sys/netinet/tcp_reass.c

   1 /*-
   2  * SPDX-License-Identifier: BSD-3-Clause
   3  *
   4  * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1994, 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_input.c 8.12 (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_tcpdebug.h"
  40
  41 /* For debugging we want counters and BB logging */
  42 /* #define TCP_REASS_COUNTERS 1 */
  43 /* #define TCP_REASS_LOGGING 1 */
  44
  45 #include <sys/param.h>
  46 #include <sys/kernel.h>
  47 #include <sys/eventhandler.h>
  48 #include <sys/malloc.h>
  49 #include <sys/mbuf.h>
  50 #include <sys/socket.h>
  51 #include <sys/socketvar.h>
  52 #include <sys/sysctl.h>
  53 #include <sys/syslog.h>
  54 #include <sys/systm.h>
  55
  56 #include <vm/uma.h>
  57
  58 #include <net/if.h>
  59 #include <net/if_var.h>
  60 #include <net/route.h>
  61 #include <net/vnet.h>
  62
  63 #include <netinet/in.h>
  64 #include <netinet/in_pcb.h>
  65 #include <netinet/in_systm.h>
  66 #include <netinet/in_var.h>
  67 #include <netinet/ip.h>
  68 #include <netinet/ip_var.h>
  69 #include <netinet/ip_options.h>
  70 #include <netinet/ip6.h>
  71 #include <netinet6/in6_pcb.h>
  72 #include <netinet6/ip6_var.h>
  73 #include <netinet6/nd6.h>
  74 #include <netinet/tcp.h>
  75 #include <netinet/tcp_fsm.h>
  76 #include <netinet/tcp_seq.h>
  77 #include <netinet/tcp_timer.h>
  78 #include <netinet/tcp_var.h>
  79 #ifdef TCP_REASS_LOGGING
  80 #include <netinet/tcp_log_buf.h>
  81 #include <netinet/tcp_hpts.h>
  82 #endif
  83 #include <netinet6/tcp6_var.h>
  84 #include <netinet/tcpip.h>
  85 #ifdef TCPDEBUG
  86 #include <netinet/tcp_debug.h>
  87 #endif /* TCPDEBUG */
  88
  89 #define TCP_R_LOG_ADD           1
  90 #define TCP_R_LOG_LIMIT_REACHED 2
  91 #define TCP_R_LOG_APPEND        3
  92 #define TCP_R_LOG_PREPEND       4
  93 #define TCP_R_LOG_REPLACE       5
  94 #define TCP_R_LOG_MERGE_INTO    6
  95 #define TCP_R_LOG_NEW_ENTRY     7
  96 #define TCP_R_LOG_READ          8
  97 #define TCP_R_LOG_ZERO          9
  98 #define TCP_R_LOG_DUMP          10
  99 #define TCP_R_LOG_TRIM          11
 100
 101 static SYSCTL_NODE(_net_inet_tcp, OID_AUTO, reass,
 102     CTLFLAG_RW | CTLFLAG_MPSAFE, 0,
 103     "TCP Segment Reassembly Queue");
 104
 105 static SYSCTL_NODE(_net_inet_tcp_reass, OID_AUTO, stats,
 106     CTLFLAG_RW | CTLFLAG_MPSAFE, 0,
 107     "TCP Segment Reassembly stats");
 108
 109 static int tcp_reass_maxseg = 0;
 110 SYSCTL_INT(_net_inet_tcp_reass, OID_AUTO, maxsegments, CTLFLAG_RDTUN,
 111     &tcp_reass_maxseg, 0,
 112     "Global maximum number of TCP Segments in Reassembly Queue");
 113
 114 static uma_zone_t tcp_reass_zone;
 115 SYSCTL_UMA_CUR(_net_inet_tcp_reass, OID_AUTO, cursegments, 0,
 116     &tcp_reass_zone,
 117     "Global number of TCP Segments currently in Reassembly Queue");
 118
 119 static u_int tcp_reass_maxqueuelen = 100;
 120 SYSCTL_UINT(_net_inet_tcp_reass, OID_AUTO, maxqueuelen, CTLFLAG_RWTUN,
 121     &tcp_reass_maxqueuelen, 0,
 122     "Maximum number of TCP Segments per Reassembly Queue");
 123
 124 static int tcp_new_limits = 0;
 125 SYSCTL_INT(_net_inet_tcp_reass, OID_AUTO, new_limit, CTLFLAG_RWTUN,
 126     &tcp_new_limits, 0,
 127     "Do we use the new limit method we are discussing?");
 128
 129 static u_int tcp_reass_queue_guard = 16;
 130 SYSCTL_UINT(_net_inet_tcp_reass, OID_AUTO, queueguard, CTLFLAG_RWTUN,
 131     &tcp_reass_queue_guard, 16,
 132     "Number of TCP Segments in Reassembly Queue where we flip over to guard mode");
 133
 134 #ifdef TCP_REASS_COUNTERS
 135
 136 counter_u64_t reass_entry;
 137 SYSCTL_COUNTER_U64(_net_inet_tcp_reass_stats, OID_AUTO, entry, CTLFLAG_RD,
 138     &reass_entry, "A segment entered reassembly ");
 139
 140 counter_u64_t reass_path1;
 141 SYSCTL_COUNTER_U64(_net_inet_tcp_reass_stats, OID_AUTO, path1, CTLFLAG_RD,
 142     &reass_path1, "Took path 1");
 143
 144 counter_u64_t reass_path2;
 145 SYSCTL_COUNTER_U64(_net_inet_tcp_reass_stats, OID_AUTO, path2, CTLFLAG_RD,
 146     &reass_path2, "Took path 2");
 147
 148 counter_u64_t reass_path3;
 149 SYSCTL_COUNTER_U64(_net_inet_tcp_reass_stats, OID_AUTO, path3, CTLFLAG_RD,
 150     &reass_path3, "Took path 3");
 151
 152 counter_u64_t reass_path4;
 153 SYSCTL_COUNTER_U64(_net_inet_tcp_reass_stats, OID_AUTO, path4, CTLFLAG_RD,
 154     &reass_path4, "Took path 4");
 155
 156 counter_u64_t reass_path5;
 157 SYSCTL_COUNTER_U64(_net_inet_tcp_reass_stats, OID_AUTO, path5, CTLFLAG_RD,
 158     &reass_path5, "Took path 5");
 159
 160 counter_u64_t reass_path6;
 161 SYSCTL_COUNTER_U64(_net_inet_tcp_reass_stats, OID_AUTO, path6, CTLFLAG_RD,
 162     &reass_path6, "Took path 6");
 163
 164 counter_u64_t reass_path7;
 165 SYSCTL_COUNTER_U64(_net_inet_tcp_reass_stats, OID_AUTO, path7, CTLFLAG_RD,
 166     &reass_path7, "Took path 7");
 167
 168 counter_u64_t reass_fullwalk;
