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
33 /*-
34 *
35 * NRL grants permission for redistribution and use in source and binary
36 * forms, with or without modification, of the software and documentation
37 * created at NRL provided that the following conditions are met:
38 *
39 * 1. Redistributions of source code must retain the above copyright
40 * notice, this list of conditions and the following disclaimer.
41 * 2. Redistributions in binary form must reproduce the above copyright
42 * notice, this list of conditions and the following disclaimer in the
43 * documentation and/or other materials provided with the distribution.
44 * 3. All advertising materials mentioning features or use of this software
45 * must display the following acknowledgements:
46 * This product includes software developed by the University of
47 * California, Berkeley and its contributors.
48 * This product includes software developed at the Information
49 * Technology Division, US Naval Research Laboratory.
50 * 4. Neither the name of the NRL nor the names of its contributors
51 * may be used to endorse or promote products derived from this software
52 * without specific prior written permission.
53 *
54 * THE SOFTWARE PROVIDED BY NRL IS PROVIDED BY NRL AND CONTRIBUTORS ``AS
55 * IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
56 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
57 * PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL NRL OR
58 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
59 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
60 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
61 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
62 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
63 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
64 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
65 *
66 * The views and conclusions contained in the software and documentation
67 * are those of the authors and should not be interpreted as representing
68 * official policies, either expressed or implied, of the US Naval
69 * Research Laboratory (NRL).
70 */
71
72 #include <sys/cdefs.h>
73 #include "opt_inet.h"
74 #include "opt_inet6.h"
75
76 #include <sys/param.h>
77 #include <sys/systm.h>
78 #include <sys/kernel.h>
79 #include <sys/sysctl.h>
80 #include <sys/malloc.h>
81 #include <sys/mbuf.h>
82 #include <sys/proc.h> /* for proc0 declaration */
83 #include <sys/protosw.h>
84 #include <sys/socket.h>
85 #include <sys/socketvar.h>
86 #include <sys/syslog.h>
87 #include <sys/systm.h>
88
89 #include <machine/cpu.h> /* before tcp_seq.h, for tcp_random18() */
90
91 #include <vm/uma.h>
92
93 #include <net/if.h>
94 #include <net/if_var.h>
95 #include <net/route.h>
96 #include <net/vnet.h>
97
98 #include <netinet/in.h>
99 #include <netinet/in_systm.h>
100 #include <netinet/ip.h>
101 #include <netinet/in_var.h>
102 #include <netinet/in_pcb.h>
103 #include <netinet/ip_var.h>
104 #include <netinet/ip6.h>
105 #include <netinet/icmp6.h>
106 #include <netinet6/nd6.h>
107 #include <netinet6/ip6_var.h>
108 #include <netinet6/in6_pcb.h>
109 #include <netinet/tcp.h>
110 #include <netinet/tcp_fsm.h>
111 #include <netinet/tcp_seq.h>
112 #include <netinet/tcp_timer.h>
113 #include <netinet/tcp_var.h>
114 #include <netinet/tcpip.h>
115 #include <netinet/cc/cc.h>
116
117 #include <machine/in_cksum.h>
118
119 VNET_DECLARE(struct uma_zone *, sack_hole_zone);
120 #define V_sack_hole_zone VNET(sack_hole_zone)
121
122 SYSCTL_NODE(_net_inet_tcp, OID_AUTO, sack, CTLFLAG_RW | CTLFLAG_MPSAFE, 0,
123 "TCP SACK");
124
125 VNET_DEFINE(int, tcp_do_sack) = 1;
126 SYSCTL_INT(_net_inet_tcp_sack, OID_AUTO, enable, CTLFLAG_VNET | CTLFLAG_RW,
127 &VNET_NAME(tcp_do_sack), 0,
