net: In unregister_netdevice_notifier unregister the netdevices.

We already synthesize events in register_netdevice_notifier and synthesizing
events in unregister_netdevice_notifier allows to us remove the need for
special case cleanup code.

This change should be safe as it adds no new cases for existing callers
of unregiser_netdevice_notifier to handle.
Signed-off-by: NEric W. Biederman <ebiederm@xmission.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/core/dev.c

@@ -1409,14 +1409,34 @@ EXPORT_SYMBOL(register_netdevice_notifier);
  *	register_netdevice_notifier(). The notifier is unlinked into the
  *	kernel structures and may then be reused. A negative errno code
  *	is returned on a failure.
+ *
+ * 	After unregistering unregister and down device events are synthesized
+ *	for all devices on the device list to the removed notifier to remove
+ *	the need for special case cleanup code.
  */
 
 int unregister_netdevice_notifier(struct notifier_block *nb)
 {
+	struct net_device *dev;
+	struct net *net;
 	int err;
 
 	rtnl_lock();
 	err = raw_notifier_chain_unregister(&netdev_chain, nb);
+	if (err)
+		goto unlock;
+
+	for_each_net(net) {
+		for_each_netdev(net, dev) {
+			if (dev->flags & IFF_UP) {
+				nb->notifier_call(nb, NETDEV_GOING_DOWN, dev);
+				nb->notifier_call(nb, NETDEV_DOWN, dev);
+			}
+			nb->notifier_call(nb, NETDEV_UNREGISTER, dev);
+			nb->notifier_call(nb, NETDEV_UNREGISTER_BATCH, dev);
+		}
+	}
+unlock:
 	rtnl_unlock();
 	return err;
 }