The Design and Implementation of the FreeBSD Operating System, Second Edition
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FreeBSD/Linux Kernel Cross Reference
sys/netinet/tcp_timewait.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  * 4. Neither the name of the University nor the names of its contributors
   14  *    may be used to endorse or promote products derived from this software
   15  *    without specific prior written permission.
   16  *
   17  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
   18  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   19  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   20  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   21  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   22  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   23  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   24  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   25  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   26  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   27  * SUCH DAMAGE.
   28  *
   29  *      @(#)tcp_subr.c  8.2 (Berkeley) 5/24/95
   30  */
   31 
   32 #include <sys/cdefs.h>
   33 __FBSDID("$FreeBSD: releng/8.1/sys/netinet/tcp_timewait.c 207695 2010-05-06 06:44:19Z bz $");
   34 
   35 #include "opt_inet.h"
   36 #include "opt_inet6.h"
   37 #include "opt_tcpdebug.h"
   38 
   39 #include <sys/param.h>
   40 #include <sys/systm.h>
   41 #include <sys/callout.h>
   42 #include <sys/kernel.h>
   43 #include <sys/sysctl.h>
   44 #include <sys/malloc.h>
   45 #include <sys/mbuf.h>
   46 #include <sys/priv.h>
   47 #include <sys/proc.h>
   48 #include <sys/socket.h>
   49 #include <sys/socketvar.h>
   50 #include <sys/protosw.h>
   51 #include <sys/random.h>
   52 
   53 #include <vm/uma.h>
   54 
   55 #include <net/route.h>
   56 #include <net/if.h>
   57 #include <net/vnet.h>
   58 
   59 #include <netinet/in.h>
   60 #include <netinet/in_systm.h>
   61 #include <netinet/ip.h>
   62 #ifdef INET6
   63 #include <netinet/ip6.h>
   64 #endif
   65 #include <netinet/in_pcb.h>
   66 #ifdef INET6
   67 #include <netinet6/in6_pcb.h>
   68 #endif
   69 #include <netinet/in_var.h>
   70 #include <netinet/ip_var.h>
   71 #ifdef INET6
   72 #include <netinet6/ip6_var.h>
   73 #include <netinet6/scope6_var.h>
   74 #include <netinet6/nd6.h>
   75 #endif
   76 #include <netinet/ip_icmp.h>
   77 #include <netinet/tcp.h>
   78 #include <netinet/tcp_fsm.h>
   79 #include <netinet/tcp_seq.h>
   80 #include <netinet/tcp_timer.h>
   81 #include <netinet/tcp_var.h>
   82 #ifdef INET6
   83 #include <netinet6/tcp6_var.h>
   84 #endif
   85 #include <netinet/tcpip.h>
   86 #ifdef TCPDEBUG
   87 #include <netinet/tcp_debug.h>
   88 #endif
   89 #include <netinet6/ip6protosw.h>
   90 
   91 #include <machine/in_cksum.h>
   92 
   93 #include <security/mac/mac_framework.h>
   94 
   95 static VNET_DEFINE(uma_zone_t, tcptw_zone);
   96 #define V_tcptw_zone                    VNET(tcptw_zone)
   97 static int      maxtcptw;
   98 
   99 /*
  100  * The timed wait queue contains references to each of the TCP sessions
  101  * currently in the TIME_WAIT state.  The queue pointers, including the
  102  * queue pointers in each tcptw structure, are protected using the global
  103  * tcbinfo lock, which must be held over queue iteration and modification.
  104  */
  105 static VNET_DEFINE(TAILQ_HEAD(, tcptw), twq_2msl);
  106 #define V_twq_2msl                      VNET(twq_2msl)
  107 
  108 static void     tcp_tw_2msl_reset(struct tcptw *, int);
  109 static void     tcp_tw_2msl_stop(struct tcptw *);
  110 
  111 static int
  112 tcptw_auto_size(void)
  113 {
  114         int halfrange;
  115 
  116         /*
  117          * Max out at half the ephemeral port range so that TIME_WAIT
  118          * sockets don't tie up too many ephemeral ports.
