On module unload call rcu_barrier(), this is needed as synchronize_rcu()
is not strong enough.  The kmem_cache_destroy() does invoke
synchronize_rcu() but it does not provide same protection.
Signed-off-by: NJesper Dangaard Brouer <hawk@comx.dk>
Acked-by: NVlad Yasevich <vladislav.yasevich@hp.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>