pgsql: Fix possibility of self-deadlock in ResolveRecoveryConflictWithB - Mailing list pgsql-committers

From Andres Freund
Subject pgsql: Fix possibility of self-deadlock in ResolveRecoveryConflictWithB
Date
Msg-id E1nlhXe-002GeV-9x@gemulon.postgresql.org
Whole thread Raw
List pgsql-committers
Fix possibility of self-deadlock in ResolveRecoveryConflictWithBufferPin().

The tests added in 9f8a050f68d failed nearly reliably on FreeBSD in CI, and
occasionally on the buildfarm. That turns out to be caused not by a bug in the
test, but by a longstanding bug in recovery conflict handling.

The standby timeout handler, used by ResolveRecoveryConflictWithBufferPin(),
executed SendRecoveryConflictWithBufferPin() inside a signal handler. A bad
idea, because the deadlock timeout handler (or a spurious latch set) could
have interrupted ProcWaitForSignal(). If unlucky that could cause a
self-deadlock on ProcArrayLock, if the deadlock check is in
SendRecoveryConflictWithBufferPin()->CancelDBBackends().

To fix, set a flag in StandbyTimeoutHandler(), and check the flag in
ResolveRecoveryConflictWithBufferPin().

Subsequently the recovery conflict tests will be backpatched.

Discussion: https://postgr.es/m/20220413002626.udl7lll7f3o7nre7@alap3.anarazel.de
Backpatch: 10-

Branch
------
REL_14_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/9ab3b2bdbb5dc4ff857685eae5645d7c35839055

Modified Files
--------------
src/backend/storage/ipc/standby.c | 20 ++++++++++----------
1 file changed, 10 insertions(+), 10 deletions(-)


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