 169 SYSCTL_COUNTER_U64(_net_inet_tcp_reass_stats, OID_AUTO, fullwalk, CTLFLAG_RD,
 170     &reass_fullwalk, "Took a full walk ");
 171
 172 counter_u64_t reass_nospace;
 173 SYSCTL_COUNTER_U64(_net_inet_tcp_reass_stats, OID_AUTO, nospace, CTLFLAG_RD,
 174     &reass_nospace, "Had no mbuf capacity ");
 175
 176 counter_u64_t merge_fwd;
 177 SYSCTL_COUNTER_U64(_net_inet_tcp_reass_stats, OID_AUTO, merge_fwd, CTLFLAG_RD,
 178     &merge_fwd, "Ran merge fwd");
 179
 180 counter_u64_t merge_into;
 181 SYSCTL_COUNTER_U64(_net_inet_tcp_reass_stats, OID_AUTO, merge_into, CTLFLAG_RD,
 182     &merge_into, "Ran merge into");
 183
 184 counter_u64_t tcp_zero_input;
 185 SYSCTL_COUNTER_U64(_net_inet_tcp_reass_stats, OID_AUTO, zero_input, CTLFLAG_RD,
 186     &tcp_zero_input, "The reassembly buffer saw a zero len segment etc");
 187
 188 #endif
 189
 190 /* Initialize TCP reassembly queue */
 191 static void
 192 tcp_reass_zone_change(void *tag)
 193 {
 194
 195         /* Set the zone limit and read back the effective value. */
 196         tcp_reass_maxseg = nmbclusters / 16;
 197         tcp_reass_maxseg = uma_zone_set_max(tcp_reass_zone,
 198             tcp_reass_maxseg);
 199 }
 200
 201 #ifdef TCP_REASS_LOGGING
 202
 203 static void
 204 tcp_log_reassm(struct tcpcb *tp, struct tseg_qent *q, struct tseg_qent *p,
 205     tcp_seq seq, int len, uint8_t action, int instance)
 206 {
 207         uint32_t cts;
 208         struct timeval tv;
 209
 210         if (tp->t_logstate != TCP_LOG_STATE_OFF) {
 211                 union tcp_log_stackspecific log;
 212
 213                 memset(&log, 0, sizeof(log));
 214                 cts = tcp_get_usecs(&tv);
 215                 log.u_bbr.flex1 = seq;
 216                 log.u_bbr.cur_del_rate = (uint64_t)q;
 217                 log.u_bbr.delRate = (uint64_t)p;
 218                 if (q != NULL) {
 219                         log.u_bbr.flex2 = q->tqe_start;
 220                         log.u_bbr.flex3 = q->tqe_len;
 221                         log.u_bbr.flex4 = q->tqe_mbuf_cnt;
 222                         log.u_bbr.hptsi_gain = q->tqe_flags;
 223                 }
 224                 if (p != NULL)  {
 225                         log.u_bbr.flex5 = p->tqe_start;
 226                         log.u_bbr.pkts_out = p->tqe_len;
 227                         log.u_bbr.epoch = p->tqe_mbuf_cnt;
 228                         log.u_bbr.cwnd_gain = p->tqe_flags;
 229                 }
 230                 log.u_bbr.flex6 = tp->t_segqmbuflen;
 231                 log.u_bbr.flex7 = instance;
 232                 log.u_bbr.flex8 = action;
 233                 log.u_bbr.timeStamp = cts;
 234                 TCP_LOG_EVENTP(tp, NULL,
 235                     &tp->t_inpcb->inp_socket->so_rcv,
 236                     &tp->t_inpcb->inp_socket->so_snd,
 237                     TCP_LOG_REASS, 0,
 238                     len, &log, false, &tv);
 239         }
 240 }
 241
 242 static void
 243 tcp_reass_log_dump(struct tcpcb *tp)
 244 {
 245         struct tseg_qent *q;
 246
 247         if (tp->t_logstate != TCP_LOG_STATE_OFF) {
 248                 TAILQ_FOREACH(q, &tp->t_segq, tqe_q) {
 249                         tcp_log_reassm(tp, q, NULL, q->tqe_start, q->tqe_len, TCP_R_LOG_DUMP, 0);
 250                 }
 251         };
 252 }
 253
 254 static void
 255 tcp_reass_log_new_in(struct tcpcb *tp, tcp_seq seq, int len, struct mbuf *m,
 256     int logval, struct tseg_qent *q)
 257 {
 258         int cnt;
 259         struct mbuf *t;
 260
 261         cnt = 0;
 262         t = m;
 263         while (t) {
 264                 cnt += t->m_len;
 265                 t = t->m_next;
 266         }
 267         tcp_log_reassm(tp, q, NULL, seq, len, logval, cnt);
 268 }
 269
 270 #endif
 271
 272 void
 273 tcp_reass_global_init(void)
 274 {
 275
 276         tcp_reass_maxseg = nmbclusters / 16;
 277         TUNABLE_INT_FETCH("net.inet.tcp.reass.maxsegments",
 278             &tcp_reass_maxseg);
 279         tcp_reass_zone = uma_zcreate("tcpreass", sizeof (struct tseg_qent),
 280             NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0);
 281         /* Set the zone limit and read back the effective value. */
 282         tcp_reass_maxseg = uma_zone_set_max(tcp_reass_zone,
 283             tcp_reass_maxseg);
 284 #ifdef TCP_REASS_COUNTERS
 285         reass_path1 = counter_u64_alloc(M_WAITOK);
 286         reass_path2 = counter_u64_alloc(M_WAITOK);
 287         reass_path3 = counter_u64_alloc(M_WAITOK);
 288         reass_path4 = counter_u64_alloc(M_WAITOK);
 289         reass_path5 = counter_u64_alloc(M_WAITOK);
 290         reass_path6 = counter_u64_alloc(M_WAITOK);
 291         reass_path7 = counter_u64_alloc(M_WAITOK);
 292         reass_fullwalk = counter_u64_alloc(M_WAITOK);
 293         reass_nospace = counter_u64_alloc(M_WAITOK);
