From: Masahiko Sawada <msawada@postgresql.org>
Date: Wed, 26 Jul 2023 05:41:23 +0000 (+0900)
Subject: Fix crash with RemoveFromWaitQueue() when detecting a deadlock.
X-Git-Tag: REL_16_BETA3~14
X-Git-Url: http://git.postgresql.org/gitweb/?a=commitdiff_plain;h=b4f14d2e433bf9f2499f07bcaca07b9ff13d641b;p=postgresql.git

Fix crash with RemoveFromWaitQueue() when detecting a deadlock.

Commit 5764f611e 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
index f595bce31b9..ec6240fbaee 100644
--- 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);