linux-ext4 - Re: [ext3] Changes to block device after an ext3 mount point has been remounted readonly

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Message-ID: <baaef4711002230042p3d6fa7fam5a80174269773d48@mail.gmail.com>
Date:	Tue, 23 Feb 2010 09:42:39 +0100
From:	Camille Moncelier <pix@...life.org>
To:	linux-fsdevel@...r.kernel.org,
	ext4 development <linux-ext4@...r.kernel.org>
Subject: Re: [ext3] Changes to block device after an ext3 mount point has been 
	remounted readonly

The fact is that I've been able to reproduce the problem on LVM block
devices, and sd* block devices so it's definitely not a loop device
specific problem.

By the way, I tried several other things other than "echo s
>/proc/sysrq_trigger" I tried multiple sync followed with a one minute
"sleep",

"echo 3 >/proc/sys/vm/drop_caches" seems to lower the chances of "hash
changes" but doesn't stops them.

On Tue, Feb 23, 2010 at 12:09 AM, Andreas Dilger <adilger@....com> wrote:
> On 2010-02-22, at 16:05, Jan Kara wrote:
>>
>>  Hmm, and apparently there is some subtlety in the loopback device code
>> because even when I use sync(1), the first and second images sometimes
>> differ (although it's much rarer). But I see a commit block of the
>> transaction  already in the first image (the commit block is written last)
>> but the contents of the transaction is present only in the second image.
>
>
> It has never been safe to run ext3 on top of a loop device, because the loop
> device does not preserve ordering, and I'm not sure whether it properly
> passes barriers either.
>
> Cheers, Andreas
> --
> Andreas Dilger
> Sr. Staff Engineer, Lustre Group
> Sun Microsystems of Canada, Inc.
>
>



-- 
Camille Moncelier
http://devlife.org/

If Java had true garbage collection, most programs would
delete themselves upon execution.
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