linux-kernel - Re: Mild filesystem corruption on ext4 (no journal)

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Message-ID: <4A298EF5.9000504@tuffmail.co.uk>
Date:	Fri, 05 Jun 2009 22:32:37 +0100
From:	Alan Jenkins <alan-jenkins@...fmail.co.uk>
To:	Eric Sandeen <sandeen@...hat.com>
CC:	Aioanei Rares <krnl.list@...il.com>, linux-ext4@...r.kernel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Mild filesystem corruption on ext4 (no journal)

Eric Sandeen wrote:
> Alan Jenkins wrote:
>   
>> Eric Sandeen wrote:
>>     
>
>   
>>> Maybe you could try some things in your shutdown script, such as
>>> explicitly fsyncing the file, or bmapping it with filefrag, or dropping
>>> caches and rereading it... see what the state is just before the
>>> shutdown compared to after the reboot.
>>>
>>> -Eric
>>>   
>>>       
>> Dropping caches (and running sync first) had no effect on the result of 
>> md5sum.  Hopefully that narrows it down a bit.
>>     
>
> And did the reread after dropping caches have the right data?
>   

Yes.

> Did the block numbers reported by filefrag -v change post-boot?
>   

Oh, I didn't understand that's what you were asking for.

The bug report Ted linked to says it's (most likely) a writeback issue.  
In which case I think the block numbers won't change.  I'll check 
tomorrow, and follow-up if it turns up any unexpected result.

There's also speculation that it's a core kernel issue, something that 
changed since 2.6.26.  Perhaps that explains how remount-ro + sync + 
drop_caches can leave the correct data sitting in the pagecache, without 
either writing it to disk or dropping it.

Thanks
Alan
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