sys/netinet/tcp_timer.c

   1 /*-
   2  * SPDX-License-Identifier: BSD-3-Clause
   3  *
   4  * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1995
   5  *      The Regents of the University of California.  All rights reserved.
   6  *
   7  * Redistribution and use in source and binary forms, with or without
   8  * modification, are permitted provided that the following conditions
   9  * are met:
  10  * 1. Redistributions of source code must retain the above copyright
  11  *    notice, this list of conditions and the following disclaimer.
  12  * 2. Redistributions in binary form must reproduce the above copyright
  13  *    notice, this list of conditions and the following disclaimer in the
  14  *    documentation and/or other materials provided with the distribution.
  15  * 3. Neither the name of the University nor the names of its contributors
  16  *    may be used to endorse or promote products derived from this software
  17  *    without specific prior written permission.
  18  *
  19  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  20  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  21  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  22  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  23  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  24  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  25  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  26  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  27  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  28  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  29  * SUCH DAMAGE.
  30  */
  31
  32 #include <sys/cdefs.h>
  33 #include "opt_inet.h"
  34 #include "opt_inet6.h"
  35 #include "opt_rss.h"
  36
  37 #include <sys/param.h>
  38 #include <sys/kernel.h>
  39 #include <sys/lock.h>
  40 #include <sys/mbuf.h>
  41 #include <sys/mutex.h>
  42 #include <sys/protosw.h>
  43 #include <sys/smp.h>
  44 #include <sys/socket.h>
  45 #include <sys/socketvar.h>
  46 #include <sys/sysctl.h>
  47 #include <sys/systm.h>
  48
  49 #include <net/if.h>
  50 #include <net/route.h>
  51 #include <net/rss_config.h>
  52 #include <net/vnet.h>
  53 #include <net/netisr.h>
  54
  55 #include <netinet/in.h>
  56 #include <netinet/in_kdtrace.h>
  57 #include <netinet/in_pcb.h>
  58 #include <netinet/in_rss.h>
  59 #include <netinet/in_systm.h>
  60 #ifdef INET6
  61 #include <netinet6/in6_pcb.h>
  62 #endif
  63 #include <netinet/ip_var.h>
  64 #include <netinet/tcp.h>
  65 #include <netinet/tcp_fsm.h>
  66 #include <netinet/tcp_timer.h>
  67 #include <netinet/tcp_var.h>
  68 #include <netinet/tcp_log_buf.h>
  69 #include <netinet/tcp_seq.h>
  70 #include <netinet/cc/cc.h>
  71 #ifdef INET6
  72 #include <netinet6/tcp6_var.h>
  73 #endif
  74 #include <netinet/tcpip.h>
  75
  76 int    tcp_persmin;
  77 SYSCTL_PROC(_net_inet_tcp, OID_AUTO, persmin,
  78     CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_NEEDGIANT,
  79     &tcp_persmin, 0, sysctl_msec_to_ticks, "I",
  80     "minimum persistence interval");
  81
  82 int    tcp_persmax;
  83 SYSCTL_PROC(_net_inet_tcp, OID_AUTO, persmax,
  84     CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_NEEDGIANT,
  85     &tcp_persmax, 0, sysctl_msec_to_ticks, "I",
  86     "maximum persistence interval");
  87
  88 int     tcp_keepinit;
  89 SYSCTL_PROC(_net_inet_tcp, TCPCTL_KEEPINIT, keepinit,
  90     CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_NEEDGIANT,
  91     &tcp_keepinit, 0, sysctl_msec_to_ticks, "I",
  92     "time to establish connection");
  93
  94 int     tcp_keepidle;
  95 SYSCTL_PROC(_net_inet_tcp, TCPCTL_KEEPIDLE, keepidle,
  96     CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_NEEDGIANT,
  97     &tcp_keepidle, 0, sysctl_msec_to_ticks, "I",
  98     "time before keepalive probes begin");
  99
 100 int     tcp_keepintvl;
 101 SYSCTL_PROC(_net_inet_tcp, TCPCTL_KEEPINTVL, keepintvl,
 102     CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_NEEDGIANT,
 103     &tcp_keepintvl, 0, sysctl_msec_to_ticks, "I",
 104     "time between keepalive probes");
 105
 106 int     tcp_delacktime;
 107 SYSCTL_PROC(_net_inet_tcp, TCPCTL_DELACKTIME, delacktime,
 108     CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_NEEDGIANT,
 109     &tcp_delacktime, 0, sysctl_msec_to_ticks, "I",
 110     "Time before a delayed ACK is sent");
 111
 112 VNET_DEFINE(int, tcp_msl);
 113 SYSCTL_PROC(_net_inet_tcp, OID_AUTO, msl,
 114     CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_VNET,
