net: Handle NETREG_UNINITIALIZED devices correctly

Fix two problems:

1. If unregister_netdevice_many() is called with both registered
   and unregistered devices, rollback_registered_many() bails out
   when it reaches the first unregistered device. The processing
   of the prior registered devices is unfinished, and the
   remaining devices are skipped, and possible registered netdev's
   are leaked/unregistered.

2. System hangs or panics depending on how the devices are passed,
   since when netdev_run_todo() runs, some devices were not fully
   processed.

Tested by passing intermingled unregistered and registered vlan
devices to unregister_netdevice_many() as follows:
	1. dev, fake_dev1, fake_dev2: hangs in run_todo
	   ("unregister_netdevice: waiting for eth1.100 to become
	    free. Usage count = 1")
	2. fake_dev1, dev, fake_dev2: failure during de-registration
	   and next registration, followed by a vlan driver Oops
	   during subsequent registration.

Confirmed that the patch fixes both cases.

Signed-off-by: Krishna Kumar <krkumar2@in.ibm.com>
Acked-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/dev.c

@@ -4771,21 +4771,23 @@ static void net_set_todo(struct net_device *dev)
 
 static void rollback_registered_many(struct list_head *head)
 {
-	struct net_device *dev;
+	struct net_device *dev, *tmp;
 
 	BUG_ON(dev_boot_phase);
 	ASSERT_RTNL();
 
-	list_for_each_entry(dev, head, unreg_list) {
+	list_for_each_entry_safe(dev, tmp, head, unreg_list) {
 		/* Some devices call without registering
-		 * for initialization unwind.
+		 * for initialization unwind. Remove those
+		 * devices and proceed with the remaining.
 		 */
 		if (dev->reg_state == NETREG_UNINITIALIZED) {
 			pr_debug("unregister_netdevice: device %s/%p never "
 				 "was registered\n", dev->name, dev);
 
 			WARN_ON(1);
-			return;
+			list_del(&dev->unreg_list);
+			continue;
 		}
 
 		BUG_ON(dev->reg_state != NETREG_REGISTERED);