IPoIB: Fix deadlock between ipoib_open() and child interface create

Fix a deadlock between child interface creation/deletion and ipoib
start/stop.  The former takes vlan_mutex, and then might take RTNL via
register_netdev()/unregister_netdev().  The latter is executed with
RTNL held, and tries to take vlan_mutex, which can lead to an AB-BA
deadlock.

Fix this by having the child interface creation/deletion code take the
RTNL first so vlan_mutex always nests inside RTNL.  We can use
register_netdevice() for child interfaces because we form the
interface name from the parent interface and hence don't need the '%'
expansion of register_netdev().

Reported-by: Yossi Etigin <yosefe@voltaire.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>

drivers/infiniband/ulp/ipoib/ipoib_vlan.c

@@ -61,6 +61,7 @@ int ipoib_vlan_add(struct net_device *pdev, unsigned short pkey)
 
 	ppriv = netdev_priv(pdev);
 
+	rtnl_lock();
 	mutex_lock(&ppriv->vlan_mutex);
 
 	/*
@@ -111,7 +112,7 @@ int ipoib_vlan_add(struct net_device *pdev, unsigned short pkey)
 		goto device_init_failed;
 	}
 
-	result = register_netdev(priv->dev);
+	result = register_netdevice(priv->dev);
 	if (result) {
 		ipoib_warn(priv, "failed to initialize; error %i", result);
 		goto register_failed;
@@ -134,12 +135,13 @@ int ipoib_vlan_add(struct net_device *pdev, unsigned short pkey)
 	list_add_tail(&priv->list, &ppriv->child_intfs);
 
 	mutex_unlock(&ppriv->vlan_mutex);
+	rtnl_unlock();
 
 	return 0;
 
 sysfs_failed:
 	ipoib_delete_debug_files(priv->dev);
-	unregister_netdev(priv->dev);
+	unregister_netdevice(priv->dev);
 
 register_failed:
 	ipoib_dev_cleanup(priv->dev);
@@ -149,6 +151,7 @@ int ipoib_vlan_add(struct net_device *pdev, unsigned short pkey)
 
 err:
 	mutex_unlock(&ppriv->vlan_mutex);
+	rtnl_unlock();
 	return result;
 }
 
@@ -162,10 +165,11 @@ int ipoib_vlan_delete(struct net_device *pdev, unsigned short pkey)
 
 	ppriv = netdev_priv(pdev);
 
+	rtnl_lock();
 	mutex_lock(&ppriv->vlan_mutex);
 	list_for_each_entry_safe(priv, tpriv, &ppriv->child_intfs, list) {
 		if (priv->pkey == pkey) {
-			unregister_netdev(priv->dev);
+			unregister_netdevice(priv->dev);
 			ipoib_dev_cleanup(priv->dev);
 			list_del(&priv->list);
 			free_netdev(priv->dev);
@@ -175,6 +179,7 @@ int ipoib_vlan_delete(struct net_device *pdev, unsigned short pkey)
 		}
 	}
 	mutex_unlock(&ppriv->vlan_mutex);
+	rtnl_unlock();
 
 	return ret;
 }