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

On Mon, Feb 15, 2021 at 02:12:30PM +0100, Johannes Berg wrote:

On Mon, 2021-02-15 at 11:44 +0100, Peter Zijlstra wrote:

quoted

I think something like so will work, but please double check.

Yeah, that looks better.

quoted

+++ b/include/linux/lockdep.h

@@ -294,11 +294,15 @@ 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)

That doesn't really need to change? It's the same.

Correct, but I found it more symmetric vs the not implementation below.

quoted

-#define lockdep_assert_held_write(l)	do {			\
+#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 {				\
 		WARN_ON(debug_locks && !lockdep_is_held_type(l, 0));	\
 	} while (0)
 

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index c1418b47f625..983ba206f7b2 100644
--- a/kernel/locking/lockdep.
+++ b/kernel/locking/lockdep.c

@@ -5467,7 +5467,7 @@ 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() */
+		return -1; /* avoid false negative lockdep_assert_held() */

Maybe add lockdep_assert_not_held() to the comment, to explain the -1
(vs non-zero)?

Yeah, or frob a '*' in there.