mm: slab: Verify the nodeid passed to ____cache_alloc_node

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.

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

index e7667a3..735e8bd 100644
@@ -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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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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Agreed.

Regards,
Aaron

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