 294         reass_entry = counter_u64_alloc(M_WAITOK);
 295         merge_fwd = counter_u64_alloc(M_WAITOK);
 296         merge_into = counter_u64_alloc(M_WAITOK);
 297         tcp_zero_input = counter_u64_alloc(M_WAITOK);
 298 #endif
 299         EVENTHANDLER_REGISTER(nmbclusters_change,
 300             tcp_reass_zone_change, NULL, EVENTHANDLER_PRI_ANY);
 301
 302 }
 303
 304 void
 305 tcp_reass_flush(struct tcpcb *tp)
 306 {
 307         struct tseg_qent *qe;
 308
 309         INP_WLOCK_ASSERT(tp->t_inpcb);
 310
 311         while ((qe = TAILQ_FIRST(&tp->t_segq)) != NULL) {
 312                 TAILQ_REMOVE(&tp->t_segq, qe, tqe_q);
 313                 m_freem(qe->tqe_m);
 314                 uma_zfree(tcp_reass_zone, qe);
 315                 tp->t_segqlen--;
 316         }
 317         tp->t_segqmbuflen = 0;
 318         KASSERT((tp->t_segqlen == 0),
 319             ("TCP reass queue %p segment count is %d instead of 0 after flush.",
 320             tp, tp->t_segqlen));
 321 }
 322
 323 static void
 324 tcp_reass_append(struct tcpcb *tp, struct tseg_qent *last,
 325     struct mbuf *m, struct tcphdr *th, int tlen,
 326     struct mbuf *mlast, int lenofoh)
 327 {
 328
 329 #ifdef TCP_REASS_LOGGING
 330         tcp_log_reassm(tp, last, NULL, th->th_seq, tlen, TCP_R_LOG_APPEND, 0);
 331 #endif
 332         last->tqe_len += tlen;
 333         last->tqe_m->m_pkthdr.len += tlen;
 334         /* Preserve the FIN bit if its there */
 335         last->tqe_flags |= (th->th_flags & TH_FIN);
 336         last->tqe_last->m_next = m;
 337         last->tqe_last = mlast;
 338         last->tqe_mbuf_cnt += lenofoh;
 339         tp->t_rcvoopack++;
 340         TCPSTAT_INC(tcps_rcvoopack);
 341         TCPSTAT_ADD(tcps_rcvoobyte, tlen);
 342 #ifdef TCP_REASS_LOGGING
 343         tcp_reass_log_new_in(tp, last->tqe_start, lenofoh, last->tqe_m,
 344                              TCP_R_LOG_APPEND,
 345                              last);
 346 #endif
 347 }
 348
 349 static void
 350 tcp_reass_prepend(struct tcpcb *tp, struct tseg_qent *first, struct mbuf *m, struct tcphdr *th,
 351                   int tlen, struct mbuf *mlast, int lenofoh)
 352 {
 353         int i;
 354
 355 #ifdef TCP_REASS_LOGGING
 356         tcp_log_reassm(tp, first, NULL, th->th_seq, tlen, TCP_R_LOG_PREPEND, 0);
 357 #endif
 358         if (SEQ_GT((th->th_seq + tlen), first->tqe_start)) {
 359                 /* The new data overlaps into the old */
 360                 i = (th->th_seq + tlen) - first->tqe_start;
 361 #ifdef TCP_REASS_LOGGING
 362                 tcp_log_reassm(tp, first, NULL, 0, i, TCP_R_LOG_TRIM, 1);
 363 #endif
 364                 m_adj(first->tqe_m, i);
 365                 first->tqe_len -= i;
 366                 first->tqe_start += i;
 367         }
 368         /* Ok now setup our chain to point to the old first */
 369         mlast->m_next = first->tqe_m;
 370         first->tqe_m = m;
 371         first->tqe_len += tlen;
 372         first->tqe_start = th->th_seq;
 373         first->tqe_m->m_pkthdr.len = first->tqe_len;
 374         first->tqe_mbuf_cnt += lenofoh;
 375         tp->t_rcvoopack++;
 376         TCPSTAT_INC(tcps_rcvoopack);
 377         TCPSTAT_ADD(tcps_rcvoobyte, tlen);
 378 #ifdef TCP_REASS_LOGGING
 379         tcp_reass_log_new_in(tp, first->tqe_start, lenofoh, first->tqe_m,
 380                              TCP_R_LOG_PREPEND,
 381                              first);
 382 #endif
 383 }
 384
 385 static void
 386 tcp_reass_replace(struct tcpcb *tp, struct tseg_qent *q, struct mbuf *m,
 387     tcp_seq seq, int len, struct mbuf *mlast, int mbufoh, uint8_t flags)
 388 {
 389         /*
 390          * Free the data in q, and replace
 391          * it with the new segment.
 392          */
 393         int len_dif;
 394
 395 #ifdef TCP_REASS_LOGGING
 396         tcp_log_reassm(tp, q, NULL, seq, len, TCP_R_LOG_REPLACE, 0);
 397 #endif
 398         m_freem(q->tqe_m);
 399         KASSERT(tp->t_segqmbuflen >= q->tqe_mbuf_cnt,
 400                 ("Tp:%p seg queue goes negative", tp));
 401         tp->t_segqmbuflen -= q->tqe_mbuf_cnt;
 402         q->tqe_mbuf_cnt = mbufoh;
 403         q->tqe_m = m;
 404         q->tqe_last = mlast;
 405         q->tqe_start = seq;
 406         if (len > q->tqe_len)
 407                 len_dif = len - q->tqe_len;
 408         else
 409                 len_dif = 0;
 410         tp->t_rcvoopack++;
 411         TCPSTAT_INC(tcps_rcvoopack);
 412         TCPSTAT_ADD(tcps_rcvoobyte, len_dif);
 413         q->tqe_len = len;
 414         q->tqe_flags = (flags & TH_FIN);
 415         q->tqe_m->m_pkthdr.len = q->tqe_len;
 416         tp->t_segqmbuflen += mbufoh;
 417
 418 }
 419
 420 static void
 421 tcp_reass_merge_into(struct tcpcb *tp, struct tseg_qent *ent,
 422     struct tseg_qent *q)
 423 {
 424         /*
 425          * Merge q into ent and free q from the list.
