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 f595bce31b942a4f415337b7bbf46118505bf3a4..ec6240fbaeed309dbddb7063df848b00d5b8778f 100644 (file)
--- 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);