locking/lockdep: Make concurrent lockdep_reset_lock() calls safe

Since zap_class() removes items from the all_lock_classes list and the
classhash_table, protect all zap_class() calls against concurrent
data structure modifications with the graph lock.

Signed-off-by: Bart Van Assche <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Cc: Johannes Berg <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Sasha Levin <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Waiman Long <[email protected]>
Cc: [email protected]
Cc: [email protected]
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>

kernel/locking/lockdep.c

@@ -4122,6 +4122,9 @@ void lockdep_reset(void)
 	raw_local_irq_restore(flags);
 }
 
+/*
+ * Remove all references to a lock class. The caller must hold the graph lock.
+ */
 static void zap_class(struct lock_class *class)
 {
 	int i;
@@ -4229,6 +4232,7 @@ void lockdep_reset_lock(struct lockdep_map *lock)
 	int j, locked;
 
 	raw_local_irq_save(flags);
+	locked = graph_lock();
 
 	/*
 	 * Remove all classes this lock might have:
@@ -4245,7 +4249,6 @@ void lockdep_reset_lock(struct lockdep_map *lock)
 	 * Debug check: in the end all mapped classes should
 	 * be gone.
 	 */
-	locked = graph_lock();
 	if (unlikely(lock_class_cache_is_registered(lock))) {
 		if (debug_locks_off_graph_unlock()) {
 			/*