sys/netinet/tcp_sack.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.
   6  * All rights reserved.
   7  *
   8  * Redistribution and use in source and binary forms, with or without
   9  * modification, are permitted provided that the following conditions
  10  * are met:
  11  * 1. Redistributions of source code must retain the above copyright
  12  *    notice, this list of conditions and the following disclaimer.
  13  * 2. Redistributions in binary form must reproduce the above copyright
  14  *    notice, this list of conditions and the following disclaimer in the
  15  *    documentation and/or other materials provided with the distribution.
  16  * 3. Neither the name of the University nor the names of its contributors
  17  *    may be used to endorse or promote products derived from this software
  18  *    without specific prior written permission.
  19  *
  20  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  21  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  22  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  23  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  24  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  25  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  26  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  27  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  28  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  29  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  30  * SUCH DAMAGE.
  31  *
  32  *      @(#)tcp_sack.c  8.12 (Berkeley) 5/24/95
  33  */
  34
  35 /*-
  36  *      @@(#)COPYRIGHT  1.1 (NRL) 17 January 1995
  37  *
  38  * NRL grants permission for redistribution and use in source and binary
  39  * forms, with or without modification, of the software and documentation
  40  * created at NRL provided that the following conditions are met:
  41  *
  42  * 1. Redistributions of source code must retain the above copyright
  43  *    notice, this list of conditions and the following disclaimer.
  44  * 2. Redistributions in binary form must reproduce the above copyright
  45  *    notice, this list of conditions and the following disclaimer in the
  46  *    documentation and/or other materials provided with the distribution.
  47  * 3. All advertising materials mentioning features or use of this software
  48  *    must display the following acknowledgements:
  49  *      This product includes software developed by the University of
  50  *      California, Berkeley and its contributors.
  51  *      This product includes software developed at the Information
  52  *      Technology Division, US Naval Research Laboratory.
  53  * 4. Neither the name of the NRL nor the names of its contributors
  54  *    may be used to endorse or promote products derived from this software
  55  *    without specific prior written permission.
  56  *
  57  * THE SOFTWARE PROVIDED BY NRL IS PROVIDED BY NRL AND CONTRIBUTORS ``AS
  58  * IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
  59  * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
  60  * PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL NRL OR
  61  * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
  62  * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
  63  * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
  64  * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
  65  * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
  66  * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
  67  * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  68  *
  69  * The views and conclusions contained in the software and documentation
  70  * are those of the authors and should not be interpreted as representing
  71  * official policies, either expressed or implied, of the US Naval
  72  * Research Laboratory (NRL).
  73  */
  74
  75 #include <sys/cdefs.h>
  76 __FBSDID("$FreeBSD$");
  77
  78 #include "opt_inet.h"
  79 #include "opt_inet6.h"
  80
  81 #include <sys/param.h>
  82 #include <sys/systm.h>
  83 #include <sys/kernel.h>
  84 #include <sys/sysctl.h>
  85 #include <sys/malloc.h>
  86 #include <sys/mbuf.h>
  87 #include <sys/proc.h>           /* for proc0 declaration */
  88 #include <sys/protosw.h>
  89 #include <sys/socket.h>
  90 #include <sys/socketvar.h>
  91 #include <sys/syslog.h>
  92 #include <sys/systm.h>
  93
  94 #include <machine/cpu.h>        /* before tcp_seq.h, for tcp_random18() */
  95
  96 #include <vm/uma.h>
  97
  98 #include <net/if.h>
  99 #include <net/if_var.h>
 100 #include <net/route.h>
 101 #include <net/vnet.h>
 102
 103 #include <netinet/in.h>
 104 #include <netinet/in_systm.h>
 105 #include <netinet/ip.h>
 106 #include <netinet/in_var.h>
 107 #include <netinet/in_pcb.h>
 108 #include <netinet/ip_var.h>
 109 #include <netinet/ip6.h>
 110 #include <netinet/icmp6.h>
 111 #include <netinet6/nd6.h>
 112 #include <netinet6/ip6_var.h>
 113 #include <netinet6/in6_pcb.h>
 114 #include <netinet/tcp.h>
 115 #include <netinet/tcp_fsm.h>
 116 #include <netinet/tcp_seq.h>
 117 #include <netinet/tcp_timer.h>
 118 #include <netinet/tcp_var.h>
 119 #include <netinet/tcpip.h>
 120 #include <netinet/cc/cc.h>
 121
 122 #include <machine/in_cksum.h>
 123
 124 VNET_DECLARE(struct uma_zone *, sack_hole_zone);
 125 #define V_sack_hole_zone                VNET(sack_hole_zone)
 126
 127 SYSCTL_NODE(_net_inet_tcp, OID_AUTO, sack, CTLFLAG_RW | CTLFLAG_MPSAFE, 0,
 128     "TCP SACK");
 129
 130 VNET_DEFINE(int, tcp_do_sack) = 1;
 131 SYSCTL_INT(_net_inet_tcp_sack, OID_AUTO, enable, CTLFLAG_VNET | CTLFLAG_RW,
 132     &VNET_NAME(tcp_do_sack), 0,
 133     "Enable/Disable TCP SACK support");
 134
 135 VNET_DEFINE(int, tcp_do_newsack) = 1;
