Re: [06/44] numa: fix slab_node(MPOL_BIND)

[Lee Schermerhorn <Lee.Schermerhorn@hp.com>]

On Tue, 2010-12-07 at 16:04 -0800, Greg KH wrote:
> 2.6.27-stable review patch.  If anyone has any objections, please let us know.
> 
> ------------------
> 
> From: Eric Dumazet <eric.dumazet@gmail.com>
> 
> commit 800416f799e0723635ac2d720ad4449917a1481c upstream.
> 
> When a node contains only HighMem memory, slab_node(MPOL_BIND)
> dereferences a NULL pointer.
> 
> [ This code seems to go back all the way to commit 19770b32609b: "mm:
>   filter based on a nodemask as well as a gfp_mask".  Which was back in
>   April 2008, and it got merged into 2.6.26.  - Linus ]
> 
> Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
> Cc: Mel Gorman <mel@csn.ul.ie>
> Cc: Christoph Lameter <cl@linux.com>
> Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
> 
> ---
>  mm/mempolicy.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> --- a/mm/mempolicy.c
> +++ b/mm/mempolicy.c
> @@ -1404,7 +1404,7 @@ unsigned slab_node(struct mempolicy *pol
>  		(void)first_zones_zonelist(zonelist, highest_zoneidx,
>  							&policy->v.nodes,
>  							&zone);
> -		return zone->node;
> +		return zone ? zone->node : numa_node_id();

I think this should be numa_mem_id().  Given the documented purpose of
slab_node(), we want a node from which page allocation is likely to
succeed.  numa_node_id() can return a memoryless node for, e.g.,  some
configurations of some HP ia64 platforms.  numa_mem_id() was introduced
to return that same node from which "local" mempolicy would allocate
pages.

Lee

>  	}
>  
>  	default:
> 
>