  119          */
  120         if (V_ipport_lastauto > V_ipport_firstauto)
  121                 halfrange = (V_ipport_lastauto - V_ipport_firstauto) / 2;
  122         else
  123                 halfrange = (V_ipport_firstauto - V_ipport_lastauto) / 2;
  124         /* Protect against goofy port ranges smaller than 32. */
  125         return (imin(imax(halfrange, 32), maxsockets / 5));
  126 }
  127 
  128 static int
  129 sysctl_maxtcptw(SYSCTL_HANDLER_ARGS)
  130 {
  131         int error, new;
  132 
  133         if (maxtcptw == 0)
  134                 new = tcptw_auto_size();
  135         else
  136                 new = maxtcptw;
  137         error = sysctl_handle_int(oidp, &new, 0, req);
  138         if (error == 0 && req->newptr)
  139                 if (new >= 32) {
  140                         maxtcptw = new;
  141                         uma_zone_set_max(V_tcptw_zone, maxtcptw);
  142                 }
  143         return (error);
  144 }
  145 
  146 SYSCTL_PROC(_net_inet_tcp, OID_AUTO, maxtcptw, CTLTYPE_INT|CTLFLAG_RW,
  147     &maxtcptw, 0, sysctl_maxtcptw, "IU",
  148     "Maximum number of compressed TCP TIME_WAIT entries");
  149 
  150 VNET_DEFINE(int, nolocaltimewait) = 0;
  151 #define V_nolocaltimewait       VNET(nolocaltimewait)
  152 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, nolocaltimewait, CTLFLAG_RW,
  153     &VNET_NAME(nolocaltimewait), 0,
  154     "Do not create compressed TCP TIME_WAIT entries for local connections");
  155 
  156 void
  157 tcp_tw_zone_change(void)
  158 {
  159 
  160         if (maxtcptw == 0)
  161                 uma_zone_set_max(V_tcptw_zone, tcptw_auto_size());
  162 }
  163 
  164 void
  165 tcp_tw_init(void)
  166 {
  167 
  168         V_tcptw_zone = uma_zcreate("tcptw", sizeof(struct tcptw),
  169             NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, UMA_ZONE_NOFREE);
  170         TUNABLE_INT_FETCH("net.inet.tcp.maxtcptw", &maxtcptw);
  171         if (maxtcptw == 0)
  172                 uma_zone_set_max(V_tcptw_zone, tcptw_auto_size());
  173         else
  174                 uma_zone_set_max(V_tcptw_zone, maxtcptw);
  175         TAILQ_INIT(&V_twq_2msl);
  176 }
  177 
  178 #ifdef VIMAGE
  179 void
  180 tcp_tw_destroy(void)
  181 {
  182         struct tcptw *tw;
  183 
  184         INP_INFO_WLOCK(&V_tcbinfo);
  185         while((tw = TAILQ_FIRST(&V_twq_2msl)) != NULL)
  186                 tcp_twclose(tw, 0);
  187         INP_INFO_WUNLOCK(&V_tcbinfo);
  188 
  189         uma_zdestroy(V_tcptw_zone);
  190 }
  191 #endif
  192 
  193 /*
  194  * Move a TCP connection into TIME_WAIT state.
  195  *    tcbinfo is locked.
  196  *    inp is locked, and is unlocked before returning.
  197  */
  198 void
  199 tcp_twstart(struct tcpcb *tp)
  200 {
  201         struct tcptw *tw;
  202         struct inpcb *inp = tp->t_inpcb;
  203         int acknow;
  204         struct socket *so;
  205 
  206         INP_INFO_WLOCK_ASSERT(&V_tcbinfo);      /* tcp_tw_2msl_reset(). */
  207         INP_WLOCK_ASSERT(inp);
  208 
  209         if (V_nolocaltimewait && in_localip(inp->inp_faddr)) {
  210                 tp = tcp_close(tp);
  211                 if (tp != NULL)
  212                         INP_WUNLOCK(inp);
  213                 return;
  214         }
  215 
  216         tw = uma_zalloc(V_tcptw_zone, M_NOWAIT);
  217         if (tw == NULL) {
  218                 tw = tcp_tw_2msl_scan(1);
  219                 if (tw == NULL) {
  220                         tp = tcp_close(tp);
  221                         if (tp != NULL)
  222                                 INP_WUNLOCK(inp);
  223                         return;
  224                 }
  225         }
  226         tw->tw_inpcb = inp;
  227 
  228         /*
  229          * Recover last window size sent.