 136 SYSCTL_INT(_net_inet_tcp_sack, OID_AUTO, revised, CTLFLAG_VNET | CTLFLAG_RW,
 137     &VNET_NAME(tcp_do_newsack), 0,
 138     "Use revised SACK loss recovery per RFC 6675");
 139
 140 VNET_DEFINE(int, tcp_sack_maxholes) = 128;
 141 SYSCTL_INT(_net_inet_tcp_sack, OID_AUTO, maxholes, CTLFLAG_VNET | CTLFLAG_RW,
 142     &VNET_NAME(tcp_sack_maxholes), 0,
 143     "Maximum number of TCP SACK holes allowed per connection");
 144
 145 VNET_DEFINE(int, tcp_sack_globalmaxholes) = 65536;
 146 SYSCTL_INT(_net_inet_tcp_sack, OID_AUTO, globalmaxholes, CTLFLAG_VNET | CTLFLAG_RW,
 147     &VNET_NAME(tcp_sack_globalmaxholes), 0,
 148     "Global maximum number of TCP SACK holes");
 149
 150 VNET_DEFINE(int, tcp_sack_globalholes) = 0;
 151 SYSCTL_INT(_net_inet_tcp_sack, OID_AUTO, globalholes, CTLFLAG_VNET | CTLFLAG_RD,
 152     &VNET_NAME(tcp_sack_globalholes), 0,
 153     "Global number of TCP SACK holes currently allocated");
 154
 155 int
 156 tcp_dsack_block_exists(struct tcpcb *tp)
 157 {
 158         /* Return true if a DSACK block exists */
 159         if (tp->rcv_numsacks == 0)
 160                 return (0);
 161         if (SEQ_LEQ(tp->sackblks[0].end, tp->rcv_nxt))
 162                 return(1);
 163         return (0);
 164 }
 165
 166 /*
 167  * This function will find overlaps with the currently stored sackblocks
 168  * and add any overlap as a dsack block upfront
 169  */
 170 void
 171 tcp_update_dsack_list(struct tcpcb *tp, tcp_seq rcv_start, tcp_seq rcv_end)
 172 {
 173         struct sackblk head_blk,mid_blk,saved_blks[MAX_SACK_BLKS];
 174         int i, j, n, identical;
 175         tcp_seq start, end;
 176
 177         INP_WLOCK_ASSERT(tptoinpcb(tp));
 178
 179         KASSERT(SEQ_LT(rcv_start, rcv_end), ("rcv_start < rcv_end"));
 180
 181         if (SEQ_LT(rcv_end, tp->rcv_nxt) ||
 182             ((rcv_end == tp->rcv_nxt) &&
 183              (tp->rcv_numsacks > 0 ) &&
 184              (tp->sackblks[0].end == tp->rcv_nxt))) {
 185                 saved_blks[0].start = rcv_start;
 186                 saved_blks[0].end = rcv_end;
 187         } else {
 188                 saved_blks[0].start = saved_blks[0].end = 0;
 189         }
 190
 191         head_blk.start = head_blk.end = 0;
 192         mid_blk.start = rcv_start;
 193         mid_blk.end = rcv_end;
 194         identical = 0;
 195
 196         for (i = 0; i < tp->rcv_numsacks; i++) {
 197                 start = tp->sackblks[i].start;
 198                 end = tp->sackblks[i].end;
 199                 if (SEQ_LT(rcv_end, start)) {
 200                         /* pkt left to sack blk */
 201                         continue;
 202                 }
 203                 if (SEQ_GT(rcv_start, end)) {
 204                         /* pkt right to sack blk */
 205                         continue;
 206                 }
 207                 if (SEQ_GT(tp->rcv_nxt, end)) {
 208                         if ((SEQ_MAX(rcv_start, start) != SEQ_MIN(rcv_end, end)) &&
 209                             (SEQ_GT(head_blk.start, SEQ_MAX(rcv_start, start)) ||
 210                             (head_blk.start == head_blk.end))) {
 211                                 head_blk.start = SEQ_MAX(rcv_start, start);
 212                                 head_blk.end = SEQ_MIN(rcv_end, end);
 213                         }
 214                         continue;
 215                 }
 216                 if (((head_blk.start == head_blk.end) ||
 217                      SEQ_LT(start, head_blk.start)) &&
 218                      (SEQ_GT(end, rcv_start) &&
 219                       SEQ_LEQ(start, rcv_end))) {
 220                         head_blk.start = start;
 221                         head_blk.end = end;
 222                 }
 223                 mid_blk.start = SEQ_MIN(mid_blk.start, start);
 224                 mid_blk.end = SEQ_MAX(mid_blk.end, end);
 225                 if ((mid_blk.start == start) &&
 226                     (mid_blk.end == end))
 227                         identical = 1;
 228         }
 229         if (SEQ_LT(head_blk.start, head_blk.end)) {
 230                 /* store overlapping range */
 231                 saved_blks[0].start = SEQ_MAX(rcv_start, head_blk.start);
 232                 saved_blks[0].end   = SEQ_MIN(rcv_end, head_blk.end);
 233         }
 234         n = 1;
 235         /*
 236          * Second, if not ACKed, store the SACK block that
 237          * overlaps with the DSACK block unless it is identical
 238          */
 239         if ((SEQ_LT(tp->rcv_nxt, mid_blk.end) &&
 240             !((mid_blk.start == saved_blks[0].start) &&
 241             (mid_blk.end == saved_blks[0].end))) ||
 242             identical == 1) {
 243                 saved_blks[n].start = mid_blk.start;
 244                 saved_blks[n++].end = mid_blk.end;
 245         }
 246         for (j = 0; (j < tp->rcv_numsacks) && (n < MAX_SACK_BLKS); j++) {
 247                 if (((SEQ_LT(tp->sackblks[j].end, mid_blk.start) ||
 248                       SEQ_GT(tp->sackblks[j].start, mid_blk.end)) &&
 249                     (SEQ_GT(tp->sackblks[j].start, tp->rcv_nxt))))
 250                 saved_blks[n++] = tp->sackblks[j];
 251         }
 252         j = 0;
 253         for (i = 0; i < n; i++) {
 254                 /* we can end up with a stale initial entry */
 255                 if (SEQ_LT(saved_blks[i].start, saved_blks[i].end)) {
 256                         tp->sackblks[j++] = saved_blks[i];
 257                 }
 258         }
 259         tp->rcv_numsacks = j;
 260 }
 261
 262 /*
 263  * This function is called upon receipt of new valid data (while not in
 264  * header prediction mode), and it updates the ordered list of sacks.
