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  *      @(#)tcp_timer.c 8.2 (Berkeley) 5/24/95
  32  */
  33
  34 #include <sys/cdefs.h>
  35 __FBSDID("$FreeBSD$");
  36
  37 #include "opt_inet.h"
  38 #include "opt_inet6.h"
  39 #include "opt_rss.h"
  40
  41 #include <sys/param.h>
  42 #include <sys/kernel.h>
  43 #include <sys/lock.h>
  44 #include <sys/mbuf.h>
  45 #include <sys/mutex.h>
  46 #include <sys/protosw.h>
  47 #include <sys/smp.h>
  48 #include <sys/socket.h>
  49 #include <sys/socketvar.h>
  50 #include <sys/sysctl.h>
  51 #include <sys/systm.h>
  52
  53 #include <net/if.h>
  54 #include <net/route.h>
  55 #include <net/rss_config.h>
  56 #include <net/vnet.h>
  57 #include <net/netisr.h>
  58
  59 #include <netinet/in.h>
  60 #include <netinet/in_kdtrace.h>
  61 #include <netinet/in_pcb.h>
  62 #include <netinet/in_rss.h>
  63 #include <netinet/in_systm.h>
  64 #ifdef INET6
  65 #include <netinet6/in6_pcb.h>
  66 #endif
  67 #include <netinet/ip_var.h>
  68 #include <netinet/tcp.h>
  69 #include <netinet/tcp_fsm.h>
  70 #include <netinet/tcp_log_buf.h>
  71 #include <netinet/tcp_timer.h>
  72 #include <netinet/tcp_var.h>
  73 #include <netinet/tcp_seq.h>
  74 #include <netinet/cc/cc.h>
  75 #ifdef INET6
  76 #include <netinet6/tcp6_var.h>
  77 #endif
  78 #include <netinet/tcpip.h>
  79
  80 int    tcp_persmin;
  81 SYSCTL_PROC(_net_inet_tcp, OID_AUTO, persmin,
  82     CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_NEEDGIANT,
  83     &tcp_persmin, 0, sysctl_msec_to_ticks, "I",
  84     "minimum persistence interval");
  85
  86 int    tcp_persmax;
  87 SYSCTL_PROC(_net_inet_tcp, OID_AUTO, persmax,
  88     CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_NEEDGIANT,
  89     &tcp_persmax, 0, sysctl_msec_to_ticks, "I",
  90     "maximum persistence interval");
  91
  92 int     tcp_keepinit;
  93 SYSCTL_PROC(_net_inet_tcp, TCPCTL_KEEPINIT, keepinit,
  94     CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_NEEDGIANT,
  95     &tcp_keepinit, 0, sysctl_msec_to_ticks, "I",
  96     "time to establish connection");
  97
  98 int     tcp_keepidle;
  99 SYSCTL_PROC(_net_inet_tcp, TCPCTL_KEEPIDLE, keepidle,
 100     CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_NEEDGIANT,
 101     &tcp_keepidle, 0, sysctl_msec_to_ticks, "I",
 102     "time before keepalive probes begin");
 103
 104 int     tcp_keepintvl;
 105 SYSCTL_PROC(_net_inet_tcp, TCPCTL_KEEPINTVL, keepintvl,
 106     CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_NEEDGIANT,
 107     &tcp_keepintvl, 0, sysctl_msec_to_ticks, "I",
 108     "time between keepalive probes");
 109
 110 int     tcp_delacktime;
 111 SYSCTL_PROC(_net_inet_tcp, TCPCTL_DELACKTIME, delacktime,
 112     CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_NEEDGIANT,
 113     &tcp_delacktime, 0, sysctl_msec_to_ticks, "I",
 114     "Time before a delayed ACK is sent");
 115
 116 VNET_DEFINE(int, tcp_msl);
 117 SYSCTL_PROC(_net_inet_tcp, OID_AUTO, msl,
 118     CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_VNET,
 119     &VNET_NAME(tcp_msl), 0, sysctl_msec_to_ticks, "I",
 120     "Maximum segment lifetime");
 121
 122 int     tcp_rexmit_initial;
 123 SYSCTL_PROC(_net_inet_tcp, OID_AUTO, rexmit_initial,
 124    CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_NEEDGIANT,
 125     &tcp_rexmit_initial, 0, sysctl_msec_to_ticks, "I",
 126     "Initial Retransmission Timeout");
 127
 128 int     tcp_rexmit_min;
 129 SYSCTL_PROC(_net_inet_tcp, OID_AUTO, rexmit_min,
 130     CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_NEEDGIANT,
 131     &tcp_rexmit_min, 0, sysctl_msec_to_ticks, "I",
 132     "Minimum Retransmission Timeout");
 133
 134 int     tcp_rexmit_slop;
 135 SYSCTL_PROC(_net_inet_tcp, OID_AUTO, rexmit_slop,
 136     CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_NEEDGIANT,
 137     &tcp_rexmit_slop, 0, sysctl_msec_to_ticks, "I",
 138     "Retransmission Timer Slop");
 139
 140 VNET_DEFINE(int, tcp_always_keepalive) = 1;
