FreeBSD/Linux Kernel Cross Reference
sys/netinet/tcp_timer.c

     /*      $NetBSD: tcp_timer.c,v 1.66 2004/01/02 15:51:04 itojun Exp $    */
     
     /*
      * Copyright (C) 1995, 1996, 1997, and 1998 WIDE Project.
      * 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 project 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 PROJECT 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 PROJECT 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.
     */
    
    /*-
     * Copyright (c) 1997, 1998, 2001 The NetBSD Foundation, Inc.
     * All rights reserved.
     *
     * This code is derived from software contributed to The NetBSD Foundation
     * by Jason R. Thorpe and Kevin M. Lahey of the Numerical Aerospace Simulation
     * Facility, NASA Ames Research Center.
     *
     * 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. All advertising materials mentioning features or use of this software
     *    must display the following acknowledgement:
     *      This product includes software developed by the NetBSD
     *      Foundation, Inc. and its contributors.
     * 4. Neither the name of The NetBSD Foundation 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 NETBSD FOUNDATION, INC. 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 FOUNDATION 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.
     */
    
    /*
     * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1995
     *      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 8.2 (Berkeley) 5/24/95
     */
    
   #include <sys/cdefs.h>
   __KERNEL_RCSID(0, "$NetBSD: tcp_timer.c,v 1.66 2004/01/02 15:51:04 itojun Exp $");
   
   #include "opt_inet.h"
   #include "opt_tcp_debug.h"
   
   #include <sys/param.h>
   #include <sys/systm.h>
   #include <sys/malloc.h>
   #include <sys/mbuf.h>
   #include <sys/socket.h>
   #include <sys/socketvar.h>
   #include <sys/protosw.h>
   #include <sys/errno.h>
   #include <sys/kernel.h>
   
   #include <net/if.h>
   #include <net/route.h>
   
   #include <netinet/in.h>
   #include <netinet/in_systm.h>
   #include <netinet/ip.h>
   #include <netinet/in_pcb.h>
   #include <netinet/ip_var.h>
   
   #ifdef INET6
   #ifndef INET
   #include <netinet/in.h>
   #endif
   #include <netinet/ip6.h>
   #include <netinet6/in6_pcb.h>
   #endif
   
   #include <netinet/tcp.h>
   #include <netinet/tcp_fsm.h>
   #include <netinet/tcp_seq.h>
   #include <netinet/tcp_timer.h>
   #include <netinet/tcp_var.h>
   #include <netinet/tcpip.h>
   #ifdef TCP_DEBUG
   #include <netinet/tcp_debug.h>
   #endif
   
   /*
    * Various tunable timer parameters.  These are initialized in tcp_init(),
    * unless they are patched.
    */
   int     tcp_keepidle = 0;
   int     tcp_keepintvl = 0;
   int     tcp_keepcnt = 0;                /* max idle probes */
   int     tcp_maxpersistidle = 0;         /* max idle time in persist */
   int     tcp_maxidle;                    /* computed in tcp_slowtimo() */
   
   /*
    * Time to delay the ACK.  This is initialized in tcp_init(), unless
    * its patched.
    */
   int     tcp_delack_ticks = 0;
   
   void    tcp_timer_rexmt(void *);
   void    tcp_timer_persist(void *);
   void    tcp_timer_keep(void *);
   void    tcp_timer_2msl(void *);
   
   const tcp_timer_func_t tcp_timer_funcs[TCPT_NTIMERS] = {
           tcp_timer_rexmt,
           tcp_timer_persist,
           tcp_timer_keep,
           tcp_timer_2msl,
   };
   
   /*
    * 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_keepcnt == 0)
                   tcp_keepcnt = TCPTV_KEEPCNT;
   
           if (tcp_maxpersistidle == 0)
                   tcp_maxpersistidle = TCPTV_KEEP_IDLE;
   
           if (tcp_delack_ticks == 0)
                   tcp_delack_ticks = TCP_DELACK_TICKS;
   }
   
