From: Chao Li <li.evan.chao@gmail.com>
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Subject: Fix bug of clearing of waitStart in ProcWakeup()
Message-Id: <537BD852-EC61-4D25-AB55-BE8BE46D07D7@gmail.com>
Date: Tue, 24 Feb 2026 14:28:15 +0800
To: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Archived-At: 
 <https://www.postgresql.org/message-id/537BD852-EC61-4D25-AB55-BE8BE46D07D7%40gmail.com>
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Hi,

I just noticed this while reviewing patch [1]. It looks like this is =
caused by a simple typo.

In ProcWakeup():
```
PGPROC *
ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus)
{
	PGPROC	   *retProc;

	/* Proc should be sleeping ... */
	if (proc->links.prev =3D=3D NULL ||
		proc->links.next =3D=3D NULL)
		return NULL;
	Assert(proc->waitStatus =3D=3D PROC_WAIT_STATUS_WAITING);

	/* Save next process before we zap the list link */
	retProc =3D (PGPROC *) proc->links.next;

	/* Remove process from wait queue */
	SHMQueueDelete(&(proc->links));
	(proc->waitLock->waitProcs.size)--;

	/* Clean up process' state and pass it the ok/fail signal */
	proc->waitLock =3D NULL;
	proc->waitProcLock =3D NULL;
	proc->waitStatus =3D waitStatus;
	pg_atomic_write_u64(&MyProc->waitStart, 0); <=3D=3D Here, it =
should operate on proc

	/* And awaken it */
	SetLatch(&proc->procLatch);

	return retProc;
}
```

Since this function is clearly operating on the parameter proc, the only =
statement that touches MyProc looks suspicious. It should reset =
proc->waitStart, not MyProc->waitStart.

As written, it will incorrectly clear the caller=E2=80=99s waitStart =
instead of the awakened backend=E2=80=99s, potentially leaving a stale =
waitStart value in the target PGPROC.

[1] =
https://postgr.es/m/CAHGQGwGw4LhNwOGQT3nbw3uWy8gL94_MB4T39Wfr4_Vgopuovg@ma=
il.gmail.com

Best regards,
--
Chao Li (Evan)
HighGo Software Co., Ltd.
https://www.highgo.com/