 141 SYSCTL_INT(_net_inet_tcp, OID_AUTO, always_keepalive, CTLFLAG_VNET|CTLFLAG_RW,
 142     &VNET_NAME(tcp_always_keepalive) , 0,
 143     "Assume SO_KEEPALIVE on all TCP connections");
 144
 145 int    tcp_fast_finwait2_recycle = 0;
 146 SYSCTL_INT(_net_inet_tcp, OID_AUTO, fast_finwait2_recycle, CTLFLAG_RW,
 147     &tcp_fast_finwait2_recycle, 0,
 148     "Recycle closed FIN_WAIT_2 connections faster");
 149
 150 int    tcp_finwait2_timeout;
 151 SYSCTL_PROC(_net_inet_tcp, OID_AUTO, finwait2_timeout,
 152     CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_NEEDGIANT,
 153     &tcp_finwait2_timeout, 0, sysctl_msec_to_ticks, "I",
 154     "FIN-WAIT2 timeout");
 155
 156 int     tcp_keepcnt = TCPTV_KEEPCNT;
 157 SYSCTL_INT(_net_inet_tcp, OID_AUTO, keepcnt, CTLFLAG_RW, &tcp_keepcnt, 0,
 158     "Number of keepalive probes to send");
 159
 160         /* max idle probes */
 161 int     tcp_maxpersistidle;
 162
 163 int     tcp_rexmit_drop_options = 0;
 164 SYSCTL_INT(_net_inet_tcp, OID_AUTO, rexmit_drop_options, CTLFLAG_RW,
 165     &tcp_rexmit_drop_options, 0,
 166     "Drop TCP options from 3rd and later retransmitted SYN");
 167
 168 int     tcp_maxunacktime = TCPTV_MAXUNACKTIME;
 169 SYSCTL_PROC(_net_inet_tcp, OID_AUTO, maxunacktime,
 170     CTLTYPE_INT|CTLFLAG_RW | CTLFLAG_NEEDGIANT,
 171     &tcp_maxunacktime, 0, sysctl_msec_to_ticks, "I",
 172     "Maximum time (in ms) that a session can linger without making progress");
 173
 174 VNET_DEFINE(int, tcp_pmtud_blackhole_detect);
 175 SYSCTL_INT(_net_inet_tcp, OID_AUTO, pmtud_blackhole_detection,
 176     CTLFLAG_RW|CTLFLAG_VNET,
 177     &VNET_NAME(tcp_pmtud_blackhole_detect), 0,
 178     "Path MTU Discovery Black Hole Detection Enabled");
 179
 180 #ifdef INET
 181 VNET_DEFINE(int, tcp_pmtud_blackhole_mss) = 1200;
 182 SYSCTL_INT(_net_inet_tcp, OID_AUTO, pmtud_blackhole_mss,
 183     CTLFLAG_RW|CTLFLAG_VNET,
 184     &VNET_NAME(tcp_pmtud_blackhole_mss), 0,
 185     "Path MTU Discovery Black Hole Detection lowered MSS");
 186 #endif
 187
 188 #ifdef INET6
 189 VNET_DEFINE(int, tcp_v6pmtud_blackhole_mss) = 1220;
 190 SYSCTL_INT(_net_inet_tcp, OID_AUTO, v6pmtud_blackhole_mss,
 191     CTLFLAG_RW|CTLFLAG_VNET,
 192     &VNET_NAME(tcp_v6pmtud_blackhole_mss), 0,
 193     "Path MTU Discovery IPv6 Black Hole Detection lowered MSS");
 194 #endif
 195
 196 #ifdef  RSS
 197 static int      per_cpu_timers = 1;
 198 #else
 199 static int      per_cpu_timers = 0;
 200 #endif
 201 SYSCTL_INT(_net_inet_tcp, OID_AUTO, per_cpu_timers, CTLFLAG_RW,
 202     &per_cpu_timers , 0, "run tcp timers on all cpus");
 203
 204 /*
 205  * Map the given inp to a CPU id.
 206  *
 207  * This queries RSS if it's compiled in, else it defaults to the current
 208  * CPU ID.
 209  */
 210 inline int
 211 inp_to_cpuid(struct inpcb *inp)
 212 {
 213         u_int cpuid;
 214
 215         if (per_cpu_timers) {
 216 #ifdef  RSS
 217                 cpuid = rss_hash2cpuid(inp->inp_flowid, inp->inp_flowtype);
 218                 if (cpuid == NETISR_CPUID_NONE)
 219                         return (curcpu);        /* XXX */
 220                 else
 221                         return (cpuid);
 222 #endif
 223                 /*
 224                  * We don't have a flowid -> cpuid mapping, so cheat and
 225                  * just map unknown cpuids to curcpu.  Not the best, but
 226                  * apparently better than defaulting to swi 0.
 227                  */
 228                 cpuid = inp->inp_flowid % (mp_maxid + 1);
 229                 if (! CPU_ABSENT(cpuid))
 230                         return (cpuid);
 231                 return (curcpu);
 232         } else {
 233                 return (0);
 234         }
 235 }
 236
 237 int     tcp_backoff[TCP_MAXRXTSHIFT + 1] =
 238     { 1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 512, 512, 512 };
 239
 240 int tcp_totbackoff = 2559;      /* sum of tcp_backoff[] */
 241
 242 /*
 243  * TCP timer processing.
