linux-kernel - Re: [PATCH] locking/lockdep: Add # of dynamic keys stat to /proc/lockdep

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Message-ID: <aBesEItGIeHf5v52@Mac.home>
Date: Sun, 4 May 2025 11:04:00 -0700
From: Boqun Feng <boqun.feng@...il.com>
To: Waiman Long <longman@...hat.com>
Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
	Will Deacon <will.deacon@....com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] locking/lockdep: Add # of dynamic keys stat to
 /proc/lockdep_stats

On Thu, Apr 24, 2025 at 08:11:55PM -0400, Waiman Long wrote:
> There have been recent reports about running out of lockdep keys
> (MAX_LOCKDEP_KEYS too low!). One possible reason is that too many
> dynamic keys have been registered. A possible culprit is the
> lockdep_register_key() call in qdisc_alloc() of net/sched/sch_generic.c.
> 
> Currently, there is no way to find out how many dynamic keys have been
> registered. Add such a stat to the /proc/lockdep_stats to get better
> clarity.
> 
> Signed-off-by: Waiman Long <longman@...hat.com>

Queued for 6.16.

Regards,
Boqun

> ---
>  kernel/locking/lockdep.c           | 3 +++
>  kernel/locking/lockdep_internals.h | 1 +
>  kernel/locking/lockdep_proc.c      | 2 ++
>  3 files changed, 6 insertions(+)
> 
> diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
> index 58d78a33ac65..aeedaaaa403c 100644
> --- a/kernel/locking/lockdep.c
> +++ b/kernel/locking/lockdep.c
> @@ -219,6 +219,7 @@ static DECLARE_BITMAP(list_entries_in_use, MAX_LOCKDEP_ENTRIES);
>  static struct hlist_head lock_keys_hash[KEYHASH_SIZE];
>  unsigned long nr_lock_classes;
>  unsigned long nr_zapped_classes;
> +unsigned long nr_dynamic_keys;
>  unsigned long max_lock_class_idx;
>  struct lock_class lock_classes[MAX_LOCKDEP_KEYS];
>  DECLARE_BITMAP(lock_classes_in_use, MAX_LOCKDEP_KEYS);
> @@ -1238,6 +1239,7 @@ void lockdep_register_key(struct lock_class_key *key)
>  			goto out_unlock;
>  	}
>  	hlist_add_head_rcu(&key->hash_entry, hash_head);
> +	nr_dynamic_keys++;
>  out_unlock:
>  	graph_unlock();
>  restore_irqs:
> @@ -6606,6 +6608,7 @@ void lockdep_unregister_key(struct lock_class_key *key)
>  		pf = get_pending_free();
>  		__lockdep_free_key_range(pf, key, 1);
>  		need_callback = prepare_call_rcu_zapped(pf);
> +		nr_dynamic_keys--;
>  	}
>  	lockdep_unlock();
>  	raw_local_irq_restore(flags);
> diff --git a/kernel/locking/lockdep_internals.h b/kernel/locking/lockdep_internals.h
> index 20f9ef58d3d0..82156caf77d1 100644
> --- a/kernel/locking/lockdep_internals.h
> +++ b/kernel/locking/lockdep_internals.h
> @@ -138,6 +138,7 @@ extern unsigned long nr_lock_classes;
>  extern unsigned long nr_zapped_classes;
>  extern unsigned long nr_zapped_lock_chains;
>  extern unsigned long nr_list_entries;
> +extern unsigned long nr_dynamic_keys;
>  long lockdep_next_lockchain(long i);
>  unsigned long lock_chain_count(void);
>  extern unsigned long nr_stack_trace_entries;
> diff --git a/kernel/locking/lockdep_proc.c b/kernel/locking/lockdep_proc.c
> index 6db0f43fc4df..b52c07c4707c 100644
> --- a/kernel/locking/lockdep_proc.c
> +++ b/kernel/locking/lockdep_proc.c
> @@ -286,6 +286,8 @@ static int lockdep_stats_show(struct seq_file *m, void *v)
>  #endif
>  	seq_printf(m, " lock-classes:                  %11lu [max: %lu]\n",
>  			nr_lock_classes, MAX_LOCKDEP_KEYS);
> +	seq_printf(m, " dynamic-keys:                  %11lu\n",
> +			nr_dynamic_keys);
>  	seq_printf(m, " direct dependencies:           %11lu [max: %lu]\n",
>  			nr_list_entries, MAX_LOCKDEP_ENTRIES);
>  	seq_printf(m, " indirect dependencies:         %11lu\n",
> -- 
> 2.49.0
>