 265  */
 266 void
 267 tcp_update_sack_list(struct tcpcb *tp, tcp_seq rcv_start, tcp_seq rcv_end)
 268 {
 269         /*
 270          * First reported block MUST be the most recent one.  Subsequent
 271          * blocks SHOULD be in the order in which they arrived at the
 272          * receiver.  These two conditions make the implementation fully
 273          * compliant with RFC 2018.
 274          */
 275         struct sackblk head_blk, saved_blks[MAX_SACK_BLKS];
 276         int num_head, num_saved, i;
 277
 278         INP_WLOCK_ASSERT(tptoinpcb(tp));
 279
 280         /* Check arguments. */
 281         KASSERT(SEQ_LEQ(rcv_start, rcv_end), ("rcv_start <= rcv_end"));
 282
 283         if ((rcv_start == rcv_end) &&
 284             (tp->rcv_numsacks >= 1) &&
 285             (rcv_end == tp->sackblks[0].end)) {
 286                 /* retaining DSACK block below rcv_nxt (todrop) */
 287                 head_blk = tp->sackblks[0];
 288         } else {
 289                 /* SACK block for the received segment. */
 290                 head_blk.start = rcv_start;
 291                 head_blk.end = rcv_end;
 292         }
 293
 294         /*
 295          * Merge updated SACK blocks into head_blk, and save unchanged SACK
 296          * blocks into saved_blks[].  num_saved will have the number of the
 297          * saved SACK blocks.
 298          */
 299         num_saved = 0;
 300         for (i = 0; i < tp->rcv_numsacks; i++) {
 301                 tcp_seq start = tp->sackblks[i].start;
 302                 tcp_seq end = tp->sackblks[i].end;
 303                 if (SEQ_GEQ(start, end) || SEQ_LEQ(start, tp->rcv_nxt)) {
 304                         /*
 305                          * Discard this SACK block.
 306                          */
 307                 } else if (SEQ_LEQ(head_blk.start, end) &&
 308                            SEQ_GEQ(head_blk.end, start)) {
 309                         /*
 310                          * Merge this SACK block into head_blk.  This SACK
 311                          * block itself will be discarded.
 312                          */
 313                         /*
 314                          * |-|
 315                          *   |---|  merge
 316                          *
 317                          *     |-|
 318                          * |---|    merge
 319                          *
 320                          * |-----|
 321                          *   |-|    DSACK smaller
 322                          *
 323                          *   |-|
 324                          * |-----|  DSACK smaller
 325                          */
 326                         if (head_blk.start == end)
 327                                 head_blk.start = start;
 328                         else if (head_blk.end == start)
 329                                 head_blk.end = end;
 330                         else {
 331                                 if (SEQ_LT(head_blk.start, start)) {
 332                                         tcp_seq temp = start;
 333                                         start = head_blk.start;
 334                                         head_blk.start = temp;
 335                                 }
 336                                 if (SEQ_GT(head_blk.end, end)) {
 337                                         tcp_seq temp = end;
 338                                         end = head_blk.end;
 339                                         head_blk.end = temp;
 340                                 }
 341                                 if ((head_blk.start != start) ||
 342                                     (head_blk.end != end)) {
 343                                         if ((num_saved >= 1) &&
 344                                            SEQ_GEQ(saved_blks[num_saved-1].start, start) &&
 345                                            SEQ_LEQ(saved_blks[num_saved-1].end, end))
 346                                                 num_saved--;
 347                                         saved_blks[num_saved].start = start;
 348                                         saved_blks[num_saved].end = end;
 349                                         num_saved++;
 350                                 }
 351                         }
 352                 } else {
 353                         /*
 354                          * This block supercedes the prior block
 355                          */
 356                         if ((num_saved >= 1) &&
 357                            SEQ_GEQ(saved_blks[num_saved-1].start, start) &&
 358                            SEQ_LEQ(saved_blks[num_saved-1].end, end))
 359                                 num_saved--;
 360                         /*
 361                          * Save this SACK block.
 362                          */
 363                         saved_blks[num_saved].start = start;
 364                         saved_blks[num_saved].end = end;
 365                         num_saved++;
 366                 }
 367         }
 368
 369         /*
 370          * Update SACK list in tp->sackblks[].
 371          */
 372         num_head = 0;
 373         if (SEQ_LT(rcv_start, rcv_end)) {
 374                 /*
 375                  * The received data segment is an out-of-order segment.  Put
 376                  * head_blk at the top of SACK list.
 377                  */
 378                 tp->sackblks[0] = head_blk;
 379                 num_head = 1;
 380                 /*
 381                  * If the number of saved SACK blocks exceeds its limit,
 382                  * discard the last SACK block.
 383                  */
 384                 if (num_saved >= MAX_SACK_BLKS)
 385                         num_saved--;
 386         }
 387         if ((rcv_start == rcv_end) &&
 388             (rcv_start == tp->sackblks[0].end)) {
 389                 num_head = 1;
 390         }
 391         if (num_saved > 0) {
 392                 /*
 393                  * Copy the saved SACK blocks back.
 394                  */
 395                 bcopy(saved_blks, &tp->sackblks[num_head],
 396                       sizeof(struct sackblk) * num_saved);
 397         }
 398
 399         /* Save the number of SACK blocks. */
 400         tp->rcv_numsacks = num_head + num_saved;
 401 }
 402
 403 void
 404 tcp_clean_dsack_blocks(struct tcpcb *tp)
 405 {
 406         struct sackblk saved_blks[MAX_SACK_BLKS];
 407         int num_saved, i;
 408
 409         INP_WLOCK_ASSERT(tptoinpcb(tp));
 410         /*
 411          * Clean up any DSACK blocks that
 412          * are in our queue of sack blocks.
 413          *
 414          */
 415         num_saved = 0;
 416         for (i = 0; i < tp->rcv_numsacks; i++) {
 417                 tcp_seq start = tp->sackblks[i].start;
 418                 tcp_seq end = tp->sackblks[i].end;
 419                 if (SEQ_GEQ(start, end) || SEQ_LEQ(start, tp->rcv_nxt)) {
 420                         /*
 421                          * Discard this D-SACK block.
