Re: FIX [1/2] slub: Do not dereference NULL pointer in node_match

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On Wed, 2013-01-23 at 21:45 +0000, Christoph Lameter wrote:
> 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.

Hi Christoph,

Since page_to_nid(NULL) will trigger bug, then how can run into
__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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