SLUB: Fix merged slab cache names

As explained by Linus "I'm Proud to be an American" Torvalds:

  Looking at the merging code, I actually think it's totally
  buggy. If you have something like this:

   - load module A: create slab cache A

   - load module B: create slab cache B that can merge with A

   - unload module A

   - "cat /proc/slabinfo": BOOM. Oops.

  exactly because the name is not handled correctly, and you'll have
  module B holding open a slab cache that has a name pointer that points
  to module A that no longer exists.

This patch fixes the problem by using kstrdup() to allocate dynamic memory for
->name of "struct kmem_cache" as suggested by Christoph Lameter.

Acked-by: Christoph Lameter <cl@linux.com>
Cc: David Rientjes <rientjes@google.com>
Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Pekka Enberg <penberg@kernel.org>

Conflicts:

	mm/slub.c