 422                          */
 423                         continue;
 424                 }
 425                 /*
 426                  * Save this SACK block.
 427                  */
 428                 saved_blks[num_saved].start = start;
 429                 saved_blks[num_saved].end = end;
 430                 num_saved++;
 431         }
 432         if (num_saved > 0) {
 433                 /*
 434                  * Copy the saved SACK blocks back.
 435                  */
 436                 bcopy(saved_blks, &tp->sackblks[0],
 437                       sizeof(struct sackblk) * num_saved);
 438         }
 439         tp->rcv_numsacks = num_saved;
 440 }
 441
 442 /*
 443  * Delete all receiver-side SACK information.
 444  */
 445 void
 446 tcp_clean_sackreport(struct tcpcb *tp)
 447 {
 448         int i;
 449
 450         INP_WLOCK_ASSERT(tptoinpcb(tp));
 451         tp->rcv_numsacks = 0;
 452         for (i = 0; i < MAX_SACK_BLKS; i++)
 453                 tp->sackblks[i].start = tp->sackblks[i].end=0;
 454 }
 455
 456 /*
 457  * Allocate struct sackhole.
 458  */
 459 static struct sackhole *
 460 tcp_sackhole_alloc(struct tcpcb *tp, tcp_seq start, tcp_seq end)
 461 {
 462         struct sackhole *hole;
 463
 464         if (tp->snd_numholes >= V_tcp_sack_maxholes ||
 465             V_tcp_sack_globalholes >= V_tcp_sack_globalmaxholes) {
 466                 TCPSTAT_INC(tcps_sack_sboverflow);
 467                 return NULL;
 468         }
 469
 470         hole = (struct sackhole *)uma_zalloc(V_sack_hole_zone, M_NOWAIT);
 471         if (hole == NULL)
 472                 return NULL;
 473
 474         hole->start = start;
 475         hole->end = end;
 476         hole->rxmit = start;
 477
 478         tp->snd_numholes++;
 479         atomic_add_int(&V_tcp_sack_globalholes, 1);
 480
 481         return hole;
 482 }
 483
 484 /*
 485  * Free struct sackhole.
 486  */
 487 static void
 488 tcp_sackhole_free(struct tcpcb *tp, struct sackhole *hole)
 489 {
 490
 491         uma_zfree(V_sack_hole_zone, hole);
 492
 493         tp->snd_numholes--;
 494         atomic_subtract_int(&V_tcp_sack_globalholes, 1);
 495
 496         KASSERT(tp->snd_numholes >= 0, ("tp->snd_numholes >= 0"));
 497         KASSERT(V_tcp_sack_globalholes >= 0, ("tcp_sack_globalholes >= 0"));
 498 }
 499
 500 /*
 501  * Insert new SACK hole into scoreboard.
 502  */
 503 static struct sackhole *
 504 tcp_sackhole_insert(struct tcpcb *tp, tcp_seq start, tcp_seq end,
 505     struct sackhole *after)
 506 {
 507         struct sackhole *hole;
 508
 509         /* Allocate a new SACK hole. */
 510         hole = tcp_sackhole_alloc(tp, start, end);
 511         if (hole == NULL)
 512                 return NULL;
 513
 514         /* Insert the new SACK hole into scoreboard. */
 515         if (after != NULL)
 516                 TAILQ_INSERT_AFTER(&tp->snd_holes, after, hole, scblink);
 517         else
 518                 TAILQ_INSERT_TAIL(&tp->snd_holes, hole, scblink);
 519
 520         /* Update SACK hint. */
 521         if (tp->sackhint.nexthole == NULL)
 522                 tp->sackhint.nexthole = hole;
 523
 524         return hole;
 525 }
 526
 527 /*
 528  * Remove SACK hole from scoreboard.
 529  */
 530 static void
 531 tcp_sackhole_remove(struct tcpcb *tp, struct sackhole *hole)
 532 {
 533
 534         /* Update SACK hint. */
 535         if (tp->sackhint.nexthole == hole)
 536                 tp->sackhint.nexthole = TAILQ_NEXT(hole, scblink);
 537
 538         /* Remove this SACK hole. */
 539         TAILQ_REMOVE(&tp->snd_holes, hole, scblink);
 540
 541         /* Free this SACK hole. */
 542         tcp_sackhole_free(tp, hole);
 543 }
 544
 545 /*
 546  * Process cumulative ACK and the TCP SACK option to update the scoreboard.
 547  * tp->snd_holes is an ordered list of holes (oldest to newest, in terms of
 548  * the sequence space).
 549  * Returns 1 if incoming ACK has previously unknown SACK information,
 550  * 0 otherwise.
 551  */
 552 int
 553 tcp_sack_doack(struct tcpcb *tp, struct tcpopt *to, tcp_seq th_ack)
 554 {
 555         struct sackhole *cur, *temp;
 556         struct sackblk sack, sack_blocks[TCP_MAX_SACK + 1], *sblkp;
 557         int i, j, num_sack_blks, sack_changed;
 558         int delivered_data, left_edge_delta;
 559
 560         INP_WLOCK_ASSERT(tptoinpcb(tp));
 561
 562         num_sack_blks = 0;
 563         sack_changed = 0;
 564         delivered_data = 0;
 565         left_edge_delta = 0;
 566         /*
 567          * If SND.UNA will be advanced by SEG.ACK, and if SACK holes exist,
 568          * treat [SND.UNA, SEG.ACK) as if it is a SACK block.
 569          * Account changes to SND.UNA always in delivered data.
