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

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Date:	Fri, 05 Jun 2009 17:43:01 +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:
>   
>> Aioanei Rares wrote:
>>     
>
>   
>>> I suspect, although I might be wrong, that this is not a kernel-related
>>> problem.
>>>       
>> "To try and rule out a faulty userspace program, I marked the file as 
>> read-only (chmod a-w) and immutable (chattr +i).  After a reboot, the 
>> file was still read-only and immutable, yet it still became corrupted."
>>
>> Since the immutable bit is not respected, I tend to think it is a kernel 
>> problem.  Unless the filesystem isn't getting unmounted/flushed properly 
>> for some reason... but I thought the modern kernel had that covered.
>>
>> I agree it is very suspicious this happens only after upgrading libc.  
>> I'll see if I can find an individual change in libc locale-handling that 
>> might trigger this.
>>     
>
> 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.

Thanks to your prodding though, I have another interesting finding:

If I remove the corrupted file and copy a "known good" copy into it's 
place, then the corruption doesn't happen.  I've verified this a couple 
of times.  The corruption only occurs if the file was created by 
"locale-gen".

I'll continue to try work out why :-).

Thanks
Alan
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