 115     &VNET_NAME(tcp_msl), 0, sysctl_msec_to_ticks, "I",
 116     "Maximum segment lifetime");
 117
 118 int     tcp_rexmit_initial;
 119 SYSCTL_PROC(_net_inet_tcp, OID_AUTO, rexmit_initial,
 120    CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_NEEDGIANT,
 121     &tcp_rexmit_initial, 0, sysctl_msec_to_ticks, "I",
 122     "Initial Retransmission Timeout");
 123
 124 int     tcp_rexmit_min;
 125 SYSCTL_PROC(_net_inet_tcp, OID_AUTO, rexmit_min,
 126     CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_NEEDGIANT,
 127     &tcp_rexmit_min, 0, sysctl_msec_to_ticks, "I",
 128     "Minimum Retransmission Timeout");
 129
 130 int     tcp_rexmit_slop;
 131 SYSCTL_PROC(_net_inet_tcp, OID_AUTO, rexmit_slop,
 132     CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_NEEDGIANT,
 133     &tcp_rexmit_slop, 0, sysctl_msec_to_ticks, "I",
 134     "Retransmission Timer Slop");
 135
 136 VNET_DEFINE(int, tcp_always_keepalive) = 1;
 137 SYSCTL_INT(_net_inet_tcp, OID_AUTO, always_keepalive, CTLFLAG_VNET|CTLFLAG_RW,
 138     &VNET_NAME(tcp_always_keepalive) , 0,
 139     "Assume SO_KEEPALIVE on all TCP connections");
 140
 141 int    tcp_fast_finwait2_recycle = 0;
 142 SYSCTL_INT(_net_inet_tcp, OID_AUTO, fast_finwait2_recycle, CTLFLAG_RW,
 143     &tcp_fast_finwait2_recycle, 0,
 144     "Recycle closed FIN_WAIT_2 connections faster");
 145
 146 int    tcp_finwait2_timeout;
 147 SYSCTL_PROC(_net_inet_tcp, OID_AUTO, finwait2_timeout,
 148     CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_NEEDGIANT,
 149     &tcp_finwait2_timeout, 0, sysctl_msec_to_ticks, "I",
 150     "FIN-WAIT2 timeout");
 151
 152 int     tcp_keepcnt = TCPTV_KEEPCNT;
 153 SYSCTL_INT(_net_inet_tcp, OID_AUTO, keepcnt, CTLFLAG_RW, &tcp_keepcnt, 0,
 154     "Number of keepalive probes to send");
 155
 156         /* max idle probes */
 157 int     tcp_maxpersistidle;
 158
 159 int     tcp_rexmit_drop_options = 0;
 160 SYSCTL_INT(_net_inet_tcp, OID_AUTO, rexmit_drop_options, CTLFLAG_RW,
 161     &tcp_rexmit_drop_options, 0,
 162     "Drop TCP options from 3rd and later retransmitted SYN");
 163
 164 int     tcp_maxunacktime = TCPTV_MAXUNACKTIME;
 165 SYSCTL_PROC(_net_inet_tcp, OID_AUTO, maxunacktime,
 166     CTLTYPE_INT|CTLFLAG_RW | CTLFLAG_NEEDGIANT,
 167     &tcp_maxunacktime, 0, sysctl_msec_to_ticks, "I",
 168     "Maximum time (in ms) that a session can linger without making progress");
 169
 170 VNET_DEFINE(int, tcp_pmtud_blackhole_detect);
 171 SYSCTL_INT(_net_inet_tcp, OID_AUTO, pmtud_blackhole_detection,
 172     CTLFLAG_RW|CTLFLAG_VNET,
 173     &VNET_NAME(tcp_pmtud_blackhole_detect), 0,
 174     "Path MTU Discovery Black Hole Detection Enabled");
 175
 176 #ifdef INET
 177 VNET_DEFINE(int, tcp_pmtud_blackhole_mss) = 1200;
 178 SYSCTL_INT(_net_inet_tcp, OID_AUTO, pmtud_blackhole_mss,
 179     CTLFLAG_RW|CTLFLAG_VNET,
 180     &VNET_NAME(tcp_pmtud_blackhole_mss), 0,
 181     "Path MTU Discovery Black Hole Detection lowered MSS");
 182 #endif
 183
 184 #ifdef INET6
 185 VNET_DEFINE(int, tcp_v6pmtud_blackhole_mss) = 1220;
 186 SYSCTL_INT(_net_inet_tcp, OID_AUTO, v6pmtud_blackhole_mss,
 187     CTLFLAG_RW|CTLFLAG_VNET,
 188     &VNET_NAME(tcp_v6pmtud_blackhole_mss), 0,
 189     "Path MTU Discovery IPv6 Black Hole Detection lowered MSS");
 190 #endif
 191
 192 #ifdef  RSS
 193 static int      per_cpu_timers = 1;
 194 #else
 195 static int      per_cpu_timers = 0;
 196 #endif
 197 SYSCTL_INT(_net_inet_tcp, OID_AUTO, per_cpu_timers, CTLFLAG_RW,
 198     &per_cpu_timers , 0, "run tcp timers on all cpus");
 199
 200 static int
 201 sysctl_net_inet_tcp_retries(SYSCTL_HANDLER_ARGS)
 202 {
 203         int error, new;
 204
 205         new = V_tcp_retries;
 206         error = sysctl_handle_int(oidp, &new, 0, req);
 207         if (error == 0 && req->newptr) {
 208                 if ((new < 1) || (new > TCP_MAXRXTSHIFT))
 209                         error = EINVAL;
 210                 else
 211                         V_tcp_retries = new;
 212         }
 213         return (error);
 214 }
 215
 216 VNET_DEFINE(int, tcp_retries) = TCP_MAXRXTSHIFT;
 217 SYSCTL_PROC(_net_inet_tcp, OID_AUTO, retries,
 218     CTLTYPE_INT | CTLFLAG_VNET | CTLFLAG_RW,
 219     &VNET_NAME(tcp_retries), 0, sysctl_net_inet_tcp_retries, "I",
 220     "maximum number of consecutive timer based retransmissions");
 221
 222 /*
 223  * Map the given inp to a CPU id.
 224  *
 225  * This queries RSS if it's compiled in, else it defaults to the current
 226  * CPU ID.
