netdev - [PATCH net-next] net/sched: don't use dynamic lockdep keys with clsact/ingress/noqueue

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Message-ID: <68f55cee98e5402af2509f1d3873fbc7a27f67e9.1769699825.git.dcaratti@redhat.com>
Date: Thu, 29 Jan 2026 16:24:35 +0100
From: Davide Caratti <dcaratti@...hat.com>
To: Jamal Hadi Salim <jhs@...atatu.com>,
	Cong Wang <xiyou.wangcong@...il.com>,
	Jiri Pirko <jiri@...nulli.us>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>,
	Simon Horman <horms@...nel.org>
Cc: netdev@...r.kernel.org
Subject: [PATCH net-next] net/sched: don't use dynamic lockdep keys with clsact/ingress/noqueue

Currently we are registering one dynamic lockdep key for each allocated
qdisc, to avoid false deadlock reports when mirred (or TC eBPF) redirects
packets to another device while the root lock is acquired [1].
Since dynamic keys are a limited resource, we can save them at least for
qdiscs that are not meant to acquire the root lock in the traffic path, or
to carry traffic at all. A good (initial) example is:

 - clsact
 - ingress
 - noqueue

Don't register dynamic keys for the above schedulers, so that we hit
MAX_LOCKDEP_KEYS later in our tests.

[1] https://github.com/multipath-tcp/mptcp_net-next/issues/451

Signed-off-by: Davide Caratti <dcaratti@...hat.com>
---
 include/net/pkt_sched.h | 22 ++++++++++++++++++++++
 net/sched/sch_api.c     |  2 +-
 net/sched/sch_generic.c |  8 +++-----
 3 files changed, 26 insertions(+), 6 deletions(-)

diff --git a/include/net/pkt_sched.h b/include/net/pkt_sched.h
index e703c507d0da..e68a7bbb84b4 100644
--- a/include/net/pkt_sched.h
+++ b/include/net/pkt_sched.h
@@ -308,4 +308,26 @@ static inline unsigned int qdisc_peek_len(struct Qdisc *sch)
 	return len;
 }
 
+static inline void qdisc_lock_init(struct Qdisc *sch, const struct Qdisc_ops *ops)
+{
+	bool skip_dynamic_key = (ops->static_flags & TCQ_F_INGRESS) ||
+				(ops == &noqueue_qdisc_ops);
+
+	if (!skip_dynamic_key)
+		lockdep_register_key(&sch->root_lock_key);
+
+	spin_lock_init(&sch->q.lock);
+	if (!skip_dynamic_key)
+		lockdep_set_class(&sch->q.lock, &sch->root_lock_key);
+}
+
+static inline void qdisc_lock_uninit(struct Qdisc *sch, const struct Qdisc_ops *ops)
+{
+	bool skip_dynamic_key = (ops->static_flags & TCQ_F_INGRESS) ||
+				(ops == &noqueue_qdisc_ops);
+
+	if (!skip_dynamic_key)
+		lockdep_unregister_key(&sch->root_lock_key);
+}
+
 #endif
diff --git a/net/sched/sch_api.c b/net/sched/sch_api.c
index f56b18c8aebf..443c116e8663 100644
--- a/net/sched/sch_api.c
+++ b/net/sched/sch_api.c
@@ -1353,7 +1353,7 @@ static struct Qdisc *qdisc_create(struct net_device *dev,
 		ops->destroy(sch);
 	qdisc_put_stab(rtnl_dereference(sch->stab));
 err_out3:
-	lockdep_unregister_key(&sch->root_lock_key);
+	qdisc_lock_uninit(sch, ops);
 	netdev_put(dev, &sch->dev_tracker);
 	qdisc_free(sch);
 err_out2:
diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
index 852e603c1755..98ffe64de51f 100644
--- a/net/sched/sch_generic.c
+++ b/net/sched/sch_generic.c
@@ -955,9 +955,7 @@ struct Qdisc *qdisc_alloc(struct netdev_queue *dev_queue,
 	__skb_queue_head_init(&sch->gso_skb);
 	__skb_queue_head_init(&sch->skb_bad_txq);
 	gnet_stats_basic_sync_init(&sch->bstats);
-	lockdep_register_key(&sch->root_lock_key);
-	spin_lock_init(&sch->q.lock);
-	lockdep_set_class(&sch->q.lock, &sch->root_lock_key);
+	qdisc_lock_init(sch, ops);
 
 	if (ops->static_flags & TCQ_F_CPUSTATS) {
 		sch->cpu_bstats =
@@ -987,7 +985,7 @@ struct Qdisc *qdisc_alloc(struct netdev_queue *dev_queue,
 
 	return sch;
 errout1:
-	lockdep_unregister_key(&sch->root_lock_key);
+	qdisc_lock_uninit(sch, ops);
 	kfree(sch);
 errout:
 	return ERR_PTR(err);
@@ -1076,7 +1074,7 @@ static void __qdisc_destroy(struct Qdisc *qdisc)
 	if (ops->destroy)
 		ops->destroy(qdisc);
 
-	lockdep_unregister_key(&qdisc->root_lock_key);
+	qdisc_lock_uninit(qdisc, ops);
 	bpf_module_put(ops, ops->owner);
 	netdev_put(dev, &qdisc->dev_tracker);
 
-- 
2.52.0