Re: [PATCH v2] mm: slab: Verify the nodeid passed to ____cache_alloc_node

[Aaron Tomlin <atomlin@redhat.com>]

Hi,

This patch is in response to bz#42967 [1]. Using VM_BUG_ON
instead of a generic BUG_ON so it's used only when 
CONFIG_DEBUG_VM is set, given that ____cache_alloc_node()
is a hot code path.

Cheers,
Aaron

[1]: https://bugzilla.kernel.org/show_bug.cgi?id=42967

---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;
 
+	VM_BUG_ON(nodeid > num_online_nodes());
 	l3 = cachep->nodelists[nodeid];
 	BUG_ON(!l3);

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