128 "Enable/Disable TCP SACK support");
129
130 VNET_DEFINE(int, tcp_do_newsack) = 1;
131 SYSCTL_INT(_net_inet_tcp_sack, OID_AUTO, revised, CTLFLAG_VNET | CTLFLAG_RW,
132 &VNET_NAME(tcp_do_newsack), 0,
133 "Use revised SACK loss recovery per RFC 6675");
134
135 VNET_DEFINE(int, tcp_do_lrd) = 1;
136 SYSCTL_INT(_net_inet_tcp_sack, OID_AUTO, lrd, CTLFLAG_VNET | CTLFLAG_RW,
137 &VNET_NAME(tcp_do_lrd), 1,
138 "Perform Lost Retransmission Detection");
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
tcp_dsack_block_exists(struct tcpcb * tp)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
tcp_update_dsack_list(struct tcpcb * tp,tcp_seq rcv_start,tcp_seq rcv_end)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
tcp_update_sack_list(struct tcpcb * tp,tcp_seq rcv_start,tcp_seq rcv_end)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
tcp_clean_dsack_blocks(struct tcpcb * tp)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
tcp_clean_sackreport(struct tcpcb * tp)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 *
tcp_sackhole_alloc(struct tcpcb * tp,tcp_seq start,tcp_seq end)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
tcp_sackhole_free(struct tcpcb * tp,struct sackhole * hole)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 *
tcp_sackhole_insert(struct tcpcb * tp,tcp_seq start,tcp_seq end,struct sackhole * after)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
tcp_sackhole_remove(struct tcpcb * tp,struct sackhole * hole)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 SACK_NEWLOSS if incoming ACK indicates ongoing loss (hole split, new hole),
550 * SACK_CHANGE if incoming ACK has previously unknown SACK information,
551 * SACK_NOCHANGE otherwise.
552 */
553 sackstatus_t
tcp_sack_doack(struct tcpcb * tp,struct tcpopt * to,tcp_seq th_ack)554 tcp_sack_doack(struct tcpcb *tp, struct tcpopt *to, tcp_seq th_ack)
555 {
556 struct sackhole *cur, *temp;
557 struct sackblk sack, sack_blocks[TCP_MAX_SACK + 1], *sblkp;
558 int i, j, num_sack_blks;
559 sackstatus_t sack_changed;
560 int delivered_data, left_edge_delta;
561
562 tcp_seq loss_hiack = 0;
563 int loss_thresh = 0;
564 int loss_sblks = 0;
565 int notlost_bytes = 0;
566
567 INP_WLOCK_ASSERT(tptoinpcb(tp));
568
569 num_sack_blks = 0;
570 sack_changed = SACK_NOCHANGE;
571 delivered_data = 0;
572 left_edge_delta = 0;
573 /*
574 * If SND.UNA will be advanced by SEG.ACK, and if SACK holes exist,
575 * treat [SND.UNA, SEG.ACK) as if it is a SACK block.
576 * Account changes to SND.UNA always in delivered data.
577 */
578 if (SEQ_LT(tp->snd_una, th_ack) && !TAILQ_EMPTY(&tp->snd_holes)) {
579 left_edge_delta = th_ack - tp->snd_una;
580 sack_blocks[num_sack_blks].start = tp->snd_una;
581 sack_blocks[num_sack_blks++].end = th_ack;
582 /*
583 * Pulling snd_fack forward if we got here
584 * due to DSACK blocks
585 */
586 if (SEQ_LT(tp->snd_fack, th_ack)) {
587 delivered_data += th_ack - tp->snd_una;
588 tp->snd_fack = th_ack;
589 sack_changed = SACK_CHANGE;
590 }
591 }
592 /*
593 * Append received valid SACK blocks to sack_blocks[], but only if we
594 * received new blocks from the other side.
595 */
596 if (to->to_flags & TOF_SACK) {
597 for (i = 0; i < to->to_nsacks; i++) {
598 bcopy((to->to_sacks + i * TCPOLEN_SACK),
599 &sack, sizeof(sack));
600 sack.start = ntohl(sack.start);
601 sack.end = ntohl(sack.end);
602 if (SEQ_GT(sack.end, sack.start) &&
603 SEQ_GT(sack.start, tp->snd_una) &&
604 SEQ_GT(sack.start, th_ack) &&
605 SEQ_LT(sack.start, tp->snd_max) &&
606 SEQ_GT(sack.end, tp->snd_una) &&
607 SEQ_LEQ(sack.end, tp->snd_max)) {
608 sack_blocks[num_sack_blks++] = sack;
609 } else if (SEQ_LEQ(sack.start, th_ack) &&
610 SEQ_LEQ(sack.end, th_ack)) {
611 /*
612 * Its a D-SACK block.
