Fix ProcWakeup() resetting wrong waitStart field.

Previously, when one process woke another that was waiting on a lock,
ProcWakeup() incorrectly cleared its own waitStart field (i.e.,
MyProc->waitStart) instead of that of the process being awakened.
As a result, the awakened process retained a stale lock-wait start timestamp.

This did not cause user-visible issues. pg_locks.waitstart was reported as
NULL for the awakened process (i.e., when pg_locks.granted is true),
regardless of the waitStart value.

This bug was introduced by commit 46d6e5f56790.

This commit fixes this by resetting the waitStart field of the process
being awakened in ProcWakeup().

Backpatch to all supported branches.

Reported-by: Chao Li <li.evan.chao@gmail.com>
Author: Chao Li <li.evan.chao@gmail.com>
Reviewed-by: ji xu <thanksgreed@gmail.com>
Reviewed-by: Álvaro Herrera <alvherre@kurilemu.de>
Discussion: https://postgr.es/m/537BD852-EC61-4D25-AB55-BE8BE46D07D7@gmail.com
Backpatch-through: 14

diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c
index e9ef0fbfe32cb724744e2381fbe9c89561a35dbb..706c11980375055f9b032e5b6c124d9c0639b06f 100644 (file)
--- a/src/backend/storage/lmgr/proc.c
+++ b/src/backend/storage/lmgr/proc.c
@@ -1722,7 +1722,7 @@ ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus)
        proc->waitLock = NULL;
        proc->waitProcLock = NULL;
        proc->waitStatus = waitStatus;
-       pg_atomic_write_u64(&MyProc->waitStart, 0);
+       pg_atomic_write_u64(&proc->waitStart, 0);
 
        /* And awaken it */
        SetLatch(&proc->procLatch);