   /*
    * Return how many timers are currently being invoked.
    */
   int
   tcp_timers_invoking(struct tcpcb *tp)
   {
           int i;
           int count = 0;
   
           for (i = 0; i < TCPT_NTIMERS; i++)
                   if (callout_invoking(&tp->t_timer[i]))
                           count++;
           if (callout_invoking(&tp->t_delack_ch))
                   count++;
   
           return count;
   }
   
   /*
    * Callout to process delayed ACKs for a TCPCB.
    */
   void
   tcp_delack(void *arg)
   {
           struct tcpcb *tp = arg;
           int s;
   
           /*
            * If tcp_output() wasn't able to transmit the ACK
            * for whatever reason, it will restart the delayed
            * ACK callout.
            */
   
           s = splsoftnet();
           callout_ack(&tp->t_delack_ch);
           if (tcp_isdead(tp)) {
                   splx(s);
                   return;
           }
   
           tp->t_flags |= TF_ACKNOW;
           (void) tcp_output(tp);
           splx(s);
   }
   
   /*
    * 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()
   {
           int s;
   
           s = splsoftnet();
           tcp_maxidle = tcp_keepcnt * tcp_keepintvl;
           tcp_iss_seq += TCP_ISSINCR;                     /* increment iss */
           tcp_now++;                                      /* for timestamps */
           splx(s);
   }
   
   /*
    * Cancel all timers for TCP tp.
    */
   void
   tcp_canceltimers(tp)
           struct tcpcb *tp;
   {
           int i;
   
           for (i = 0; i < TCPT_NTIMERS; i++)
                   TCP_TIMER_DISARM(tp, i);
   }
   
   const int       tcp_backoff[TCP_MAXRXTSHIFT + 1] =
       { 1, 2, 4, 8, 16, 32, 64, 64, 64, 64, 64, 64, 64 };
   
   const int       tcp_totbackoff = 511;   /* sum of tcp_backoff[] */
   
   /*
    * TCP timer processing.
    */
   
   void
   tcp_timer_rexmt(void *arg)
   {
           struct tcpcb *tp = arg;
           uint32_t rto;
           int s;
   #ifdef TCP_DEBUG
           struct socket *so = NULL;
           short ostate;
   #endif
   
           s = splsoftnet();
           callout_ack(&tp->t_timer[TCPT_REXMT]);
           if (tcp_isdead(tp)) {
                   splx(s);
                   return;
           }
   
   #ifdef TCP_DEBUG
   #ifdef INET
           if (tp->t_inpcb)
                   so = tp->t_inpcb->inp_socket;
   #endif
   #ifdef INET6
           if (tp->t_in6pcb)
                   so = tp->t_in6pcb->in6p_socket;
   #endif
           ostate = tp->t_state;
   #endif /* TCP_DEBUG */
   
           /*
            * Retransmission timer went off.  Message has not
            * been acked within retransmit interval.  Back off
            * to a longer retransmit interval and retransmit one segment.
            */
   
           if (++tp->t_rxtshift > TCP_MAXRXTSHIFT) {
                   tp->t_rxtshift = TCP_MAXRXTSHIFT;
                   tcpstat.tcps_timeoutdrop++;
                   tp = tcp_drop(tp, tp->t_softerror ?
                       tp->t_softerror : ETIMEDOUT);
                   goto out;
           }
           tcpstat.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 (tp->t_mtudisc && tp->t_rxtshift > TCP_MAXRXTSHIFT / 6) {
                   tcpstat.tcps_pmtublackhole++;
   
   #ifdef INET
                   /* try turning PMTUD off */
                   if (tp->t_inpcb)
                           tp->t_mtudisc = 0;
   #endif
   #ifdef INET6
                   /* try using IPv6 minimum MTU */
                   if (tp->t_in6pcb)
                           tp->t_mtudisc = 0;
   #endif
   