 227  */
 228 inline int
 229 inp_to_cpuid(struct inpcb *inp)
 230 {
 231         u_int cpuid;
 232
 233         if (per_cpu_timers) {
 234 #ifdef  RSS
 235                 cpuid = rss_hash2cpuid(inp->inp_flowid, inp->inp_flowtype);
 236                 if (cpuid == NETISR_CPUID_NONE)
 237                         return (curcpu);        /* XXX */
 238                 else
 239                         return (cpuid);
 240 #endif
 241                 /*
 242                  * We don't have a flowid -> cpuid mapping, so cheat and
 243                  * just map unknown cpuids to curcpu.  Not the best, but
 244                  * apparently better than defaulting to swi 0.
 245                  */
 246                 cpuid = inp->inp_flowid % (mp_maxid + 1);
 247                 if (! CPU_ABSENT(cpuid))
 248                         return (cpuid);
 249                 return (curcpu);
 250         } else {
 251                 return (0);
 252         }
 253 }
 254
 255 int     tcp_backoff[TCP_MAXRXTSHIFT + 1] =
 256     { 1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 512, 512, 512 };
 257
 258 int tcp_totbackoff = 2559;      /* sum of tcp_backoff[] */
 259
 260 /*
 261  * TCP timer processing.
 262  *
 263  * Each connection has 5 timers associated with it, which can be scheduled
 264  * simultaneously.  They all are serviced by one callout tcp_timer_enter().
 265  * This function executes the next timer via tcp_timersw[] vector.  Each
 266  * timer is supposed to return 'true' unless the connection was destroyed.
 267  * In the former case tcp_timer_enter() will schedule callout for next timer.
 268  */
 269
 270 typedef bool tcp_timer_t(struct tcpcb *);
 271 static tcp_timer_t tcp_timer_delack;
 272 static tcp_timer_t tcp_timer_2msl;
 273 static tcp_timer_t tcp_timer_keep;
 274 static tcp_timer_t tcp_timer_persist;
 275 static tcp_timer_t tcp_timer_rexmt;
 276
 277 static tcp_timer_t * const tcp_timersw[TT_N] = {
 278         [TT_DELACK] = tcp_timer_delack,
 279         [TT_REXMT] = tcp_timer_rexmt,
 280         [TT_PERSIST] = tcp_timer_persist,
 281         [TT_KEEP] = tcp_timer_keep,
 282         [TT_2MSL] = tcp_timer_2msl,
 283 };
 284
 285 /*
 286  * tcp_output_locked() s a timer specific variation of call to tcp_output(),
 287  * see tcp_var.h for the rest.  It handles drop request from advanced stacks,
 288  * but keeps tcpcb locked unless tcp_drop() destroyed it.
 289  * Returns true if tcpcb is valid and locked.
 290  */
 291 static inline bool
 292 tcp_output_locked(struct tcpcb *tp)
 293 {
 294         int rv;
 295
 296         INP_WLOCK_ASSERT(tptoinpcb(tp));
 297
 298         if ((rv = tp->t_fb->tfb_tcp_output(tp)) < 0) {
 299                 KASSERT(tp->t_fb->tfb_flags & TCP_FUNC_OUTPUT_CANDROP,
 300                     ("TCP stack %s requested tcp_drop(%p)",
 301                     tp->t_fb->tfb_tcp_block_name, tp));
 302                 tp = tcp_drop(tp, rv);
 303         }
 304
 305         return (tp != NULL);
 306 }
 307
 308 static bool
 309 tcp_timer_delack(struct tcpcb *tp)
 310 {
 311         struct epoch_tracker et;
 312 #if defined(INVARIANTS) || defined(VIMAGE)
 313         struct inpcb *inp = tptoinpcb(tp);
 314 #endif
 315         bool rv;
 316
 317         INP_WLOCK_ASSERT(inp);
 318
 319         CURVNET_SET(inp->inp_vnet);
 320         tp->t_flags |= TF_ACKNOW;
 321         TCPSTAT_INC(tcps_delack);
 322         NET_EPOCH_ENTER(et);
 323         rv = tcp_output_locked(tp);
 324         NET_EPOCH_EXIT(et);
 325         CURVNET_RESTORE();
 326
 327         return (rv);
 328 }
 329
 330 static bool
 331 tcp_timer_2msl(struct tcpcb *tp)
 332 {
 333         struct inpcb *inp = tptoinpcb(tp);
 334         bool close = false;
 335
 336         INP_WLOCK_ASSERT(inp);
 337
 338         TCP_PROBE2(debug__user, tp, PRU_SLOWTIMO);
 339         CURVNET_SET(inp->inp_vnet);
 340         tcp_log_end_status(tp, TCP_EI_STATUS_2MSL);
 341         tcp_free_sackholes(tp);
 342         /*
 343          * 2 MSL timeout in shutdown went off.  If we're closed but
 344          * still waiting for peer to close and connection has been idle
 345          * too long delete connection control block.  Otherwise, check
 346          * again in a bit.
 347          *
 348          * If fastrecycle of FIN_WAIT_2, in FIN_WAIT_2 and receiver has closed,
 349          * there's no point in hanging onto FIN_WAIT_2 socket. Just close it.
 350          * Ignore fact that there were recent incoming segments.
 351          *
 352          * XXXGL: check if inp_socket shall always be !NULL here?