  230          */
  231         tw->last_win = (tp->rcv_adv - tp->rcv_nxt) >> tp->rcv_scale;
  232 
  233         /*
  234          * Set t_recent if timestamps are used on the connection.
  235          */
  236         if ((tp->t_flags & (TF_REQ_TSTMP|TF_RCVD_TSTMP|TF_NOOPT)) ==
  237             (TF_REQ_TSTMP|TF_RCVD_TSTMP)) {
  238                 tw->t_recent = tp->ts_recent;
  239                 tw->ts_offset = tp->ts_offset;
  240         } else {
  241                 tw->t_recent = 0;
  242                 tw->ts_offset = 0;
  243         }
  244 
  245         tw->snd_nxt = tp->snd_nxt;
  246         tw->rcv_nxt = tp->rcv_nxt;
  247         tw->iss     = tp->iss;
  248         tw->irs     = tp->irs;
  249         tw->t_starttime = tp->t_starttime;
  250         tw->tw_time = 0;
  251 
  252 /* XXX
  253  * If this code will
  254  * be used for fin-wait-2 state also, then we may need
  255  * a ts_recent from the last segment.
  256  */
  257         acknow = tp->t_flags & TF_ACKNOW;
  258 
  259         /*
  260          * First, discard tcpcb state, which includes stopping its timers and
  261          * freeing it.  tcp_discardcb() used to also release the inpcb, but
  262          * that work is now done in the caller.
  263          *
  264          * Note: soisdisconnected() call used to be made in tcp_discardcb(),
  265          * and might not be needed here any longer.
  266          */
  267         tcp_discardcb(tp);
  268         so = inp->inp_socket;
  269         soisdisconnected(so);
  270         tw->tw_cred = crhold(so->so_cred);
  271         SOCK_LOCK(so);
  272         tw->tw_so_options = so->so_options;
  273         SOCK_UNLOCK(so);
  274         if (acknow)
  275                 tcp_twrespond(tw, TH_ACK);
  276         inp->inp_ppcb = tw;
  277         inp->inp_flags |= INP_TIMEWAIT;
  278         tcp_tw_2msl_reset(tw, 0);
  279 
  280         /*
  281          * If the inpcb owns the sole reference to the socket, then we can
  282          * detach and free the socket as it is not needed in time wait.
  283          */
  284         if (inp->inp_flags & INP_SOCKREF) {
  285                 KASSERT(so->so_state & SS_PROTOREF,
  286                     ("tcp_twstart: !SS_PROTOREF"));
  287                 inp->inp_flags &= ~INP_SOCKREF;
  288                 INP_WUNLOCK(inp);
  289                 ACCEPT_LOCK();
  290                 SOCK_LOCK(so);
  291                 so->so_state &= ~SS_PROTOREF;
  292                 sofree(so);
  293         } else
  294                 INP_WUNLOCK(inp);
  295 }
  296 
  297 #if 0
  298 /*
  299  * The appromixate rate of ISN increase of Microsoft TCP stacks;
  300  * the actual rate is slightly higher due to the addition of
  301  * random positive increments.
  302  *
  303  * Most other new OSes use semi-randomized ISN values, so we
  304  * do not need to worry about them.
  305  */
  306 #define MS_ISN_BYTES_PER_SECOND         250000
  307 
  308 /*
  309  * Determine if the ISN we will generate has advanced beyond the last
  310  * sequence number used by the previous connection.  If so, indicate
  311  * that it is safe to recycle this tw socket by returning 1.
