pkt_sched: Fix qdisc_watchdog() vs. dev_deactivate() race

dev_deactivate() can skip rescheduling of a qdisc by qdisc_watchdog()
or other timer calling netif_schedule() after dev_queue_deactivate().
We prevent this checking aliveness before scheduling the timer. Since
during deactivation the root qdisc is available only as qdisc_sleeping
additional accessor qdisc_root_sleeping() is created.

With feedback from Herbert Xu <[e-mail]>

Signed-off-by: Jarek Poplawski <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

include/net/sch_generic.h

···
 	return qdisc->dev_queue->qdisc;
 }
 
+static inline struct Qdisc *qdisc_root_sleeping(struct Qdisc *qdisc)
+{
+	return qdisc->dev_queue->qdisc_sleeping;
+}
+
 /* The qdisc root lock is a mechanism by which to top level
  * of a qdisc tree can be locked from any qdisc node in the
  * forest.  This allows changing the configuration of some

net/sched/sch_api.c

···
 {
 	ktime_t time;
 
+	if (test_bit(__QDISC_STATE_DEACTIVATED,
+		     &qdisc_root_sleeping(wd->qdisc)->state))
+		return;
+
 	wd->qdisc->flags |= TCQ_F_THROTTLED;
 	time = ktime_set(0, 0);
 	time = ktime_add_ns(time, PSCHED_US2NS(expires));

net/sched/sch_cbq.c

···
 	struct cbq_sched_data *q = qdisc_priv(cl->qdisc);
 	psched_tdiff_t delay = cl->undertime - q->now;
 
+	if (test_bit(__QDISC_STATE_DEACTIVATED,
+		     &qdisc_root_sleeping(cl->qdisc)->state))
+		return;
+
 	if (!cl->delayed) {
 		psched_time_t sched = q->now;
 		ktime_t expires;