[PKT_SCHED]: Fix rcu_assign_pointer fallout, use it in the right place

The patch 'RCU: use rcu_assign_pointer()'
http://linux.bkbits.net:8080/linux-2.6/diffs/net/sched/sch_api.c@1.39?nav=index.html|src/net/|src/net|src/net/sched|related/net/sched/sch_api.c|cset@1.2287
changed a list_add_tail to list_add_tail_rcu in qdisc_create. It's
dev->qdisc not dev->qdisc_list that is protected by RCU, this patch
reverts that change. It also removes a misleading comment and replaces
the smp_wmb in qdisc_create_dflt by rcu_assign_pointer in dev_activate
to document more clearly what is protected.
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sched/sch_api.c

@@ -451,11 +451,9 @@ qdisc_create(struct net_device *dev, u32 handle, struct rtattr **tca, int *errp)
         else
                 sch->handle = handle;
 
-	/* enqueue is accessed locklessly - make sure it's visible
-	 * before we set a netdevice's qdisc pointer to sch */
 	if (!ops->init || (err = ops->init(sch, tca[TCA_OPTIONS-1])) == 0) {
 		qdisc_lock_tree(dev);
-		list_add_tail_rcu(&sch->list, &dev->qdisc_list);
+		list_add_tail(&sch->list, &dev->qdisc_list);
 		qdisc_unlock_tree(dev);
 
 #ifdef CONFIG_NET_ESTIMATOR

net/sched/sch_generic.c

@@ -438,9 +438,6 @@ struct Qdisc * qdisc_create_dflt(struct net_device *dev, struct Qdisc_ops *ops)
 	dev_hold(dev);
 	sch->stats_lock = &dev->queue_lock;
 	atomic_set(&sch->refcnt, 1);
-	/* enqueue is accessed locklessly - make sure it's visible
-	 * before we set a netdevice's qdisc pointer to sch */
-	smp_wmb();
 	if (!ops->init || ops->init(sch, NULL) == 0)
 		return sch;
 
@@ -521,7 +518,8 @@ void dev_activate(struct net_device *dev)
 	}
 
 	spin_lock_bh(&dev->queue_lock);
-	if ((dev->qdisc = dev->qdisc_sleeping) != &noqueue_qdisc) {
+	rcu_assign_pointer(dev->qdisc, dev->qdisc_sleeping);
+	if (dev->qdisc != &noqueue_qdisc) {
 		dev->trans_start = jiffies;
 		dev_watchdog_up(dev);
 	}