                   /* XXX: more sophisticated Black hole recovery code? */
           }
   
           /*
            * 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) {
   #ifdef INET
                   if (tp->t_inpcb)
                           in_losing(tp->t_inpcb);
   #endif
   #ifdef INET6
                   if (tp->t_in6pcb)
                           in6_losing(tp->t_in6pcb);
   #endif
                   tp->t_rttvar += (tp->t_srtt >> TCP_RTT_SHIFT);
                   tp->t_srtt = 0;
           }
           tp->snd_nxt = tp->snd_una;
           /*
            * If timing a segment in this window, stop the timer.
            */
           tp->t_rtttime = 0;
           /*
            * Remember if we are retransmitting a SYN, because if
            * we do, set the initial congestion window must be set
            * to 1 segment.
            */
           if (tp->t_state == TCPS_SYN_SENT)
                   tp->t_flags |= TF_SYN_REXMT;
           /*
            * 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 threshhold size.
            * For a threshhold, 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 threshhold
            * to go below this.)
            */
           {
           u_int win = min(tp->snd_wnd, tp->snd_cwnd) / 2 / tp->t_segsz;
           if (win < 2)
                   win = 2;
           /* Loss Window MUST be one segment. */
           tp->snd_cwnd = tp->t_segsz;
           tp->snd_ssthresh = win * tp->t_segsz;
           tp->t_dupacks = 0;
           }
           (void) tcp_output(tp);
   
    out:
   #ifdef TCP_DEBUG
           if (tp && so->so_options & SO_DEBUG)
                   tcp_trace(TA_USER, ostate, tp, NULL,
                       PRU_SLOWTIMO | (TCPT_REXMT << 8));
   #endif
           splx(s);
   }
   
   void
   tcp_timer_persist(void *arg)
   {
           struct tcpcb *tp = arg;
           uint32_t rto;
           int s;
   #ifdef TCP_DEBUG
           struct socket *so = NULL;
           short ostate;
   #endif
   
           s = splsoftnet();
           callout_ack(&tp->t_timer[TCPT_PERSIST]);
           if (tcp_isdead(tp)) {
                   splx(s);
                   return;
           }
   
   #ifdef TCP_DEBUG
   #ifdef INET
           if (tp->t_inpcb)
                   so = tp->t_inpcb->inp_socket;
   #endif
   #ifdef INET6
           if (tp->t_in6pcb)
                   so = tp->t_in6pcb->in6p_socket;
   #endif
   
           ostate = tp->t_state;
   #endif /* TCP_DEBUG */
   
           /*
            * Persistance timer into zero window.
            * Force a byte to be output, if possible.
            */
   
           /*
            * 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;
           if (tp->t_rxtshift == TCP_MAXRXTSHIFT &&
               ((tcp_now - tp->t_rcvtime) >= tcp_maxpersistidle ||
               (tcp_now - tp->t_rcvtime) >= rto * tcp_totbackoff)) {
                   tcpstat.tcps_persistdrops++;
                   tp = tcp_drop(tp, ETIMEDOUT);
                   goto out;
           }
           tcpstat.tcps_persisttimeo++;
           tcp_setpersist(tp);
           tp->t_force = 1;
           (void) tcp_output(tp);
           tp->t_force = 0;
   
    out:
   #ifdef TCP_DEBUG
           if (tp && so->so_options & SO_DEBUG)
                   tcp_trace(TA_USER, ostate, tp, NULL,
                       PRU_SLOWTIMO | (TCPT_PERSIST << 8));
   #endif
           splx(s);
   }
   
   void
   tcp_timer_keep(void *arg)
   {
           struct tcpcb *tp = arg;
           struct socket *so = NULL;       /* Quell compiler warning */
           int s;
   #ifdef TCP_DEBUG
           short ostate;
   #endif
   
           s = splsoftnet();
           callout_ack(&tp->t_timer[TCPT_KEEP]);
           if (tcp_isdead(tp)) {
                   splx(s);
                   return;
           }
   