 426          */
 427 #ifdef TCP_REASS_LOGGING
 428         tcp_log_reassm(tp, q, ent, 0, 0, TCP_R_LOG_MERGE_INTO, 0);
 429 #endif
 430 #ifdef TCP_REASS_COUNTERS
 431         counter_u64_add(merge_into, 1);
 432 #endif
 433         ent->tqe_last->m_next = q->tqe_m;
 434         ent->tqe_last = q->tqe_last;
 435         ent->tqe_len += q->tqe_len;
 436         ent->tqe_mbuf_cnt += q->tqe_mbuf_cnt;
 437         ent->tqe_m->m_pkthdr.len += q->tqe_len;
 438         ent->tqe_flags |= (q->tqe_flags & TH_FIN);
 439         TAILQ_REMOVE(&tp->t_segq, q, tqe_q);
 440         uma_zfree(tcp_reass_zone, q);
 441         tp->t_segqlen--;
 442
 443 }
 444
 445 static void
 446 tcp_reass_merge_forward(struct tcpcb *tp, struct tseg_qent *ent)
 447 {
 448         struct tseg_qent *q, *qtmp;
 449         int i;
 450         tcp_seq max;
 451         /*
 452          * Given an entry merge forward anyplace
 453          * that ent overlaps forward.
 454          */
 455
 456         max = ent->tqe_start + ent->tqe_len;
 457         q = TAILQ_NEXT(ent, tqe_q);
 458         if (q == NULL) {
 459                 /* Nothing left */
 460                 return;
 461         }
 462         TAILQ_FOREACH_FROM_SAFE(q, &tp->t_segq, tqe_q, qtmp) {
 463                 if (SEQ_GT(q->tqe_start, max)) {
 464                         /* Beyond q */
 465                         break;
 466                 }
 467                 /* We have some or all that are overlapping */
 468                 if (SEQ_GEQ(max, (q->tqe_start + q->tqe_len))) {
 469                         /* It consumes it all */
 470                         tp->t_segqmbuflen -= q->tqe_mbuf_cnt;
 471                         m_freem(q->tqe_m);
 472                         TAILQ_REMOVE(&tp->t_segq, q, tqe_q);
 473                         uma_zfree(tcp_reass_zone, q);
 474                         tp->t_segqlen--;
 475                         continue;
 476                 }
 477                 /*
 478                  * Trim the q entry to dovetail to this one
 479                  * and then merge q into ent updating max
 480                  * in the process.
 481                  */
 482                 i = max - q->tqe_start;
 483 #ifdef TCP_REASS_LOGGING
 484                 tcp_log_reassm(tp, q, NULL, 0, i, TCP_R_LOG_TRIM, 2);
 485 #endif
 486                 m_adj(q->tqe_m, i);
 487                 q->tqe_len -= i;
 488                 q->tqe_start += i;
 489                 tcp_reass_merge_into(tp, ent, q);
 490                 max = ent->tqe_start + ent->tqe_len;
 491         }
 492 #ifdef TCP_REASS_COUNTERS
 493         counter_u64_add(merge_fwd, 1);
 494 #endif
 495 }
 496
 497 static int
 498 tcp_reass_overhead_of_chain(struct mbuf *m, struct mbuf **mlast)
 499 {
 500         int len = MSIZE;
 501
 502         if (m->m_flags & M_EXT)
 503                 len += m->m_ext.ext_size;
 504         while (m->m_next != NULL) {
 505                 m = m->m_next;
 506                 len += MSIZE;
 507                 if (m->m_flags & M_EXT)
 508                         len += m->m_ext.ext_size;
 509         }
 510         *mlast = m;
 511         return (len);
 512 }
 513
 514 /*
 515  * NOTE!!! the new tcp-reassembly code *must not* use
 516  * m_adj() with a negative index. That alters the chain
 517  * of mbufs (by possibly chopping trailing mbufs). At
 518  * the front of tcp_reass we count the mbuf overhead
 519  * and setup the tail pointer. If we use m_adj(m, -5)
 520  * we could corrupt the tail pointer. Currently the
 521  * code only uses m_adj(m, postive-num). If this
 522  * changes appropriate changes to update mlast would
 523  * be needed.
 524  */
 525 int
 526 tcp_reass(struct tcpcb *tp, struct tcphdr *th, tcp_seq *seq_start,
 527           int *tlenp, struct mbuf *m)
 528 {
 529         struct tseg_qent *q, *last, *first;
 530         struct tseg_qent *p = NULL;
 531         struct tseg_qent *nq = NULL;
 532         struct tseg_qent *te = NULL;
 533         struct mbuf *mlast = NULL;
 534         struct sockbuf *sb;
 535         struct socket *so = tp->t_inpcb->inp_socket;
 536         char *s = NULL;
 537         int flags, i, lenofoh;
 538
 539         INP_WLOCK_ASSERT(tp->t_inpcb);
 540         /*
 541          * XXX: tcp_reass() is rather inefficient with its data structures
 542          * and should be rewritten (see NetBSD for optimizations).
 543          */
 544
 545         KASSERT(th == NULL || (seq_start != NULL && tlenp != NULL),
 546                 ("tcp_reass called with illegal parameter combination "
 547                  "(tp=%p, th=%p, seq_start=%p, tlenp=%p, m=%p)",
 548                  tp, th, seq_start, tlenp, m));
 549         /*
 550          * Call with th==NULL after become established to
 551          * force pre-ESTABLISHED data up to user socket.
 552          */
 553         if (th == NULL)
 554                 goto present;
 555         KASSERT(SEQ_GEQ(th->th_seq, tp->rcv_nxt),
 556                 ("Attempt to add old entry to reassembly queue (th=%p, tp=%p)",
 557                  th, tp));
 558 #ifdef TCP_REASS_LOGGING
 559         tcp_reass_log_new_in(tp, th->th_seq, *tlenp, m, TCP_R_LOG_ADD, NULL);
 560 #endif
 561 #ifdef TCP_REASS_COUNTERS
 562         counter_u64_add(reass_entry, 1);
 563 #endif
 564         /*
 565          * Check for zero length data.