 570          */
 571         if (SEQ_LT(tp->snd_una, th_ack) && !TAILQ_EMPTY(&tp->snd_holes)) {
 572                 left_edge_delta = th_ack - tp->snd_una;
 573                 sack_blocks[num_sack_blks].start = tp->snd_una;
 574                 sack_blocks[num_sack_blks++].end = th_ack;
 575                 /*
 576                  * Pulling snd_fack forward if we got here
 577                  * due to DSACK blocks
 578                  */
 579                 if (SEQ_LT(tp->snd_fack, th_ack)) {
 580                         delivered_data += th_ack - tp->snd_una;
 581                         tp->snd_fack = th_ack;
 582                         sack_changed = 1;
 583                 }
 584         }
 585         /*
 586          * Append received valid SACK blocks to sack_blocks[], but only if we
 587          * received new blocks from the other side.
 588          */
 589         if (to->to_flags & TOF_SACK) {
 590                 for (i = 0; i < to->to_nsacks; i++) {
 591                         bcopy((to->to_sacks + i * TCPOLEN_SACK),
 592                             &sack, sizeof(sack));
 593                         sack.start = ntohl(sack.start);
 594                         sack.end = ntohl(sack.end);
 595                         if (SEQ_GT(sack.end, sack.start) &&
 596                             SEQ_GT(sack.start, tp->snd_una) &&
 597                             SEQ_GT(sack.start, th_ack) &&
 598                             SEQ_LT(sack.start, tp->snd_max) &&
 599                             SEQ_GT(sack.end, tp->snd_una) &&
 600                             SEQ_LEQ(sack.end, tp->snd_max)) {
 601                                 sack_blocks[num_sack_blks++] = sack;
 602                         } else if (SEQ_LEQ(sack.start, th_ack) &&
 603                             SEQ_LEQ(sack.end, th_ack)) {
 604                                 /*
 605                                  * Its a D-SACK block.
 606                                  */
 607                                 tcp_record_dsack(tp, sack.start, sack.end, 0);
 608                         }
 609                 }
 610         }
 611         /*
 612          * Return if SND.UNA is not advanced and no valid SACK block is
 613          * received.
 614          */
 615         if (num_sack_blks == 0)
 616                 return (sack_changed);
 617
 618         /*
 619          * Sort the SACK blocks so we can update the scoreboard with just one
 620          * pass. The overhead of sorting up to 4+1 elements is less than
 621          * making up to 4+1 passes over the scoreboard.
 622          */
 623         for (i = 0; i < num_sack_blks; i++) {
 624                 for (j = i + 1; j < num_sack_blks; j++) {
 625                         if (SEQ_GT(sack_blocks[i].end, sack_blocks[j].end)) {
 626                                 sack = sack_blocks[i];
 627                                 sack_blocks[i] = sack_blocks[j];
 628                                 sack_blocks[j] = sack;
 629                         }
 630                 }
 631         }
 632         if (TAILQ_EMPTY(&tp->snd_holes)) {
 633                 /*
 634                  * Empty scoreboard. Need to initialize snd_fack (it may be
 635                  * uninitialized or have a bogus value). Scoreboard holes
 636                  * (from the sack blocks received) are created later below
 637                  * (in the logic that adds holes to the tail of the
 638                  * scoreboard).
 639                  */
 640                 tp->snd_fack = SEQ_MAX(tp->snd_una, th_ack);
 641                 tp->sackhint.sacked_bytes = 0;  /* reset */
 642         }
 643         /*
 644          * In the while-loop below, incoming SACK blocks (sack_blocks[]) and
 645          * SACK holes (snd_holes) are traversed from their tails with just
 646          * one pass in order to reduce the number of compares especially when
 647          * the bandwidth-delay product is large.
 648          *
 649          * Note: Typically, in the first RTT of SACK recovery, the highest
 650          * three or four SACK blocks with the same ack number are received.
 651          * In the second RTT, if retransmitted data segments are not lost,
 652          * the highest three or four SACK blocks with ack number advancing
 653          * are received.
 654          */
 655         sblkp = &sack_blocks[num_sack_blks - 1];        /* Last SACK block */
 656         tp->sackhint.last_sack_ack = sblkp->end;
 657         if (SEQ_LT(tp->snd_fack, sblkp->start)) {
 658                 /*
 659                  * The highest SACK block is beyond fack.  First,
 660                  * check if there was a successful Rescue Retransmission,
 661                  * and move this hole left. With normal holes, snd_fack
 662                  * is always to the right of the end.
 663                  */
 664                 if (((temp = TAILQ_LAST(&tp->snd_holes, sackhole_head)) != NULL) &&
 665                     SEQ_LEQ(tp->snd_fack,temp->end)) {
 666                         temp->start = SEQ_MAX(tp->snd_fack, SEQ_MAX(tp->snd_una, th_ack));
 667                         temp->end = sblkp->start;
 668                         temp->rxmit = temp->start;
 669                         delivered_data += sblkp->end - sblkp->start;
 670                         tp->snd_fack = sblkp->end;
 671                         sblkp--;
 672                         sack_changed = 1;
 673                 } else {
 674                         /*
 675                          * Append a new SACK hole at the tail.  If the
 676                          * second or later highest SACK blocks are also
 677                          * beyond the current fack, they will be inserted
 678                          * by way of hole splitting in the while-loop below.
 679                          */
 680                         temp = tcp_sackhole_insert(tp, tp->snd_fack,sblkp->start,NULL);
 681                         if (temp != NULL) {
 682                                 delivered_data += sblkp->end - sblkp->start;
 683                                 tp->snd_fack = sblkp->end;
 684                                 /* Go to the previous sack block. */
 685                                 sblkp--;
 686                                 sack_changed = 1;
 687                         } else {
 688                                 /*
 689                                  * We failed to add a new hole based on the current
 690                                  * sack block.  Skip over all the sack blocks that
 691                                  * fall completely to the right of snd_fack and
 692                                  * proceed to trim the scoreboard based on the
 693                                  * remaining sack blocks.  This also trims the
 694                                  * scoreboard for th_ack (which is sack_blocks[0]).
