[PATCH 1/2] lockdep: add lockdep_assert_not_held()

[Shuah Khan]

Some kernel functions must not be called holding a specific lock. Doing
so could lead to locking problems. Currently these routines call
lock_is_held() to check for lock hold followed by WARN_ON.

Adding a common lockdep interface will help reduce the duplication of this
logic in the rest of the kernel.

Add lockdep_assert_not_held() to be used in these functions to detect
incorrect calls while holding a lock.

lockdep_assert_not_held() provides the opposite functionality of
lockdep_assert_held() which is used to assert calls that require
holding a specific lock.

The need for lockdep_assert_not_held() came up in a discussion on
ath10k patch. ath10k_drain_tx() and i915_vma_pin_ww() are examples
of functions that can use lockdep_assert_not_held().

Link: https://lore.kernel.org/linux-wireless/871rdmu9z9.fsf@xxxxxxxxxxxxxx/
Signed-off-by: Shuah Khan <skhan@xxxxxxxxxxxxxxxxxxx>
---
 include/linux/lockdep.h | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index b9e9adec73e8..567e3a1a27ce 100644
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h
@@ -294,6 +294,10 @@ extern void lock_unpin_lock(struct lockdep_map *lock, struct pin_cookie);
 
 #define lockdep_depth(tsk)	(debug_locks ? (tsk)->lockdep_depth : 0)
 
+#define lockdep_assert_not_held(l)	do {			\
+		WARN_ON(debug_locks && lockdep_is_held(l));	\
+	} while (0)
+
 #define lockdep_assert_held(l)	do {				\
 		WARN_ON(debug_locks && !lockdep_is_held(l));	\
 	} while (0)
@@ -383,8 +387,9 @@ extern int lock_is_held(const void *);
 extern int lockdep_is_held(const void *);
 #define lockdep_is_held_type(l, r)		(1)
 
+#define lockdep_assert_not_held(l)		do { (void)(l); } while (0)
 #define lockdep_assert_held(l)			do { (void)(l); } while (0)
-#define lockdep_assert_held_write(l)	do { (void)(l); } while (0)
+#define lockdep_assert_held_write(l)		do { (void)(l); } while (0)
 #define lockdep_assert_held_read(l)		do { (void)(l); } while (0)
 #define lockdep_assert_held_once(l)		do { (void)(l); } while (0)
 
-- 
2.27.0