vxlan: 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.

v4: (Paolo feedback : https://netdev-3.bots.linux.dev/vmksft-net/results/453141/17-udpgro-fwd-sh/stdout )
  - Changed vxlan_destroy_tunnels() to use vxlan_dellink()
    instead of unregister_netdevice_queue to propely remove
    devices from vn->vxlan_list.
  - vxlan_destroy_tunnels() can simply iterate one list (vn->vxlan_list)
    to find all devices in the most efficient way.
  - Moved sanity checks in a separate vxlan_exit_net() method.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Antoine Tenart <atenart@kernel.org>
Link: https://lore.kernel.org/r/20240206144313.2050392-10-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/vxlan/vxlan_core.c

@@ -4826,55 +4826,43 @@ static __net_init int vxlan_init_net(struct net *net)
 					 NULL);
 }
 
-static void vxlan_destroy_tunnels(struct net *net, struct list_head *head)
+static void __net_exit vxlan_destroy_tunnels(struct vxlan_net *vn,
+					     struct list_head *dev_to_kill)
 {
-	struct vxlan_net *vn = net_generic(net, vxlan_net_id);
 	struct vxlan_dev *vxlan, *next;
-	struct net_device *dev, *aux;
-
-	for_each_netdev_safe(net, dev, aux)
-		if (dev->rtnl_link_ops == &vxlan_link_ops)
-			unregister_netdevice_queue(dev, head);
-
-	list_for_each_entry_safe(vxlan, next, &vn->vxlan_list, next) {
-		/* If vxlan->dev is in the same netns, it has already been added
-		 * to the list by the previous loop.
-		 */
-		if (!net_eq(dev_net(vxlan->dev), net))
-			unregister_netdevice_queue(vxlan->dev, head);
-	}
 
+	list_for_each_entry_safe(vxlan, next, &vn->vxlan_list, next)
+		vxlan_dellink(vxlan->dev, dev_to_kill);
 }
 
-static void __net_exit vxlan_exit_batch_net(struct list_head *net_list)
+static void __net_exit vxlan_exit_batch_rtnl(struct list_head *net_list,
+					     struct list_head *dev_to_kill)
 {
 	struct net *net;
-	LIST_HEAD(list);
-	unsigned int h;
 
+	ASSERT_RTNL();
 	list_for_each_entry(net, net_list, exit_list) {
 		struct vxlan_net *vn = net_generic(net, vxlan_net_id);
 
-		unregister_nexthop_notifier(net, &vn->nexthop_notifier_block);
-	}
-	rtnl_lock();
-	list_for_each_entry(net, net_list, exit_list)
-		vxlan_destroy_tunnels(net, &list);
+		__unregister_nexthop_notifier(net, &vn->nexthop_notifier_block);
 
-	unregister_netdevice_many(&list);
-	rtnl_unlock();
+		vxlan_destroy_tunnels(vn, dev_to_kill);
+	}
+}
 
-	list_for_each_entry(net, net_list, exit_list) {
-		struct vxlan_net *vn = net_generic(net, vxlan_net_id);
+static void __net_exit vxlan_exit_net(struct net *net)
+{
+	struct vxlan_net *vn = net_generic(net, vxlan_net_id);
+	unsigned int h;
 
-		for (h = 0; h < PORT_HASH_SIZE; ++h)
-			WARN_ON_ONCE(!hlist_empty(&vn->sock_list[h]));
-	}
+	for (h = 0; h < PORT_HASH_SIZE; ++h)
+		WARN_ON_ONCE(!hlist_empty(&vn->sock_list[h]));
 }
 
 static struct pernet_operations vxlan_net_ops = {
 	.init = vxlan_init_net,
-	.exit_batch = vxlan_exit_batch_net,
+	.exit_batch_rtnl = vxlan_exit_batch_rtnl,
+	.exit = vxlan_exit_net,
 	.id   = &vxlan_net_id,
 	.size = sizeof(struct vxlan_net),
 };