 695                                  */
 696                                 while (sblkp >= sack_blocks &&
 697                                        SEQ_LT(tp->snd_fack, sblkp->start))
 698                                         sblkp--;
 699                                 if (sblkp >= sack_blocks &&
 700                                     SEQ_LT(tp->snd_fack, sblkp->end)) {
 701                                         delivered_data += sblkp->end - tp->snd_fack;
 702                                         tp->snd_fack = sblkp->end;
 703                                         sack_changed = 1;
 704                                 }
 705                         }
 706                 }
 707         } else if (SEQ_LT(tp->snd_fack, sblkp->end)) {
 708                 /* fack is advanced. */
 709                 delivered_data += sblkp->end - tp->snd_fack;
 710                 tp->snd_fack = sblkp->end;
 711                 sack_changed = 1;
 712         }
 713         cur = TAILQ_LAST(&tp->snd_holes, sackhole_head); /* Last SACK hole. */
 714         /*
 715          * Since the incoming sack blocks are sorted, we can process them
 716          * making one sweep of the scoreboard.
 717          */
 718         while (sblkp >= sack_blocks  && cur != NULL) {
 719                 if (SEQ_GEQ(sblkp->start, cur->end)) {
 720                         /*
 721                          * SACKs data beyond the current hole.  Go to the
 722                          * previous sack block.
 723                          */
 724                         sblkp--;
 725                         continue;
 726                 }
 727                 if (SEQ_LEQ(sblkp->end, cur->start)) {
 728                         /*
 729                          * SACKs data before the current hole.  Go to the
 730                          * previous hole.
 731                          */
 732                         cur = TAILQ_PREV(cur, sackhole_head, scblink);
 733                         continue;
 734                 }
 735                 tp->sackhint.sack_bytes_rexmit -=
 736                     (SEQ_MIN(cur->rxmit, cur->end) - cur->start);
 737                 KASSERT(tp->sackhint.sack_bytes_rexmit >= 0,
 738                     ("sackhint bytes rtx >= 0"));
 739                 sack_changed = 1;
 740                 if (SEQ_LEQ(sblkp->start, cur->start)) {
 741                         /* Data acks at least the beginning of hole. */
 742                         if (SEQ_GEQ(sblkp->end, cur->end)) {
 743                                 /* Acks entire hole, so delete hole. */
 744                                 delivered_data += (cur->end - cur->start);
 745                                 temp = cur;
 746                                 cur = TAILQ_PREV(cur, sackhole_head, scblink);
 747                                 tcp_sackhole_remove(tp, temp);
 748                                 /*
 749                                  * The sack block may ack all or part of the
 750                                  * next hole too, so continue onto the next
 751                                  * hole.
 752                                  */
 753                                 continue;
 754                         } else {
 755                                 /* Move start of hole forward. */
 756                                 delivered_data += (sblkp->end - cur->start);
 757                                 cur->start = sblkp->end;
 758                                 cur->rxmit = SEQ_MAX(cur->rxmit, cur->start);
 759                         }
 760                 } else {
 761                         /* Data acks at least the end of hole. */
 762                         if (SEQ_GEQ(sblkp->end, cur->end)) {
 763                                 /* Move end of hole backward. */
 764                                 delivered_data += (cur->end - sblkp->start);
 765                                 cur->end = sblkp->start;
 766                                 cur->rxmit = SEQ_MIN(cur->rxmit, cur->end);
 767                                 if ((tp->t_flags & TF_LRD) && SEQ_GEQ(cur->rxmit, cur->end))
 768                                         cur->rxmit = tp->snd_recover;
 769                         } else {
 770                                 /*
 771                                  * ACKs some data in middle of a hole; need
 772                                  * to split current hole
 773                                  */
 774                                 temp = tcp_sackhole_insert(tp, sblkp->end,
 775                                     cur->end, cur);
 776                                 if (temp != NULL) {
 777                                         if (SEQ_GT(cur->rxmit, temp->rxmit)) {
 778                                                 temp->rxmit = cur->rxmit;
 779                                                 tp->sackhint.sack_bytes_rexmit +=
 780                                                     (SEQ_MIN(temp->rxmit,
 781                                                     temp->end) - temp->start);
 782                                         }
 783                                         cur->end = sblkp->start;
 784                                         cur->rxmit = SEQ_MIN(cur->rxmit,
 785                                             cur->end);
 786                                         if ((tp->t_flags & TF_LRD) && SEQ_GEQ(cur->rxmit, cur->end))
 787                                                 cur->rxmit = tp->snd_recover;
 788                                         delivered_data += (sblkp->end - sblkp->start);
 789                                 }
 790                         }
 791                 }
 792                 tp->sackhint.sack_bytes_rexmit +=
 793                     (SEQ_MIN(cur->rxmit, cur->end) - cur->start);
 794                 /*
 795                  * Testing sblkp->start against cur->start tells us whether
 796                  * we're done with the sack block or the sack hole.
 797                  * Accordingly, we advance one or the other.
 798                  */
 799                 if (SEQ_LEQ(sblkp->start, cur->start))
 800                         cur = TAILQ_PREV(cur, sackhole_head, scblink);
 801                 else
 802                         sblkp--;
 803         }
 804         if (!(to->to_flags & TOF_SACK))
 805                 /*
 806                  * If this ACK did not contain any
 807                  * SACK blocks, any only moved the
 808                  * left edge right, it is a pure
 809                  * cumulative ACK. Do not count
 810                  * DupAck for this. Also required
 811                  * for RFC6675 rescue retransmission.
 812                  */
 813                 sack_changed = 0;
 814         tp->sackhint.delivered_data = delivered_data;
 815         tp->sackhint.sacked_bytes += delivered_data - left_edge_delta;
 816         KASSERT((delivered_data >= 0), ("delivered_data < 0"));
 817         KASSERT((tp->sackhint.sacked_bytes >= 0), ("sacked_bytes < 0"));
 818         return (sack_changed);
 819 }
 820
 821 /*
 822  * Free all SACK holes to clear the scoreboard.
