/* $OpenBSD: tcp_timer.c,v 1.76 2024/01/28 20:34:25 bluhm Exp $ */ /* $NetBSD: tcp_timer.c,v 1.14 1996/02/13 23:44:09 christos Exp $ */ /* * Copyright (c) 1982, 1986, 1988, 1990, 1993 * The Regents of the University of California. All rights reserved. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * 1. Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * 2. Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in the * documentation and/or other materials provided with the distribution. * 3. Neither the name of the University nor the names of its contributors * may be used to endorse or promote products derived from this software * without specific prior written permission. * * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF * SUCH DAMAGE. * * @(#)tcp_timer.c 8.1 (Berkeley) 6/10/93 */ #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include /* * Locks used to protect struct members in this file: * T tcp_timer_mtx global tcp timer data structures */ int tcp_always_keepalive; int tcp_keepidle; int tcp_keepintvl; int tcp_maxpersistidle; /* max idle time in persist */ int tcp_maxidle; /* [T] max idle time for keep alive */ /* * Time to delay the ACK. This is initialized in tcp_init(), unless * its patched. */ int tcp_delack_msecs; void tcp_timer_rexmt(void *); void tcp_timer_persist(void *); void tcp_timer_keep(void *); void tcp_timer_2msl(void *); void tcp_timer_reaper(void *); void tcp_timer_delack(void *); const tcp_timer_func_t tcp_timer_funcs[TCPT_NTIMERS] = { tcp_timer_rexmt, tcp_timer_persist, tcp_timer_keep, tcp_timer_2msl, tcp_timer_reaper, tcp_timer_delack, }; /* * Timer state initialization, called from tcp_init(). */ void tcp_timer_init(void) { if (tcp_keepidle == 0) tcp_keepidle = TCPTV_KEEP_IDLE; if (tcp_keepintvl == 0) tcp_keepintvl = TCPTV_KEEPINTVL; if (tcp_maxpersistidle == 0) tcp_maxpersistidle = TCPTV_KEEP_IDLE; if (tcp_delack_msecs == 0) tcp_delack_msecs = TCP_DELACK_MSECS; } /* * Callout to process delayed ACKs for a TCPCB. */ void tcp_timer_delack(void *arg) { struct tcpcb *otp = NULL, *tp = arg; short ostate; /* * If tcp_output() wasn't able to transmit the ACK * for whatever reason, it will restart the delayed * ACK callout. */ NET_LOCK(); /* Ignore canceled timeouts or timeouts that have been rescheduled. */ if (!ISSET((tp)->t_flags, TF_TMR_DELACK) || timeout_pending(&tp->t_timer[TCPT_DELACK])) goto out; CLR((tp)->t_flags, TF_TMR_DELACK); if (tp->t_inpcb->inp_socket->so_options & SO_DEBUG) { otp = tp; ostate = tp->t_state; } tp->t_flags |= TF_ACKNOW; (void) tcp_output(tp); if (otp) tcp_trace(TA_TIMER, ostate, tp, otp, NULL, TCPT_DELACK, 0); out: NET_UNLOCK(); } /* * Tcp protocol timeout routine called every 500 ms. * Updates the timers in all active tcb's and * causes finite state machine actions if timers expire. */ void tcp_slowtimo(void) { mtx_enter(&tcp_timer_mtx); tcp_maxidle = TCPTV_KEEPCNT * tcp_keepintvl; tcp_iss += TCP_ISSINCR2/PR_SLOWHZ; /* increment iss */ mtx_leave(&tcp_timer_mtx); } /* * Cancel all timers for TCP tp. */ void tcp_canceltimers(struct tcpcb *tp) { int i; for (i = 0; i < TCPT_NTIMERS; i++) TCP_TIMER_DISARM(tp, i); } int tcp_backoff[TCP_MAXRXTSHIFT + 1] = { 1, 2, 4, 8, 16, 32, 64, 