613 */
614 tcp_record_dsack(tp, sack.start, sack.end, 0);
615 }
616 }
617 }
618 /*
619 * Return if SND.UNA is not advanced and no valid SACK block is
620 * received.
621 */
622 if (num_sack_blks == 0)
623 return (sack_changed);
624
625 /*
626 * Sort the SACK blocks so we can update the scoreboard with just one
627 * pass. The overhead of sorting up to 4+1 elements is less than
628 * making up to 4+1 passes over the scoreboard.
629 */
630 for (i = 0; i < num_sack_blks; i++) {
631 for (j = i + 1; j < num_sack_blks; j++) {
632 if (SEQ_GT(sack_blocks[i].end, sack_blocks[j].end)) {
633 sack = sack_blocks[i];
634 sack_blocks[i] = sack_blocks[j];
635 sack_blocks[j] = sack;
636 }
637 }
638 }
639 if (TAILQ_EMPTY(&tp->snd_holes)) {
640 /*
641 * Empty scoreboard. Need to initialize snd_fack (it may be
642 * uninitialized or have a bogus value). Scoreboard holes
643 * (from the sack blocks received) are created later below
644 * (in the logic that adds holes to the tail of the
645 * scoreboard).
646 */
647 tp->snd_fack = SEQ_MAX(tp->snd_una, th_ack);
648 tp->sackhint.sacked_bytes = 0; /* reset */
649 tp->sackhint.hole_bytes = 0;
650 }
651 /*
652 * In the while-loop below, incoming SACK blocks (sack_blocks[]) and
653 * SACK holes (snd_holes) are traversed from their tails with just
654 * one pass in order to reduce the number of compares especially when
655 * the bandwidth-delay product is large.
656 *
657 * Note: Typically, in the first RTT of SACK recovery, the highest
658 * three or four SACK blocks with the same ack number are received.
659 * In the second RTT, if retransmitted data segments are not lost,
660 * the highest three or four SACK blocks with ack number advancing
661 * are received.
662 */
663 sblkp = &sack_blocks[num_sack_blks - 1]; /* Last SACK block */
664 tp->sackhint.last_sack_ack = sblkp->end;
665 if (SEQ_LT(tp->snd_fack, sblkp->start)) {
666 /*
667 * The highest SACK block is beyond fack. First,
668 * check if there was a successful Rescue Retransmission,
669 * and move this hole left. With normal holes, snd_fack
670 * is always to the right of the end.
671 */
672 if (((temp = TAILQ_LAST(&tp->snd_holes, sackhole_head)) != NULL) &&
673 SEQ_LEQ(tp->snd_fack,temp->end)) {
674 tp->sackhint.hole_bytes -= temp->end - temp->start;
675 temp->start = SEQ_MAX(tp->snd_fack, SEQ_MAX(tp->snd_una, th_ack));
676 temp->end = sblkp->start;
677 temp->rxmit = temp->start;
678 delivered_data += sblkp->end - sblkp->start;
679 tp->sackhint.hole_bytes += temp->end - temp->start;
680 KASSERT(tp->sackhint.hole_bytes >= 0,
681 ("sackhint hole bytes >= 0"));
682 tp->snd_fack = sblkp->end;
683 sblkp--;
684 sack_changed = SACK_NEWLOSS;
685 } else {
686 /*
687 * Append a new SACK hole at the tail. If the
688 * second or later highest SACK blocks are also
689 * beyond the current fack, they will be inserted
690 * by way of hole splitting in the while-loop below.
691 */
692 temp = tcp_sackhole_insert(tp, tp->snd_fack,sblkp->start,NULL);
693 if (temp != NULL) {
694 delivered_data += sblkp->end - sblkp->start;
695 tp->sackhint.hole_bytes += temp->end - temp->start;
696 tp->snd_fack = sblkp->end;
697 /* Go to the previous sack block. */
698 sblkp--;
699 sack_changed = SACK_CHANGE;
700 } else {
701 /*
702 * We failed to add a new hole based on the current
703 * sack block. Skip over all the sack blocks that
704 * fall completely to the right of snd_fack and
705 * proceed to trim the scoreboard based on the
706 * remaining sack blocks. This also trims the
707 * scoreboard for th_ack (which is sack_blocks[0]).
