[NET_SCHED] qdisc: avoid transmit softirq on watchdog wakeup

If possible, avoid having to do a transmit softirq when a qdisc
watchdog decides to re-enable.  The watchdog routine runs off
a timer, so it is already in the same effective context as
the softirq.
Signed-off-by: Stephen Hemminger <shemminger@linux-foundation.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sched/sch_api.c

@@ -296,10 +296,16 @@ static enum hrtimer_restart qdisc_watchdog(struct hrtimer *timer)
 {
 	struct qdisc_watchdog *wd = container_of(timer, struct qdisc_watchdog,
 						 timer);
+	struct net_device *dev = wd->qdisc->dev;
 
 	wd->qdisc->flags &= ~TCQ_F_THROTTLED;
 	smp_wmb();
-	netif_schedule(wd->qdisc->dev);
+	if (spin_trylock(&dev->queue_lock)) {
+		qdisc_run(dev);
+		spin_unlock(&dev->queue_lock);
+	} else
+		netif_schedule(dev);
+
 	return HRTIMER_NORESTART;
 }