pgsql: Fix crash with RemoveFromWaitQueue() when detecting a deadlock.

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

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/bd88404d3cda53810e0b0144713c4b1a1dd965a8

Modified Files
--------------
src/backend/storage/lmgr/lock.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)