mmap vs mtime in 2.6.26 and up

[Christoph Hellwig]

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

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