net/sched: mq_prio: no longer acquire qdisc spinlocks in mqprio_dump()

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>
Acked-by: Toke Høiland-Jørgensen <toke@toke.dk>
Link: https://patch.msgid.link/20260510091455.4039245-8-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/sched/sch_mqprio.c b/net/sched/sch_mqprio.c
index 3b4881c389c535368687454ea268bec892ecb942..f9dab76f40ebbd1363121198bbc3af2bd951c101 100644 (file)
--- a/net/sched/sch_mqprio.c
+++ b/net/sched/sch_mqprio.c
@@ -551,35 +551,46 @@ nla_put_failure:
 
 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);