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

Author: Waiman-Long

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);

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;

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",