linux-kernel - Re: [PATCH] tmpfs: fix shared mempolicy leak

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Date:	Wed, 5 Dec 2012 09:52:21 +0000
From:	Mel Gorman <mgorman@...e.de>
To:	Hugh Dickins <hughd@...gle.com>
Cc:	Tommi Rantala <tt.rantala@...il.com>,
	Stable <stable@...r.kernel.org>, Andi Kleen <ak@...ux.intel.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Dave Jones <davej@...hat.com>,
	Christoph Lameter <cl@...ux.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux-MM <linux-mm@...ck.org>
Subject: Re: [PATCH] tmpfs: fix shared mempolicy leak

On Tue, Dec 04, 2012 at 11:24:30PM -0800, Hugh Dickins wrote:
> From: Mel Gorman <mgorman@...e.de>
> 
> Commit 00442ad04a5e ("mempolicy: fix a memory corruption by refcount
> imbalance in alloc_pages_vma()") changed get_vma_policy() to raise the
> refcount on a shmem shared mempolicy; whereas shmem_alloc_page() went
> on expecting alloc_page_vma() to drop the refcount it had acquired.
> This deserves a rework: but for now fix the leak in shmem_alloc_page().
> 
> Hugh: shmem_swapin() did not need a fix, but surely it's clearer to use
> the same refcounting there as in shmem_alloc_page(), delete its onstack
> mempolicy, and the strange mpol_cond_copy() and __mpol_cond_copy() -
> those were invented to let swapin_readahead() make an unknown number of
> calls to alloc_pages_vma() with one mempolicy; but since 00442ad04a5e,
> alloc_pages_vma() has kept refcount in balance, so now no problem.
> 

Agreed. Anything that reduces the complexity of the mempolicy ref counting
is worthwhile even if it's only by a small bit.

> Reported-by: Tommi Rantala <tt.rantala@...il.com>
> Awaiting-signed-off-by: Mel Gorman <mgorman@...e.de>
> Signed-off-by: Hugh Dickins <hughd@...gle.com>
> Cc: stable@...r.kernel.org

Thanks Hugh for turning gibber into a patch!

Signed-off-by: Mel Gorman <mgorman@...e.de>

Tommi, just in case, can you confirm this fixes the problem for you please?

-- 
Mel Gorman
SUSE Labs
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