 823  */
 824 void
 825 tcp_free_sackholes(struct tcpcb *tp)
 826 {
 827         struct sackhole *q;
 828
 829         INP_WLOCK_ASSERT(tptoinpcb(tp));
 830         while ((q = TAILQ_FIRST(&tp->snd_holes)) != NULL)
 831                 tcp_sackhole_remove(tp, q);
 832         tp->sackhint.sack_bytes_rexmit = 0;
 833
 834         KASSERT(tp->snd_numholes == 0, ("tp->snd_numholes == 0"));
 835         KASSERT(tp->sackhint.nexthole == NULL,
 836                 ("tp->sackhint.nexthole == NULL"));
 837 }
 838
 839 /*
 840  * Partial ack handling within a sack recovery episode.  Keeping this very
 841  * simple for now.  When a partial ack is received, force snd_cwnd to a value
 842  * that will allow the sender to transmit no more than 2 segments.  If
 843  * necessary, a better scheme can be adopted at a later point, but for now,
 844  * the goal is to prevent the sender from bursting a large amount of data in
 845  * the midst of sack recovery.
 846  */
 847 void
 848 tcp_sack_partialack(struct tcpcb *tp, struct tcphdr *th)
 849 {
 850         int num_segs = 1;
 851         u_int maxseg = tcp_maxseg(tp);
 852
 853         INP_WLOCK_ASSERT(tptoinpcb(tp));
 854         tcp_timer_activate(tp, TT_REXMT, 0);
 855         tp->t_rtttime = 0;
 856         /* Send one or 2 segments based on how much new data was acked. */
 857         if ((BYTES_THIS_ACK(tp, th) / maxseg) >= 2)
 858                 num_segs = 2;
 859         tp->snd_cwnd = (tp->sackhint.sack_bytes_rexmit +
 860             (tp->snd_nxt - tp->snd_recover) + num_segs * maxseg);
 861         if (tp->snd_cwnd > tp->snd_ssthresh)
 862                 tp->snd_cwnd = tp->snd_ssthresh;
 863         tp->t_flags |= TF_ACKNOW;
 864         /*
 865          * RFC6675 rescue retransmission
 866          * Add a hole between th_ack (snd_una is not yet set) and snd_max,
 867          * if this was a pure cumulative ACK and no data was send beyond
 868          * recovery point. Since the data in the socket has not been freed
 869          * at this point, we check if the scoreboard is empty, and the ACK
 870          * delivered some new data, indicating a full ACK. Also, if the
 871          * recovery point is still at snd_max, we are probably application
 872          * limited. However, this inference might not always be true. The
 873          * rescue retransmission may rarely be slightly premature
 874          * compared to RFC6675.
 875          * The corresponding ACK+SACK will cause any further outstanding
 876          * segments to be retransmitted. This addresses a corner case, when
 877          * the trailing packets of a window are lost and no further data
 878          * is available for sending.
 879          */
 880         if ((V_tcp_do_newsack) &&
 881             SEQ_LT(th->th_ack, tp->snd_recover) &&
 882             TAILQ_EMPTY(&tp->snd_holes) &&
 883             (tp->sackhint.delivered_data > 0)) {
 884                 /*
 885                  * Exclude FIN sequence space in
 886                  * the hole for the rescue retransmission,
 887                  * and also don't create a hole, if only
 888                  * the ACK for a FIN is outstanding.
 889                  */
 890                 tcp_seq highdata = tp->snd_max;
 891                 if (tp->t_flags & TF_SENTFIN)
 892                         highdata--;
 893                 highdata = SEQ_MIN(highdata, tp->snd_recover);
 894                 if (th->th_ack != highdata) {
 895                         tp->snd_fack = th->th_ack;
 896                         (void)tcp_sackhole_insert(tp, SEQ_MAX(th->th_ack,
 897                             highdata - maxseg), highdata, NULL);
 898                 }
 899         }
 900         (void) tcp_output(tp);
 901 }
 902
 903 #if 0
 904 /*
 905  * Debug version of tcp_sack_output() that walks the scoreboard.  Used for
 906  * now to sanity check the hint.
 907  */
 908 static struct sackhole *
 909 tcp_sack_output_debug(struct tcpcb *tp, int *sack_bytes_rexmt)
 910 {
 911         struct sackhole *p;
 912
 913         INP_WLOCK_ASSERT(tptoinpcb(tp));
 914         *sack_bytes_rexmt = 0;
 915         TAILQ_FOREACH(p, &tp->snd_holes, scblink) {
 916                 if (SEQ_LT(p->rxmit, p->end)) {
 917                         if (SEQ_LT(p->rxmit, tp->snd_una)) {/* old SACK hole */
 918                                 continue;
 919                         }
 920                         *sack_bytes_rexmt += (p->rxmit - p->start);
 921                         break;
 922                 }
 923                 *sack_bytes_rexmt += (SEQ_MIN(p->rxmit, p->end) - p->start);
 924         }
 925         return (p);
 926 }
 927 #endif
 928
 929 /*
 930  * Returns the next hole to retransmit and the number of retransmitted bytes
 931  * from the scoreboard.  We store both the next hole and the number of
 932  * retransmitted bytes as hints (and recompute these on the fly upon SACK/ACK
 933  * reception).  This avoids scoreboard traversals completely.
 934  *
 935  * The loop here will traverse *at most* one link.  Here's the argument.  For
 936  * the loop to traverse more than 1 link before finding the next hole to
 937  * retransmit, we would need to have at least 1 node following the current
 938  * hint with (rxmit == end).  But, for all holes following the current hint,
 939  * (start == rxmit), since we have not yet retransmitted from them.
 940  * Therefore, in order to traverse more 1 link in the loop below, we need to
 941  * have at least one node following the current hint with (start == rxmit ==
 942  * end).  But that can't happen, (start == end) means that all the data in
 943  * that hole has been sacked, in which case, the hole would have been removed
 944  * from the scoreboard.