 566          */
 567         if ((*tlenp == 0) && ((th->th_flags & TH_FIN) == 0)) {
 568                 /*
 569                  * A zero length segment does no
 570                  * one any good. We could check
 571                  * the rcv_nxt <-> rcv_wnd but thats
 572                  * already done for us by the caller.
 573                  */
 574 strip_fin:
 575 #ifdef TCP_REASS_COUNTERS
 576                 counter_u64_add(tcp_zero_input, 1);
 577 #endif
 578                 m_freem(m);
 579 #ifdef TCP_REASS_LOGGING
 580                 tcp_reass_log_dump(tp);
 581 #endif
 582                 return (0);
 583         } else if ((*tlenp == 0) &&
 584                    (th->th_flags & TH_FIN) &&
 585                    !TCPS_HAVEESTABLISHED(tp->t_state)) {
 586                 /*
 587                  * We have not established, and we
 588                  * have a FIN and no data. Lets treat
 589                  * this as the same as if the FIN were
 590                  * not present. We don't want to save
 591                  * the FIN bit in a reassembly buffer
 592                  * we want to get established first before
 593                  * we do that (the peer will retransmit).
 594                  */
 595                 goto strip_fin;
 596         }
 597         /*
 598          * Will it fit?
 599          */
 600         lenofoh = tcp_reass_overhead_of_chain(m, &mlast);
 601         sb = &tp->t_inpcb->inp_socket->so_rcv;
 602         if ((th->th_seq != tp->rcv_nxt || !TCPS_HAVEESTABLISHED(tp->t_state)) &&
 603             (sb->sb_mbcnt + tp->t_segqmbuflen + lenofoh) > sb->sb_mbmax) {
 604                 /* No room */
 605                 TCPSTAT_INC(tcps_rcvreassfull);
 606 #ifdef TCP_REASS_COUNTERS
 607                 counter_u64_add(reass_nospace, 1);
 608 #endif
 609 #ifdef TCP_REASS_LOGGING
 610                 tcp_log_reassm(tp, NULL, NULL, th->th_seq, lenofoh, TCP_R_LOG_LIMIT_REACHED, 0);
 611 #endif
 612                 if ((s = tcp_log_addrs(&tp->t_inpcb->inp_inc, th, NULL, NULL))) {
 613                         log(LOG_DEBUG, "%s; %s: mbuf count limit reached, "
 614                             "segment dropped\n", s, __func__);
 615                         free(s, M_TCPLOG);
 616                 }
 617                 m_freem(m);
 618                 *tlenp = 0;
 619 #ifdef TCP_REASS_LOGGING
 620                 tcp_reass_log_dump(tp);
 621 #endif
 622                 return (0);
 623         }
 624         /*
 625          * First lets deal with two common cases, the
 626          * segment appends to the back of our collected
 627          * segments. Or the segment is the next in line.
 628          */
 629         last = TAILQ_LAST_FAST(&tp->t_segq, tseg_qent, tqe_q);
 630         if (last != NULL) {
 631                 if ((th->th_flags & TH_FIN) &&
 632                     SEQ_LT((th->th_seq + *tlenp), (last->tqe_start + last->tqe_len))) {
 633                         /*
 634                          * Someone is trying to game us, dump
 635                          * the segment.
 636                          */
 637                         *tlenp = 0;
 638                         m_freem(m);
 639                         return (0);
 640                 }
 641                 if ((SEQ_GEQ(th->th_seq, last->tqe_start)) &&
 642                     (SEQ_GEQ((last->tqe_start + last->tqe_len), th->th_seq))) {
 643                         /* Common case, trailing segment is added */
 644                         /**
 645                          *                                 +--last
 646                          *                                 v
 647                          *  reassembly buffer |---|  |---| |---|
 648                          *  new segment                       |---|
 649                          */
 650 #ifdef TCP_REASS_COUNTERS
 651                         counter_u64_add(reass_path1, 1);
 652 #endif
 653                         if (SEQ_GT((last->tqe_start + last->tqe_len), th->th_seq)) {
 654                                 i = (last->tqe_start + last->tqe_len) - th->th_seq;
 655                                 if (i < *tlenp) {
 656 #ifdef TCP_REASS_LOGGING
 657                                         tcp_log_reassm(tp, last, NULL, 0, i, TCP_R_LOG_TRIM, 3);
 658                                         th->th_seq += i;
 659 #endif
 660                                         m_adj(m, i);
 661                                         *tlenp -= i;
 662                                 } else {
 663                                         /* Complete overlap */
 664                                         TCPSTAT_INC(tcps_rcvduppack);
 665                                         TCPSTAT_ADD(tcps_rcvdupbyte, *tlenp);
 666                                         m_freem(m);
 667                                         *tlenp = last->tqe_len;
 668                                         *seq_start = last->tqe_start;
 669                                         return (0);
 670                                 }
 671                         }
 672                         if (last->tqe_flags & TH_FIN) {
 673                                 /*
 674                                  * We have data after the FIN on the last?
 675                                  */
 676                                 *tlenp = 0;
 677                                 m_freem(m);
 678                                 return(0);
 679                         }
 680                         tcp_reass_append(tp, last, m, th, *tlenp, mlast, lenofoh);
 681                         tp->t_segqmbuflen += lenofoh;
 682                         *seq_start = last->tqe_start;
 683                         *tlenp = last->tqe_len;
 684                         return (0);
 685                 } else if (SEQ_GT(th->th_seq, (last->tqe_start + last->tqe_len))) {
 686                         /*
 687                          * Second common case, we missed
 688                          * another one and have something more
 689                          * for the end.
 690                          */
 691                         /**
 692                          *                                 +--last
 693                          *                                 v
 694                          *  reassembly buffer |---|  |---| |---|
 695                          *  new segment                           |---|
 696                          */
 697                         if (last->tqe_flags & TH_FIN) {
 698                                 /*
 699                                  * We have data after the FIN on the last?