   #ifdef TCP_DEBUG
           ostate = tp->t_state;
   #endif /* TCP_DEBUG */
   
           /*
            * Keep-alive timer went off; send something
            * or drop connection if idle for too long.
            */
   
           tcpstat.tcps_keeptimeo++;
           if (TCPS_HAVEESTABLISHED(tp->t_state) == 0)
                   goto dropit;
   #ifdef INET
           if (tp->t_inpcb)
                   so = tp->t_inpcb->inp_socket;
   #endif
   #ifdef INET6
           if (tp->t_in6pcb)
                   so = tp->t_in6pcb->in6p_socket;
   #endif
           if (so->so_options & SO_KEEPALIVE &&
               tp->t_state <= TCPS_CLOSE_WAIT) {
                   if ((tcp_maxidle > 0) &&
                       ((tcp_now - tp->t_rcvtime) >=
                        tcp_keepidle + tcp_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.tcps_keepprobe++;
                   if (tcp_compat_42) {
                           /*
                            * The keepalive packet must have nonzero
                            * length to get a 4.2 host to respond.
                            */
                           (void)tcp_respond(tp, tp->t_template,
                               (struct mbuf *)NULL, NULL, tp->rcv_nxt - 1,
                               tp->snd_una - 1, 0);
                   } else {
                           (void)tcp_respond(tp, tp->t_template,
                               (struct mbuf *)NULL, NULL, tp->rcv_nxt,
                               tp->snd_una - 1, 0);
                   }
                   TCP_TIMER_ARM(tp, TCPT_KEEP, tcp_keepintvl);
           } else
                   TCP_TIMER_ARM(tp, TCPT_KEEP, tcp_keepidle);
   
   #ifdef TCP_DEBUG
           if (tp && so->so_options & SO_DEBUG)
                   tcp_trace(TA_USER, ostate, tp, NULL,
                       PRU_SLOWTIMO | (TCPT_KEEP << 8));
   #endif
           splx(s);
           return;
   
    dropit:
           tcpstat.tcps_keepdrops++;
           (void) tcp_drop(tp, ETIMEDOUT);
           splx(s);
   }
   
   void
   tcp_timer_2msl(void *arg)
   {
           struct tcpcb *tp = arg;
           int s;
   #ifdef TCP_DEBUG
           struct socket *so = NULL;
           short ostate;
   #endif
   
           s = splsoftnet();
           callout_ack(&tp->t_timer[TCPT_2MSL]);
           if (tcp_isdead(tp)) {
                   splx(s);
                   return;
           }
   
   #ifdef TCP_DEBUG
   #ifdef INET
           if (tp->t_inpcb)
                   so = tp->t_inpcb->inp_socket;
   #endif
   #ifdef INET6
           if (tp->t_in6pcb)
                   so = tp->t_in6pcb->in6p_socket;
   #endif
   
           ostate = tp->t_state;
   #endif /* TCP_DEBUG */
   
           /*
            * 2 MSL timeout in shutdown went off.  If we're closed but
            * still waiting for peer to close and connection has been idle
            * too long, or if 2MSL time is up from TIME_WAIT, delete connection
            * control block.  Otherwise, check again in a bit.
            */
           if (tp->t_state != TCPS_TIME_WAIT &&
               ((tcp_maxidle == 0) || ((tcp_now - tp->t_rcvtime) <= tcp_maxidle)))
                   TCP_TIMER_ARM(tp, TCPT_2MSL, tcp_keepintvl);
           else
                   tp = tcp_close(tp);
   
   #ifdef TCP_DEBUG
           if (tp && so->so_options & SO_DEBUG)
                   tcp_trace(TA_USER, ostate, tp, NULL,
                       PRU_SLOWTIMO | (TCPT_2MSL << 8));
   #endif
           splx(s);
   }

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