 945  */
 946 struct sackhole *
 947 tcp_sack_output(struct tcpcb *tp, int *sack_bytes_rexmt)
 948 {
 949         struct sackhole *hole = NULL;
 950
 951         INP_WLOCK_ASSERT(tptoinpcb(tp));
 952         *sack_bytes_rexmt = tp->sackhint.sack_bytes_rexmit;
 953         hole = tp->sackhint.nexthole;
 954         if (hole == NULL)
 955                 return (hole);
 956         if (SEQ_GEQ(hole->rxmit, hole->end)) {
 957                 for (;;) {
 958                         hole = TAILQ_NEXT(hole, scblink);
 959                         if (hole == NULL)
 960                                 return (hole);
 961                         if (SEQ_LT(hole->rxmit, hole->end)) {
 962                                 tp->sackhint.nexthole = hole;
 963                                 break;
 964                         }
 965                 }
 966         }
 967         KASSERT(SEQ_LT(hole->start, hole->end), ("%s: hole.start >= hole.end", __func__));
 968         if (!(V_tcp_do_newsack)) {
 969                 KASSERT(SEQ_LT(hole->start, tp->snd_fack), ("%s: hole.start >= snd.fack", __func__));
 970                 KASSERT(SEQ_LT(hole->end, tp->snd_fack), ("%s: hole.end >= snd.fack", __func__));
 971                 KASSERT(SEQ_LT(hole->rxmit, tp->snd_fack), ("%s: hole.rxmit >= snd.fack", __func__));
 972                 if (SEQ_GEQ(hole->start, hole->end) ||
 973                     SEQ_GEQ(hole->start, tp->snd_fack) ||
 974                     SEQ_GEQ(hole->end, tp->snd_fack) ||
 975                     SEQ_GEQ(hole->rxmit, tp->snd_fack)) {
 976                         log(LOG_CRIT,"tcp: invalid SACK hole (%u-%u,%u) vs fwd ack %u, ignoring.\n",
 977                                         hole->start, hole->end, hole->rxmit, tp->snd_fack);
 978                         return (NULL);
 979                 }
 980         }
 981         return (hole);
 982 }
 983
 984 /*
 985  * After a timeout, the SACK list may be rebuilt.  This SACK information
 986  * should be used to avoid retransmitting SACKed data.  This function
 987  * traverses the SACK list to see if snd_nxt should be moved forward.
 988  */
 989 void
 990 tcp_sack_adjust(struct tcpcb *tp)
 991 {
 992         struct sackhole *p, *cur = TAILQ_FIRST(&tp->snd_holes);
 993
 994         INP_WLOCK_ASSERT(tptoinpcb(tp));
 995         if (cur == NULL)
 996                 return; /* No holes */
 997         if (SEQ_GEQ(tp->snd_nxt, tp->snd_fack))
 998                 return; /* We're already beyond any SACKed blocks */
 999         /*-
1000          * Two cases for which we want to advance snd_nxt:
1001          * i) snd_nxt lies between end of one hole and beginning of another
1002          * ii) snd_nxt lies between end of last hole and snd_fack
1003          */
1004         while ((p = TAILQ_NEXT(cur, scblink)) != NULL) {
1005                 if (SEQ_LT(tp->snd_nxt, cur->end))
1006                         return;
1007                 if (SEQ_GEQ(tp->snd_nxt, p->start))
1008                         cur = p;
1009                 else {
1010                         tp->snd_nxt = p->start;
1011                         return;
1012                 }
1013         }
1014         if (SEQ_LT(tp->snd_nxt, cur->end))
1015                 return;
1016         tp->snd_nxt = tp->snd_fack;
1017 }
1018
1019 /*
1020  * Lost Retransmission Detection
1021  * Check is FACK is beyond the rexmit of the leftmost hole.
1022  * If yes, we restart sending from still existing holes,
1023  * and adjust cwnd via the congestion control module.
1024  */
1025 void
1026 tcp_sack_lost_retransmission(struct tcpcb *tp, struct tcphdr *th)
1027 {
1028         struct sackhole *temp;
1029
1030         if (IN_RECOVERY(tp->t_flags) &&
1031             SEQ_GT(tp->snd_fack, tp->snd_recover) &&
1032             ((temp = TAILQ_FIRST(&tp->snd_holes)) != NULL) &&
1033             SEQ_GEQ(temp->rxmit, temp->end) &&
1034             SEQ_GEQ(tp->snd_fack, temp->rxmit)) {
1035                 TCPSTAT_INC(tcps_sack_lostrexmt);
1036                 /*
1037                  * Start retransmissions from the first hole, and
1038                  * subsequently all other remaining holes, including
1039                  * those, which had been sent completely before.
1040                  */
1041                 tp->sackhint.nexthole = temp;
1042                 TAILQ_FOREACH(temp, &tp->snd_holes, scblink) {
1043                         if (SEQ_GEQ(tp->snd_fack, temp->rxmit) &&
1044                             SEQ_GEQ(temp->rxmit, temp->end))
1045                                 temp->rxmit = temp->start;
1046                 }
1047                 /*
1048                  * Remember the old ssthresh, to deduct the beta factor used
1049                  * by the CC module. Finally, set cwnd to ssthresh just
1050                  * prior to invoking another cwnd reduction by the CC
1051                  * module, to not shrink it excessively.
1052                  */
1053                 tp->snd_cwnd = tp->snd_ssthresh;
1054                 /*
1055                  * Formally exit recovery, and let the CC module adjust
1056                  * ssthresh as intended.
1057                  */
1058                 EXIT_RECOVERY(tp->t_flags);
1059                 cc_cong_signal(tp, th, CC_NDUPACK);
1060                 /*
1061                  * For PRR, adjust recover_fs as if this new reduction
1062                  * initialized this variable.
1063                  * cwnd will be adjusted by SACK or PRR processing
1064                  * subsequently, only set it to a safe value here.
1065                  */
1066                 tp->snd_cwnd = tcp_maxseg(tp);
1067                 tp->sackhint.recover_fs = (tp->snd_max - tp->snd_una) -
1068                                             tp->sackhint.recover_fs;
1069         }
1070 }