kunit, slub: Add test_kfree_rcu_wq_destroy use case

kunit, slub: Add test_kfree_rcu_wq_destroy use case

Add a test_kfree_rcu_wq_destroy test to verify a kmem_cache_destroy()
from a workqueue context. The problem is that, before destroying any
cache the kvfree_rcu_barrier() is invoked to guarantee that in-flight
freed objects are flushed.

The _barrier() function queues and flushes its own internal workers
which might conflict with a workqueue type a kmem-cache gets destroyed
from.

One example is when a WQ_MEM_RECLAIM workqueue is flushing !WQ_MEM_RECLAIM
events which leads to a kernel splat. See the check_flush_dependency() in
the workqueue.c file.

If this test does not emits any kernel warning, it is passed.

Reviewed-by: Keith Busch <kbusch@kernel.org>
Co-developed-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>