vxlan: Use a per-namespace nexthop listener instead of a global one

The nexthop notification chain is a per-namespace chain and not a global
one like the netdev notification chain.

Therefore, a single (global) listener cannot be registered to all these
chains simultaneously as it will result in list corruptions whenever
listeners are registered / unregistered.

Instead, register a different listener in each namespace.

Currently this is not an issue because only the VXLAN driver registers a
listener to this chain, but this is going to change with netdevsim and
mlxsw also registering their own listeners.

Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Link: https://lore.kernel.org/r/20201101113926.705630-1-idosch@idosch.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/vxlan.c

@@ -66,6 +66,7 @@ struct vxlan_net {
 	struct list_head  vxlan_list;
 	struct hlist_head sock_list[PORT_HASH_SIZE];
 	spinlock_t	  sock_lock;
+	struct notifier_block nexthop_notifier_block;
 };
 
 /* Forwarding table entry */
@@ -4693,10 +4694,6 @@ static int vxlan_nexthop_event(struct notifier_block *nb,
 	return NOTIFY_DONE;
 }
 
-static struct notifier_block vxlan_nexthop_notifier_block __read_mostly = {
-	.notifier_call = vxlan_nexthop_event,
-};
-
 static __net_init int vxlan_init_net(struct net *net)
 {
 	struct vxlan_net *vn = net_generic(net, vxlan_net_id);
@@ -4704,11 +4701,12 @@ static __net_init int vxlan_init_net(struct net *net)
 
 	INIT_LIST_HEAD(&vn->vxlan_list);
 	spin_lock_init(&vn->sock_lock);
+	vn->nexthop_notifier_block.notifier_call = vxlan_nexthop_event;
 
 	for (h = 0; h < PORT_HASH_SIZE; ++h)
 		INIT_HLIST_HEAD(&vn->sock_list[h]);
 
-	return register_nexthop_notifier(net, &vxlan_nexthop_notifier_block);
+	return register_nexthop_notifier(net, &vn->nexthop_notifier_block);
 }
 
 static void vxlan_destroy_tunnels(struct net *net, struct list_head *head)
@@ -4740,8 +4738,11 @@ static void __net_exit vxlan_exit_batch_net(struct list_head *net_list)
 	LIST_HEAD(list);
 
 	rtnl_lock();
-	list_for_each_entry(net, net_list, exit_list)
-		unregister_nexthop_notifier(net, &vxlan_nexthop_notifier_block);
+	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);
+	}
 	list_for_each_entry(net, net_list, exit_list)
 		vxlan_destroy_tunnels(net, &list);