 244  *
 245  * Each connection has 5 timers associated with it, which can be scheduled
 246  * simultaneously.  They all are serviced by one callout tcp_timer_enter().
 247  * This function executes the next timer via tcp_timersw[] vector.  Each
 248  * timer is supposed to return 'true' unless the connection was destroyed.
 249  * In the former case tcp_timer_enter() will schedule callout for next timer.
 250  */
 251
 252 typedef bool tcp_timer_t(struct tcpcb *);
 253 static tcp_timer_t tcp_timer_delack;
 254 static tcp_timer_t tcp_timer_2msl;
 255 static tcp_timer_t tcp_timer_keep;
 256 static tcp_timer_t tcp_timer_persist;
 257 static tcp_timer_t tcp_timer_rexmt;
 258
 259 static tcp_timer_t * const tcp_timersw[TT_N] = {
 260         [TT_DELACK] = tcp_timer_delack,
 261         [TT_REXMT] = tcp_timer_rexmt,
 262         [TT_PERSIST] = tcp_timer_persist,
 263         [TT_KEEP] = tcp_timer_keep,
 264         [TT_2MSL] = tcp_timer_2msl,
 265 };
 266
 267 /*
 268  * tcp_output_locked() s a timer specific variation of call to tcp_output(),
 269  * see tcp_var.h for the rest.  It handles drop request from advanced stacks,
 270  * but keeps tcpcb locked unless tcp_drop() destroyed it.
 271  * Returns true if tcpcb is valid and locked.
 272  */
 273 static inline bool
 274 tcp_output_locked(struct tcpcb *tp)
 275 {
 276         int rv;
 277
 278         INP_WLOCK_ASSERT(tptoinpcb(tp));
 279
 280         if ((rv = tp->t_fb->tfb_tcp_output(tp)) < 0) {
 281                 KASSERT(tp->t_fb->tfb_flags & TCP_FUNC_OUTPUT_CANDROP,
 282                     ("TCP stack %s requested tcp_drop(%p)",
 283                     tp->t_fb->tfb_tcp_block_name, tp));
 284                 tp = tcp_drop(tp, rv);
 285         }
 286
 287         return (tp != NULL);
 288 }
 289
 290 static bool
 291 tcp_timer_delack(struct tcpcb *tp)
 292 {
 293         struct epoch_tracker et;
 294 #if defined(INVARIANTS) || defined(VIMAGE)
 295         struct inpcb *inp = tptoinpcb(tp);
 296 #endif
 297         bool rv;
 298
 299         INP_WLOCK_ASSERT(inp);
 300
 301         CURVNET_SET(inp->inp_vnet);
 302         tp->t_flags |= TF_ACKNOW;
 303         TCPSTAT_INC(tcps_delack);
 304         NET_EPOCH_ENTER(et);
 305         rv = tcp_output_locked(tp);
 306         NET_EPOCH_EXIT(et);
 307         CURVNET_RESTORE();
 308
 309         return (rv);
 310 }
 311
 312 static bool
 313 tcp_timer_2msl(struct tcpcb *tp)
 314 {
 315         struct inpcb *inp = tptoinpcb(tp);
 316         bool close = false;
 317
 318         INP_WLOCK_ASSERT(inp);
 319
 320         TCP_PROBE2(debug__user, tp, PRU_SLOWTIMO);
 321         CURVNET_SET(inp->inp_vnet);
 322         tcp_log_end_status(tp, TCP_EI_STATUS_2MSL);
 323         tcp_free_sackholes(tp);
 324         /*
 325          * 2 MSL timeout in shutdown went off.  If we're closed but
 326          * still waiting for peer to close and connection has been idle
 327          * too long delete connection control block.  Otherwise, check
 328          * again in a bit.
 329          *
 330          * If fastrecycle of FIN_WAIT_2, in FIN_WAIT_2 and receiver has closed,
 331          * there's no point in hanging onto FIN_WAIT_2 socket. Just close it.
 332          * Ignore fact that there were recent incoming segments.
 333          *
 334          * XXXGL: check if inp_socket shall always be !NULL here?
 335          */
 336         if (tp->t_state == TCPS_TIME_WAIT) {
 337                 close = true;
 338         } else if (tp->t_state == TCPS_FIN_WAIT_2 &&
 339             tcp_fast_finwait2_recycle && inp->inp_socket &&
 340             (inp->inp_socket->so_rcv.sb_state & SBS_CANTRCVMORE)) {
 341                 TCPSTAT_INC(tcps_finwait2_drops);
 342                 close = true;
 343         } else {
 344                 if (ticks - tp->t_rcvtime <= TP_MAXIDLE(tp))
 345                         tcp_timer_activate(tp, TT_2MSL, TP_KEEPINTVL(tp));
 346                 else
 347                         close = true;
 348         }
 349         if (close) {
 350                 struct epoch_tracker et;
 351
 352                 NET_EPOCH_ENTER(et);
 353                 tp = tcp_close(tp);
 354                 NET_EPOCH_EXIT(et);
 355         }
 356         CURVNET_RESTORE();
 357
 358         return (tp != NULL);
 359 }
 360
 361 static bool
 362 tcp_timer_keep(struct tcpcb *tp)
 363 {
 364         struct epoch_tracker et;
 365         struct inpcb *inp = tptoinpcb(tp);
 366         struct tcptemp *t_template;
 367
 368         INP_WLOCK_ASSERT(inp);
 369
 370         TCP_PROBE2(debug__user, tp, PRU_SLOWTIMO);
 371         CURVNET_SET(inp->inp_vnet);
 372         /*
 373          * Because we don't regularly reset the keepalive callout in
 374          * the ESTABLISHED state, it may be that we don't actually need
 375          * to send a keepalive yet. If that occurs, schedule another
 376          * call for the next time the keepalive timer might expire.
