[PATCH] mm: slab: Verify the nodeid passed to ____cache_alloc_node

[PATCH] mm: slab: Verify the nodeid passed to ____cache_alloc_node

[Aaron Tomlin]

Hi,

The addition of this BUG_ON should make debugging easier.
While I understand that this code path is "hot", surely
it is better to assert the condition than to wait until
some random NULL pointer dereference or page fault. If the
caller passes an invalid nodeid, at this stage in my opinion
it's already a BUG.

Cheers,
Aaron

---8<---
mm: slab: Verify the nodeid passed to ____cache_alloc_node
    
If the nodeid is > num_online_nodes() this can cause an
Oops and a panic(). The purpose of this patch is to assert
if this condition is true to aid debugging efforts rather
than some random NULL pointer dereference or page fault.
    
Signed-off-by: Aaron Tomlin <atomlin@redhat.com>

 slab.c |    1 +
 1 file changed, 1 insertion(+)

diff --git a/mm/slab.c b/mm/slab.c
index e7667a3..735e8bd 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -3412,6 +3412,7 @@ static void *____cache_alloc_node(struct kmem_cache *cachep, gfp_t flags,
 	void *obj;
 	int x;
 
+	BUG_ON(nodeid > num_online_nodes());
 	l3 = cachep->nodelists[nodeid];
 	BUG_ON(!l3);

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Re: [PATCH] mm: slab: Verify the nodeid passed to ____cache_alloc_node

[Glauber Costa]

On 02/22/2013 02:07 AM, Aaron Tomlin wrote:
> The addition of this BUG_ON should make debugging easier.
> While I understand that this code path is "hot", surely
> it is better to assert the condition than to wait until
> some random NULL pointer dereference or page fault. If the
> caller passes an invalid nodeid, at this stage in my opinion
> it's already a BUG.
If you assert with VM_BUG_ON, it will be active on debugging kernels
only, which I believe is better suited for a hotpath.

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Re: [PATCH] mm: slab: Verify the nodeid passed to ____cache_alloc_node

[Aaron Tomlin]

> If you assert with VM_BUG_ON, it will be active on debugging kernels
> only, which I believe is better suited for a hotpath.

Agreed.

Regards,
Aaron

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