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Fix blackhole detection.

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There were two bugs related to the blackhole detection:
* The smalles size was tried more than two times.
* The restored MSS was not the original one, but the second
  candidate.

MFC after:	1 week
Sponsored by:	Netflix, Inc.
This commit is contained in:
Michael Tuexen 2017-08-28 11:41:18 +00:00
parent 5d17a1d629
commit 3d5af7a127
1 changed files with 9 additions and 7 deletions
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16
sys/netinet/tcp_timer.c
View File

@ -726,18 +726,20 @@ tcp_timer_rexmt(void * xtp)
*/
if (((tp->t_flags2 & (TF2_PLPMTU_PMTUD|TF2_PLPMTU_MAXSEGSNT)) ==
(TF2_PLPMTU_PMTUD|TF2_PLPMTU_MAXSEGSNT)) &&
(tp->t_rxtshift >= 2 && tp->t_rxtshift % 2 == 0)) {
(tp->t_rxtshift >= 2 && tp->t_rxtshift < 6 &&
tp->t_rxtshift % 2 == 0)) {
/*
* Enter Path MTU Black-hole Detection mechanism:
* - Disable Path MTU Discovery (IP "DF" bit).
* - Reduce MTU to lower value than what we
* negotiated with peer.
*/
/* Record that we may have found a black hole. */
tp->t_flags2 |= TF2_PLPMTU_BLACKHOLE;
/* Keep track of previous MSS. */
tp->t_pmtud_saved_maxseg = tp->t_maxseg;
if ((tp->t_flags2 & TF2_PLPMTU_BLACKHOLE) == 0) {
/* Record that we may have found a black hole. */
tp->t_flags2 |= TF2_PLPMTU_BLACKHOLE;
/* Keep track of previous MSS. */
tp->t_pmtud_saved_maxseg = tp->t_maxseg;
}
/*
* Reduce the MSS to blackhole value or to the default
@ -796,7 +798,7 @@ tcp_timer_rexmt(void * xtp)
* stage (1448, 1188, 524) 2 chances to recover.
*/
if ((tp->t_flags2 & TF2_PLPMTU_BLACKHOLE) &&
(tp->t_rxtshift > 6)) {
(tp->t_rxtshift >= 6)) {
tp->t_flags2 |= TF2_PLPMTU_PMTUD;
tp->t_flags2 &= ~TF2_PLPMTU_BLACKHOLE;
tp->t_maxseg = tp->t_pmtud_saved_maxseg;