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 (tp->snd_recover == tp->snd_max) &&
883 TAILQ_EMPTY(&tp->snd_holes) &&
884 (tp->sackhint.delivered_data > 0)) {
885 /*
886 * Exclude FIN sequence space in
887 * the hole for the rescue retransmission,
888 * and also don't create a hole, if only
889 * the ACK for a FIN is outstanding.
890 */
891 tcp_seq highdata = tp->snd_max;
892 if (tp->t_flags & TF_SENTFIN)
893 highdata--;
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 }
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