Re: [RFC][PATCH v2] slub: Keep page and object in sync inslab_alloc_node()

[Christoph Lameter]

On Fri, 18 Jan 2013, Joonsoo Kim wrote:

> How about this?

The easiest fix is to just check for NULL in node_match since a similar
situation can occur in slab_free.

Subject: 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 cmpxchg
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@xxxxxxxxx>

Index: linux/mm/slub.c
===================================================================
--- linux.orig/mm/slub.c	2013-01-18 08:47:29.198954250 -0600
+++ linux/mm/slub.c	2013-01-18 08:47:40.579126371 -0600
@@ -2041,7 +2041,7 @@ static void flush_all(struct kmem_cache
 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;
--
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