708 */
709 while (sblkp >= sack_blocks &&
710 SEQ_LT(tp->snd_fack, sblkp->start))
711 sblkp--;
712 if (sblkp >= sack_blocks &&
713 SEQ_LT(tp->snd_fack, sblkp->end)) {
714 delivered_data += sblkp->end - tp->snd_fack;
715 tp->snd_fack = sblkp->end;
716 /*
717 * While the Scoreboard didn't change in
718 * size, we only ended up here because
719 * some SACK data had to be dismissed.
720 */
721 sack_changed = SACK_NEWLOSS;
722 }
723 }
724 }
725 } else if (SEQ_LT(tp->snd_fack, sblkp->end)) {
726 /* fack is advanced. */
727 delivered_data += sblkp->end - tp->snd_fack;
728 tp->snd_fack = sblkp->end;
729 sack_changed = SACK_CHANGE;
730 }
731 cur = TAILQ_LAST(&tp->snd_holes, sackhole_head); /* Last SACK hole. */
732 loss_hiack = tp->snd_fack;
733
734 /*
735 * Since the incoming sack blocks are sorted, we can process them
736 * making one sweep of the scoreboard.
737 */
738 while (cur != NULL) {
739 if (!(sblkp >= sack_blocks)) {
740 if (((loss_sblks >= tcprexmtthresh) ||
741 (loss_thresh > (tcprexmtthresh-1)*tp->t_maxseg)))
742 break;
743 loss_thresh += loss_hiack - cur->end;
744 loss_hiack = cur->start;
745 loss_sblks++;
746 if (!((loss_sblks >= tcprexmtthresh) ||
747 (loss_thresh > (tcprexmtthresh-1)*tp->t_maxseg))) {
748 notlost_bytes += cur->end - cur->start;
749 } else {
750 break;
751 }
752 cur = TAILQ_PREV(cur, sackhole_head, scblink);
753 continue;
754 }
755 if (SEQ_GEQ(sblkp->start, cur->end)) {
756 /*
757 * SACKs data beyond the current hole. Go to the
758 * previous sack block.
759 */
760 sblkp--;
761 continue;
762 }
763 if (SEQ_LEQ(sblkp->end, cur->start)) {
764 /*
765 * SACKs data before the current hole. Go to the
766 * previous hole.
767 */
768 loss_thresh += loss_hiack - cur->end;
769 loss_hiack = cur->start;
770 loss_sblks++;
771 if (!((loss_sblks >= tcprexmtthresh) ||
772 (loss_thresh > (tcprexmtthresh-1)*tp->t_maxseg)))
773 notlost_bytes += cur->end - cur->start;
774 cur = TAILQ_PREV(cur, sackhole_head, scblink);
775 continue;
776 }
777 tp->sackhint.sack_bytes_rexmit -=
778 (SEQ_MIN(cur->rxmit, cur->end) - cur->start);
779 KASSERT(tp->sackhint.sack_bytes_rexmit >= 0,
780 ("sackhint bytes rtx >= 0"));
781 sack_changed = SACK_CHANGE;
782 if (SEQ_LEQ(sblkp->start, cur->start)) {
783 /* Data acks at least the beginning of hole. */
784 if (SEQ_GEQ(sblkp->end, cur->end)) {
785 /* Acks entire hole, so delete hole. */
786 delivered_data += (cur->end - cur->start);
787 temp = cur;
788 cur = TAILQ_PREV(cur, sackhole_head, scblink);
789 tp->sackhint.hole_bytes -= temp->end - temp->start;
790 tcp_sackhole_remove(tp, temp);
791 /*
792 * The sack block may ack all or part of the
793 * next hole too, so continue onto the next
794 * hole.
