net: use batched device unregister in veth and macvlan

veth devices dont use the batched device unregisters yet.

Since veth are a pair of devices, it makes sense to use a batch of two
unregisters, this roughly divides dismantle time by two.

Fix this by changing dellink() callers to always provide a non NULL
head. (Idea from Michał Mirosław)

This patch also handles macvlan case : We now dismantle all macvlans on
top of a lower dev at once.
Reported-by: Alex Bligh <alex@alex.org.uk>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Michał Mirosław <mirqus@gmail.com>
Cc: Jesse Gross <jesse@nicira.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Ben Greear <greearb@candelatech.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/macvlan.c

@@ -785,6 +785,7 @@ static int macvlan_device_event(struct notifier_block *unused,
 	struct net_device *dev = ptr;
 	struct macvlan_dev *vlan, *next;
 	struct macvlan_port *port;
+	LIST_HEAD(list_kill);
 
 	if (!macvlan_port_exists(dev))
 		return NOTIFY_DONE;
@@ -810,7 +811,9 @@ static int macvlan_device_event(struct notifier_block *unused,
 			break;
 
 		list_for_each_entry_safe(vlan, next, &port->vlans, list)
-			vlan->dev->rtnl_link_ops->dellink(vlan->dev, NULL);
+			vlan->dev->rtnl_link_ops->dellink(vlan->dev, &list_kill);
+		unregister_netdevice_many(&list_kill);
+		list_del(&list_kill);
 		break;
 	case NETDEV_PRE_TYPE_CHANGE:
 		/* Forbid underlaying device to change its type. */

net/core/rtnetlink.c

@@ -1501,6 +1501,7 @@ static int rtnl_dellink(struct sk_buff *skb, struct nlmsghdr *nlh, void *arg)
 	char ifname[IFNAMSIZ];
 	struct nlattr *tb[IFLA_MAX+1];
 	int err;
+	LIST_HEAD(list_kill);
 
 	err = nlmsg_parse(nlh, sizeof(*ifm), tb, IFLA_MAX, ifla_policy);
 	if (err < 0)
@@ -1524,7 +1525,9 @@ static int rtnl_dellink(struct sk_buff *skb, struct nlmsghdr *nlh, void *arg)
 	if (!ops)
 		return -EOPNOTSUPP;
 
-	ops->dellink(dev, NULL);
+	ops->dellink(dev, &list_kill);
+	unregister_netdevice_many(&list_kill);
+	list_del(&list_kill);
 	return 0;
 }