtudisc); 221 goto out; 222 } 223 224 #ifdef TCP_SACK 225 tcp_timer_freesack(tp); 226 #endif 227 if (++tp->t_rxtshift > TCP_MAXRXTSHIFT) { 228 tp->t_rxtshift = TCP_MAXRXTSHIFT; 229 tcpstat.tcps_timeoutdrop++; 230 (void)tcp_drop(tp, tp->t_softerror ? 231 tp->t_softerror : ETIMEDOUT); 232 goto out; 233 } 234 tcpstat.tcps_rexmttimeo++; 235 rto = TCP_REXMTVAL(tp); 236 if (rto < tp->t_rttmin) 237 rto = tp->t_rttmin; 238 TCPT_RANGESET(tp->t_rxtcur, 239 rto * tcp_backoff[tp->t_rxtshift], 240 tp->t_rttmin, TCPTV_REXMTMAX); 241 TCP_TIMER_ARM(tp, TCPT_REXMT, tp->t_rxtcur); 242 243 /* 244 * If we are losing and we are trying path MTU discovery, 245 * try turning it off. This will avoid black holes in 246 * the network which suppress or fail to send "packet 247 * too big" ICMP messages. We should ideally do 248 * lots more sophisticated searching to find the right 249 * value here... 250 */ 251 if (ip_mtudisc && tp->t_inpcb && 252 TCPS_HAVEESTABLISHED(tp->t_state) && 253 tp->t_rxtshift > TCP_MAXRXTSHIFT / 6) { 254 struct inpcb *inp = tp->t_inpcb; 255 struct rtentry *rt = NULL; 256 257 /* No data to send means path mtu is not a problem */ 258 if (!inp->inp_socket->so_snd.sb_cc) 259 goto leave; 260 261 rt = in_pcbrtentry(inp); 262 /* Check if path MTU discovery is disabled already */ 263 if (rt && (rt->rt_flags & RTF_HOST) && 264 (rt->rt_rmx.rmx_locks & RTV_MTU)) 265 goto leave; 266 267 rt = NULL; 268 switch(tp->pf) { 269 #ifdef INET6 270 case PF_INET6: 271 /* 272 * We can not turn off path MTU for IPv6. 273 * Do nothing for now, maybe lower to 274 * minimum MTU. 275 */ 276 break; 277 #endif 278 case PF_INET: 279 rt = icmp_mtudisc_clone(inp->inp_faddr, 280 inp->inp_rtableid); 281 break; 282 } 283 if (rt != NULL) { 284 /* Disable path MTU discovery */ 285 if ((rt->rt_rmx.rmx_locks & RTV_MTU) == 0) { 286 rt->rt_rmx.rmx_locks |= RTV_MTU; 287 in_rtchange(inp, 0); 288 } 289 290 rtfree(rt); 291 } 292 leave: 293 ; 294 } 295 296 /* 297 * If losing, let the lower level know and try for 298 * a better route. Also, if we backed off this far, 299 * our srtt estimate is probably bogus. Clobber it 300 * so we'll take the next rtt measurement as our srtt; 301 * move the current srtt into rttvar to keep the current 302 * retransmit times until then. 303 */ 304 if (tp->t_rxtshift > TCP_MAXRXTSHIFT / 4) { 305 in_losing(tp->t_inpcb); 306 tp->t_rttvar += (tp->t_srtt >> TCP_RTT_SHIFT); 307 tp->t_srtt = 0; 308 } 309 tp->snd_nxt = tp->snd_una; 310 #if defined(TCP_SACK) 311 /* 312 * Note: We overload snd_last to function also as the 313 * snd_last variable described in RFC 2582 314 */ 315 tp->snd_last = tp->snd_max; 316 #endif /* TCP_SACK */ 317 /* 318 * If timing a segment in this window, stop the timer. 319 */ 320 tp->t_rtttime = 0; 321 #ifdef TCP_ECN 322 /* 323 * if ECN is enabled, there might be a broken firewall which 324 * blocks ecn packets. fall back to non-ecn. 325 */ 326 if ((tp->t_state == TCPS_SYN_SENT || tp->t_state == TCPS_SYN_RECEIVED) 327 && tcp_do_ecn && !(tp->t_flags & TF_DISABLE_ECN)) 328 tp->t_flags |= TF_DISABLE_ECN; 329 #endif 330 /* 331 * Close the congestion window down to one segment 332 * (we'll open it by one segment for each ack we get). 333 * Since we probably have a window's worth of unacked 334 * data accumulated, this "slow start" keeps us from 335 * dumping all that data as back-to-back packets (which 336 * might overwhelm an intermediate gateway). 