bridge: switch br_net_exit to batch mode

cleanup_net() is competing with other rtnl users.

Instead of calling br_net_exit() for each netns,
call br_net_exit_batch() once.

This gives cleanup_net() ability to group more devices
and call unregister_netdevice_many() only once for all bridge devices.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Roopa Prabhu <roopa@nvidia.com>
Cc: Nikolay Aleksandrov <razor@blackwall.org>
Acked-by: Nikolay Aleksandrov <razor@blackwall.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/bridge/br.c

@@ -342,23 +342,26 @@ void br_opt_toggle(struct net_bridge *br, enum net_bridge_opts opt, bool on)
 		clear_bit(opt, &br->options);
 }
 
-static void __net_exit br_net_exit(struct net *net)
+static void __net_exit br_net_exit_batch(struct list_head *net_list)
 {
 	struct net_device *dev;
+	struct net *net;
 	LIST_HEAD(list);
 
 	rtnl_lock();
+
+	list_for_each_entry(net, net_list, exit_list)
 		for_each_netdev(net, dev)
 			if (netif_is_bridge_master(dev))
 				br_dev_delete(dev, &list);
 
 	unregister_netdevice_many(&list);
-	rtnl_unlock();
 
+	rtnl_unlock();
 }
 
 static struct pernet_operations br_net_ops = {
-	.exit	= br_net_exit,
+	.exit_batch	= br_net_exit_batch,
 };
 
 static const struct stp_proto br_stp_proto = {