Fix crash with RemoveFromWaitQueue() when detecting a deadlock.

MasahikoSawada · MasahikoSawada · commit bd88404d3cda · 2023-07-26T14:41:26.000+09:00
Commit 5764f61 used dclist_delete_from() to remove the proc from the wait queue. However, since it doesn't clear dist_node's next/prev to NULL, it could call RemoveFromWaitQueue() twice: when the process detects a deadlock and then when cleaning up locks on aborting the transaction. The waiting lock information is cleared in the first call, so it led to a crash in the second call. Backpatch to v16, where the change was introduced. Bug: #18031 Reported-by: Justin Pryzby, Alexander Lakhin Reviewed-by: Andres Freund Discussion: https://postgr.es/m/ZKy4AdrLEfbqrxGJ%40telsasoft.com Discussion: https://postgr.es/m/18031-ebe2d08cb405f6cc@postgresql.org Backpatch-through: 16
diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c
@@ -1881,7 +1881,7 @@ RemoveFromWaitQueue(PGPROC *proc, uint32 hashcode)
 	Assert(0 < lockmethodid && lockmethodid < lengthof(LockMethods));
 
 	/* Remove proc from lock's wait queue */
-	dclist_delete_from(&waitLock->waitProcs, &proc->links);
+	dclist_delete_from_thoroughly(&waitLock->waitProcs, &proc->links);
 
 	/* Undo increments of request counts by waiting process */
 	Assert(waitLock->nRequested > 0);
