linux-kernel - Re: [PATCH] mm: Remove usages of ACCESS

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Date:	Wed, 25 Mar 2015 08:51:23 +0100
From:	Michal Hocko <mhocko@...e.cz>
To:	Jason Low <jason.low2@...com>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	cgroups@...r.kernel.org, Johannes Weiner <hannes@...xchg.org>,
	Christoph Lameter <cl@...ux.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	David Rientjes <rientjes@...gle.com>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Aswin Chandramouleeswaran <aswin@...com>,
	Christian Borntraeger <borntraeger@...ibm.com>,
	Mel Gorman <mgorman@...e.de>, Hugh Dickins <hughd@...gle.com>,
	Minchan Kim <minchan@...nel.org>,
	Davidlohr Bueso <dave@...olabs.net>,
	Rik van Riel <riel@...hat.com>
Subject: Re: [PATCH] mm: Remove usages of ACCESS_ONCE

On Tue 24-03-15 11:30:35, Jason Low wrote:
> On Tue, 2015-03-24 at 11:30 +0100, Michal Hocko wrote:
> > On Mon 23-03-15 15:44:40, Jason Low wrote:
> > > Commit 38c5ce936a08 converted ACCESS_ONCE usage in gup_pmd_range() to
> > > READ_ONCE, since ACCESS_ONCE doesn't work reliably on non-scalar types.
> > > 
> > > This patch removes the rest of the usages of ACCESS_ONCE, and use
> > > READ_ONCE for the read accesses. This also makes things cleaner,
> > > instead of using separate/multiple sets of APIs.
> > > 
> > > Signed-off-by: Jason Low <jason.low2@...com>
> > 
> > Makes sense to me. I would prefer a patch split into two parts. One which
> > changes potentially dangerous usage of ACCESS_ONCE and the cleanup. This
> > will make the life of those who backport patches into older kernels
> > easier a bit.
> 
> Okay, so have a patch 1 which fixes the following:
> 
>     pte_t pte = ACCESS_ONCE(*ptep);
>     pgd_t pgd = ACCESS_ONCE(*pgdp);
> 
> and the rest of the changes in the cleanup patch 2?

Thanks!

> 
> > I won't insist though.
> > 
> > Acked-by: Michal Hocko <mhocko@...e.cz>
> 
> Thanks,
> Jason
> 

-- 
Michal Hocko
SUSE Labs
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