795 */
796 continue;
797 } else {
798 /* Move start of hole forward. */
799 delivered_data += (sblkp->end - cur->start);
800 tp->sackhint.hole_bytes -= sblkp->end - cur->start;
801 cur->start = sblkp->end;
802 cur->rxmit = SEQ_MAX(cur->rxmit, cur->start);
803 }
804 } else {
805 /* Data acks at least the end of hole. */
806 if (SEQ_GEQ(sblkp->end, cur->end)) {
807 /* Move end of hole backward. */
808 delivered_data += (cur->end - sblkp->start);
809 tp->sackhint.hole_bytes -= cur->end - sblkp->start;
810 cur->end = sblkp->start;
811 cur->rxmit = SEQ_MIN(cur->rxmit, cur->end);
812 if ((tp->t_flags & TF_LRD) && SEQ_GEQ(cur->rxmit, cur->end))
813 cur->rxmit = tp->snd_recover;
814 } else {
815 /*
816 * ACKs some data in middle of a hole; need
817 * to split current hole
818 */
819 temp = tcp_sackhole_insert(tp, sblkp->end,
820 cur->end, cur);
821 sack_changed = SACK_NEWLOSS;
822 if (temp != NULL) {
823 if (SEQ_GT(cur->rxmit, temp->rxmit)) {
824 temp->rxmit = cur->rxmit;
825 tp->sackhint.sack_bytes_rexmit +=
826 (SEQ_MIN(temp->rxmit,
827 temp->end) - temp->start);
828 }
829 tp->sackhint.hole_bytes -= sblkp->end - sblkp->start;
830 loss_thresh += loss_hiack - temp->end;
831 loss_hiack = temp->start;
832 loss_sblks++;
833 if (!((loss_sblks >= tcprexmtthresh) ||
834 (loss_thresh > (tcprexmtthresh-1)*tp->t_maxseg)))
835 notlost_bytes += temp->end - temp->start;
836 cur->end = sblkp->start;
837 cur->rxmit = SEQ_MIN(cur->rxmit,
838 cur->end);
839 if ((tp->t_flags & TF_LRD) && SEQ_GEQ(cur->rxmit, cur->end))
840 cur->rxmit = tp->snd_recover;
841 delivered_data += (sblkp->end - sblkp->start);
842 }
843 }
844 }
845 tp->sackhint.sack_bytes_rexmit +=
846 (SEQ_MIN(cur->rxmit, cur->end) - cur->start);
847 /*
848 * Testing sblkp->start against cur->start tells us whether
849 * we're done with the sack block or the sack hole.
850 * Accordingly, we advance one or the other.
851 */
852 if (SEQ_LEQ(sblkp->start, cur->start)) {
853 loss_thresh += loss_hiack - cur->end;
854 loss_hiack = cur->start;
855 loss_sblks++;
856 if (!((loss_sblks >= tcprexmtthresh) ||
857 (loss_thresh > (tcprexmtthresh-1)*tp->t_maxseg)))
858 notlost_bytes += cur->end - cur->start;
859 cur = TAILQ_PREV(cur, sackhole_head, scblink);
860 } else {
861 sblkp--;
862 }
863 }
864
865 KASSERT(!(TAILQ_EMPTY(&tp->snd_holes) && (tp->sackhint.hole_bytes != 0)),
866 ("SACK scoreboard empty, but accounting non-zero\n"));
867
868 KASSERT(notlost_bytes <= tp->sackhint.hole_bytes,
869 ("SACK: more bytes marked notlost than in scoreboard holes"));
870
871 if (!(to->to_flags & TOF_SACK))
872 /*
873 * If this ACK did not contain any
874 * SACK blocks, any only moved the
875 * left edge right, it is a pure
876 * cumulative ACK. Do not count
877 * DupAck for this. Also required
878 * for RFC6675 rescue retransmission.
879 */
880 sack_changed = SACK_NOCHANGE;
881 tp->sackhint.delivered_data = delivered_data;
882 tp->sackhint.sacked_bytes += delivered_data - left_edge_delta;
883 tp->sackhint.lost_bytes = tp->sackhint.hole_bytes - notlost_bytes;
884 KASSERT((delivered_data >= 0), ("delivered_data < 0"));
885 KASSERT((tp->sackhint.sacked_bytes >= 0), ("sacked_bytes < 0"));
886 return (sack_changed);
887 }
888
889 /*
890 * Free all SACK holes to clear the scoreboard.