  312  */
  313 int
  314 tcp_twrecycleable(struct tcptw *tw)
  315 {
  316         tcp_seq new_iss = tw->iss;
  317         tcp_seq new_irs = tw->irs;
  318 
  319         INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
  320         new_iss += (ticks - tw->t_starttime) * (ISN_BYTES_PER_SECOND / hz);
  321         new_irs += (ticks - tw->t_starttime) * (MS_ISN_BYTES_PER_SECOND / hz);
  322 
  323         if (SEQ_GT(new_iss, tw->snd_nxt) && SEQ_GT(new_irs, tw->rcv_nxt))
  324                 return (1);
  325         else
  326                 return (0);
  327 }
  328 #endif
  329 
  330 /*
  331  * Returns 1 if the TIME_WAIT state was killed and we should start over,
  332  * looking for a pcb in the listen state.  Returns 0 otherwise.
  333  */
  334 int
  335 tcp_twcheck(struct inpcb *inp, struct tcpopt *to, struct tcphdr *th,
  336     struct mbuf *m, int tlen)
  337 {
  338         struct tcptw *tw;
  339         int thflags;
  340         tcp_seq seq;
  341 
  342         /* tcbinfo lock required for tcp_twclose(), tcp_tw_2msl_reset(). */
  343         INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
  344         INP_WLOCK_ASSERT(inp);
  345 
  346         /*
  347          * XXXRW: Time wait state for inpcb has been recycled, but inpcb is
  348          * still present.  This is undesirable, but temporarily necessary
  349          * until we work out how to handle inpcb's who's timewait state has
  350          * been removed.
  351          */
  352         tw = intotw(inp);
  353         if (tw == NULL)
  354                 goto drop;
  355 
  356         thflags = th->th_flags;
  357 
  358         /*
  359          * NOTE: for FIN_WAIT_2 (to be added later),
  360          * must validate sequence number before accepting RST
  361          */
  362 
  363         /*
  364          * If the segment contains RST:
  365          *      Drop the segment - see Stevens, vol. 2, p. 964 and
  366          *      RFC 1337.
  367          */
  368         if (thflags & TH_RST)
  369                 goto drop;
  370 
  371 #if 0
  372 /* PAWS not needed at the moment */
  373         /*
  374          * RFC 1323 PAWS: If we have a timestamp reply on this segment
  375          * and it's less than ts_recent, drop it.
  376          */
  377         if ((to.to_flags & TOF_TS) != 0 && tp->ts_recent &&
  378             TSTMP_LT(to.to_tsval, tp->ts_recent)) {
  379                 if ((thflags & TH_ACK) == 0)
  380                         goto drop;
  381                 goto ack;
  382         }
  383         /*
  384          * ts_recent is never updated because we never accept new segments.
  385          */
  386 #endif
  387 
  388         /*
  389          * If a new connection request is received
  390          * while in TIME_WAIT, drop the old connection
  391          * and start over if the sequence numbers
  392          * are above the previous ones.
  393          */
  394         if ((thflags & TH_SYN) && SEQ_GT(th->th_seq, tw->rcv_nxt)) {
  395                 tcp_twclose(tw, 0);
  396                 return (1);
  397         }
  398 
  399         /*
  400          * Drop the the segment if it does not contain an ACK.
  401          */
  402         if ((thflags & TH_ACK) == 0)
  403                 goto drop;
  404 
  405         /*
  406          * Reset the 2MSL timer if this is a duplicate FIN.
  407          */
  408         if (thflags & TH_FIN) {
  409                 seq = th->th_seq + tlen + (thflags & TH_SYN ? 1 : 0);
  410                 if (seq + 1 == tw->rcv_nxt)
  411                         tcp_tw_2msl_reset(tw, 1);
  412         }
  413 
  414         /*
  415          * Acknowledge the segment if it has data or is not a duplicate ACK.