 700                                  */
 701                                 *tlenp = 0;
 702                                 m_freem(m);
 703                                 return(0);
 704                         }
 705 #ifdef TCP_REASS_COUNTERS
 706                         counter_u64_add(reass_path2, 1);
 707 #endif
 708                         p = last;
 709                         goto new_entry;
 710                 }
 711         } else {
 712                 /* First segment (it's NULL). */
 713                 goto new_entry;
 714         }
 715         first = TAILQ_FIRST(&tp->t_segq);
 716         if (SEQ_LT(th->th_seq, first->tqe_start) &&
 717             SEQ_GEQ((th->th_seq + *tlenp),first->tqe_start) &&
 718             SEQ_LT((th->th_seq + *tlenp), (first->tqe_start + first->tqe_len))) {
 719                 /*
 720                  * The head of the queue is prepended by this and
 721                  * it may be the one I want most.
 722                  */
 723                 /**
 724                  *       first-------+
 725                  *                   v
 726                  *  rea:             |---|  |---| |---|
 727                  *  new:         |---|
 728                  * Note the case we do not deal with here is:
 729                  *   rea=     |---|   |---|   |---|
 730                  *   new=  |----|
 731                  * Due to the fact that it could be
 732                  *   new   |--------------------|
 733                  * And we might need to merge forward.
 734                  */
 735 #ifdef INVARIANTS
 736                 struct mbuf *firstmbuf;
 737 #endif
 738
 739 #ifdef TCP_REASS_COUNTERS
 740                 counter_u64_add(reass_path3, 1);
 741 #endif
 742                 if (SEQ_LT(th->th_seq, tp->rcv_nxt)) {
 743                         /*
 744                          * The resend was even before
 745                          * what we have. We need to trim it.
 746                          * Note TSNH (it should be trimmed
 747                          * before the call to tcp_reass()).
 748                          */
 749 #ifdef INVARIANTS
 750                         panic("th->th_seq:%u rcv_nxt:%u tp:%p not pre-trimmed",
 751                               th->th_seq, tp->rcv_nxt, tp);
 752 #else
 753                         i = tp->rcv_nxt - th->th_seq;
 754 #ifdef TCP_REASS_LOGGING
 755                         tcp_log_reassm(tp, first, NULL, 0, i, TCP_R_LOG_TRIM, 4);
 756 #endif
 757                         m_adj(m, i);
 758                         th->th_seq += i;
 759                         *tlenp -= i;
 760 #endif
 761                 }
 762 #ifdef INVARIANTS
 763                 firstmbuf = first->tqe_m;
 764 #endif
 765                 tcp_reass_prepend(tp, first, m, th, *tlenp, mlast, lenofoh);
 766 #ifdef INVARIANTS
 767                 if (firstmbuf == first->tqe_m) {
 768                         panic("First stayed same m:%p foobar:%p first->tqe_m:%p tp:%p first:%p",
 769                               m, firstmbuf, first->tqe_m, tp, first);
 770                 } else if (first->tqe_m != m) {
 771                         panic("First did not change to m:%p foobar:%p first->tqe_m:%p tp:%p first:%p",
 772                               m, firstmbuf, first->tqe_m, tp, first);
 773                 }
 774 #endif
 775                 tp->t_segqmbuflen += lenofoh;
 776                 *seq_start = first->tqe_start;
 777                 *tlenp = first->tqe_len;
 778                 goto present;
 779         } else if (SEQ_LT((th->th_seq + *tlenp), first->tqe_start)) {
 780                 /* New segment is before our earliest segment. */
 781                 /**
 782                  *           first---->+
 783                  *                      v
 784                  *  rea=                |---| ....
 785                  *  new"         |---|
 786                  *
 787                  */
 788                 goto new_entry;
 789         }
 790         /*
 791          * Find a segment which begins after this one does.
 792          */
 793 #ifdef TCP_REASS_COUNTERS
 794         counter_u64_add(reass_fullwalk, 1);
 795 #endif
 796         TAILQ_FOREACH(q, &tp->t_segq, tqe_q) {
 797                 if (SEQ_GT(q->tqe_start, th->th_seq))
 798                         break;
 799         }
 800         p = TAILQ_PREV(q, tsegqe_head, tqe_q);
 801         /**
 802          * Now is this fit just in-between only?
 803          * i.e.:
 804          *      p---+        +----q
 805          *          v        v
 806          *     res= |--|     |--|    |--|
 807          *     nee       |-|
 808          */
 809         if (SEQ_LT((th->th_seq + *tlenp), q->tqe_start) &&
 810             ((p == NULL) || (SEQ_GT(th->th_seq, (p->tqe_start + p->tqe_len))))) {
 811                 /* Yep no overlap */
 812                 goto new_entry;
 813         }
 814         /**
 815          * If we reach here we have some (possibly all) overlap
 816          * such as:
 817          *     res=     |--|     |--|    |--|
 818          *     new=  |----|
 819          * or  new=  |-----------------|
 820          * or  new=      |--------|
 821          * or  new=            |---|
 822          * or  new=            |-----------|
 823          */
 824         if ((p != NULL) &&
 825             (SEQ_LEQ(th->th_seq, (p->tqe_start + p->tqe_len)))) {
 826                 /* conversion to int (in i) handles seq wraparound */
 827
 828 #ifdef TCP_REASS_COUNTERS
 829                 counter_u64_add(reass_path4, 1);
 830 #endif
 831                 i = p->tqe_start + p->tqe_len - th->th_seq;
 832                 if (i >= 0) {
 833                         if (i >= *tlenp) {
 834                                 /**
 835                                  *       prev seg---->+
 836                                  *                    v
 837                                  *  reassembly buffer |---|
 838                                  *  new segment        |-|
 839                                  */
 840                                 TCPSTAT_INC(tcps_rcvduppack);
 841                                 TCPSTAT_ADD(tcps_rcvdupbyte, *tlenp);
 842                                 *tlenp = p->tqe_len;
 843                                 *seq_start = p->tqe_start;
 844                                 m_freem(m);
 845                                 /*
 846                                  * Try to present any queued data
 847                                  * at the left window edge to the user.
 848                                  * This is needed after the 3-WHS
 849                                  * completes. Note this probably
 850                                  * will not work and we will return.
