Re: Double content-lock acquisition silently leaks a lock

Hi,

On 2026-09-22 11:15:11 -0400, Andres Freund wrote:
> On 2026-09-22 14:54:33 +0000, Greg Burd wrote:
> > BufferLockAcquire() only asserts that the current backend does not already hold
> > a content lock on the buffer. I hit that assertion on a buildfarm animal, and
> > while chasing it I convinced myself that the non-assert behaviour is worse than
> > the crash in that it can permanently wedges the buffer.
>
> That's completely normal for assertion paths IME.
>
>
> > Patch attached to turn the assertion into an error. I am not proposing it
> > as the whole fix; details and an open question below.
>
> -0.5, it shows up in profiles for me. If we had support for something like
> production assertions, with a lower overhead, I'd maybe +0.5 instead, but we
> don't.
>
> And I am fundamentally opposed to not make this an assertion failure. This is
> a fundamentally broken program, that needs to trigger assertion
> failures. There's way way too many contexts where an ERROR is basically
> invisible.

Also note that for lwlocks you'd indefinitely hang on a double exclusive
acquisition - no assertion.

Greetings,

Andres Freund