lockdep: lockdep_set_notrack_class()

Add a new helper to disable lockdep tracking entirely for a given class.

This is needed for bcachefs, which takes too many btree node locks for
lockdep to track. Instead, we have a single lockdep_map for "btree_trans
has any btree nodes locked", which makes more since given that we have
centralized lock management and a cycle detector.

Cc: Peter Zijlstra <[e-mail]>
Cc: Ingo Molnar <[e-mail]>
Cc: Will Deacon <[e-mail]>
Cc: Waiman Long <[e-mail]>
Cc: Boqun Feng <[e-mail]>
Signed-off-by: Kent Overstreet <[e-mail]>

fs/bcachefs/btree_locking.c

···
 			  enum six_lock_init_flags flags)
 {
 	__six_lock_init(&b->lock, "b->c.lock", &bch2_btree_node_lock_key, flags);
-	lockdep_set_novalidate_class(&b->lock);
+	lockdep_set_notrack_class(&b->lock);
 }
 
 #ifdef CONFIG_LOCKDEP

include/linux/lockdep.h

···
 #define lockdep_set_novalidate_class(lock) \
 	lockdep_set_class_and_name(lock, &__lockdep_no_validate__, #lock)
 
+#define lockdep_set_notrack_class(lock) \
+	lockdep_set_class_and_name(lock, &__lockdep_no_track__, #lock)
+
 /*
  * Compare locking classes
  */
···
 #define lockdep_set_subclass(lock, sub)		do { } while (0)
 
 #define lockdep_set_novalidate_class(lock) do { } while (0)
+#define lockdep_set_notrack_class(lock) do { } while (0)
 
 /*
  * We don't define lockdep_match_class() and lockdep_match_key() for !LOCKDEP

include/linux/lockdep_types.h

···
 };
 
 extern struct lock_class_key __lockdep_no_validate__;
+extern struct lock_class_key __lockdep_no_track__;
 
 struct lock_trace;
 

kernel/locking/lockdep.c

···
 struct lock_class_key __lockdep_no_validate__;
 EXPORT_SYMBOL_GPL(__lockdep_no_validate__);
 
+struct lock_class_key __lockdep_no_track__;
+EXPORT_SYMBOL_GPL(__lockdep_no_track__);
+
 #ifdef CONFIG_PROVE_LOCKING
 void lockdep_set_lock_cmp_fn(struct lockdep_map *lock, lock_cmp_fn cmp_fn,
 			     lock_print_fn print_fn)
···
 	u64 chain_key;
 
 	if (unlikely(!debug_locks))
+		return 0;
+
+	if (unlikely(lock->key == &__lockdep_no_track__))
 		return 0;
 
 	if (!prove_locking || lock->key == &__lockdep_no_validate__)
···
 
 	trace_lock_release(lock, ip);
 
-	if (unlikely(!lockdep_enabled()))
+	if (unlikely(!lockdep_enabled() ||
+		     lock->key == &__lockdep_no_track__))
 		return;
 
 	raw_local_irq_save(flags);