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

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Date:	Fri, 05 Jun 2009 17:40:33 +0300
From:	Aioanei Rares <krnl.list@...il.com>
To:	Alan Jenkins <alan-jenkins@...fmail.co.uk>
CC:	linux-ext4@...r.kernel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Mild filesystem corruption on ext4 (no journal)

Alan Jenkins wrote:
> Hi,
>
> I run ext4 without a journal on my cheap netbook with a 4 gig SSD.  I 
> suspect "without a journal" is significant, I don't think I'm doing 
> anything else strange.
>
> When I upgrade libc from 2.7 (debian stable) to 2.9 (debian unstable), 
> the locale breaks every reboot, and I have to repair it by running 
> locale-gen.  This happened now when I only upgraded libc, in order to 
> play with signalfd().  It also happened before, when I upgraded the 
> entire machine to debian unstable (which I later reverted).
>
> The problem is that /usr/lib/locale/locale-archive gets corrupted when 
> I reboot.  The exact corruption differs with each reboot (i.e. the 
> md5sum differs).  Last time, the first ~70K was overwritten with data 
> from xorg.log and my web browsing history.  I have copies of the 
> original and corrupted state which I can send, the full file is 1.3 
> megs, but I can limit it to the first 70K, since that's all that was 
> corrupted.
>
> 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.
>
> Also, I ran md5sum in the shutdown scripts, after mounting the root 
> filesystem read-only (which is also preceeded by a sync in a different 
> script).  This showed that the file did not appear corrupted at this 
> point.  (Though maybe it was ok in page-cache, but corrupted on-disk).
>
> The locale-archive file is read by the libc locale routines using 
> mmap().  The mapping is read only and is not modified.  It seems 
> likely that some process has it mapped when the kernel shuts down.
>
> I tried reproducing this by writting a minimal daemon which maps a 
> copy of the locale-archive file, and starting it just before the 
> filesystem is remounted read-only.  It didn't work though; this copy 
> of the locale-archive file remained uncorrupted.
>
> I forced a fsck on boot, and the filesystem was reported to be clean.  
> I am currently running with e2fsprogs v1.41.6 (from debian unstable), 
> and a custom-built kernel, 2.6.30-rc7.
>
> Thanks in advance!
> Alan
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I suspect, although I might be wrong, that this is not a kernel-related
problem.
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