 377          */
 378         if (TCPS_HAVEESTABLISHED(tp->t_state)) {
 379                 u_int idletime;
 380
 381                 idletime = ticks - tp->t_rcvtime;
 382                 if (idletime < TP_KEEPIDLE(tp)) {
 383                         tcp_timer_activate(tp, TT_KEEP,
 384                             TP_KEEPIDLE(tp) - idletime);
 385                         CURVNET_RESTORE();
 386                         return (true);
 387                 }
 388         }
 389
 390         /*
 391          * Keep-alive timer went off; send something
 392          * or drop connection if idle for too long.
 393          */
 394         TCPSTAT_INC(tcps_keeptimeo);
 395         if (tp->t_state < TCPS_ESTABLISHED)
 396                 goto dropit;
 397         if ((V_tcp_always_keepalive ||
 398             inp->inp_socket->so_options & SO_KEEPALIVE) &&
 399             tp->t_state <= TCPS_CLOSING) {
 400                 if (ticks - tp->t_rcvtime >= TP_KEEPIDLE(tp) + TP_MAXIDLE(tp))
 401                         goto dropit;
 402                 /*
 403                  * Send a packet designed to force a response
 404                  * if the peer is up and reachable:
 405                  * either an ACK if the connection is still alive,
 406                  * or an RST if the peer has closed the connection
 407                  * due to timeout or reboot.
 408                  * Using sequence number tp->snd_una-1
 409                  * causes the transmitted zero-length segment
 410                  * to lie outside the receive window;
 411                  * by the protocol spec, this requires the
 412                  * correspondent TCP to respond.
 413                  */
 414                 TCPSTAT_INC(tcps_keepprobe);
 415                 t_template = tcpip_maketemplate(inp);
 416                 if (t_template) {
 417                         NET_EPOCH_ENTER(et);
 418                         tcp_respond(tp, t_template->tt_ipgen,
 419                                     &t_template->tt_t, (struct mbuf *)NULL,
 420                                     tp->rcv_nxt, tp->snd_una - 1, 0);
 421                         NET_EPOCH_EXIT(et);
 422                         free(t_template, M_TEMP);
 423                 }
 424                 tcp_timer_activate(tp, TT_KEEP, TP_KEEPINTVL(tp));
 425         } else
 426                 tcp_timer_activate(tp, TT_KEEP, TP_KEEPIDLE(tp));
 427
 428         CURVNET_RESTORE();
 429         return (true);
 430
 431 dropit:
 432         TCPSTAT_INC(tcps_keepdrops);
 433         NET_EPOCH_ENTER(et);
 434         tcp_log_end_status(tp, TCP_EI_STATUS_KEEP_MAX);
 435         tp = tcp_drop(tp, ETIMEDOUT);
 436         NET_EPOCH_EXIT(et);
 437         CURVNET_RESTORE();
 438
 439         return (tp != NULL);
 440 }
 441
 442 /*
 443  * Has this session exceeded the maximum time without seeing a substantive
 444  * acknowledgement? If so, return true; otherwise false.
 445  */
 446 static bool
 447 tcp_maxunacktime_check(struct tcpcb *tp)
 448 {
 449
 450         /* Are we tracking this timer for this session? */
 451         if (TP_MAXUNACKTIME(tp) == 0)
 452                 return false;
 453
 454         /* Do we have a current measurement. */
 455         if (tp->t_acktime == 0)
 456                 return false;
 457
 458         /* Are we within the acceptable range? */
 459         if (TSTMP_GT(TP_MAXUNACKTIME(tp) + tp->t_acktime, (u_int)ticks))
 460                 return false;
 461
 462         /* We exceeded the timer. */
 463         TCPSTAT_INC(tcps_progdrops);
 464         return true;
 465 }
 466
 467 static bool
 468 tcp_timer_persist(struct tcpcb *tp)
 469 {
 470         struct epoch_tracker et;
 471 #if defined(INVARIANTS) || defined(VIMAGE)
 472         struct inpcb *inp = tptoinpcb(tp);
 473 #endif
 474         bool progdrop, rv;
 475
 476         INP_WLOCK_ASSERT(inp);
 477
 478         TCP_PROBE2(debug__user, tp, PRU_SLOWTIMO);
 479         CURVNET_SET(inp->inp_vnet);
 480         /*
 481          * Persistence timer into zero window.
