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From: Chao Li <[email protected]>
To: Antonin Houska <[email protected]>
Cc: Postgres hackers <[email protected]>
Subject: Re: repack: fix uninitialized DecodingWorkerShared.initialized
Date: Fri, 17 Apr 2026 11:41:37 +0800
Message-ID: <[email protected]> (raw)
In-Reply-To: <26785.1776265652@localhost>
References: <[email protected]>
	<26785.1776265652@localhost>



> On Apr 15, 2026, at 23:07, Antonin Houska <[email protected]> wrote:
> 
> Chao Li <[email protected]> wrote:
> 
>> I have not reviewed the repack-related patches before. Recently, I started trying to understand how repack works and trace through the code.
> 
> Thanks, I appreciate that!
> 
>> While tracing start_repack_decoding_worker(), I noticed something suspicious:
>> 
>> ```
>> seg = dsm_create(size, 0);
>> shared = (DecodingWorkerShared *) dsm_segment_address(seg);
>> shared->lsn_upto = InvalidXLogRecPtr;
>> shared->done = false;
>> SharedFileSetInit(&shared->sfs, seg);
>> shared->last_exported = -1;
>> SpinLockInit(&shared->mutex);
>> shared->dbid = MyDatabaseId;
>> ```
>> 
>> Here, the code creates a shared-memory segment and lets “shared" point to that memory. It then initializes some fields of “shared". However, later code reads shared->initialized, but this field was not initialized:
> 
> The problem was noticed earlier this week and I already posted a fix [1].
> 
>> For the fix, since start_repack_decoding_worker() is not on a hot path, I think it is fine to zero the whole shared struct explicitly, and then initialize the non-zero fields afterwards.
> 
> Although not strongly, I prefer setting individual fields explicitly.
> 
> 
> [1] https://www.postgresql.org/message-id/182883.1776073323%40localhost
> 
> -- 
> Antonin Houska
> Web: https://www.cybertec-postgresql.com

I saw 05c401d5786a05ea630e884ffa492aa01683d15b has fixed this issue, so this patch is no longer needed.

Best regards,
--
Chao Li (Evan)
HighGo Software Co., Ltd.
https://www.highgo.com/

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