Author: tuexen
Date: Mon Aug 28 11:41:18 2017
New Revision: 322967
URL: https://svnweb.freebsd.org/changeset/base/322967
Log:
Fix blackhole detection.
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.
Modified:
head/sys/netinet/tcp_timer.c
Modified: head/sys/netinet/tcp_timer.c
==============================================================================
--- head/sys/netinet/tcp_timer.c Mon Aug 28 10:02:47 2017
(r322966)
+++ head/sys/netinet/tcp_timer.c Mon Aug 28 11:41:18 2017
(r322967)
@@ -726,19 +726,21 @@ 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;
+ 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;
+ }
- /* Keep track of previous MSS. */
- tp->t_pmtud_saved_maxseg = tp->t_maxseg;
-
/*
* Reduce the MSS to blackhole value or to the default
* in an attempt to retransmit.
@@ -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;
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