[PATCH v2] mm: Fix slab->page _count corruption.

From: Pravin B Shelar
Date: Mon May 14 2012 - 18:30:02 EST

On arches that do not support this_cpu_cmpxchg_double slab_lock is used
to do atomic cmpxchg() on double word which contains page->_count.
page count can be changed from get_page() or put_page() without taking
slab_lock. That corrupts page counter.

Following patch fixes it by moving page->_count out of cmpxchg_double
data. So that slub does no change it while updating slub meta-data in
struct page.

Reported-by: Amey Bhide <abhide@xxxxxxxxxx>
Signed-off-by: Pravin B Shelar <pshelar@xxxxxxxxxx>
include/linux/mm_types.h | 8 ++++++++
1 file changed, 8 insertions(+)

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index dad95bd..5f558dc 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -57,8 +57,16 @@ struct page {

union {
/* Used for cmpxchg_double in slub */
unsigned long counters;
+ /* Keep _count separate from slub cmpxchg_double data,
+ * As rest of double word is protected by slab_lock
+ * but _count is not. */
+ unsigned counters;

struct {


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