891 */
892 void
tcp_free_sackholes(struct tcpcb * tp)893 tcp_free_sackholes(struct tcpcb *tp)
894 {
895 struct sackhole *q;
896
897 INP_WLOCK_ASSERT(tptoinpcb(tp));
898 while ((q = TAILQ_FIRST(&tp->snd_holes)) != NULL)
899 tcp_sackhole_remove(tp, q);
900 tp->sackhint.sack_bytes_rexmit = 0;
901 tp->sackhint.delivered_data = 0;
902 tp->sackhint.sacked_bytes = 0;
903 tp->sackhint.hole_bytes = 0;
904 tp->sackhint.lost_bytes = 0;
905
906 KASSERT(tp->snd_numholes == 0, ("tp->snd_numholes == 0"));
907 KASSERT(tp->sackhint.nexthole == NULL,
908 ("tp->sackhint.nexthole == NULL"));
909 }
910
911 /*
912 * Resend all the currently existing SACK holes of
913 * the scoreboard. This is in line with the Errata to
914 * RFC 2018, which allows the use of SACK data past
915 * an RTO to good effect typically.
916 */
917 void
tcp_resend_sackholes(struct tcpcb * tp)918 tcp_resend_sackholes(struct tcpcb *tp)
919 {
920 struct sackhole *p;
921
922 INP_WLOCK_ASSERT(tptoinpcb(tp));
923 TAILQ_FOREACH(p, &tp->snd_holes, scblink) {
924 p->rxmit = p->start;
925 }
926 tp->sackhint.nexthole = TAILQ_FIRST(&tp->snd_holes);
927 tp->sackhint.sack_bytes_rexmit = 0;
928 }
929
930 /*
931 * Partial ack handling within a sack recovery episode. Keeping this very
932 * simple for now. When a partial ack is received, force snd_cwnd to a value
933 * that will allow the sender to transmit no more than 2 segments. If
934 * necessary, a better scheme can be adopted at a later point, but for now,
935 * the goal is to prevent the sender from bursting a large amount of data in
936 * the midst of sack recovery.
937 */
938 void
tcp_sack_partialack(struct tcpcb * tp,struct tcphdr * th,u_int * maxsegp)939 tcp_sack_partialack(struct tcpcb *tp, struct tcphdr *th, u_int *maxsegp)
940 {
941 struct sackhole *temp;
942 int num_segs = 1;
943 u_int maxseg;
944
945 INP_WLOCK_ASSERT(tptoinpcb(tp));
946
947 if (*maxsegp == 0) {
948 *maxsegp = tcp_maxseg(tp);
949 }
950 maxseg = *maxsegp;
951 tcp_timer_activate(tp, TT_REXMT, 0);
952 tp->t_rtttime = 0;
953 /* Send one or 2 segments based on how much new data was acked. */
954 if ((BYTES_THIS_ACK(tp, th) / maxseg) >= 2)
955 num_segs = 2;
956 if (V_tcp_do_newsack) {
957 tp->snd_cwnd = imax(tp->snd_nxt - th->th_ack +
958 tp->sackhint.sack_bytes_rexmit -
959 tp->sackhint.sacked_bytes -
960 tp->sackhint.lost_bytes, maxseg) +
961 num_segs * maxseg;
962 } else {
963 tp->snd_cwnd = (tp->sackhint.sack_bytes_rexmit +
964 imax(0, tp->snd_nxt - tp->snd_recover) +
965 num_segs * maxseg);
966 }
967 if (tp->snd_cwnd > tp->snd_ssthresh)
968 tp->snd_cwnd = tp->snd_ssthresh;
969 tp->t_flags |= TF_ACKNOW;
970 /*
971 * RFC6675 rescue retransmission
972 * Add a hole between th_ack (snd_una is not yet set) and snd_max,
973 * if this was a pure cumulative ACK and no data was send beyond
974 * recovery point. Since the data in the socket has not been freed
975 * at this point, we check if the scoreboard is empty, and the ACK
976 * delivered some new data, indicating a full ACK. Also, if the
977 * recovery point is still at snd_max, we are probably application
978 * limited. However, this inference might not always be true. The
979 * rescue retransmission may rarely be slightly premature
980 * compared to RFC6675.
981 * The corresponding ACK+SACK will cause any further outstanding
982 * segments to be retransmitted. This addresses a corner case, when
983 * the trailing packets of a window are lost and no further data
984 * is available for sending.
