On Monday 30 November 2009 03:45:58 you wrote:

+       /* Process any work delayed until the end of the batch */
+       dev = list_entry(head->next, struct net_device, unreg_list);
+       call_netdevice_notifiers(NETDEV_UNREGISTER_BATCH, dev);
 
-       list_for_each_entry_safe(dev, aux, head, unreg_list) {
-               int new_net = 1;
-               list_for_each_entry(fdev, &pernet_list, unreg_list) {
-                       if (net_eq(dev_net(dev), dev_net(fdev))) {
-                               new_net = 0;
-                               dev_put(dev);
-                               break;
-                       }
-               }
-               if (new_net)
-                       list_move(&dev->unreg_list, &pernet_list);
-       }

This implies that the devices we want to batch unregister needs to be part of 
the same namespace. It might be worth mentioning that in the 
unregister_netdevice_many() function comments.

And, fortunately, it seems that all of the current batch unregister users 
comply with this requirement.