Kmem_cache_alloc_node is not capable of handling a null cachep pointer as
its input argument.

If I try to increase a slab limit by echoing a very large number into
/proc/slabinfo, kernel will panic from alloc_arraycache() because
Kmem_find_general_cachep() can actually return a NULL pointer if the size
argument is sufficiently large.
Signed-off-by: Ken Chen <kenneth.w.chen@intel.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>