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help / color / mirror / Atom feedFrom: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
To: Michael Paquier <michael@paquier.xyz>
Cc: Ewan Young <kdbase.hack@gmail.com>
Cc: pgsql-hackers@lists.postgresql.org
Subject: Re: Prevent crash when calling pgstat functions with unregistered stats kind
Date: Thu, 2 Jul 2026 04:06:01 +0000
Message-ID: <akXjqbXRTLNcwHyE@bdtpg> (raw)
In-Reply-To: <akXebziFr_eQgQi8@paquier.xyz>
References: <akS/ldidWeqG1FWk@bdtpg>
<CAON2xHOA23Oq8EERoV9ERBZof1O_vN-tYf0q58TwdkrTNZ-SPg@mail.gmail.com>
<akXalpb3zjPX3ZEl@bdtpg>
<akXebziFr_eQgQi8@paquier.xyz>
Hi,
On Thu, Jul 02, 2026 at 12:43:43PM +0900, Michael Paquier wrote:
> On Thu, Jul 02, 2026 at 03:27:18AM +0000, Bertrand Drouvot wrote:
> > On Wed, Jul 01, 2026 at 04:20:39PM +0800, Ewan Young wrote:
> >> One small thing: in pgstat_snapshot_fixed(), the existing
> >> Assert(pgstat_is_kind_valid(kind)); becomes redundant after the new NULL
> >> check. A non-NULL kind_info already implies the kind is valid (that's the
> >> only way pgstat_get_kind_info() returns non-NULL), so the assert can never
> >> fire. Might as well drop it and keep just the fixed_amount one.
> >
> > Yeah good catch, done in the attached.
>
> I am not convinced that it is worth bothering in the core code about
> this class of failures; they are just not interesting, and impossible
> to miss.
>
> It seems to me that this error is in the _PG_init() of the modules in
> modules/test_custom_stats/: we should not bypass the
> pgstat_register_kind() if not loading the library from
> shared_preload_libraries, but let the call happen and fail.
I agree that the responsibility should primarily be in the extension. However,
the issue is that the NULL dereference happens inside core code (pgstat_prep_pending_entry,
etc.), and the resulting segfault(s) cause the postmaster to terminate all
backends (not just the offending session).
Given that one misconfigured extension can crash all connections on the server,
a defensive check in core seems reasonable (kind of similar to 341e9a05e7b).
Regards,
--
Bertrand Drouvot
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com
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To: pgsql-hackers@postgresql.org
Cc: bertranddrouvot.pg@gmail.com, michael@paquier.xyz, kdbase.hack@gmail.com, pgsql-hackers@lists.postgresql.org
Subject: Re: Prevent crash when calling pgstat functions with unregistered stats kind
In-Reply-To: <akXjqbXRTLNcwHyE@bdtpg>
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