337 * 338 * There are two phases to the opening: Initially we 339 * open by one mss on each ack. This makes the window 340 * size increase exponentially with time. If the 341 * window is larger than the path can handle, this 342 * exponential growth results in dropped packet(s) 343 * almost immediately. To get more time between 344 * drops but still "push" the network to take advantage 345 * of improving conditions, we switch from exponential 346 * to linear window opening at some threshold size. 347 * For a threshold, we use half the current window 348 * size, truncated to a multiple of the mss. 349 * 350 * (the minimum cwnd that will give us exponential 351 * growth is 2 mss. We don't allow the threshold 352 * to go below this.) 353 */ 354 { 355 u_long win = ulmin(tp->snd_wnd, tp->snd_cwnd) / 2 / tp->t_maxseg; 356 if (win < 2) 357 win = 2; 358 tp->snd_cwnd = tp->t_maxseg; 359 tp->snd_ssthresh = win * tp->t_maxseg; 360 tp->t_dupacks = 0; 361 #ifdef TCP_ECN 362 tp->snd_last = tp->snd_max; 363 tp->t_flags |= TF_SEND_CWR; 364 #endif 365 #if 1 /* TCP_ECN */ 366 tcpstat.tcps_cwr_timeout++; 367 #endif 368 } 369 (void) tcp_output(tp); 370 371 out: 372 NET_UNLOCK(s); 373 } 374 375 void 376 tcp_timer_persist(void *arg) 377 { 378 struct tcpcb *tp = arg; 379 uint32_t rto; 380 int s; 381 382 NET_LOCK(s); 383 if ((tp->t_flags & TF_DEAD) || 384 TCP_TIMER_ISARMED(tp, TCPT_REXMT)) { 385 goto out; 386 } 387 tcpstat.tcps_persisttimeo++; 388 /* 389 * Hack: if the peer is dead/unreachable, we do not 390 * time out if the window is closed. After a full 391 * backoff, drop the connection if the idle time 392 * (no responses to probes) reaches the maximum 393 * backoff that we would use if retransmitting. 394 */ 395 rto = TCP_REXMTVAL(tp); 396 if (rto < tp->t_rttmin) 397 rto = tp->t_rttmin; 398 if (tp->t_rxtshift == TCP_MAXRXTSHIFT && 399 ((tcp_now - tp->t_rcvtime) >= tcp_maxpersistidle || 400 (tcp_now - tp->t_rcvtime) >= rto * tcp_totbackoff)) { 401 tcpstat.tcps_persistdrop++; 402 tp = tcp_drop(tp, ETIMEDOUT); 403 goto out; 404 } 405 tcp_setpersist(tp); 406 tp->t_force = 1; 407 (void) tcp_output(tp); 408 tp->t_force = 0; 409 out: 410 NET_UNLOCK(s); 411 } 412 413 void 414 tcp_timer_keep(void *arg) 415 { 416 struct tcpcb *tp = arg; 417 int s; 418 419 NET_LOCK(s); 420 if (tp->t_flags & TF_DEAD) 421 goto out; 422 423 tcpstat.tcps_keeptimeo++; 424 if (TCPS_HAVEESTABLISHED(tp->t_state) == 0) 425 goto dropit; 426 if ((tcp_always_keepalive || 427 tp->t_inpcb->inp_socket->so_options & SO_KEEPALIVE) && 428 tp->t_state <= TCPS_CLOSING) { 429 if ((tcp_maxidle > 0) && 430 ((tcp_now - tp->t_rcvtime) >= tcp_keepidle + tcp_maxidle)) 431 goto dropit; 432 /* 433 * Send a packet designed to force a response 434 * if the peer is up and reachable: 435 * either an ACK if the connection is still alive, 436 * or an RST if the peer has closed the connection 437 * due to timeout or reboot. 438 * Using sequence number tp->snd_una-1 439 * causes the transmitted zero-length segment 440 * to lie outside the receive window; 441 * by the protocol spec, this requires the 442 * correspondent TCP to respond. 443 */ 444 tcpstat.tcps_keepprobe++; 445 tcp_respond(tp, mtod(tp->t_template, caddr_t), 446 NULL, tp->rcv_nxt, tp->snd_una - 1, 0, 0); 447 TCP_TIMER_ARM(tp, TCPT_KEEP, tcp_keepintvl); 448 } else 449 TCP_TIMER_ARM(tp, TCPT_KEEP, tcp_keepidle); 450 out: 451 NET_UNLOCK(s); 452 return; 453 454 dropit: 455 tcpstat.tcps_keepdrops++; 456 tp = tcp_drop(tp, ETIMEDOUT); 457 NET_UNLOCK(s); 458 } 459 460 void 461 tcp_timer_2msl(void *arg) 462 { 463 struct tcpcb *tp = arg; 464 int s; 465 466 NET_LOCK(s); 467 if (tp->t_flags & TF_DEAD) 468 goto out; 469 470 #ifdef TCP_SACK 471 tcp_timer_freesack(tp); 472 #endif 473 474 if (tp->t_state != TCPS_TIME_WAIT && 475 ((tcp_maxidle == 0) || ((tcp_now - tp->t_rcvtime) <= tcp_maxidle))) 476 TCP_TIMER_ARM(tp, TCPT_2MSL, tcp_keepintvl); 477 else 478 tp = tcp_close(tp); 479 480 out: 481 NET_UNLOCK(s); 482 } 483