[PATCH v2 net-next 7/8] net/sched: mq_prio: no longer acquire qdisc spinlocks in mqprio_dump()

[Eric Dumazet <edumazet@google.com>]

Prepare mqprio_dump() for RTNL avoidance.

Use RCU instead of RTNL, and no longer acquire each children spinlock.

Signed-off-by: Eric Dumazet <edumazet@google.com>
---
 net/sched/sch_mqprio.c | 37 ++++++++++++++++++++++++-------------
 1 file changed, 24 insertions(+), 13 deletions(-)

diff --git a/net/sched/sch_mqprio.c b/net/sched/sch_mqprio.c
index 3b4881c389c535368687454ea268bec892ecb942..f9dab76f40ebbd1363121198bbc3af2bd951c101 100644
--- a/net/sched/sch_mqprio.c
+++ b/net/sched/sch_mqprio.c
@@ -551,35 +551,46 @@ static int mqprio_dump_tc_entries(struct mqprio_sched *priv,
 
 static int mqprio_dump(struct Qdisc *sch, struct sk_buff *skb)
 {
-	struct net_device *dev = qdisc_dev(sch);
-	struct mqprio_sched *priv = qdisc_priv(sch);
 	struct nlattr *nla = (struct nlattr *)skb_tail_pointer(skb);
+	struct mqprio_sched *priv = qdisc_priv(sch);
+	struct net_device *dev = qdisc_dev(sch);
+	struct gnet_stats_queue qstats = { 0 };
+	struct gnet_stats_basic_sync bstats;
 	struct tc_mqprio_qopt opt = { 0 };
+	const struct Qdisc *qdisc;
 	unsigned int qlen = 0;
-	struct Qdisc *qdisc;
 	unsigned int ntx;
 
-	qlen = 0;
-	gnet_stats_basic_sync_init(&sch->bstats);
-	memset(&sch->qstats, 0, sizeof(sch->qstats));
+	gnet_stats_basic_sync_init(&bstats);
 
 	/* MQ supports lockless qdiscs. However, statistics accounting needs
 	 * to account for all, none, or a mix of locked and unlocked child
 	 * qdiscs. Percpu stats are added to counters in-band and locking
 	 * qdisc totals are added at end.
 	 */
+	rcu_read_lock();
 	for (ntx = 0; ntx < dev->num_tx_queues; ntx++) {
-		qdisc = rtnl_dereference(netdev_get_tx_queue(dev, ntx)->qdisc_sleeping);
-		spin_lock_bh(qdisc_lock(qdisc));
+		qdisc = rcu_dereference(netdev_get_tx_queue(dev, ntx)->qdisc_sleeping);
 
-		gnet_stats_add_basic(&sch->bstats, qdisc->cpu_bstats,
-				     &qdisc->bstats, false);
-		gnet_stats_add_queue(&sch->qstats, qdisc->cpu_qstats,
+		gnet_stats_add_basic(&bstats, qdisc->cpu_bstats,
+				     &qdisc->bstats, true);
+		gnet_stats_add_queue(&qstats, qdisc->cpu_qstats,
 				     &qdisc->qstats);
 		qlen += qdisc_qlen_lockless(qdisc);
-
-		spin_unlock_bh(qdisc_lock(qdisc));
 	}
+	rcu_read_unlock();
+
+	spin_lock_bh(qdisc_lock(sch));
+	_bstats_set(&sch->bstats, u64_stats_read(&bstats.bytes),
+		    u64_stats_read(&bstats.packets));
+	spin_unlock_bh(qdisc_lock(sch));
+
+	WRITE_ONCE(sch->qstats.qlen, qstats.qlen);
+	WRITE_ONCE(sch->qstats.backlog, qstats.backlog);
+	WRITE_ONCE(sch->qstats.drops, qstats.drops);
+	WRITE_ONCE(sch->qstats.requeues, qstats.requeues);
+	WRITE_ONCE(sch->qstats.overlimits, qstats.overlimits);
+
 	WRITE_ONCE(sch->q.qlen, qlen);
 
 	mqprio_qopt_reconstruct(dev, &opt);
-- 
2.54.0.563.g4f69b47b94-goog