From: Mel Gorman <mgorman@suse.de>
Date: Tue, 9 Oct 2012 16:58:41 +0000 (+0100)
Subject: mempolicy: fix a memory corruption by refcount imbalance in alloc_pages_vma()
X-Git-Tag: v3.2.32~17
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=b99a7496c734f388f65aab959e0c8d32cc8938c6;p=pandora-kernel.git

mempolicy: fix a memory corruption by refcount imbalance in alloc_pages_vma()

commit 00442ad04a5eac08a98255697c510e708f6082e2 upstream.

Commit cc9a6c877661 ("cpuset: mm: reduce large amounts of memory barrier
related damage v3") introduced a potential memory corruption.
shmem_alloc_page() uses a pseudo vma and it has one significant unique
combination, vma->vm_ops=NULL and vma->policy->flags & MPOL_F_SHARED.

get_vma_policy() does NOT increase a policy ref when vma->vm_ops=NULL
and mpol_cond_put() DOES decrease a policy ref when a policy has
MPOL_F_SHARED.  Therefore, when a cpuset update race occurs,
alloc_pages_vma() falls in 'goto retry_cpuset' path, decrements the
reference count and frees the policy prematurely.

Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: Mel Gorman <mgorman@suse.de>
Reviewed-by: Christoph Lameter <cl@linux.com>
Cc: Josh Boyer <jwboyer@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Mel Gorman <mgorman@suse.de>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---

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