 851                                  */
 852                                 return (0);
 853                         }
 854                         if (i > 0) {
 855                                 /**
 856                                  *       prev seg---->+
 857                                  *                    v
 858                                  *  reassembly buffer |---|
 859                                  *  new segment         |-----|
 860                                  */
 861 #ifdef TCP_REASS_COUNTERS
 862                                 counter_u64_add(reass_path5, 1);
 863 #endif
 864 #ifdef TCP_REASS_LOGGING
 865                                 tcp_log_reassm(tp, p, NULL, 0, i, TCP_R_LOG_TRIM, 5);
 866 #endif
 867                                 m_adj(m, i);
 868                                 *tlenp -= i;
 869                                 th->th_seq += i;
 870                         }
 871                 }
 872                 if (th->th_seq == (p->tqe_start + p->tqe_len)) {
 873                         /*
 874                          * If dovetails in with this one
 875                          * append it.
 876                          */
 877                         /**
 878                          *       prev seg---->+
 879                          *                    v
 880                          *  reassembly buffer |--|     |---|
 881                          *  new segment          |--|
 882                          * (note: it was trimmed above if it overlapped)
 883                          */
 884                         tcp_reass_append(tp, p, m, th, *tlenp, mlast, lenofoh);
 885                         tp->t_segqmbuflen += lenofoh;
 886                 } else {
 887 #ifdef INVARIANTS
 888                         panic("Impossible cut th_seq:%u p->seq:%u(%d) p:%p tp:%p",
 889                               th->th_seq, p->tqe_start, p->tqe_len,
 890                               p, tp);
 891 #endif
 892                         *tlenp = 0;
 893                         m_freem(m);
 894                         return (0);
 895                 }
 896                 q = p;
 897         } else {
 898                 /*
 899                  * The new data runs over the
 900                  * top of previously sack'd data (in q).
 901                  * It may be partially overlapping, or
 902                  * it may overlap the entire segment.
 903                  */
 904 #ifdef TCP_REASS_COUNTERS
 905                 counter_u64_add(reass_path6, 1);
 906 #endif
 907                 if (SEQ_GEQ((th->th_seq + *tlenp), (q->tqe_start + q->tqe_len))) {
 908                         /* It consumes it all */
 909                         /**
 910                          *             next seg---->+
 911                          *                          v
 912                          *  reassembly buffer |--|     |---|
 913                          *  new segment              |----------|
 914                          */
 915 #ifdef TCP_REASS_COUNTERS
 916                         counter_u64_add(reass_path7, 1);
 917 #endif
 918                         tcp_reass_replace(tp, q, m, th->th_seq, *tlenp, mlast, lenofoh, th->th_flags);
 919                 } else {
 920                         /*
 921                          * We just need to prepend the data
 922                          * to this. It does not overrun
 923                          * the end.
 924                          */
 925                         /**
 926                          *                next seg---->+
 927                          *                             v
 928                          *  reassembly buffer |--|     |---|
 929                          *  new segment                   |----------|
 930                          */
 931                         tcp_reass_prepend(tp, q, m, th, *tlenp, mlast, lenofoh);
 932                         tp->t_segqmbuflen += lenofoh;
 933                 }
 934         }
 935         /* Now does it go further than that? */
 936         tcp_reass_merge_forward(tp, q);
 937         *seq_start = q->tqe_start;
 938         *tlenp = q->tqe_len;
 939         goto present;
 940
 941         /*
 942          * When we reach here we can't combine it
 943          * with any existing segment.
 944          *
 945          * Limit the number of segments that can be queued to reduce the
 946          * potential for mbuf exhaustion. For best performance, we want to be
 947          * able to queue a full window's worth of segments. The size of the
 948          * socket receive buffer determines our advertised window and grows
 949          * automatically when socket buffer autotuning is enabled. Use it as the
 950          * basis for our queue limit.
 951          *
 952          * However, allow the user to specify a ceiling for the number of
 953          * segments in each queue.
 954          *
 955          * Always let the missing segment through which caused this queue.
 956          * NB: Access to the socket buffer is left intentionally unlocked as we
 957          * can tolerate stale information here.
 958          *
 959          * XXXLAS: Using sbspace(so->so_rcv) instead of so->so_rcv.sb_hiwat
 960          * should work but causes packets to be dropped when they shouldn't.
 961          * Investigate why and re-evaluate the below limit after the behaviour
 962          * is understood.
 963          */
 964 new_entry:
 965         if (th->th_seq == tp->rcv_nxt && TCPS_HAVEESTABLISHED(tp->t_state)) {
 966                 tp->rcv_nxt += *tlenp;
 967                 flags = th->th_flags & TH_FIN;
 968                 TCPSTAT_INC(tcps_rcvoopack);
 969                 TCPSTAT_ADD(tcps_rcvoobyte, *tlenp);
 970                 SOCKBUF_LOCK(&so->so_rcv);
 971                 if (so->so_rcv.sb_state & SBS_CANTRCVMORE) {
 972                         m_freem(m);
 973                 } else {
 974                         sbappendstream_locked(&so->so_rcv, m, 0);
 975                 }
 976                 tp->t_flags |= TF_WAKESOR;
 977                 return (flags);
 978         }
 979         if (tcp_new_limits) {
 980                 if ((tp->t_segqlen > tcp_reass_queue_guard) &&
 981                     (*tlenp < MSIZE)) {
 982                         /*
 983                          * This is really a lie, we are not full but
 984                          * are getting a segment that is above
 985                          * guard threshold. If it is and its below
 986                          * a mbuf size (256) we drop it if it
 987                          * can't fill in some place.
