Fix assertion failure with latch wait in single-user mode

michaelpq · rdunklau · michaelpq · commit f7dfccf9605d · 2025-07-25T16:17:31.000+09:00
LatchWaitSetPostmasterDeathPos, the latch event position for the postmaster death event, is initialized under IsUnderPostmaster. WaitLatch() considered it as a valid wait target in single-user mode (!IsUnderPostmaster), which was incorrect. One code path found to fail with an assertion failure is a database drop in single-user mode while waiting in WaitForProcSignalBarrier() after the drop. Oversight in commit 84e5b2f. Author: Patrick Stählin <me@packi.ch> Co-authored-by: Ronan Dunklau <ronan.dunklau@aiven.io> Discussion: https://postgr.es/m/18996-3a2744c8140488de@postgresql.org Backpatch-through: 18
diff --git a/src/backend/storage/ipc/latch.c b/src/backend/storage/ipc/latch.c
@@ -187,9 +187,11 @@ WaitLatch(Latch *latch, int wakeEvents, long timeout,
 	if (!(wakeEvents & WL_LATCH_SET))
 		latch = NULL;
 	ModifyWaitEvent(LatchWaitSet, LatchWaitSetLatchPos, WL_LATCH_SET, latch);
-	ModifyWaitEvent(LatchWaitSet, LatchWaitSetPostmasterDeathPos,
-					(wakeEvents & (WL_EXIT_ON_PM_DEATH | WL_POSTMASTER_DEATH)),
-					NULL);
+
+	if (IsUnderPostmaster)
+		ModifyWaitEvent(LatchWaitSet, LatchWaitSetPostmasterDeathPos,
+						(wakeEvents & (WL_EXIT_ON_PM_DEATH | WL_POSTMASTER_DEATH)),
+						NULL);
 
 	if (WaitEventSetWait(LatchWaitSet,
 						 (wakeEvents & WL_TIMEOUT) ? timeout : -1,
