linux-kernel - Re: 2.6.19 file content corruption on ext3

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Date:	Mon, 18 Dec 2006 17:21:26 -0800
From:	Andrew Morton <akpm@...l.org>
To:	Linus Torvalds <torvalds@...l.org>
Cc:	Andrei Popa <andrei.popa@...eo.ro>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Hugh Dickins <hugh@...itas.com>,
	Florian Weimer <fw@...eb.enyo.de>,
	Marc Haber <mh+linux-kernel@...schlus.de>,
	Martin Michlmayr <tbm@...ius.com>
Subject: Re: 2.6.19 file content corruption on ext3

On Mon, 18 Dec 2006 16:57:30 -0800 (PST)
Linus Torvalds <torvalds@...l.org> wrote:

> What happens if you only ifdef out that single thing? 
> 
> The actual page-cleaning functions make sure to only clear the TAG_DIRTY 
> bit _after_ the page has been marked for writeback. Is there some ordering 
> constraint there, perhaps?
> 
> I'm really reaching here. I'm trying to see the pattern, and I'm not 
> seeing it. I'm asking you to test things just to get more of a feel for 
> what triggers the failure, than because I actually have any kind of idea 
> of what the heck is going on.
> 
> Andrew, Nick, Hugh - any ideas?

If all of test_clear_page_dirty() has been commented out then the page will
never become clean hence will never fall out of pagecache, so unless Andrei
is doing a reboot before checking for corruption, perhaps the underlying
data on-disk is incorrect, but we can't see it.

Andrei, how _are_ you running this test?    What's the exact sequence of steps?

In particular, are you doing anything which would cause the corrupted file
to be evicted from memory, thus forcing a read from disk?  Such as
unmounting and then remounting the filesystem?

The point of my question is to check that the data is really incorrect
on-disk, or whether it is incorrect in pagecache.

Also, it'd be useful if you could determine whether the bug appears with
the ext2 filesystem: do s/ext3/ext2/ in /etc/fstab, or boot with
rootfstype=ext2 if it's the root filesystem.

Thanks.
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