[4.1] 3e19f33 Fix race in the VSL segment counter initialization
PÃ¥l Hermunn Johansen
hermunn at varnish-software.com
Tue Apr 4 17:10:07 CEST 2017
commit 3e19f335e78e8100ae0eb3c9ddc0d4f14c389430
Author: Martin Blix Grydeland <martin at varnish-software.com>
Date: Tue Mar 7 17:13:26 2017 +0100
Fix race in the VSL segment counter initialization
Fix a stupid misstake where the segment counter in the VSL segment was
set just before the entire struct was cleared during
initialization. This didn't cause problems in the common case because
it would be set correctly on the very first log line produced. But it
did open a race where an unfortunate early log client would assume it
was lagging indefinetely behind varnishd on the log reading and report
overflow error. This was most commonly experienced with varnishtest.
Fixes: #2241
diff --git a/bin/varnishd/cache/cache_shmlog.c b/bin/varnishd/cache/cache_shmlog.c
index 789e902..b96bf73 100644
--- a/bin/varnishd/cache/cache_shmlog.c
+++ b/bin/varnishd/cache/cache_shmlog.c
@@ -470,13 +470,13 @@ VSM_Init(void)
problems with regard to readers on that event visible */
vsl_segment_n = UINT_MAX - VSL_SEGMENTS + 1;
AZ(vsl_segment_n % VSL_SEGMENTS);
- vsl_head->segment_n = vsl_segment_n;
vsl_ptr = vsl_head->log;
*vsl_ptr = VSL_ENDMARKER;
memset(vsl_head, 0, sizeof *vsl_head);
vsl_head->segsize = vsl_segsize;
vsl_head->offset[0] = 0;
+ vsl_head->segment_n = vsl_segment_n;
for (i = 1; i < VSL_SEGMENTS; i++)
vsl_head->offset[i] = -1;
VWMB();
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