linux-kernel - Re: mmap vs mtime in 2.6.26 and up

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Date:	Wed, 22 Jul 2009 19:52:09 +0200
From:	Ferenc Wagner <wferi@...f.hu>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Ray Lee <ray-lk@...rabbit.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Staubach <staubach@...hat.com>,
	Miklos Szeredi <mszeredi@...e.cz>, xfs@....sgi.com,
	linux-kernel@...r.kernel.org
Subject: Re: mmap vs mtime in 2.6.26 and up

Christoph Hellwig <hch@...radead.org> 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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