985 */
986 if ((V_tcp_do_newsack) &&
987 SEQ_LT(th->th_ack, tp->snd_recover) &&
988 TAILQ_EMPTY(&tp->snd_holes) &&
989 (tp->sackhint.delivered_data > 0)) {
990 /*
991 * Exclude FIN sequence space in
992 * the hole for the rescue retransmission,
993 * and also don't create a hole, if only
994 * the ACK for a FIN is outstanding.
995 */
996 tcp_seq highdata = tp->snd_max;
997 if (tp->t_flags & TF_SENTFIN)
998 highdata--;
999 highdata = SEQ_MIN(highdata, tp->snd_recover);
1000 if (SEQ_LT(th->th_ack, highdata)) {
1001 tp->snd_fack = th->th_ack;
1002 if ((temp = tcp_sackhole_insert(tp, SEQ_MAX(th->th_ack,
1003 highdata - maxseg), highdata, NULL)) != NULL) {
1004 tp->sackhint.hole_bytes +=
1005 temp->end - temp->start;
1006 }
1007 }
1008 }
1009 (void) tcp_output(tp);
1010 }
1011
1012 /*
1013 * Returns the next hole to retransmit and the number of retransmitted bytes
1014 * from the scoreboard. We store both the next hole and the number of
1015 * retransmitted bytes as hints (and recompute these on the fly upon SACK/ACK
1016 * reception). This avoids scoreboard traversals completely.
1017 *
1018 * The loop here will traverse *at most* one link. Here's the argument. For
1019 * the loop to traverse more than 1 link before finding the next hole to
1020 * retransmit, we would need to have at least 1 node following the current
1021 * hint with (rxmit == end). But, for all holes following the current hint,
1022 * (start == rxmit), since we have not yet retransmitted from them.
1023 * Therefore, in order to traverse more 1 link in the loop below, we need to
1024 * have at least one node following the current hint with (start == rxmit ==
1025 * end). But that can't happen, (start == end) means that all the data in
1026 * that hole has been sacked, in which case, the hole would have been removed
1027 * from the scoreboard.
1028 */
1029 struct sackhole *
tcp_sack_output(struct tcpcb * tp,int * sack_bytes_rexmt)1030 tcp_sack_output(struct tcpcb *tp, int *sack_bytes_rexmt)
1031 {
1032 struct sackhole *hole = NULL;
1033
1034 INP_WLOCK_ASSERT(tptoinpcb(tp));
1035 *sack_bytes_rexmt = tp->sackhint.sack_bytes_rexmit;
1036 hole = tp->sackhint.nexthole;
1037 if (hole == NULL)
1038 return (hole);
1039 if (SEQ_GEQ(hole->rxmit, hole->end)) {
1040 for (;;) {
1041 hole = TAILQ_NEXT(hole, scblink);
1042 if (hole == NULL)
1043 return (hole);
1044 if (SEQ_LT(hole->rxmit, hole->end)) {
1045 tp->sackhint.nexthole = hole;
1046 break;
1047 }
1048 }
1049 }
1050 KASSERT(SEQ_LT(hole->start, hole->end), ("%s: hole.start >= hole.end", __func__));
1051 if (!(V_tcp_do_newsack)) {
1052 KASSERT(SEQ_LT(hole->start, tp->snd_fack), ("%s: hole.start >= snd.fack", __func__));
1053 KASSERT(SEQ_LT(hole->end, tp->snd_fack), ("%s: hole.end >= snd.fack", __func__));
1054 KASSERT(SEQ_LT(hole->rxmit, tp->snd_fack), ("%s: hole.rxmit >= snd.fack", __func__));
1055 if (SEQ_GEQ(hole->start, hole->end) ||
1056 SEQ_GEQ(hole->start, tp->snd_fack) ||
1057 SEQ_GEQ(hole->end, tp->snd_fack) ||
1058 SEQ_GEQ(hole->rxmit, tp->snd_fack)) {
1059 log(LOG_CRIT,"tcp: invalid SACK hole (%u-%u,%u) vs fwd ack %u, ignoring.\n",
1060 hole->start, hole->end, hole->rxmit, tp->snd_fack);
1061 return (NULL);
1062 }
1063 }
1064 return (hole);
1065 }
1066
1067 /*
1068 * After a timeout, the SACK list may be rebuilt. This SACK information
1069 * should be used to avoid retransmitting SACKed data. This function
1070 * traverses the SACK list to see if snd_nxt should be moved forward.
