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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Peter Geoghegan <pg@bowt.ie>
Cc: Andres Freund <andres@anarazel.de>
Cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Subject: Re: PANIC: wrong buffer passed to visibilitymap_clear
Date: Mon, 12 Apr 2021 21:33:19 -0400
Message-ID: <3139938.1618277599@sss.pgh.pa.us> (raw)
In-Reply-To: <CAH2-WznPo0D2t9fBgK5jKjprdLxsJvy_PnnFxUeF2ftFxXstsg@mail.gmail.com>
References: <2247102.1618008027@sss.pgh.pa.us>
	<20210409232739.sazp5p4xnnagrusa@alap3.anarazel.de>
	<20210409233203.3khg3s5iw34g4xrc@alap3.anarazel.de>
	<2644575.1618117467@sss.pgh.pa.us>
	<CAH2-WzmWOLaWhQgEC1BJN0JZpOCOwxCAhjmd2Nd4yh4wrqju8Q@mail.gmail.com>
	<2679216.1618156670@sss.pgh.pa.us>
	<CAH2-WzmJ7THDU3jPgRH8J++b+pSoOh8nfGZEhNHh+4=LFatDeg@mail.gmail.com>
	<CAH2-WzkCXg6RQJdc_7ZGHcKvyoJAfFu9R2ZVAiE9mCcOfaXJdQ@mail.gmail.com>
	<2689873.1618161194@sss.pgh.pa.us>
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	<2691724.1618163730@sss.pgh.pa.us>
	<CAH2-Wz=_u6ObPqg1Ar638U2CB6thvuni=StjLQ7iniuKX9YZdA@mail.gmail.com>
	<2692613.1618164979@sss.pgh.pa.us>
	<CAH2-WzkmFhemeqNvKKuf9orpSq8DOBjeMPN1G-=c+441hvr0NQ@mail.gmail.com>
	<2902168.1618244388@sss.pgh.pa.us>
	<CAH2-WznPo0D2t9fBgK5jKjprdLxsJvy_PnnFxUeF2ftFxXstsg@mail.gmail.com>

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





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