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Re: mmap vs mtime in 2.6.26 and up

To: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Subject: Re: mmap vs mtime in 2.6.26 and up
From: Ferenc Wagner <wferi@xxxxxxx>
Date: Wed, 22 Jul 2009 19:52:09 +0200
Cc: Ray Lee <ray-lk@xxxxxxxxxxxxx>, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>, Peter Staubach <staubach@xxxxxxxxxx>, Miklos Szeredi <mszeredi@xxxxxxx>, xfs@xxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx
In-reply-to: <20090518114305.GA6303@xxxxxxxxxxxxx> (Christoph Hellwig's message of "Mon, 18 May 2009 07:43:05 -0400")
References: <20090518114305.GA6303@xxxxxxxxxxxxx>
User-agent: Gnus/5.110006 (No Gnus v0.6) Emacs/21.4 (gnu/linux)
Christoph Hellwig <hch@xxxxxxxxxxxxx> writes:

> On Fri, May 15, 2009 at 12:50:54PM -0400, Christoph Hellwig wrote:
>> On Fri, May 15, 2009 at 06:40:29PM +0200, Ferenc Wagner wrote:
>>> Thanks for the analysis.  Unfortunately I don't nearly know enough to
>>> work on this issue, but would like to track it as it affects our
>>> backup system.  So, shouldn't #2645 be reopened again?
>> 
>> Yes, definitively as the current "fix" is incorrected.  I'll try to cook
>> up a correct version once I get some time.
>
> Doing this correctly in the framework of the current codee is
> unfortunately not so easy, as calling ->setattr requires taking i_mutex
> which we can't in the pagefaul path.
>
> To fix this properly we need to actually update the timestamps during
> msync and co as done by the patches from Miklos:
>       http://lkml.org/lkml/2007/2/28/166
> and Peter:
>       http://lkml.org/lkml/2006/5/31/176

Hi Christoph,

http://bugzilla.kernel.org/show_bug.cgi?id=2645#c53 shows that Anton
doesn't quite agree with you on this.  I really can't tell, would you
(or anybody from the accused XFS community) please comment?  Or did
you perhaps fix it meanwhile?  I can't easily test never kernels, but
I will if there's some chance.
-- 
Thanks,
Feri.

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