1071 */
1072 void
tcp_sack_adjust(struct tcpcb * tp)1073 tcp_sack_adjust(struct tcpcb *tp)
1074 {
1075 struct sackhole *p, *cur = TAILQ_FIRST(&tp->snd_holes);
1076
1077 INP_WLOCK_ASSERT(tptoinpcb(tp));
1078 if (cur == NULL) {
1079 /* No holes */
1080 return;
1081 }
1082 if (SEQ_GEQ(tp->snd_nxt, tp->snd_fack)) {
1083 /* We're already beyond any SACKed blocks */
1084 return;
1085 }
1086 /*-
1087 * Two cases for which we want to advance snd_nxt:
1088 * i) snd_nxt lies between end of one hole and beginning of another
1089 * ii) snd_nxt lies between end of last hole and snd_fack
1090 */
1091 while ((p = TAILQ_NEXT(cur, scblink)) != NULL) {
1092 if (SEQ_LT(tp->snd_nxt, cur->end)) {
1093 return;
1094 }
1095 if (SEQ_GEQ(tp->snd_nxt, p->start)) {
1096 cur = p;
1097 } else {
1098 tp->snd_nxt = p->start;
1099 return;
1100 }
1101 }
1102 if (SEQ_LT(tp->snd_nxt, cur->end)) {
1103 return;
1104 }
1105 tp->snd_nxt = tp->snd_fack;
1106 }
1107
1108 /*
1109 * Lost Retransmission Detection
1110 * Check is FACK is beyond the rexmit of the leftmost hole.
1111 * If yes, we restart sending from still existing holes,
1112 * and adjust cwnd via the congestion control module.
1113 */
1114 void
tcp_sack_lost_retransmission(struct tcpcb * tp,struct tcphdr * th)1115 tcp_sack_lost_retransmission(struct tcpcb *tp, struct tcphdr *th)
1116 {
1117 struct sackhole *temp;
1118
1119 if (IN_RECOVERY(tp->t_flags) &&
1120 SEQ_GT(tp->snd_fack, tp->snd_recover) &&
1121 ((temp = TAILQ_FIRST(&tp->snd_holes)) != NULL) &&
1122 SEQ_GEQ(temp->rxmit, temp->end) &&
1123 SEQ_GEQ(tp->snd_fack, temp->rxmit)) {
1124 TCPSTAT_INC(tcps_sack_lostrexmt);
1125 /*
1126 * Start retransmissions from the first hole, and
1127 * subsequently all other remaining holes, including
1128 * those, which had been sent completely before.
1129 */
1130 tp->sackhint.nexthole = temp;
1131 TAILQ_FOREACH(temp, &tp->snd_holes, scblink) {
1132 if (SEQ_GEQ(tp->snd_fack, temp->rxmit) &&
1133 SEQ_GEQ(temp->rxmit, temp->end))
1134 temp->rxmit = temp->start;
1135 }
1136 /*
1137 * Remember the old ssthresh, to deduct the beta factor used
1138 * by the CC module. Finally, set cwnd to ssthresh just
1139 * prior to invoking another cwnd reduction by the CC
1140 * module, to not shrink it excessively.
1141 */
1142 tp->snd_cwnd = tp->snd_ssthresh;
1143 /*
1144 * Formally exit recovery, and let the CC module adjust
1145 * ssthresh as intended.
1146 */
1147 EXIT_RECOVERY(tp->t_flags);
1148 cc_cong_signal(tp, th, CC_NDUPACK);
1149 /*
1150 * For PRR, adjust recover_fs as if this new reduction
1151 * initialized this variable.
1152 * cwnd will be adjusted by SACK or PRR processing
1153 * subsequently, only set it to a safe value here.
1154 */
1155 tp->snd_cwnd = tcp_maxseg(tp);
1156 tp->sackhint.recover_fs = (tp->snd_max - tp->snd_una) -
1157 tp->sackhint.recover_fs;
1158 }
1159 }
1160