8021q: Vlan driver should use rcu_barrier() on unload instead of syncronize_net()

The VLAN 8021q driver needs to call rcu_barrier() when unloading the module,
instead of syncronize_net().  This is needed to make sure that outstanding
call_rcu() callbacks have completed, before the callback function code is
removed on module unload.
Signed-off-by: Jesper Dangaard Brouer <hawk@comx.dk>
Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/8021q/vlan.c

@@ -758,7 +758,7 @@ static void __exit vlan_cleanup_module(void)
 		BUG_ON(!hlist_empty(&vlan_group_hash[i]));
 
 	unregister_pernet_gen_device(vlan_net_id, &vlan_net_ops);
-	synchronize_net();
+	rcu_barrier(); /* Wait for completion of call_rcu()'s */
 
 	vlan_gvrp_uninit();
 }