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

Prepare mqprio_dump_class_stats() for RTNL avoidance.

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

As a bonus we no longer have to release/acquire d->lock.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Toke Høiland-Jørgensen <toke@toke.dk>
Link: https://patch.msgid.link/20260510091455.4039245-9-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 f9dab76f40ebbd1363121198bbc3af2bd951c101..ae991fc25b43f24efb3b53fce6f6b53718a9b774 100644 (file)
--- a/net/sched/sch_mqprio.c
+++ b/net/sched/sch_mqprio.c
@@ -672,9 +672,11 @@ static int mqprio_dump_class(struct Qdisc *sch, unsigned long cl,
 
 static int mqprio_dump_class_stats(struct Qdisc *sch, unsigned long cl,
                                   struct gnet_dump *d)
-       __releases(d->lock)
-       __acquires(d->lock)
 {
+       const struct Qdisc *qdisc;
+       int res = 0;
+
+       rcu_read_lock();
        if (cl >= TC_H_MIN_PRIORITY) {
                struct net_device *dev = qdisc_dev(sch);
                struct netdev_tc_txq tc = dev->tc_to_txq[cl & TC_BITMASK];
@@ -684,46 +686,34 @@ static int mqprio_dump_class_stats(struct Qdisc *sch, unsigned long cl,
                int i;
 
                gnet_stats_basic_sync_init(&bstats);
-               /* Drop lock here it will be reclaimed before touching
-                * statistics this is required because the d->lock we
-                * hold here is the look on dev_queue->qdisc_sleeping
-                * also acquired below.
-                */
-               if (d->lock)
-                       spin_unlock_bh(d->lock);
 
                for (i = tc.offset; i < tc.offset + tc.count; i++) {
                        struct netdev_queue *q = netdev_get_tx_queue(dev, i);
-                       struct Qdisc *qdisc = rtnl_dereference(q->qdisc);
-
-                       spin_lock_bh(qdisc_lock(qdisc));
 
+                       qdisc = rcu_dereference(q->qdisc);
                        gnet_stats_add_basic(&bstats, qdisc->cpu_bstats,
-                                            &qdisc->bstats, false);
+                                            &qdisc->bstats, true);
                        gnet_stats_add_queue(&qstats, qdisc->cpu_qstats,
                                             &qdisc->qstats);
                        qlen += qdisc_qlen_lockless(qdisc);
-
-                       spin_unlock_bh(qdisc_lock(qdisc));
                }
+
                qlen = qlen + qstats.qlen;
 
-               /* Reclaim root sleeping lock before completing stats */
-               if (d->lock)
-                       spin_lock_bh(d->lock);
                if (gnet_stats_copy_basic(d, NULL, &bstats, false) < 0 ||
                    gnet_stats_copy_queue(d, NULL, &qstats, qlen) < 0)
-                       return -1;
+                       res = -1;
        } else {
                struct netdev_queue *dev_queue = mqprio_queue_get(sch, cl);
 
-               sch = rtnl_dereference(dev_queue->qdisc_sleeping);
-               if (gnet_stats_copy_basic(d, sch->cpu_bstats,
-                                         &sch->bstats, true) < 0 ||
-                   qdisc_qstats_copy(d, sch) < 0)
-                       return -1;
+               qdisc = rcu_dereference(dev_queue->qdisc_sleeping);
+               if (gnet_stats_copy_basic(d, qdisc->cpu_bstats,
+                                         &qdisc->bstats, true) < 0 ||
+                   qdisc_qstats_copy(d, qdisc) < 0)
+                       res = -1;
        }
-       return 0;
+       rcu_read_unlock();
+       return res;
 }
 
 static void mqprio_walk(struct Qdisc *sch, struct qdisc_walker *arg)