From: Michael Paquier <michael@paquier.xyz>
To: feichanghong <feichanghong@qq.com>
Cc: pgsql-bugs <pgsql-bugs@lists.postgresql.org>
Cc: andres <andres@anarazel.de>
Cc: sawada.mshk <sawada.mshk@gmail.com>
Cc: horikyota.ntt <horikyota.ntt@gmail.com>
Subject: Re: ReplicationSlotRelease may set the statusFlags of other processes in PG14
Date: Tue, 19 Mar 2024 12:57:51 +0900
Message-ID: <ZfkNP1OdgBSPPTsR@paquier.xyz> (raw)
In-Reply-To: <tencent_CA7420C82971BC4B64F0748A7D2898A4720A@qq.com>
References: <tencent_CA7420C82971BC4B64F0748A7D2898A4720A@qq.com>
On Sat, Mar 16, 2024 at 10:29:03PM +0800, feichanghong wrote:
> A process utilizing replication slots (usually walsender) calls callback
> functions in the order of RemoveProcFromArray->ProcKill upon abnormal exit.
> Within RemoveProcFromArray, MyProc is already removed from the ProcArray.
> ProcKill then attempts to set ProcGlobal->statusFlags[MyProc->pgxactoff] again
> via ReplicationSlotRelease. By this time, the flag may already be assigned to
> another process.
Oops.
> To replicate the issue, execute the following steps:
> 1. Apply the attached v1-0000-v14-invalidate-pgxactoff-after-remove-pgproc.patch,
> where pgxactoff is set to an invalid value in ProcArrayRemove, and some
> checks are added.
> 2. Use the SQL below to terminate the walsender process.
> ```
> select pg_terminate_backend(pid) from pg_stat_activity where backend_type = 'walsender';
> ```
> # Fix
>
> To fix the issue, I have provided some patches in the attachment:
> 1. Backpatching 2f6501f into the PG14 version will fix the problem.
> 2. In PG14-head, ProcArrayRemove needs to reset pgxactoff, and some assert
> checks should be done when setting ProcGlobal->statusFlags.
Yeah, that's something that we had better fix in all stable branches.
The asserts would offer some protection moving on, but I would take
the safer move of only adding a protection like what you are
suggestion on HEAD and not in stable branches, just in case we're
missing something around them.
--
Michael
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To: pgsql-bugs@postgresql.org
Cc: michael@paquier.xyz, feichanghong@qq.com, pgsql-bugs@lists.postgresql.org, andres@anarazel.de, sawada.mshk@gmail.com, horikyota.ntt@gmail.com
Subject: Re: ReplicationSlotRelease may set the statusFlags of other processes in PG14
In-Reply-To: <ZfkNP1OdgBSPPTsR@paquier.xyz>
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