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net/sched: don't use dynamic lockdep keys with clsact/ingress/noqueue

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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] https://github.com/multipath-tcp/mptcp_net-next/issues/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>
This commit is contained in:
Davide Caratti 2026-02-04 17:02:31 +01:00 • committed by Jakub Kicinski
parent 7e7fcfb079
commit a90f6dcefc
3 changed files with 28 additions and 6 deletions
Download patch file Download diff file Expand all files Collapse all files

24
include/net/pkt_sched.h
View file

@ -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

2
net/sched/sch_api.c
View file

@ -1353,7 +1353,7 @@ err_out4:
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:

8
net/sched/sch_generic.c
View file

@ -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);