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 6fbbf5c16570b2ba48f7b4e546d2cf7de5374b5f..93c4324534b41a18d0ed111d8793e6a6eb529c59 100644 (file)
--- a/src/backend/storage/lmgr/proc.c
+++ b/src/backend/storage/lmgr/proc.c
@@ -1695,7 +1695,7 @@ 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);