sch_prio: update backlog as well

We need to update backlog too when we update qlen.

Joint work with Stas.

Reported-by: Stas Nichiporovich <stasn77@gmail.com>
Tested-by: Stas Nichiporovich <stasn77@gmail.com>
Fixes: 2ccccf5fb43f ("net_sched: update hierarchical backlog too")
Cc: Jamal Hadi Salim <jhs@mojatatu.com>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sched/sch_prio.c

diff --git a/net/sched/sch_prio.c b/net/sched/sch_prio.c
index fee1b15..4b0a821 100644
--- a/net/sched/sch_prio.c
+++ b/net/sched/sch_prio.c
@@ -85,6 +85,7 @@
 
 	ret = qdisc_enqueue(skb, qdisc);
 	if (ret == NET_XMIT_SUCCESS) {
+		qdisc_qstats_backlog_inc(sch, skb);
 		sch->q.qlen++;
 		return NET_XMIT_SUCCESS;
 	}
@@ -117,6 +118,7 @@
 		struct sk_buff *skb = qdisc_dequeue_peeked(qdisc);
 		if (skb) {
 			qdisc_bstats_update(sch, skb);
+			qdisc_qstats_backlog_dec(sch, skb);
 			sch->q.qlen--;
 			return skb;
 		}
@@ -135,6 +137,7 @@
 	for (prio = q->bands-1; prio >= 0; prio--) {
 		qdisc = q->queues[prio];
 		if (qdisc->ops->drop && (len = qdisc->ops->drop(qdisc)) != 0) {
+			sch->qstats.backlog -= len;
 			sch->q.qlen--;
 			return len;
 		}
@@ -151,6 +154,7 @@
 
 	for (prio = 0; prio < q->bands; prio++)
 		qdisc_reset(q->queues[prio]);
+	sch->qstats.backlog = 0;
 	sch->q.qlen = 0;
 }