 353          */
 354         if (tp->t_state == TCPS_TIME_WAIT) {
 355                 close = true;
 356         } else if (tp->t_state == TCPS_FIN_WAIT_2 &&
 357             tcp_fast_finwait2_recycle && inp->inp_socket &&
 358             (inp->inp_socket->so_rcv.sb_state & SBS_CANTRCVMORE)) {
 359                 TCPSTAT_INC(tcps_finwait2_drops);
 360                 close = true;
 361         } else {
 362                 if (ticks - tp->t_rcvtime <= TP_MAXIDLE(tp))
 363                         tcp_timer_activate(tp, TT_2MSL, TP_KEEPINTVL(tp));
 364                 else
 365                         close = true;
 366         }
 367         if (close) {
 368                 struct epoch_tracker et;
 369
 370                 NET_EPOCH_ENTER(et);
 371                 tp = tcp_close(tp);
 372                 NET_EPOCH_EXIT(et);
 373         }
 374         CURVNET_RESTORE();
 375
 376         return (tp != NULL);
 377 }
 378
 379 static bool
 380 tcp_timer_keep(struct tcpcb *tp)
 381 {
 382         struct epoch_tracker et;
 383         struct inpcb *inp = tptoinpcb(tp);
 384         struct tcptemp *t_template;
 385
 386         INP_WLOCK_ASSERT(inp);
 387
 388         TCP_PROBE2(debug__user, tp, PRU_SLOWTIMO);
 389         CURVNET_SET(inp->inp_vnet);
 390         /*
 391          * Because we don't regularly reset the keepalive callout in
 392          * the ESTABLISHED state, it may be that we don't actually need
 393          * to send a keepalive yet. If that occurs, schedule another
 394          * call for the next time the keepalive timer might expire.
 395          */
 396         if (TCPS_HAVEESTABLISHED(tp->t_state)) {
 397                 u_int idletime;
 398
 399                 idletime = ticks - tp->t_rcvtime;
 400                 if (idletime < TP_KEEPIDLE(tp)) {
 401                         tcp_timer_activate(tp, TT_KEEP,
 402                             TP_KEEPIDLE(tp) - idletime);
 403                         CURVNET_RESTORE();
 404                         return (true);
 405                 }
 406         }
 407
 408         /*
 409          * Keep-alive timer went off; send something
 410          * or drop connection if idle for too long.
 411          */
 412         TCPSTAT_INC(tcps_keeptimeo);
 413         if (tp->t_state < TCPS_ESTABLISHED)
 414                 goto dropit;
 415         if ((V_tcp_always_keepalive ||
 416             inp->inp_socket->so_options & SO_KEEPALIVE) &&
 417             tp->t_state <= TCPS_CLOSING) {
 418                 if (ticks - tp->t_rcvtime >= TP_KEEPIDLE(tp) + TP_MAXIDLE(tp))
 419                         goto dropit;
 420                 /*
 421                  * Send a packet designed to force a response
 422                  * if the peer is up and reachable:
 423                  * either an ACK if the connection is still alive,
 424                  * or an RST if the peer has closed the connection
 425                  * due to timeout or reboot.
 426                  * Using sequence number tp->snd_una-1
 427                  * causes the transmitted zero-length segment
 428                  * to lie outside the receive window;
 429                  * by the protocol spec, this requires the
 430                  * correspondent TCP to respond.
 431                  */
 432                 TCPSTAT_INC(tcps_keepprobe);
 433                 t_template = tcpip_maketemplate(inp);
 434                 if (t_template) {
 435                         NET_EPOCH_ENTER(et);
 436                         tcp_respond(tp, t_template->tt_ipgen,
 437                                     &t_template->tt_t, (struct mbuf *)NULL,
 438                                     tp->rcv_nxt, tp->snd_una - 1, 0);
 439                         NET_EPOCH_EXIT(et);
 440                         free(t_template, M_TEMP);
 441                 }
 442                 tcp_timer_activate(tp, TT_KEEP, TP_KEEPINTVL(tp));
 443         } else
 444                 tcp_timer_activate(tp, TT_KEEP, TP_KEEPIDLE(tp));
 445
 446         CURVNET_RESTORE();
 447         return (true);
 448
 449 dropit:
 450         TCPSTAT_INC(tcps_keepdrops);
 451         NET_EPOCH_ENTER(et);
 452         tcp_log_end_status(tp, TCP_EI_STATUS_KEEP_MAX);
 453         tp = tcp_drop(tp, ETIMEDOUT);
 454         NET_EPOCH_EXIT(et);
 455         CURVNET_RESTORE();
 456
 457         return (tp != NULL);
 458 }
 459
 460 /*
 461  * Has this session exceeded the maximum time without seeing a substantive
 462  * acknowledgement? If so, return true; otherwise false.
 463  */
 464 static bool
 465 tcp_maxunacktime_check(struct tcpcb *tp)
 466 {
 467
 468         /* Are we tracking this timer for this session? */
 469         if (TP_MAXUNACKTIME(tp) == 0)
 470                 return false;
 471
 472         /* Do we have a current measurement. */
 473         if (tp->t_acktime == 0)
 474                 return false;
 475
 476         /* Are we within the acceptable range? */
 477         if (TSTMP_GT(TP_MAXUNACKTIME(tp) + tp->t_acktime, (u_int)ticks))
 478                 return false;
 479
 480         /* We exceeded the timer. */
 481         TCPSTAT_INC(tcps_progdrops);
 482         return true;
 483 }
 484
 485 static bool
 486 tcp_timer_persist(struct tcpcb *tp)
 487 {
 488         struct epoch_tracker et;
 489 #if defined(INVARIANTS) || defined(VIMAGE)
 490         struct inpcb *inp = tptoinpcb(tp);
 491 #endif
 492         bool progdrop, rv;
 493
 494         INP_WLOCK_ASSERT(inp);
 495
 496         TCP_PROBE2(debug__user, tp, PRU_SLOWTIMO);
 497         CURVNET_SET(inp->inp_vnet);
 498         /*
 499          * Persistence timer into zero window.