 988                          */
 989                         TCPSTAT_INC(tcps_rcvreassfull);
 990                         *tlenp = 0;
 991                         if ((s = tcp_log_addrs(&tp->t_inpcb->inp_inc, th, NULL, NULL))) {
 992                                 log(LOG_DEBUG, "%s; %s: queue limit reached, "
 993                                     "segment dropped\n", s, __func__);
 994                                 free(s, M_TCPLOG);
 995                         }
 996                         m_freem(m);
 997 #ifdef TCP_REASS_LOGGING
 998                         tcp_reass_log_dump(tp);
 999 #endif
1000                         return (0);
1001                 }
1002         } else {
1003                 if (tp->t_segqlen >= min((so->so_rcv.sb_hiwat / tp->t_maxseg) + 1,
1004                                          tcp_reass_maxqueuelen)) {
1005                         TCPSTAT_INC(tcps_rcvreassfull);
1006                         *tlenp = 0;
1007                         if ((s = tcp_log_addrs(&tp->t_inpcb->inp_inc, th, NULL, NULL))) {
1008                                 log(LOG_DEBUG, "%s; %s: queue limit reached, "
1009                                     "segment dropped\n", s, __func__);
1010                                 free(s, M_TCPLOG);
1011                         }
1012                         m_freem(m);
1013 #ifdef TCP_REASS_LOGGING
1014                         tcp_reass_log_dump(tp);
1015 #endif
1016                         return (0);
1017                 }
1018         }
1019         /*
1020          * Allocate a new queue entry. If we can't, or hit the zone limit
1021          * just drop the pkt.
1022          */
1023         te = uma_zalloc(tcp_reass_zone, M_NOWAIT);
1024         if (te == NULL) {
1025                 TCPSTAT_INC(tcps_rcvmemdrop);
1026                 m_freem(m);
1027                 *tlenp = 0;
1028                 if ((s = tcp_log_addrs(&tp->t_inpcb->inp_inc, th, NULL,
1029                                        NULL))) {
1030                         log(LOG_DEBUG, "%s; %s: global zone limit "
1031                             "reached, segment dropped\n", s, __func__);
1032                         free(s, M_TCPLOG);
1033                 }
1034                 return (0);
1035         }
1036         tp->t_segqlen++;
1037         tp->t_rcvoopack++;
1038         TCPSTAT_INC(tcps_rcvoopack);
1039         TCPSTAT_ADD(tcps_rcvoobyte, *tlenp);
1040         /* Insert the new segment queue entry into place. */
1041         te->tqe_m = m;
1042         te->tqe_flags = th->th_flags;
1043         te->tqe_len = *tlenp;
1044         te->tqe_start = th->th_seq;
1045         te->tqe_last = mlast;
1046         te->tqe_mbuf_cnt = lenofoh;
1047         tp->t_segqmbuflen += te->tqe_mbuf_cnt;
1048         if (p == NULL) {
1049                 TAILQ_INSERT_HEAD(&tp->t_segq, te, tqe_q);
1050         } else {
1051                 TAILQ_INSERT_AFTER(&tp->t_segq, p, te, tqe_q);
1052         }
1053 #ifdef TCP_REASS_LOGGING
1054         tcp_reass_log_new_in(tp, th->th_seq, *tlenp, m, TCP_R_LOG_NEW_ENTRY, te);
1055 #endif
1056 present:
1057         /*
1058          * Present data to user, advancing rcv_nxt through
1059          * completed sequence space.
1060          */
1061         if (!TCPS_HAVEESTABLISHED(tp->t_state))
1062                 return (0);
1063         q = TAILQ_FIRST(&tp->t_segq);
1064         KASSERT(q == NULL || SEQ_GEQ(q->tqe_start, tp->rcv_nxt),
1065                 ("Reassembly queue for %p has stale entry at head", tp));
1066         if (!q || q->tqe_start != tp->rcv_nxt) {
1067 #ifdef TCP_REASS_LOGGING
1068                 tcp_reass_log_dump(tp);
1069 #endif
1070                 return (0);
1071         }
1072         SOCKBUF_LOCK(&so->so_rcv);
1073         do {
1074                 tp->rcv_nxt += q->tqe_len;
1075                 flags = q->tqe_flags & TH_FIN;
1076                 nq = TAILQ_NEXT(q, tqe_q);
1077                 TAILQ_REMOVE(&tp->t_segq, q, tqe_q);
1078                 if (so->so_rcv.sb_state & SBS_CANTRCVMORE) {
1079                         m_freem(q->tqe_m);
1080                 } else {
1081 #ifdef TCP_REASS_LOGGING
1082                         tcp_reass_log_new_in(tp, q->tqe_start, q->tqe_len, q->tqe_m, TCP_R_LOG_READ, q);
1083                         if (th != NULL) {
1084                                 tcp_log_reassm(tp, q, NULL, th->th_seq, *tlenp, TCP_R_LOG_READ, 1);
1085                         } else {
1086                                 tcp_log_reassm(tp, q, NULL, 0, 0, TCP_R_LOG_READ, 1);
1087                         }
1088 #endif
1089                         sbappendstream_locked(&so->so_rcv, q->tqe_m, 0);
1090                 }
1091 #ifdef TCP_REASS_LOGGING
1092                 if (th != NULL) {
1093                         tcp_log_reassm(tp, q, NULL, th->th_seq, *tlenp, TCP_R_LOG_READ, 2);
1094                 } else {
1095                         tcp_log_reassm(tp, q, NULL, 0, 0, TCP_R_LOG_READ, 2);
1096                 }
1097 #endif
1098                 KASSERT(tp->t_segqmbuflen >= q->tqe_mbuf_cnt,
1099                         ("tp:%p seg queue goes negative", tp));
1100                 tp->t_segqmbuflen -= q->tqe_mbuf_cnt;
1101                 uma_zfree(tcp_reass_zone, q);
1102                 tp->t_segqlen--;
1103                 q = nq;
1104         } while (q && q->tqe_start == tp->rcv_nxt);
1105         if (TAILQ_EMPTY(&tp->t_segq) &&
1106             (tp->t_segqmbuflen != 0)) {
1107 #ifdef INVARIANTS
1108                 panic("tp:%p segq:%p len:%d queue empty",
1109                       tp, &tp->t_segq, tp->t_segqmbuflen);
1110 #else
1111 #ifdef TCP_REASS_LOGGING
1112                 if (th != NULL) {
1113                         tcp_log_reassm(tp, NULL, NULL, th->th_seq, *tlenp, TCP_R_LOG_ZERO, 0);
1114                 } else {
1115                         tcp_log_reassm(tp, NULL, NULL, 0, 0, TCP_R_LOG_ZERO, 0);
1116                 }
1117 #endif
1118                 tp->t_segqmbuflen = 0;
1119 #endif
1120         }
1121 #ifdef TCP_REASS_LOGGING
1122         tcp_reass_log_dump(tp);
1123 #endif
1124         tp->t_flags |= TF_WAKESOR;
1125         return (flags);
1126 }