Subject: [PATCH vREL_10_STABLE 1/2] Fix possibility of self-deadlock in ResolveRecoveryConflictWithBufferPin().

From: Andres Freund <[email-masked]>
Date: Fri, 29 Apr 2022 12:50:10 -0700

Author:
Reviewed-By:
Discussion: https://postgr.es/m/[email-masked]
Backpatch:
---
 src/backend/storage/ipc/standby.c | 22 ++++++++++++----------
 1 file changed, 12 insertions(+), 10 deletions(-)

diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index 863cb641007..47cdaead9e6 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -44,6 +44,7 @@ static HTAB *RecoveryLockLists;
 
 /* Flags set by timeout handlers */
 static volatile sig_atomic_t got_standby_deadlock_timeout = false;
+static volatile sig_atomic_t got_standby_delay_timeout = false;
 static volatile sig_atomic_t got_standby_lock_timeout = false;
 
 static void ResolveRecoveryConflictWithVirtualXIDs(VirtualTransactionId *waitlist,
@@ -593,10 +594,15 @@ ResolveRecoveryConflictWithBufferPin(void)
 		enable_timeouts(timeouts, cnt);
 	}
 
-	/* Wait to be signaled by UnpinBuffer() */
+	/*
+	 * Wait to be signaled by UnpinBuffer() or for the wait to be interrupted
+	 * by one of the timeouts established above.
+	 */
 	ProcWaitForSignal(PG_WAIT_BUFFER_PIN);
 
-	if (got_standby_deadlock_timeout)
+	if (got_standby_delay_timeout)
+		SendRecoveryConflictWithBufferPin(PROCSIG_RECOVERY_CONFLICT_BUFFERPIN);
+	else if (got_standby_deadlock_timeout)
 	{
 		/*
 		 * Send out a request for hot-standby backends to check themselves for
@@ -622,6 +628,7 @@ ResolveRecoveryConflictWithBufferPin(void)
 	 * individually, but that'd be slower.
 	 */
 	disable_all_timeouts(false);
+	got_standby_delay_timeout = false;
 	got_standby_deadlock_timeout = false;
 }
 
@@ -681,8 +688,8 @@ CheckRecoveryConflictDeadlock(void)
  */
 
 /*
- * StandbyDeadLockHandler() will be called if STANDBY_DEADLOCK_TIMEOUT
- * occurs before STANDBY_TIMEOUT.
+ * StandbyDeadLockHandler() will be called if STANDBY_DEADLOCK_TIMEOUT is
+ * exceeded.
  */
 void
 StandbyDeadLockHandler(void)
@@ -692,16 +699,11 @@ StandbyDeadLockHandler(void)
 
 /*
  * StandbyTimeoutHandler() will be called if STANDBY_TIMEOUT is exceeded.
- * Send out a request to release conflicting buffer pins unconditionally,
- * so we can press ahead with applying changes in recovery.
  */
 void
 StandbyTimeoutHandler(void)
 {
-	/* forget any pending STANDBY_DEADLOCK_TIMEOUT request */
-	disable_timeout(STANDBY_DEADLOCK_TIMEOUT, false);
-
-	SendRecoveryConflictWithBufferPin(PROCSIG_RECOVERY_CONFLICT_BUFFERPIN);
+	got_standby_delay_timeout = true;
 }
 
 /*
-- 
2.35.1.677.gabf474a5dd

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