 500          * Force a byte to be output, if possible.
 501          */
 502         TCPSTAT_INC(tcps_persisttimeo);
 503         /*
 504          * Hack: if the peer is dead/unreachable, we do not
 505          * time out if the window is closed.  After a full
 506          * backoff, drop the connection if the idle time
 507          * (no responses to probes) reaches the maximum
 508          * backoff that we would use if retransmitting.
 509          * Also, drop the connection if we haven't been making
 510          * progress.
 511          */
 512         progdrop = tcp_maxunacktime_check(tp);
 513         if (progdrop || (tp->t_rxtshift >= V_tcp_retries &&
 514             (ticks - tp->t_rcvtime >= tcp_maxpersistidle ||
 515              ticks - tp->t_rcvtime >= TCP_REXMTVAL(tp) * tcp_totbackoff))) {
 516                 if (!progdrop)
 517                         TCPSTAT_INC(tcps_persistdrop);
 518                 tcp_log_end_status(tp, TCP_EI_STATUS_PERSIST_MAX);
 519                 goto dropit;
 520         }
 521         /*
 522          * If the user has closed the socket then drop a persisting
 523          * connection after a much reduced timeout.
 524          */
 525         if (tp->t_state > TCPS_CLOSE_WAIT &&
 526             (ticks - tp->t_rcvtime) >= TCPTV_PERSMAX) {
 527                 TCPSTAT_INC(tcps_persistdrop);
 528                 tcp_log_end_status(tp, TCP_EI_STATUS_PERSIST_MAX);
 529                 goto dropit;
 530         }
 531         tcp_setpersist(tp);
 532         tp->t_flags |= TF_FORCEDATA;
 533         NET_EPOCH_ENTER(et);
 534         if ((rv = tcp_output_locked(tp)))
 535                 tp->t_flags &= ~TF_FORCEDATA;
 536         NET_EPOCH_EXIT(et);
 537         CURVNET_RESTORE();
 538
 539         return (rv);
 540
 541 dropit:
 542         NET_EPOCH_ENTER(et);
 543         tp = tcp_drop(tp, ETIMEDOUT);
 544         NET_EPOCH_EXIT(et);
 545         CURVNET_RESTORE();
 546
 547         return (tp != NULL);
 548 }
 549
 550 static bool
 551 tcp_timer_rexmt(struct tcpcb *tp)
 552 {
 553         struct epoch_tracker et;
 554         struct inpcb *inp = tptoinpcb(tp);
 555         int rexmt;
 556         bool isipv6, rv;
 557
 558         INP_WLOCK_ASSERT(inp);
 559
 560         TCP_PROBE2(debug__user, tp, PRU_SLOWTIMO);
 561         CURVNET_SET(inp->inp_vnet);
 562         tcp_free_sackholes(tp);
 563         if (tp->t_fb->tfb_tcp_rexmit_tmr) {
 564                 /* The stack has a timer action too. */
 565                 (*tp->t_fb->tfb_tcp_rexmit_tmr)(tp);
 566         }
 567         /*
 568          * Retransmission timer went off.  Message has not
 569          * been acked within retransmit interval.  Back off
 570          * to a longer retransmit interval and retransmit one segment.
 571          *
 572          * If we've either exceeded the maximum number of retransmissions,
 573          * or we've gone long enough without making progress, then drop
 574          * the session.
 575          */
 576         if (++tp->t_rxtshift > V_tcp_retries || tcp_maxunacktime_check(tp)) {
 577                 if (tp->t_rxtshift > V_tcp_retries)
 578                         TCPSTAT_INC(tcps_timeoutdrop);
 579                 tp->t_rxtshift = V_tcp_retries;
 580                 tcp_log_end_status(tp, TCP_EI_STATUS_RETRAN);
 581                 NET_EPOCH_ENTER(et);
 582                 tp = tcp_drop(tp, ETIMEDOUT);
 583                 NET_EPOCH_EXIT(et);
 584                 CURVNET_RESTORE();
 585
 586                 return (tp != NULL);
 587         }
 588         if (tp->t_state == TCPS_SYN_SENT) {
 589                 /*
 590                  * If the SYN was retransmitted, indicate CWND to be
 591                  * limited to 1 segment in cc_conn_init().
 592                  */
 593                 tp->snd_cwnd = 1;
 594         } else if (tp->t_rxtshift == 1) {
 595                 /*
 596                  * first retransmit; record ssthresh and cwnd so they can
 597                  * be recovered if this turns out to be a "bad" retransmit.
 598                  * A retransmit is considered "bad" if an ACK for this
 599                  * segment is received within RTT/2 interval; the assumption
 600                  * here is that the ACK was already in flight.  See
 601                  * "On Estimating End-to-End Network Path Properties" by
 602                  * Allman and Paxson for more details.
