Lockdep: add lockdep_set_class_and_subclass() and lockdep_set_subclass()

This annotation makes it possible to assign a subclass on lock init. This
annotation is meant to reduce the _nested() annotations by assigning a
default subclass.

One could do without this annotation and rely on lockdep_set_class()
exclusively, but that would require a manual stack of struct lock_class_key
objects.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>

2 files changed, 7 insertions, 5 deletions

diff --git a/kernel/lockdep.c b/kernel/lockdep.c
index 4c0553461000..ba7156ac70c1 100644
--- a/kernel/lockdep.c
+++ b/kernel/lockdep.c
@@ -1177,7 +1177,7 @@ look_up_lock_class(struct lockdep_map *lock, unsigned int subclass)
  * itself, so actual lookup of the hash should be once per lock object.
  */
 static inline struct lock_class *
-register_lock_class(struct lockdep_map *lock, unsigned int subclass)
+register_lock_class(struct lockdep_map *lock, unsigned int subclass, int force)
 {
         struct lockdep_subclass_key *key;
         struct list_head *hash_head;
@@ -1249,7 +1249,7 @@ register_lock_class(struct lockdep_map *lock, unsigned int subclass)
 out_unlock_set:
         __raw_spin_unlock(&hash_lock);
 
-        if (!subclass)
+        if (!subclass || force)
                 lock->class_cache = class;
 
         DEBUG_LOCKS_WARN_ON(class->subclass != subclass);
@@ -1937,7 +1937,7 @@ void trace_softirqs_off(unsigned long ip)
  * Initialize a lock instance's lock-class mapping info:
  */
 void lockdep_init_map(struct lockdep_map *lock, const char *name,
-                      struct lock_class_key *key)
+                      struct lock_class_key *key, int subclass)
 {
         if (unlikely(!debug_locks))
                 return;
@@ -1957,6 +1957,8 @@ void lockdep_init_map(struct lockdep_map *lock, const char *name,
         lock->name = name;
         lock->key = key;
         lock->class_cache = NULL;
+        if (subclass)
+                register_lock_class(lock, subclass, 1);
 }
 
 EXPORT_SYMBOL_GPL(lockdep_init_map);
@@ -1995,7 +1997,7 @@ static int __lock_acquire(struct lockdep_map *lock, unsigned int subclass,
          * Not cached yet or subclass?
          */
         if (unlikely(!class)) {
-                class = register_lock_class(lock, subclass);
+                class = register_lock_class(lock, subclass, 0);
                 if (!class)
                         return 0;
         }
diff --git a/kernel/mutex-debug.c b/kernel/mutex-debug.c
index e3203c654dda..18651641a7b5 100644
--- a/kernel/mutex-debug.c
+++ b/kernel/mutex-debug.c
@@ -91,7 +91,7 @@ void debug_mutex_init(struct mutex *lock, const char *name,
          * Make sure we are not reinitializing a held lock:
          */
         debug_check_no_locks_freed((void *)lock, sizeof(*lock));
-        lockdep_init_map(&lock->dep_map, name, key);
+        lockdep_init_map(&lock->dep_map, name, key, 0);
 #endif
         lock->owner = NULL;
         lock->magic = lock;