  416          */
  417         if (thflags != TH_ACK || tlen != 0 ||
  418             th->th_seq != tw->rcv_nxt || th->th_ack != tw->snd_nxt)
  419                 tcp_twrespond(tw, TH_ACK);
  420 drop:
  421         INP_WUNLOCK(inp);
  422         m_freem(m);
  423         return (0);
  424 }
  425 
  426 void
  427 tcp_twclose(struct tcptw *tw, int reuse)
  428 {
  429         struct socket *so;
  430         struct inpcb *inp;
  431 
  432         /*
  433          * At this point, we are in one of two situations:
  434          *
  435          * (1) We have no socket, just an inpcb<->twtcp pair.  We can free
  436          *     all state.
  437          *
  438          * (2) We have a socket -- if we own a reference, release it and
  439          *     notify the socket layer.
  440          */
  441         inp = tw->tw_inpcb;
  442         KASSERT((inp->inp_flags & INP_TIMEWAIT), ("tcp_twclose: !timewait"));
  443         KASSERT(intotw(inp) == tw, ("tcp_twclose: inp_ppcb != tw"));
  444         INP_INFO_WLOCK_ASSERT(&V_tcbinfo);      /* tcp_tw_2msl_stop(). */
  445         INP_WLOCK_ASSERT(inp);
  446 
  447         tw->tw_inpcb = NULL;
  448         tcp_tw_2msl_stop(tw);
  449         inp->inp_ppcb = NULL;
  450         in_pcbdrop(inp);
  451 
  452         so = inp->inp_socket;
  453         if (so != NULL) {
  454                 /*
  455                  * If there's a socket, handle two cases: first, we own a
  456                  * strong reference, which we will now release, or we don't
  457                  * in which case another reference exists (XXXRW: think
  458                  * about this more), and we don't need to take action.
  459                  */
  460                 if (inp->inp_flags & INP_SOCKREF) {
  461                         inp->inp_flags &= ~INP_SOCKREF;
  462                         INP_WUNLOCK(inp);
  463                         ACCEPT_LOCK();
  464                         SOCK_LOCK(so);
  465                         KASSERT(so->so_state & SS_PROTOREF,
  466                             ("tcp_twclose: INP_SOCKREF && !SS_PROTOREF"));
  467                         so->so_state &= ~SS_PROTOREF;
  468                         sofree(so);
  469                 } else {
  470                         /*
  471                          * If we don't own the only reference, the socket and
  472                          * inpcb need to be left around to be handled by
  473                          * tcp_usr_detach() later.
  474                          */
  475                         INP_WUNLOCK(inp);
  476                 }
  477         } else
  478                 in_pcbfree(inp);
  479         TCPSTAT_INC(tcps_closed);
  480         crfree(tw->tw_cred);
  481         tw->tw_cred = NULL;
  482         if (reuse)
  483                 return;
  484         uma_zfree(V_tcptw_zone, tw);
  485 }
  486 
  487 int
  488 tcp_twrespond(struct tcptw *tw, int flags)
  489 {
  490         struct inpcb *inp = tw->tw_inpcb;
  491         struct tcphdr *th;
  492         struct mbuf *m;
  493         struct ip *ip = NULL;
  494         u_int hdrlen, optlen;
  495         int error;
  496         struct tcpopt to;
  497 #ifdef INET6
  498         struct ip6_hdr *ip6 = NULL;
  499         int isipv6 = inp->inp_inc.inc_flags & INC_ISIPV6;
  500 #endif
  501 
  502         INP_WLOCK_ASSERT(inp);
  503 
  504         m = m_gethdr(M_DONTWAIT, MT_DATA);
  505         if (m == NULL)
  506                 return (ENOBUFS);
  507         m->m_data += max_linkhdr;
  508 
  509 #ifdef MAC
  510         mac_inpcb_create_mbuf(inp, m);
  511 #endif
  512 
  513 #ifdef INET6
  514         if (isipv6) {
  515                 hdrlen = sizeof(struct ip6_hdr) + sizeof(struct tcphdr);
  516                 ip6 = mtod(m, struct ip6_hdr *);
  517                 th = (struct tcphdr *)(ip6 + 1);
  518                 tcpip_fillheaders(inp, ip6, th);
  519         } else
  520 #endif
  521         {
  522                 hdrlen = sizeof(struct tcpiphdr);
  523                 ip = mtod(m, struct ip *);
  524                 th = (struct tcphdr *)(ip + 1);
  525                 tcpip_fillheaders(inp, ip, th);
  526         }
  527         to.to_flags = 0;
  528 
  529         /*
  530          * Send a timestamp and echo-reply if both our side and our peer
  531          * have sent timestamps in our SYN's and this is not a RST.