 482          * Force a byte to be output, if possible.
 483          */
 484         TCPSTAT_INC(tcps_persisttimeo);
 485         /*
 486          * Hack: if the peer is dead/unreachable, we do not
 487          * time out if the window is closed.  After a full
 488          * backoff, drop the connection if the idle time
 489          * (no responses to probes) reaches the maximum
 490          * backoff that we would use if retransmitting.
 491          * Also, drop the connection if we haven't been making
 492          * progress.
 493          */
 494         progdrop = tcp_maxunacktime_check(tp);
 495         if (progdrop || (tp->t_rxtshift == TCP_MAXRXTSHIFT &&
 496             (ticks - tp->t_rcvtime >= tcp_maxpersistidle ||
 497              ticks - tp->t_rcvtime >= TCP_REXMTVAL(tp) * tcp_totbackoff))) {
 498                 if (!progdrop)
 499                         TCPSTAT_INC(tcps_persistdrop);
 500                 tcp_log_end_status(tp, TCP_EI_STATUS_PERSIST_MAX);
 501                 goto dropit;
 502         }
 503         /*
 504          * If the user has closed the socket then drop a persisting
 505          * connection after a much reduced timeout.
 506          */
 507         if (tp->t_state > TCPS_CLOSE_WAIT &&
 508             (ticks - tp->t_rcvtime) >= TCPTV_PERSMAX) {
 509                 TCPSTAT_INC(tcps_persistdrop);
 510                 tcp_log_end_status(tp, TCP_EI_STATUS_PERSIST_MAX);
 511                 goto dropit;
 512         }
 513         tcp_setpersist(tp);
 514         tp->t_flags |= TF_FORCEDATA;
 515         NET_EPOCH_ENTER(et);
 516         if ((rv = tcp_output_locked(tp)))
 517                 tp->t_flags &= ~TF_FORCEDATA;
 518         NET_EPOCH_EXIT(et);
 519         CURVNET_RESTORE();
 520
 521         return (rv);
 522
 523 dropit:
 524         NET_EPOCH_ENTER(et);
 525         tp = tcp_drop(tp, ETIMEDOUT);
 526         NET_EPOCH_EXIT(et);
 527         CURVNET_RESTORE();
 528
 529         return (tp != NULL);
 530 }
 531
 532 static bool
 533 tcp_timer_rexmt(struct tcpcb *tp)
 534 {
 535         struct epoch_tracker et;
 536         struct inpcb *inp = tptoinpcb(tp);
 537         int rexmt;
 538         bool isipv6, rv;
 539
 540         INP_WLOCK_ASSERT(inp);
 541
 542         TCP_PROBE2(debug__user, tp, PRU_SLOWTIMO);
 543         CURVNET_SET(inp->inp_vnet);
 544         tcp_free_sackholes(tp);
 545         TCP_LOG_EVENT(tp, NULL, NULL, NULL, TCP_LOG_RTO, 0, 0, NULL, false);
 546         if (tp->t_fb->tfb_tcp_rexmit_tmr) {
 547                 /* The stack has a timer action too. */
 548                 (*tp->t_fb->tfb_tcp_rexmit_tmr)(tp);
 549         }
 550         /*
 551          * Retransmission timer went off.  Message has not
 552          * been acked within retransmit interval.  Back off
 553          * to a longer retransmit interval and retransmit one segment.
 554          *
 555          * If we've either exceeded the maximum number of retransmissions,
 556          * or we've gone long enough without making progress, then drop
 557          * the session.
 558          */
 559         if (++tp->t_rxtshift > TCP_MAXRXTSHIFT || tcp_maxunacktime_check(tp)) {
 560                 if (tp->t_rxtshift > TCP_MAXRXTSHIFT)
 561                         TCPSTAT_INC(tcps_timeoutdrop);
 562                 tp->t_rxtshift = TCP_MAXRXTSHIFT;
 563                 tcp_log_end_status(tp, TCP_EI_STATUS_RETRAN);
 564                 NET_EPOCH_ENTER(et);
 565                 tp = tcp_drop(tp, ETIMEDOUT);
 566                 NET_EPOCH_EXIT(et);
 567                 CURVNET_RESTORE();
 568
 569                 return (tp != NULL);
 570         }
 571         if (tp->t_state == TCPS_SYN_SENT) {
 572                 /*
 573                  * If the SYN was retransmitted, indicate CWND to be
 574                  * limited to 1 segment in cc_conn_init().
 575                  */
 576                 tp->snd_cwnd = 1;
 577         } else if (tp->t_rxtshift == 1) {
 578                 /*
 579                  * first retransmit; record ssthresh and cwnd so they can
 580                  * be recovered if this turns out to be a "bad" retransmit.
 581                  * A retransmit is considered "bad" if an ACK for this
 582                  * segment is received within RTT/2 interval; the assumption
 583                  * here is that the ACK was already in flight.  See
 584                  * "On Estimating End-to-End Network Path Properties" by
 585                  * Allman and Paxson for more details.