 603                  */
 604                 tp->snd_cwnd_prev = tp->snd_cwnd;
 605                 tp->snd_ssthresh_prev = tp->snd_ssthresh;
 606                 tp->snd_recover_prev = tp->snd_recover;
 607                 if (IN_FASTRECOVERY(tp->t_flags))
 608                         tp->t_flags |= TF_WASFRECOVERY;
 609                 else
 610                         tp->t_flags &= ~TF_WASFRECOVERY;
 611                 if (IN_CONGRECOVERY(tp->t_flags))
 612                         tp->t_flags |= TF_WASCRECOVERY;
 613                 else
 614                         tp->t_flags &= ~TF_WASCRECOVERY;
 615                 if ((tp->t_flags & TF_RCVD_TSTMP) == 0)
 616                         tp->t_badrxtwin = ticks + (tp->t_srtt >> (TCP_RTT_SHIFT + 1));
 617                 /* In the event that we've negotiated timestamps
 618                  * badrxtwin will be set to the value that we set
 619                  * the retransmitted packet's to_tsval to by tcp_output
 620                  */
 621                 tp->t_flags |= TF_PREVVALID;
 622         } else
 623                 tp->t_flags &= ~TF_PREVVALID;
 624         TCPSTAT_INC(tcps_rexmttimeo);
 625         if ((tp->t_state == TCPS_SYN_SENT) ||
 626             (tp->t_state == TCPS_SYN_RECEIVED))
 627                 rexmt = tcp_rexmit_initial * tcp_backoff[tp->t_rxtshift];
 628         else
 629                 rexmt = TCP_REXMTVAL(tp) * tcp_backoff[tp->t_rxtshift];
 630         TCPT_RANGESET(tp->t_rxtcur, rexmt,
 631                       tp->t_rttmin, TCPTV_REXMTMAX);
 632
 633         /*
 634          * We enter the path for PLMTUD if connection is established or, if
 635          * connection is FIN_WAIT_1 status, reason for the last is that if
 636          * amount of data we send is very small, we could send it in couple of
 637          * packets and process straight to FIN. In that case we won't catch
 638          * ESTABLISHED state.
 639          */
 640 #ifdef INET6
 641         isipv6 = (inp->inp_vflag & INP_IPV6) ? true : false;
 642 #else
 643         isipv6 = false;
 644 #endif
 645         if (((V_tcp_pmtud_blackhole_detect == 1) ||
 646             (V_tcp_pmtud_blackhole_detect == 2 && !isipv6) ||
 647             (V_tcp_pmtud_blackhole_detect == 3 && isipv6)) &&
 648             ((tp->t_state == TCPS_ESTABLISHED) ||
 649             (tp->t_state == TCPS_FIN_WAIT_1))) {
 650                 if (tp->t_rxtshift == 1) {
 651                         /*
 652                          * We enter blackhole detection after the first
 653                          * unsuccessful timer based retransmission.
 654                          * Then we reduce up to two times the MSS, each
 655                          * candidate giving two tries of retransmissions.
 656                          * But we give a candidate only two tries, if it
 657                          * actually reduces the MSS.
 658                          */
 659                         tp->t_blackhole_enter = 2;
 660                         tp->t_blackhole_exit = tp->t_blackhole_enter;
 661                         if (isipv6) {
 662 #ifdef INET6
 663                                 if (tp->t_maxseg > V_tcp_v6pmtud_blackhole_mss)
 664                                         tp->t_blackhole_exit += 2;
 665                                 if (tp->t_maxseg > V_tcp_v6mssdflt &&
 666                                     V_tcp_v6pmtud_blackhole_mss > V_tcp_v6mssdflt)
 667                                         tp->t_blackhole_exit += 2;
 668 #endif
 669                         } else {
 670 #ifdef INET
 671                                 if (tp->t_maxseg > V_tcp_pmtud_blackhole_mss)
 672                                         tp->t_blackhole_exit += 2;
 673                                 if (tp->t_maxseg > V_tcp_mssdflt &&
 674                                     V_tcp_pmtud_blackhole_mss > V_tcp_mssdflt)
 675                                         tp->t_blackhole_exit += 2;
 676 #endif
 677                         }
 678                 }
 679                 if (((tp->t_flags2 & (TF2_PLPMTU_PMTUD|TF2_PLPMTU_MAXSEGSNT)) ==
 680                     (TF2_PLPMTU_PMTUD|TF2_PLPMTU_MAXSEGSNT)) &&
 681                     (tp->t_rxtshift >= tp->t_blackhole_enter &&
 682                     tp->t_rxtshift < tp->t_blackhole_exit &&
 683                     (tp->t_rxtshift - tp->t_blackhole_enter) % 2 == 0)) {
 684                         /*
 685                          * Enter Path MTU Black-hole Detection mechanism:
 686                          * - Disable Path MTU Discovery (IP "DF" bit).
 687                          * - Reduce MTU to lower value than what we
 688                          *   negotiated with peer.
 689                          */
 690                         if ((tp->t_flags2 & TF2_PLPMTU_BLACKHOLE) == 0) {
 691                                 /* Record that we may have found a black hole. */
 692                                 tp->t_flags2 |= TF2_PLPMTU_BLACKHOLE;
 693                                 /* Keep track of previous MSS. */
 694                                 tp->t_pmtud_saved_maxseg = tp->t_maxseg;
 695                         }
 696
 697                         /*
 698                          * Reduce the MSS to blackhole value or to the default
 699                          * in an attempt to retransmit.
 700                          */
 701 #ifdef INET6
 702                         if (isipv6 &&
 703                             tp->t_maxseg > V_tcp_v6pmtud_blackhole_mss &&
 704                             V_tcp_v6pmtud_blackhole_mss > V_tcp_v6mssdflt) {
 705                                 /* Use the sysctl tuneable blackhole MSS. */
 706                                 tp->t_maxseg = V_tcp_v6pmtud_blackhole_mss;
 707                                 TCPSTAT_INC(tcps_pmtud_blackhole_activated);
 708                         } else if (isipv6) {
 709                                 /* Use the default MSS. */
 710                                 tp->t_maxseg = V_tcp_v6mssdflt;
 711                                 /*
 712                                  * Disable Path MTU Discovery when we switch to
 713                                  * minmss.