  532          */
  533         if (tw->t_recent && flags == TH_ACK) {
  534                 to.to_flags |= TOF_TS;
  535                 to.to_tsval = ticks + tw->ts_offset;
  536                 to.to_tsecr = tw->t_recent;
  537         }
  538         optlen = tcp_addoptions(&to, (u_char *)(th + 1));
  539 
  540         m->m_len = hdrlen + optlen;
  541         m->m_pkthdr.len = m->m_len;
  542 
  543         KASSERT(max_linkhdr + m->m_len <= MHLEN, ("tcptw: mbuf too small"));
  544 
  545         th->th_seq = htonl(tw->snd_nxt);
  546         th->th_ack = htonl(tw->rcv_nxt);
  547         th->th_off = (sizeof(struct tcphdr) + optlen) >> 2;
  548         th->th_flags = flags;
  549         th->th_win = htons(tw->last_win);
  550 
  551 #ifdef INET6
  552         if (isipv6) {
  553                 th->th_sum = in6_cksum(m, IPPROTO_TCP, sizeof(struct ip6_hdr),
  554                     sizeof(struct tcphdr) + optlen);
  555                 ip6->ip6_hlim = in6_selecthlim(inp, NULL);
  556                 error = ip6_output(m, inp->in6p_outputopts, NULL,
  557                     (tw->tw_so_options & SO_DONTROUTE), NULL, NULL, inp);
  558         } else
  559 #endif
  560         {
  561                 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr,
  562                     htons(sizeof(struct tcphdr) + optlen + IPPROTO_TCP));
  563                 m->m_pkthdr.csum_flags = CSUM_TCP;
  564                 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
  565                 ip->ip_len = m->m_pkthdr.len;
  566                 if (V_path_mtu_discovery)
  567                         ip->ip_off |= IP_DF;
  568                 error = ip_output(m, inp->inp_options, NULL,
  569                     ((tw->tw_so_options & SO_DONTROUTE) ? IP_ROUTETOIF : 0),
  570                     NULL, inp);
  571         }
  572         if (flags & TH_ACK)
  573                 TCPSTAT_INC(tcps_sndacks);
  574         else
  575                 TCPSTAT_INC(tcps_sndctrl);
  576         TCPSTAT_INC(tcps_sndtotal);
  577         return (error);
  578 }
  579 
  580 static void
  581 tcp_tw_2msl_reset(struct tcptw *tw, int rearm)
  582 {
  583 
  584         INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
  585         INP_WLOCK_ASSERT(tw->tw_inpcb);
  586         if (rearm)
  587                 TAILQ_REMOVE(&V_twq_2msl, tw, tw_2msl);
  588         tw->tw_time = ticks + 2 * tcp_msl;
  589         TAILQ_INSERT_TAIL(&V_twq_2msl, tw, tw_2msl);
  590 }
  591 
  592 static void
  593 tcp_tw_2msl_stop(struct tcptw *tw)
  594 {
  595 
  596         INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
  597         TAILQ_REMOVE(&V_twq_2msl, tw, tw_2msl);
  598 }
  599 
  600 struct tcptw *
  601 tcp_tw_2msl_scan(int reuse)
  602 {
  603         struct tcptw *tw;
  604 
  605         INP_INFO_WLOCK_ASSERT(&V_tcbinfo);
  606         for (;;) {
  607                 tw = TAILQ_FIRST(&V_twq_2msl);
  608                 if (tw == NULL || (!reuse && (tw->tw_time - ticks) > 0))
  609                         break;
  610                 INP_WLOCK(tw->tw_inpcb);
  611                 tcp_twclose(tw, reuse);
  612                 if (reuse)
  613                         return (tw);
  614         }
  615         return (NULL);
  616 }

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