64, 64, 64, 64, 64, 64 }; int tcp_totbackoff = 511; /* sum of tcp_backoff[] */ /* * TCP timer processing. */ void tcp_timer_freesack(struct tcpcb *); void tcp_timer_freesack(struct tcpcb *tp) { struct sackhole *p, *q; /* * Free SACK holes for 2MSL and REXMT timers. */ q = tp->snd_holes; while (q != NULL) { p = q; q = q->next; pool_put(&sackhl_pool, p); } tp->snd_holes = 0; } void tcp_timer_rexmt(void *arg) { struct tcpcb *otp = NULL, *tp = arg; struct inpcb *inp; uint32_t rto; short ostate; NET_LOCK(); inp = tp->t_inpcb; /* Ignore canceled timeouts or timeouts that have been rescheduled. */ if (!ISSET((tp)->t_flags, TF_TMR_REXMT) || timeout_pending(&tp->t_timer[TCPT_REXMT])) goto out; CLR((tp)->t_flags, TF_TMR_REXMT); if ((tp->t_flags & TF_PMTUD_PEND) && inp && SEQ_GEQ(tp->t_pmtud_th_seq, tp->snd_una) && SEQ_LT(tp->t_pmtud_th_seq, (int)(tp->snd_una + tp->t_maxseg))) { struct sockaddr_in sin; struct icmp icmp; /* TF_PMTUD_PEND is set in tcp_ctlinput() which is IPv4 only */ KASSERT(!ISSET(inp->inp_flags, INP_IPV6)); tp->t_flags &= ~TF_PMTUD_PEND; /* XXX create fake icmp message with relevant entries */ icmp.icmp_nextmtu = tp->t_pmtud_nextmtu; icmp.icmp_ip.ip_len = tp->t_pmtud_ip_len; icmp.icmp_ip.ip_hl = tp->t_pmtud_ip_hl; icmp.icmp_ip.ip_dst = inp->inp_faddr; icmp_mtudisc(&icmp, inp->inp_rtableid); /* * Notify all connections to the same peer about * new mss and trigger retransmit. */ bzero(&sin, sizeof(sin)); sin.sin_len = sizeof(sin); sin.sin_family = AF_INET; sin.sin_addr = inp->inp_faddr; in_pcbnotifyall(&tcbtable, &sin, inp->inp_rtableid, EMSGSIZE, tcp_mtudisc); goto out; } tcp_timer_freesack(tp); if (++tp->t_rxtshift > TCP_MAXRXTSHIFT) { tp->t_rxtshift = TCP_MAXRXTSHIFT; tcpstat_inc(tcps_timeoutdrop); tp = tcp_drop(tp, tp->t_softerror ? tp->t_softerror : ETIMEDOUT); goto out; } if (inp->inp_socket->so_options & SO_DEBUG) { otp = tp; ostate = tp->t_state; } tcpstat_inc(tcps_rexmttimeo); rto = TCP_REXMTVAL(tp); if (rto < tp->t_rttmin) rto = tp->t_rttmin; TCPT_RANGESET(tp->t_rxtcur, rto * tcp_backoff[tp->t_rxtshift], tp->t_rttmin, TCPTV_REXMTMAX); TCP_TIMER_ARM(tp, TCPT_REXMT, tp->t_rxtcur); /* * If we are losing and we are trying path MTU discovery, * try turning it off. This will avoid black holes in * the network which suppress or fail to send "packet * too big" ICMP messages. We should ideally do * lots more sophisticated searching to find the right * value here... */ if (ip_mtudisc && inp && TCPS_HAVEESTABLISHED(tp->t_state) && tp->t_rxtshift > TCP_MAXRXTSHIFT / 6) { struct rtentry *rt = NULL; /* No data to send means path mtu is not a problem */ if (!inp->inp_socket->so_snd.sb_cc) goto leave; rt = in_pcbrtentry(inp); /* Check if path MTU discovery is disabled already */ if (rt && (rt->rt_flags & RTF_HOST) && (rt->rt_locks & RTV_MTU)) goto leave; rt = NULL; switch(tp->pf) { #ifdef INET6 case PF_INET6: /* * We can not turn off path MTU for IPv6. * Do nothing for now, maybe lower to * minimum MTU. */ break; #endif case PF_INET: rt = icmp_mtudisc_clone(inp->inp_faddr, inp->inp_rtableid, 0); break; } if (rt != NULL) { /* Disable path MTU discovery */ if ((rt->rt_locks & RTV_MTU) == 0) { rt->rt_locks |= RTV_MTU; in_rtchange(inp, 0); } rtfree(rt); } leave: ; } /* * If losing, let the lower level know and try for * a better route. Also, if we backed off this far, * our srtt estimate is probably bogus. Clobber it * so we'll take the next rtt measurement as our srtt; * move the current srtt into rttvar to keep the current * retransmit times until then. */ if (tp->t_rxtshift > TCP_MAXRXTSHIFT / 4) { in_losing(inp); tp->t_rttvar += (tp->t_srtt >> TCP_RTT_SHIFT); tp->t_srtt = 0; } tp->snd_nxt = tp->snd_una; /* * Note: We overload snd_last to function also as the * snd_last variable described in RFC 2582 */ tp->snd_last = tp->snd_max; /* * If timing a segment in this window, stop the timer. */ tp->t_rtttime = 0; #ifdef TCP_ECN /* * if ECN is enabled, there might be a broken firewall which * blocks ecn packets. fall back to non-ecn. */ if ((tp->t_state == TCPS_SYN_SENT || tp->t_state == TCPS_SYN_RECEIVED) && tcp_do_ecn && !(tp->t_flags & TF_DISABLE_ECN)) tp->t_flags |= TF_DISABLE_ECN; #endif /* * Close the congestion window down to one segment * (we'll open it by one segment for each ack we get). * Since we probably have a window's worth of unacked * data accumulated, this "slow start" keeps us from * dumping all that data as back-to-back packets (which * might overwhelm an intermediate gateway). * * There are two phases to the opening: Initially we * open by one mss on each ack. This makes the window * size increase exponentially with time. If the * window is larger than the path can handle, this * exponential growth results in dropped packet(s) * almost immediately. To get more time between * drops but still "push" the network to take advantage * of improving conditions, we switch from exponential * to linear window opening at some threshold size. * For a threshold, we use half the current window * size, truncated to a multiple of the mss. * * (the minimum cwnd that will give us exponential * growth is 2 mss. We don't allow the threshold * to go below this.) */ { u_long win; win = ulmin(tp->snd_wnd, tp->snd_cwnd) / 2 / tp->t_maxseg; if (win < 2) win = 2; tp->snd_cwnd = tp->t_maxseg; tp->snd_ssthresh = win * tp->t_maxseg; tp->t_dupacks = 0; #ifdef TCP_ECN tp->snd_last = tp->snd_max; tp->t_flags |= TF_SEND_CWR; #endif #if 1 /* TCP_ECN */ tcpstat_inc(tcps_cwr_timeout); #endif } (void) tcp_output(tp); if (otp) tcp_trace(TA_TIMER, ostate, tp, otp, NULL, TCPT_REXMT, 0); out: NET_UNLOCK(); } void tcp_timer_persist(void *arg) { struct tcpcb *otp = NULL, *tp = arg; uint32_t rto; short ostate; uint64_t now; NET_LOCK(); /* Ignore canceled timeouts or timeouts that have been rescheduled. */ if (!ISSET((tp)->t_flags, TF_TMR_PERSIST) || timeout_pending(&tp->t_timer[TCPT_PERSIST])) goto out; CLR((tp)->t_flags, TF_TMR_PERSIST); if (TCP_TIMER_ISARMED(tp, TCPT_REXMT)) goto out; if (tp->t_inpcb->inp_socket->so_options & SO_DEBUG) { otp = tp; ostate = tp->t_state; } tcpstat_inc(tcps_persisttimeo); /* * Hack: if the peer is dead/unreachable, we do not * time out if the window is closed. After a full * backoff, drop the connection if the idle time * (no responses to probes) reaches the maximum * backoff that we would use if retransmitting. */ rto = TCP_REXMTVAL(tp); if (rto < tp->t_rttmin) rto = tp->t_rttmin; now = tcp_now(); if (tp->t_rxtshift == TCP_MAXRXTSHIFT && ((now - tp->t_rcvtime) >= tcp_maxpersistidle || (now - tp->t_rcvtime) >= rto * tcp_totbackoff)) { tcpstat_inc(tcps_persistdrop); tp = tcp_drop(tp, ETIMEDOUT); goto out; } tcp_setpersist(tp); tp->t_force = 1; (void) tcp_output(tp); tp->t_force = 0; if (otp) tcp_trace(TA_TIMER, ostate, tp, otp, NULL, TCPT_PERSIST, 0); out: NET_UNLOCK(); } void tcp_timer_keep(void *arg) { struct tcpcb *otp = NULL, *tp = arg; short ostate; NET_LOCK(); /* Ignore canceled timeouts or timeouts that have been rescheduled. */ if (!ISSET((tp)->t_flags, TF_TMR_KEEP) || timeout_pending(&tp->t_timer[TCPT_KEEP])) goto out; CLR((tp)->t_flags, TF_TMR_KEEP); if (tp->t_inpcb->inp_socket->so_options & SO_DEBUG) { otp = tp; ostate = tp->t_state; } tcpstat_inc(tcps_keeptimeo); if (TCPS_HAVEESTABLISHED(tp->t_state) == 0) goto dropit; if ((tcp_always_keepalive || tp->t_inpcb->inp_socket->so_options & SO_KEEPALIVE) && tp->t_state <= TCPS_CLOSING) { int maxidle; uint64_t now; maxidle = READ_ONCE(tcp_maxidle); now = tcp_now(); if ((maxidle > 0) && ((now - tp->t_rcvtime) >= tcp_keepidle + maxidle)) goto dropit; /* * Send a packet designed to force a response * if the peer is up and reachable: * either an ACK if the connection is still alive, * or an RST if the peer has closed the connection * due to timeout or reboot. * Using sequence number tp->snd_una-1 * causes the transmitted zero-length segment * to lie outside the receive window; * by the protocol spec, this requires the * correspondent TCP to respond. */ tcpstat_inc(tcps_keepprobe); tcp_respond(tp, mtod(tp->t_template, caddr_t), NULL, tp->rcv_nxt, tp->snd_una - 1, 0, 0, now); TCP_TIMER_ARM(tp, TCPT_KEEP, tcp_keepintvl); } else TCP_TIMER_ARM(tp, TCPT_KEEP, tcp_keepidle); if (otp) tcp_trace(TA_TIMER, ostate, tp, otp, NULL, TCPT_KEEP, 0); out: NET_UNLOCK(); return; dropit: tcpstat_inc(tcps_keepdrops); tp = tcp_drop(tp, ETIMEDOUT); NET_UNLOCK(); } void tcp_timer_2msl(void *arg) { struct tcpcb *otp = NULL, *tp = arg; short ostate; int maxidle; uint64_t now; NET_LOCK(); /* Ignore canceled timeouts or timeouts that have been rescheduled. */ if (!ISSET((tp)->t_flags, TF_TMR_2MSL) || timeout_pending(&tp->t_timer[TCPT_2MSL])) goto out; CLR((tp)->t_flags, TF_TMR_2MSL); if (tp->t_inpcb->inp_socket->so_options & SO_DEBUG) { otp = tp; ostate = tp->t_state; } tcp_timer_freesack(tp); maxidle = READ_ONCE(tcp_maxidle); now = tcp_now(); if (tp->t_state != TCPS_TIME_WAIT && ((maxidle == 0) || ((now - tp->t_rcvtime) <= maxidle))) TCP_TIMER_ARM(tp, TCPT_2MSL, tcp_keepintvl); else tp = tcp_close(tp); if (otp) tcp_trace(TA_TIMER, ostate, tp, otp, NULL, TCPT_2MSL, 0); out: NET_UNLOCK(); } void tcp_timer_reaper(void *arg) { struct tcpcb *tp = arg; /* * This timer is necessary to delay the pool_put() after all timers * have finished, even if they were sleeping to grab the net lock. * Putting the pool_put() in a timer is sufficient as all timers run * from the same timeout thread. Note that neither softnet thread nor * user process may access the tcpcb after arming the reaper timer. * Freeing may run in parallel as it does not grab the net lock. */ pool_put(&tcpcb_pool, tp); tcpstat_inc(tcps_closed); }