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, like:

 - clsact
 - ingress
 - noqueue

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

[1] multipath-tcp/mptcp_net-next#451

Changes in v2:
 - change ordering of spin_lock_init() vs. lockdep_register_key()
   (Jakub Kicinski)

Signed-off-by: Davide Caratti <dcaratti@redhat.com>
Link: https://patch.msgid.link/94448f7fa7c4f52d2ce416a4895ec87d456d7417.1770220576.git.dcaratti@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: dcaratti

include/net/pkt_sched.h

@@ -308,4 +308,28 @@ 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)
+{
+	spin_lock_init(&sch->q.lock);
+
+	/* Skip dynamic keys if nesting is not possible */
+	if (ops->static_flags & TCQ_F_INGRESS ||
+	    ops == &noqueue_qdisc_ops)
+		return;
+
+	lockdep_register_key(&sch->root_lock_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)
+{
+	if (ops->static_flags & TCQ_F_INGRESS ||
+	    ops == &noqueue_qdisc_ops)
+		return;
+
+	lockdep_unregister_key(&sch->root_lock_key);
+}
+
 #endif

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:

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);