[ 07/48] mm: fix slab->page _count corruption when using slub

Ben Hutchings
2012-07-01T18:25:26Z

From: Pravin B Shelar <pshelar@nicira.com>

commit abca7c4965845924f65d40e0aa1092bdd895e314 upstream.

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. The
page count can be changed from get_page() or put_page() without taking
slab_lock. That corrupts page counter.

Fix 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.

[akpm@linux-foundation.org: use standard comment layout, tweak comment text]
Reported-by: Amey Bhide <abhide@nicira.com>
Signed-off-by: Pravin B Shelar <pshelar@nicira.com>
Acked-by: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@cs.helsinki.fi>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
include/linux/mm_types.h | 10 ++++++++++
1 file changed, 10 insertions(+)

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index dad95bd..704a626 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -57,8 +57,18 @@ struct page {
};

union {
+#if defined(CONFIG_HAVE_CMPXCHG_DOUBLE) && \
+ defined(CONFIG_HAVE_ALIGNED_STRUCT_PAGE)
/* Used for cmpxchg_double in slub */
unsigned long counters;
+#else
+ /*
+ * Keep _count separate from slub cmpxchg_double data.
+ * As the rest of the double word is protected by
+ * slab_lock but _count is not.
+ */
+ unsigned counters;
+#endif

struct {