 586                  */
 587                 tp->snd_cwnd_prev = tp->snd_cwnd;
 588                 tp->snd_ssthresh_prev = tp->snd_ssthresh;
 589                 tp->snd_recover_prev = tp->snd_recover;
 590                 if (IN_FASTRECOVERY(tp->t_flags))
 591                         tp->t_flags |= TF_WASFRECOVERY;
 592                 else
 593                         tp->t_flags &= ~TF_WASFRECOVERY;
 594                 if (IN_CONGRECOVERY(tp->t_flags))
 595                         tp->t_flags |= TF_WASCRECOVERY;
 596                 else
 597                         tp->t_flags &= ~TF_WASCRECOVERY;
 598                 if ((tp->t_flags & TF_RCVD_TSTMP) == 0)
 599                         tp->t_badrxtwin = ticks + (tp->t_srtt >> (TCP_RTT_SHIFT + 1));
 600                 /* In the event that we've negotiated timestamps
 601                  * badrxtwin will be set to the value that we set
 602                  * the retransmitted packet's to_tsval to by tcp_output
 603                  */
 604                 tp->t_flags |= TF_PREVVALID;
 605         } else
 606                 tp->t_flags &= ~TF_PREVVALID;
 607         TCPSTAT_INC(tcps_rexmttimeo);
 608         if ((tp->t_state == TCPS_SYN_SENT) ||
 609             (tp->t_state == TCPS_SYN_RECEIVED))
 610                 rexmt = tcp_rexmit_initial * tcp_backoff[tp->t_rxtshift];
 611         else
 612                 rexmt = TCP_REXMTVAL(tp) * tcp_backoff[tp->t_rxtshift];
 613         TCPT_RANGESET(tp->t_rxtcur, rexmt,
 614                       tp->t_rttmin, TCPTV_REXMTMAX);
 615
 616         /*
 617          * We enter the path for PLMTUD if connection is established or, if
 618          * connection is FIN_WAIT_1 status, reason for the last is that if
 619          * amount of data we send is very small, we could send it in couple of
 620          * packets and process straight to FIN. In that case we won't catch
 621          * ESTABLISHED state.
 622          */
 623 #ifdef INET6
 624         isipv6 = (inp->inp_vflag & INP_IPV6) ? true : false;
 625 #else
 626         isipv6 = false;
 627 #endif
 628         if (((V_tcp_pmtud_blackhole_detect == 1) ||
 629             (V_tcp_pmtud_blackhole_detect == 2 && !isipv6) ||
 630             (V_tcp_pmtud_blackhole_detect == 3 && isipv6)) &&
 631             ((tp->t_state == TCPS_ESTABLISHED) ||
 632             (tp->t_state == TCPS_FIN_WAIT_1))) {
 633                 if (tp->t_rxtshift == 1) {
 634                         /*
 635                          * We enter blackhole detection after the first
 636                          * unsuccessful timer based retransmission.
 637                          * Then we reduce up to two times the MSS, each
 638                          * candidate giving two tries of retransmissions.
 639                          * But we give a candidate only two tries, if it
 640                          * actually reduces the MSS.
 641                          */
 642                         tp->t_blackhole_enter = 2;
 643                         tp->t_blackhole_exit = tp->t_blackhole_enter;
 644                         if (isipv6) {
 645 #ifdef INET6
 646                                 if (tp->t_maxseg > V_tcp_v6pmtud_blackhole_mss)
 647                                         tp->t_blackhole_exit += 2;
 648                                 if (tp->t_maxseg > V_tcp_v6mssdflt &&
 649                                     V_tcp_v6pmtud_blackhole_mss > V_tcp_v6mssdflt)
 650                                         tp->t_blackhole_exit += 2;
 651 #endif
 652                         } else {
 653 #ifdef INET
 654                                 if (tp->t_maxseg > V_tcp_pmtud_blackhole_mss)
 655                                         tp->t_blackhole_exit += 2;
 656                                 if (tp->t_maxseg > V_tcp_mssdflt &&
 657                                     V_tcp_pmtud_blackhole_mss > V_tcp_mssdflt)
 658                                         tp->t_blackhole_exit += 2;
 659 #endif
 660                         }
 661                 }
 662                 if (((tp->t_flags2 & (TF2_PLPMTU_PMTUD|TF2_PLPMTU_MAXSEGSNT)) ==
 663                     (TF2_PLPMTU_PMTUD|TF2_PLPMTU_MAXSEGSNT)) &&
 664                     (tp->t_rxtshift >= tp->t_blackhole_enter &&
 665                     tp->t_rxtshift < tp->t_blackhole_exit &&
 666                     (tp->t_rxtshift - tp->t_blackhole_enter) % 2 == 0)) {
 667                         /*
 668                          * Enter Path MTU Black-hole Detection mechanism:
 669                          * - Disable Path MTU Discovery (IP "DF" bit).
 670                          * - Reduce MTU to lower value than what we
 671                          *   negotiated with peer.
 672                          */
 673                         if ((tp->t_flags2 & TF2_PLPMTU_BLACKHOLE) == 0) {
 674                                 /* Record that we may have found a black hole. */
 675                                 tp->t_flags2 |= TF2_PLPMTU_BLACKHOLE;
 676                                 /* Keep track of previous MSS. */
 677                                 tp->t_pmtud_saved_maxseg = tp->t_maxseg;
 678                         }
 679
 680                         /*
 681                          * Reduce the MSS to blackhole value or to the default
 682                          * in an attempt to retransmit.
