linux-kernel - Re: [PATCH 2/2] [RFC] fadvise: Add _VOLATILE,_ISVOLATILE, and

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Date:	Thu, 16 Feb 2012 21:24:11 -0800
From:	John Stultz <johnstul@...ibm.com>
To:	Dmitry Adamushko <dmitry.adamushko@...il.com>
Cc:	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Android Kernel Team <kernel-team@...roid.com>,
	Robert Love <rlove@...gle.com>, Mel Gorman <mel@....ul.ie>,
	Hugh Dickins <hughd@...gle.com>,
	Dave Hansen <dave@...ux.vnet.ibm.com>,
	Rik van Riel <riel@...hat.com>
Subject: Re: [PATCH 2/2] [RFC] fadvise: Add _VOLATILE,_ISVOLATILE, and
 _NONVOLATILE flags

On Thu, 2012-02-16 at 19:43 -0800, John Stultz wrote:
> On Sun, 2012-02-12 at 13:48 +0100, Dmitry Adamushko wrote:
> > 
> > On 10 February 2012 01:16, John Stultz <john.stultz@...aro.org> wrote:
> 
> >         +static inline void volatile_range_shrink(struct
> >         volatile_range *range,
> >         +                               pgoff_t start_index, pgoff_t
> >         end_index)
> >         +{
> >         +       size_t pre = range_size(range);
> >         +
> >         +       range->range_node.start = start_index;
> >         +       range->range_node.end = end_index;
> >         +
> > 
> > I guess, here we get a whole range of races with volatile_shrink(),
> > which may see inconsistent (in-the-middle-of-update) ranges
> > (e.g. .start and .end).
> 
> We should be holding the vlist_mutex to avoid any such races. But you
> also make clear that volatile_range_shrink() should really be called
> volatile_range_resize(), since having two _shrink calls is terrible. My
> apologies.

And sure enough in the shrinker we're not holding the vlist_mutex.
Thanks for pointing that out. 
-john

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