slub: Do not dereference NULL pointer in node_match

The variables accessed in slab_alloc are volatile and therefore
the page pointer passed to node_match can be NULL. The processing
of data in slab_alloc is tentative until either the cmpxhchg
succeeds or the __slab_alloc slowpath is invoked. Both are
able to perform the same allocation from the freelist.

Check for the NULL pointer in node_match.

A false positive will lead to a retry of the loop in __slab_alloc.

Signed-off-by: Christoph Lameter <cl@linux.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>

diff --git a/mm/slub.c b/mm/slub.c
index 21b3f00..8b1b99d 100644 (file)
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -2042,7 +2042,7 @@ static void flush_all(struct kmem_cache *s)
 static inline int node_match(struct page *page, int node)
 {
 #ifdef CONFIG_NUMA
-       if (node != NUMA_NO_NODE && page_to_nid(page) != node)
+       if (!page || (node != NUMA_NO_NODE && page_to_nid(page) != node))
                return 0;
 #endif
        return 1;