From: Tom Lane <tgl@sss.pgh.pa.us>
To: Peter Geoghegan <pg@bowt.ie>
cc: Andres Freund <andres@anarazel.de>,
        PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Subject: Re: PANIC: wrong buffer passed to visibilitymap_clear
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Comments: In-reply-to Peter Geoghegan <pg@bowt.ie>
	message dated "Mon, 12 Apr 2021 11:03:13 -0700"
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Date: Mon, 12 Apr 2021 21:33:19 -0400
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Peter Geoghegan <pg@bowt.ie> writes:
> On Mon, Apr 12, 2021 at 9:19 AM Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> Hence, I propose the attached.  It passes check-world, but that proves
>> absolutely nothing of course :-(.  I wonder if there is any way to
>> exercise these code paths deterministically.

> This approach seems reasonable to me. At least you've managed to
> structure the visibility map page pin check as concomitant with the
> existing space recheck.

Thanks for looking it over.  Do you have an opinion on whether or not
to back-patch?  As far as we know, these bugs aren't exposed in the
back branches for lack of code that would set the all-visible flag
without superexclusive lock.  But I'd still say that heap_update
is failing to honor its API contract in these edge cases, and that
seems like something that could bite us after future back-patches.
Or there might be third-party code that can set all-visible flags.
So I'm kind of tempted to back-patch, but it's a judgment call.

			regards, tom lane