 683                          */
 684 #ifdef INET6
 685                         if (isipv6 &&
 686                             tp->t_maxseg > V_tcp_v6pmtud_blackhole_mss &&
 687                             V_tcp_v6pmtud_blackhole_mss > V_tcp_v6mssdflt) {
 688                                 /* Use the sysctl tuneable blackhole MSS. */
 689                                 tp->t_maxseg = V_tcp_v6pmtud_blackhole_mss;
 690                                 TCPSTAT_INC(tcps_pmtud_blackhole_activated);
 691                         } else if (isipv6) {
 692                                 /* Use the default MSS. */
 693                                 tp->t_maxseg = V_tcp_v6mssdflt;
 694                                 /*
 695                                  * Disable Path MTU Discovery when we switch to
 696                                  * minmss.
 697                                  */
 698                                 tp->t_flags2 &= ~TF2_PLPMTU_PMTUD;
 699                                 TCPSTAT_INC(tcps_pmtud_blackhole_activated_min_mss);
 700                         }
 701 #endif
 702 #if defined(INET6) && defined(INET)
 703                         else
 704 #endif
 705 #ifdef INET
 706                         if (tp->t_maxseg > V_tcp_pmtud_blackhole_mss &&
 707                             V_tcp_pmtud_blackhole_mss > V_tcp_mssdflt) {
 708                                 /* Use the sysctl tuneable blackhole MSS. */
 709                                 tp->t_maxseg = V_tcp_pmtud_blackhole_mss;
 710                                 TCPSTAT_INC(tcps_pmtud_blackhole_activated);
 711                         } else {
 712                                 /* Use the default MSS. */
 713                                 tp->t_maxseg = V_tcp_mssdflt;
 714                                 /*
 715                                  * Disable Path MTU Discovery when we switch to
 716                                  * minmss.
 717                                  */
 718                                 tp->t_flags2 &= ~TF2_PLPMTU_PMTUD;
 719                                 TCPSTAT_INC(tcps_pmtud_blackhole_activated_min_mss);
 720                         }
 721 #endif
 722                         /*
 723                          * Reset the slow-start flight size
 724                          * as it may depend on the new MSS.
 725                          */
 726                         if (CC_ALGO(tp)->conn_init != NULL)
 727                                 CC_ALGO(tp)->conn_init(&tp->t_ccv);
 728                 } else {
 729                         /*
 730                          * If further retransmissions are still unsuccessful
 731                          * with a lowered MTU, maybe this isn't a blackhole and
 732                          * we restore the previous MSS and blackhole detection
 733                          * flags.
 734                          */
 735                         if ((tp->t_flags2 & TF2_PLPMTU_BLACKHOLE) &&
 736                             (tp->t_rxtshift >= tp->t_blackhole_exit)) {
 737                                 tp->t_flags2 |= TF2_PLPMTU_PMTUD;
 738                                 tp->t_flags2 &= ~TF2_PLPMTU_BLACKHOLE;
 739                                 tp->t_maxseg = tp->t_pmtud_saved_maxseg;
 740                                 TCPSTAT_INC(tcps_pmtud_blackhole_failed);
 741                                 /*
 742                                  * Reset the slow-start flight size as it
 743                                  * may depend on the new MSS.
 744                                  */
 745                                 if (CC_ALGO(tp)->conn_init != NULL)
 746                                         CC_ALGO(tp)->conn_init(&tp->t_ccv);
 747                         }
 748                 }
 749         }
 750
 751         /*
 752          * Disable RFC1323 and SACK if we haven't got any response to
 753          * our third SYN to work-around some broken terminal servers
 754          * (most of which have hopefully been retired) that have bad VJ
 755          * header compression code which trashes TCP segments containing
 756          * unknown-to-them TCP options.
 757          */
 758         if (tcp_rexmit_drop_options && (tp->t_state == TCPS_SYN_SENT) &&
 759             (tp->t_rxtshift == 3))
 760                 tp->t_flags &= ~(TF_REQ_SCALE|TF_REQ_TSTMP|TF_SACK_PERMIT);
 761         /*
 762          * If we backed off this far, notify the L3 protocol that we're having
 763          * connection problems.
 764          */
 765         if (tp->t_rxtshift > TCP_RTT_INVALIDATE) {
 766 #ifdef INET6
 767                 if ((inp->inp_vflag & INP_IPV6) != 0)
 768                         in6_losing(inp);
 769                 else
 770 #endif
 771                         in_losing(inp);
 772         }
 773         tp->snd_nxt = tp->snd_una;
 774         tp->snd_recover = tp->snd_max;
 775         /*
 776          * Force a segment to be sent.
 777          */
 778         tp->t_flags |= TF_ACKNOW;
 779         /*
 780          * If timing a segment in this window, stop the timer.
