xfrm: interface: 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.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Antoine Tenart <atenart@kernel.org>
Link: https://lore.kernel.org/r/20240206144313.2050392-17-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/xfrm/xfrm_interface_core.c

@@ -957,12 +957,12 @@ static struct rtnl_link_ops xfrmi_link_ops __read_mostly = {
 	.get_link_net	= xfrmi_get_link_net,
 };
 
-static void __net_exit xfrmi_exit_batch_net(struct list_head *net_exit_list)
+static void __net_exit xfrmi_exit_batch_rtnl(struct list_head *net_exit_list,
+					     struct list_head *dev_to_kill)
 {
 	struct net *net;
-	LIST_HEAD(list);
 
-	rtnl_lock();
+	ASSERT_RTNL();
 	list_for_each_entry(net, net_exit_list, exit_list) {
 		struct xfrmi_net *xfrmn = net_generic(net, xfrmi_net_id);
 		struct xfrm_if __rcu **xip;
@@ -973,18 +973,16 @@ static void __net_exit xfrmi_exit_batch_net(struct list_head *net_exit_list)
 			for (xip = &xfrmn->xfrmi[i];
 			     (xi = rtnl_dereference(*xip)) != NULL;
 			     xip = &xi->next)
-				unregister_netdevice_queue(xi->dev, &list);
+				unregister_netdevice_queue(xi->dev, dev_to_kill);
 		}
 		xi = rtnl_dereference(xfrmn->collect_md_xfrmi);
 		if (xi)
-			unregister_netdevice_queue(xi->dev, &list);
+			unregister_netdevice_queue(xi->dev, dev_to_kill);
 	}
-	unregister_netdevice_many(&list);
-	rtnl_unlock();
 }
 
 static struct pernet_operations xfrmi_net_ops = {
-	.exit_batch = xfrmi_exit_batch_net,
+	.exit_batch_rtnl = xfrmi_exit_batch_rtnl,
 	.id   = &xfrmi_net_id,
 	.size = sizeof(struct xfrmi_net),
 };