gtp: use exit_batch_rtnl() method

exit_batch_rtnl() is called while RTNL is held,
and devices to be unregistered can be queued in the dev_kill_list.

This saves one rtnl_lock()/rtnl_unlock() pair per netns
and one unregister_netdevice_many() call per netns.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Antoine Tenart <atenart@kernel.org>
Link: https://lore.kernel.org/r/20240206144313.2050392-8-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/gtp.c

@@ -1876,23 +1876,23 @@ static int __net_init gtp_net_init(struct net *net)
 	return 0;
 }
 
-static void __net_exit gtp_net_exit(struct net *net)
+static void __net_exit gtp_net_exit_batch_rtnl(struct list_head *net_list,
+					       struct list_head *dev_to_kill)
 {
-	struct gtp_net *gn = net_generic(net, gtp_net_id);
-	struct gtp_dev *gtp;
-	LIST_HEAD(list);
+	struct net *net;
 
-	rtnl_lock();
-	list_for_each_entry(gtp, &gn->gtp_dev_list, list)
-		gtp_dellink(gtp->dev, &list);
+	list_for_each_entry(net, net_list, exit_list) {
+		struct gtp_net *gn = net_generic(net, gtp_net_id);
+		struct gtp_dev *gtp;
 
-	unregister_netdevice_many(&list);
-	rtnl_unlock();
+		list_for_each_entry(gtp, &gn->gtp_dev_list, list)
+			gtp_dellink(gtp->dev, dev_to_kill);
+	}
 }
 
 static struct pernet_operations gtp_net_ops = {
 	.init	= gtp_net_init,
-	.exit	= gtp_net_exit,
+	.exit_batch_rtnl = gtp_net_exit_batch_rtnl,
 	.id	= &gtp_net_id,
 	.size	= sizeof(struct gtp_net),
 };