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mempolicy: fix a race in shared_policy_replace()

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commit b22d127a39 upstream.

shared_policy_replace() use of sp_alloc() is unsafe.  1) sp_node cannot
be dereferenced if sp->lock is not held and 2) another thread can modify
sp_node between spin_unlock for allocating a new sp node and next
spin_lock.  The bug was introduced before 2.6.12-rc2.

Kosaki's original patch for this problem was to allocate an sp node and
policy within shared_policy_replace and initialise it when the lock is
reacquired.  I was not keen on this approach because it partially
duplicates sp_alloc().  As the paths were sp->lock is taken are not that
performance critical this patch converts sp->lock to sp->mutex so it can
sleep when calling sp_alloc().

[kosaki.motohiro@jp.fujitsu.com: Original patch]
Signed-off-by: Mel Gorman <mgorman@suse.de>
Acked-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Mel Gorman
2012-10-08 16:29:17 -07:00
committed by Greg Kroah-Hartman
parent e12681ffb1
commit cedd186e31
2 changed files with 17 additions and 22 deletions
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2
include/linux/mempolicy.h
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@@ -188,7 +188,7 @@ struct sp_node {
struct shared_policy {
struct rb_root root;
spinlock_t lock;
struct mutex mutex;
};
void mpol_shared_policy_init(struct shared_policy *sp, struct mempolicy *mpol);