net: use rcu for network scheduler API

Use RCU to walk list of network devices in qdisc dump.
This could be optimized for large number of devices.
Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Acked-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sched/sch_api.c

@@ -1279,9 +1279,10 @@ static int tc_dump_qdisc(struct sk_buff *skb, struct netlink_callback *cb)
 
 	s_idx = cb->args[0];
 	s_q_idx = q_idx = cb->args[1];
-	read_lock(&dev_base_lock);
+
+	rcu_read_lock();
 	idx = 0;
-	for_each_netdev(&init_net, dev) {
+	for_each_netdev_rcu(&init_net, dev) {
 		struct netdev_queue *dev_queue;
 
 		if (idx < s_idx)
@@ -1302,7 +1303,7 @@ static int tc_dump_qdisc(struct sk_buff *skb, struct netlink_callback *cb)
 	}
 
 done:
-	read_unlock(&dev_base_lock);
+	rcu_read_unlock();
 
 	cb->args[0] = idx;
 	cb->args[1] = q_idx;