 714                                  */
 715                                 tp->t_flags2 &= ~TF2_PLPMTU_PMTUD;
 716                                 TCPSTAT_INC(tcps_pmtud_blackhole_activated_min_mss);
 717                         }
 718 #endif
 719 #if defined(INET6) && defined(INET)
 720                         else
 721 #endif
 722 #ifdef INET
 723                         if (tp->t_maxseg > V_tcp_pmtud_blackhole_mss &&
 724                             V_tcp_pmtud_blackhole_mss > V_tcp_mssdflt) {
 725                                 /* Use the sysctl tuneable blackhole MSS. */
 726                                 tp->t_maxseg = V_tcp_pmtud_blackhole_mss;
 727                                 TCPSTAT_INC(tcps_pmtud_blackhole_activated);
 728                         } else {
 729                                 /* Use the default MSS. */
 730                                 tp->t_maxseg = V_tcp_mssdflt;
 731                                 /*
 732                                  * Disable Path MTU Discovery when we switch to
 733                                  * minmss.
 734                                  */
 735                                 tp->t_flags2 &= ~TF2_PLPMTU_PMTUD;
 736                                 TCPSTAT_INC(tcps_pmtud_blackhole_activated_min_mss);
 737                         }
 738 #endif
 739                         /*
 740                          * Reset the slow-start flight size
 741                          * as it may depend on the new MSS.
 742                          */
 743                         if (CC_ALGO(tp)->conn_init != NULL)
 744                                 CC_ALGO(tp)->conn_init(&tp->t_ccv);
 745                 } else {
 746                         /*
 747                          * If further retransmissions are still unsuccessful
 748                          * with a lowered MTU, maybe this isn't a blackhole and
 749                          * we restore the previous MSS and blackhole detection
 750                          * flags.
 751                          */
 752                         if ((tp->t_flags2 & TF2_PLPMTU_BLACKHOLE) &&
 753                             (tp->t_rxtshift >= tp->t_blackhole_exit)) {
 754                                 tp->t_flags2 |= TF2_PLPMTU_PMTUD;
 755                                 tp->t_flags2 &= ~TF2_PLPMTU_BLACKHOLE;
 756                                 tp->t_maxseg = tp->t_pmtud_saved_maxseg;
 757                                 TCPSTAT_INC(tcps_pmtud_blackhole_failed);
 758                                 /*
 759                                  * Reset the slow-start flight size as it
 760                                  * may depend on the new MSS.
 761                                  */
 762                                 if (CC_ALGO(tp)->conn_init != NULL)
 763                                         CC_ALGO(tp)->conn_init(&tp->t_ccv);
 764                         }
 765                 }
 766         }
 767
 768         /*
 769          * Disable RFC1323 and SACK if we haven't got any response to
 770          * our third SYN to work-around some broken terminal servers
 771          * (most of which have hopefully been retired) that have bad VJ
 772          * header compression code which trashes TCP segments containing
 773          * unknown-to-them TCP options.
 774          */
 775         if (tcp_rexmit_drop_options && (tp->t_state == TCPS_SYN_SENT) &&
 776             (tp->t_rxtshift == 3))
 777                 tp->t_flags &= ~(TF_REQ_SCALE|TF_REQ_TSTMP|TF_SACK_PERMIT);
 778         /*
 779          * If we backed off this far, notify the L3 protocol that we're having
 780          * connection problems.
 781          */
 782         if (tp->t_rxtshift > TCP_RTT_INVALIDATE) {
 783 #ifdef INET6
 784                 if ((inp->inp_vflag & INP_IPV6) != 0)
 785                         in6_losing(inp);
 786                 else
 787 #endif
 788                         in_losing(inp);
 789         }
 790         tp->snd_nxt = tp->snd_una;
 791         tp->snd_recover = tp->snd_max;
 792         /*
 793          * Force a segment to be sent.
 794          */
 795         tp->t_flags |= TF_ACKNOW;
 796         /*
 797          * If timing a segment in this window, stop the timer.
