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

     /*      $OpenBSD: tcp_timer.c,v 1.71 2022/11/07 11:22:55 yasuoka 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 <sys/param.h>
    #include <sys/systm.h>
    #include <sys/mbuf.h>
    #include <sys/socket.h>
    #include <sys/socketvar.h>
    #include <sys/protosw.h>
    #include <sys/kernel.h>
    #include <sys/pool.h>
    
    #include <net/route.h>
    
    #include <netinet/in.h>
    #include <netinet/ip.h>
    #include <netinet/in_pcb.h>
    #include <netinet/ip_var.h>
    #include <netinet/tcp.h>
    #include <netinet/tcp_fsm.h>
    #include <netinet/tcp_timer.h>
    #include <netinet/tcp_var.h>
    #include <netinet/tcp_debug.h>
    #include <netinet/ip_icmp.h>
    #include <netinet/tcp_seq.h>
    
    /*
     * 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;
           uint32_t rto;
           short ostate;
   
           NET_LOCK();
           /* 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) && tp->t_inpcb &&
               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;
   
                   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 = tp->t_inpcb->inp_faddr;
                   icmp_mtudisc(&icmp, tp->t_inpcb->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 = tp->t_inpcb->inp_faddr;
                   in_pcbnotifyall(&tcbtable, sintosa(&sin),
                       tp->t_inpcb->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 (tp->t_inpcb->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 && tp->t_inpcb &&
               TCPS_HAVEESTABLISHED(tp->t_state) &&
               tp->t_rxtshift > TCP_MAXRXTSHIFT / 6) {
                   struct inpcb *inp = tp->t_inpcb;
                   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(tp->t_inpcb);
                   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 = 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;
           uint32_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_TIME(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;
                   uint32_t now;
   
                   maxidle = READ_ONCE(tcp_maxidle);
                   now = tcp_now();
                   if ((maxidle > 0) && ((now - tp->t_rcvtime) >=
                       TCP_TIME(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_TIME(tcp_keepintvl));
           } else
                   TCP_TIMER_ARM(tp, TCPT_KEEP, TCP_TIME(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;
           uint32_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) <= TCP_TIME(maxidle))))
                   TCP_TIMER_ARM(tp, TCPT_2MSL, TCP_TIME(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);
   }

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