From: Philippe Elie <phil.el@wanadoo.fr>

kmem_cache_destroy() can fail with the following error: slab error in
kmem_cache_destroy(): cache `xxx': Can't free all objects but the cache
user really free'd all objects

This is because drain_array_locked() only frees 80% of thge objects.

Fix it by adding a parameter to drain_array_locked() telling it to drain
100% of the objects.