 781          */
 782         tp->t_rtttime = 0;
 783
 784         cc_cong_signal(tp, NULL, CC_RTO);
 785         NET_EPOCH_ENTER(et);
 786         rv = tcp_output_locked(tp);
 787         NET_EPOCH_EXIT(et);
 788         CURVNET_RESTORE();
 789
 790         return (rv);
 791 }
 792
 793 static inline tt_which
 794 tcp_timer_next(struct tcpcb *tp, sbintime_t *precision)
 795 {
 796         tt_which i, rv;
 797         sbintime_t after, before;
 798
 799         for (i = 0, rv = TT_N, after = before = SBT_MAX; i < TT_N; i++) {
 800                 if (tp->t_timers[i] < after) {
 801                         after = tp->t_timers[i];
 802                         rv = i;
 803                 }
 804                 before = MIN(before, tp->t_timers[i] + tp->t_precisions[i]);
 805         }
 806         if (precision != NULL)
 807                 *precision = before - after;
 808
 809         return (rv);
 810 }
 811
 812 static void
 813 tcp_timer_enter(void *xtp)
 814 {
 815         struct tcpcb *tp = xtp;
 816         struct inpcb *inp = tptoinpcb(tp);
 817         sbintime_t precision;
 818         tt_which which;
 819
 820         INP_WLOCK_ASSERT(inp);
 821         MPASS((curthread->td_pflags & TDP_INTCPCALLOUT) == 0);
 822
 823         curthread->td_pflags |= TDP_INTCPCALLOUT;
 824
 825         which = tcp_timer_next(tp, NULL);
 826         MPASS(which < TT_N);
 827         tp->t_timers[which] = SBT_MAX;
 828         tp->t_precisions[which] = 0;
 829
 830         if (tcp_timersw[which](tp)) {
 831                 if ((which = tcp_timer_next(tp, &precision)) != TT_N) {
 832                         callout_reset_sbt_on(&tp->t_callout,
 833                             tp->t_timers[which], precision, tcp_timer_enter,
 834                             tp, inp_to_cpuid(inp), C_ABSOLUTE);
 835                 }
 836                 INP_WUNLOCK(inp);
 837         }
 838
 839         curthread->td_pflags &= ~TDP_INTCPCALLOUT;
 840 }
 841
 842 /*
 843  * Activate or stop (delta == 0) a TCP timer.
 844  */
 845 void
 846 tcp_timer_activate(struct tcpcb *tp, tt_which which, u_int delta)
 847 {
 848         struct inpcb *inp = tptoinpcb(tp);
 849         sbintime_t precision;
 850
 851 #ifdef TCP_OFFLOAD
 852         if (tp->t_flags & TF_TOE)
 853                 return;
 854 #endif
 855
 856         INP_WLOCK_ASSERT(inp);
 857
 858         if (delta > 0)
 859                 callout_when(tick_sbt * delta, 0, C_HARDCLOCK,
 860                     &tp->t_timers[which], &tp->t_precisions[which]);
 861         else
 862                 tp->t_timers[which] = SBT_MAX;
 863
 864         if ((which = tcp_timer_next(tp, &precision)) != TT_N)
 865                 callout_reset_sbt_on(&tp->t_callout, tp->t_timers[which],
 866                     precision, tcp_timer_enter, tp, inp_to_cpuid(inp),
 867                     C_ABSOLUTE);
 868         else
 869                 callout_stop(&tp->t_callout);
 870 }
 871
 872 bool
 873 tcp_timer_active(struct tcpcb *tp, tt_which which)
 874 {
 875
 876         INP_WLOCK_ASSERT(tptoinpcb(tp));
 877
 878         return (tp->t_timers[which] != SBT_MAX);
 879 }
 880
 881 /*
 882  * Stop all timers associated with tcpcb.
 883  *
 884  * Called only on tcpcb destruction.  The tcpcb shall already be dropped from
 885  * the pcb lookup database and socket is not losing the last reference.
 886  *
 887  * XXXGL: unfortunately our callout(9) is not able to fully stop a locked
 888  * callout even when only two threads are involved: the callout itself and the
 889  * thread that does callout_stop().  See where softclock_call_cc() swaps the
 890  * callwheel lock to callout lock and then checks cc_exec_cancel().  This is
 891  * the race window.  If it happens, the tcp_timer_enter() won't be executed,
 892  * however pcb lock will be locked and released, hence we can't free memory.
 893  * Until callout(9) is improved, just keep retrying.  In my profiling I've seen
 894  * such event happening less than 1 time per hour with 20-30 Gbit/s of traffic.
 895  */
 896 void
 897 tcp_timer_stop(struct tcpcb *tp)
 898 {
 899         struct inpcb *inp = tptoinpcb(tp);
 900
 901         INP_WLOCK_ASSERT(inp);
 902
 903         if (curthread->td_pflags & TDP_INTCPCALLOUT) {
 904                 int stopped __diagused;
 905
 906                 stopped = callout_stop(&tp->t_callout);
 907                 MPASS(stopped == 0);
 908         } else while(__predict_false(callout_stop(&tp->t_callout) == 0)) {
 909                 INP_WUNLOCK(inp);
 910                 kern_yield(PRI_UNCHANGED);
 911                 INP_WLOCK(inp);
 912         }
 913 }