 798          */
 799         tp->t_rtttime = 0;
 800
 801         cc_cong_signal(tp, NULL, CC_RTO);
 802         NET_EPOCH_ENTER(et);
 803         rv = tcp_output_locked(tp);
 804         NET_EPOCH_EXIT(et);
 805         CURVNET_RESTORE();
 806
 807         return (rv);
 808 }
 809
 810 static void
 811 tcp_bblog_timer(struct tcpcb *tp, tt_which which, tt_what what, uint32_t ticks)
 812 {
 813         struct tcp_log_buffer *lgb;
 814         uint64_t ms;
 815
 816         INP_WLOCK_ASSERT(tptoinpcb(tp));
 817         if (tcp_bblogging_on(tp))
 818                 lgb = tcp_log_event(tp, NULL, NULL, NULL, TCP_LOG_RTO, 0, 0,
 819                     NULL, false, NULL, NULL, 0, NULL);
 820         else
 821                 lgb = NULL;
 822         if (lgb != NULL) {
 823                 lgb->tlb_flex1 = (what << 8) | which;
 824                 if (what == TT_STARTING) {
 825                         /* Convert ticks to ms and store it in tlb_flex2. */
 826                         if (hz == 1000)
 827                                 lgb->tlb_flex2 = ticks;
 828                         else {
 829                                 ms = (((uint64_t)ticks * 1000) + (hz - 1)) / hz;
 830                                 if (ms > UINT32_MAX)
 831                                         lgb->tlb_flex2 = UINT32_MAX;
 832                                 else
 833                                         lgb->tlb_flex2 = (uint32_t)ms;
 834                         }
 835                 }
 836         }
 837 }
 838
 839 static inline tt_which
 840 tcp_timer_next(struct tcpcb *tp, sbintime_t *precision)
 841 {
 842         tt_which i, rv;
 843         sbintime_t after, before;
 844
 845         for (i = 0, rv = TT_N, after = before = SBT_MAX; i < TT_N; i++) {
 846                 if (tp->t_timers[i] < after) {
 847                         after = tp->t_timers[i];
 848                         rv = i;
 849                 }
 850                 before = MIN(before, tp->t_timers[i] + tp->t_precisions[i]);
 851         }
 852         if (precision != NULL)
 853                 *precision = before - after;
 854
 855         return (rv);
 856 }
 857
 858 static void
 859 tcp_timer_enter(void *xtp)
 860 {
 861         struct tcpcb *tp = xtp;
 862         struct inpcb *inp = tptoinpcb(tp);
 863         sbintime_t precision;
 864         tt_which which;
 865         bool tp_valid;
 866
 867         INP_WLOCK_ASSERT(inp);
 868         MPASS((curthread->td_pflags & TDP_INTCPCALLOUT) == 0);
 869
 870         curthread->td_pflags |= TDP_INTCPCALLOUT;
 871
 872         which = tcp_timer_next(tp, NULL);
 873         MPASS(which < TT_N);
 874         tp->t_timers[which] = SBT_MAX;
 875         tp->t_precisions[which] = 0;
 876
 877         tcp_bblog_timer(tp, which, TT_PROCESSING, 0);
 878         tp_valid = tcp_timersw[which](tp);
 879         if (tp_valid) {
 880                 tcp_bblog_timer(tp, which, TT_PROCESSED, 0);
 881                 if ((which = tcp_timer_next(tp, &precision)) != TT_N) {
 882                         callout_reset_sbt_on(&tp->t_callout,
 883                             tp->t_timers[which], precision, tcp_timer_enter,
 884                             tp, inp_to_cpuid(inp), C_ABSOLUTE);
 885                 }
 886                 INP_WUNLOCK(inp);
 887         }
 888
 889         curthread->td_pflags &= ~TDP_INTCPCALLOUT;
 890 }
 891
 892 /*
 893  * Activate or stop (delta == 0) a TCP timer.
 894  */
 895 void
 896 tcp_timer_activate(struct tcpcb *tp, tt_which which, u_int delta)
 897 {
 898         struct inpcb *inp = tptoinpcb(tp);
 899         sbintime_t precision;
 900         tt_what what;
 901
 902 #ifdef TCP_OFFLOAD
 903         if (tp->t_flags & TF_TOE)
 904                 return;
 905 #endif
 906
 907         INP_WLOCK_ASSERT(inp);
 908
 909         if (delta > 0) {
 910                 what = TT_STARTING;
 911                 callout_when(tick_sbt * delta, 0, C_HARDCLOCK,
 912                     &tp->t_timers[which], &tp->t_precisions[which]);
 913         } else {
 914                 what = TT_STOPPING;
 915                 tp->t_timers[which] = SBT_MAX;
 916         }
 917         tcp_bblog_timer(tp, which, what, delta);
 918
 919         if ((which = tcp_timer_next(tp, &precision)) != TT_N)
 920                 callout_reset_sbt_on(&tp->t_callout, tp->t_timers[which],
 921                     precision, tcp_timer_enter, tp, inp_to_cpuid(inp),
 922                     C_ABSOLUTE);
 923         else
 924                 callout_stop(&tp->t_callout);
 925 }
 926
 927 bool
 928 tcp_timer_active(struct tcpcb *tp, tt_which which)
 929 {
 930
 931         INP_WLOCK_ASSERT(tptoinpcb(tp));
 932
 933         return (tp->t_timers[which] != SBT_MAX);
 934 }
 935
 936 /*
 937  * Stop all timers associated with tcpcb.
 938  *
 939  * Called only on tcpcb destruction.  The tcpcb shall already be dropped from
 940  * the pcb lookup database and socket is not losing the last reference.
 941  *
 942  * XXXGL: unfortunately our callout(9) is not able to fully stop a locked
 943  * callout even when only two threads are involved: the callout itself and the
 944  * thread that does callout_stop().  See where softclock_call_cc() swaps the
 945  * callwheel lock to callout lock and then checks cc_exec_cancel().  This is
 946  * the race window.  If it happens, the tcp_timer_enter() won't be executed,
 947  * however pcb lock will be locked and released, hence we can't free memory.
 948  * Until callout(9) is improved, just keep retrying.  In my profiling I've seen
 949  * such event happening less than 1 time per hour with 20-30 Gbit/s of traffic.
 950  */
 951 void
 952 tcp_timer_stop(struct tcpcb *tp)
 953 {
 954         struct inpcb *inp = tptoinpcb(tp);
 955
 956         INP_WLOCK_ASSERT(inp);
 957
 958         if (curthread->td_pflags & TDP_INTCPCALLOUT) {
 959                 int stopped __diagused;
 960
 961                 stopped = callout_stop(&tp->t_callout);
 962                 MPASS(stopped == 0);
 963         } else while(__predict_false(callout_stop(&tp->t_callout) == 0)) {
 964                 INP_WUNLOCK(inp);
 965                 kern_yield(PRI_UNCHANGED);
 966                 INP_WLOCK(inp);
 967         }
 968 }