From: Tom Lane <tgl@sss.pgh.pa.us>
To: Peter Geoghegan <pg@bowt.ie>
cc: Jaime Casanova <jcasanov@systemguards.com.ec>,
        pgsql-committers@lists.postgresql.org
Subject: Re: pgsql: Avoid improbable PANIC during heap_update.
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Comments: In-reply-to Peter Geoghegan <pg@bowt.ie>
	message dated "Fri, 30 Sep 2022 14:39:20 -0700"
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Date: Fri, 30 Sep 2022 17:56:11 -0400
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Peter Geoghegan <pg@bowt.ie> writes:
> On Fri, Sep 30, 2022 at 2:28 PM Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> Ugh ... I think I see the problem.  There's still one path through
>> RelationGetBufferForTuple that fails to guarantee that it's acquired
>> a vmbuffer pin if the all-visible flag becomes set in the otherBuffer.

> FWIW it seems possible that the Postgres 15 vacuumlazy.c work that
> added lazy_scan_noprune() made this scenario more likely in practice
> -- even compared to Postgres 14.

Could be, because we haven't seen field reports of this in v14 yet.
And there's still no hard evidence of a bug pre-14.  Nonetheless,
I'm inclined to backpatch to v12 as 34f581c39 was.

			regards, tom lane