[PATCH v2 1/3] lockdep: add lockdep_assert_not_held()

[Shuah Khan]

Some kernel functions must be called without holding a specific lock.
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.

Incorporates suggestions from Peter Zijlstra to avoid misfires when
lockdep_off() is employed.

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/lkml/37a29c383bff2fb1605241ee6c7c9be3784fb3c6.1613171185.git.skhan@xxxxxxxxxxxxxxxxxxx/
Link: https://lore.kernel.org/linux-wireless/871rdmu9z9.fsf@xxxxxxxxxxxxxx/
Signed-off-by: Shuah Khan <skhan@xxxxxxxxxxxxxxxxxxx>
---
 include/linux/lockdep.h  | 11 ++++++++---
 kernel/locking/lockdep.c |  5 ++++-
 2 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index b9e9adec73e8..93eb5f797fc1 100644
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h
@@ -294,8 +294,12 @@ 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_held(l)	do {				\
-		WARN_ON(debug_locks && !lockdep_is_held(l));	\
+#define lockdep_assert_held(l)	do {					\
+		WARN_ON(debug_locks && lockdep_is_held(l) == 0);	\
+	} while (0)
+
+#define lockdep_assert_not_held(l)	do {				\
+		WARN_ON(debug_locks && lockdep_is_held(l) == 1);	\
 	} while (0)
 
 #define lockdep_assert_held_write(l)	do {			\
@@ -384,7 +388,8 @@ extern int lockdep_is_held(const void *);
 #define lockdep_is_held_type(l, r)		(1)
 
 #define lockdep_assert_held(l)			do { (void)(l); } while (0)
-#define lockdep_assert_held_write(l)	do { (void)(l); } while (0)
+#define lockdep_assert_not_held(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)
 
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index bdaf4829098c..d3299fd85c4a 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -5472,7 +5472,10 @@ noinstr int lock_is_held_type(const struct lockdep_map *lock, int read)
 	int ret = 0;
 
 	if (unlikely(!lockdep_enabled()))
-		return 1; /* avoid false negative lockdep_assert_held() */
+		/* avoid false negative lockdep_assert_not_held()
+		 * and lockdep_assert_held()
+		 */
+		return -1;
 
 	raw_local_irq_save(flags);
 	check_flags(flags);
-- 
2.27.0