locking/lockdep: Add number of dynamic keys to /proc/lockdep_stats

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@redhat.com>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Bill Wendling <morbo@google.com>
Cc: Justin Stitt <justinstitt@google.com>
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: Nick Desaulniers <nick.desaulniers+lkml@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Will Deacon <will@kernel.org>
Cc: llvm@lists.linux.dev
Link: https://lore.kernel.org/r/20250506042049.50060-4-boqun.feng@gmail.com

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 050dbe9eec3c4c2c194c422aa8f4f95ed833b24e..dd2bbf73718b06caf9ded9aa6be73d616b154785 100644 (file)
--- 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:
@@ -6609,6 +6611,7 @@ 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 20f9ef58d3d06951c666be25390956f5fc21a4c3..82156caf77d1c0c3d1f91b84d30f4dabd8249df4 100644 (file)
--- 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 6db0f43fc4df548fa4476d1571e4f743e844718d..b52c07c4707cd33f2a270a3c73a29628309c9aab 100644 (file)
--- 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",