net: sched: prio: delay destroying child qdiscs on change

Move destroying of the old child qdiscs outside of the sch_tree_lock()
section.  This should improve the software qdisc replace but is even
more important for offloads.  Calling offloads under a spin lock is
best avoided, and child's destroy would be called under sch_tree_lock().
Signed-off-by: NJakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: NJohn Hurley <john.hurley@netronome.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/sched/sch_prio.c

@@ -220,7 +220,6 @@ static int prio_tune(struct Qdisc *sch, struct nlattr *opt,
 
 		qdisc_tree_reduce_backlog(child, child->q.qlen,
 					  child->qstats.backlog);
-		qdisc_put(child);
 	}
 
 	for (i = oldbands; i < q->bands; i++) {
@@ -230,6 +229,9 @@ static int prio_tune(struct Qdisc *sch, struct nlattr *opt,
 	}
 
 	sch_tree_unlock(sch);
+
+	for (i = q->bands; i < oldbands; i++)
+		qdisc_put(q->queues[i]);
 	return 0;
 }