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

[Peter Zijlstra]

On Sun, Feb 14, 2021 at 06:53:01PM +0100, Peter Zijlstra wrote:
> On Fri, Feb 12, 2021 at 04:28:42PM -0700, Shuah Khan wrote:
> 
> > +#define lockdep_assert_not_held(l) do {                    \
> > +           WARN_ON(debug_locks && lockdep_is_held(l));     \
> > +   } while (0)
> > +
> 
> This thing isn't as straight forward as you might think, but it'll
> mostly work.
> 
> Notably this thing will misfire when lockdep_off() is employed. It
> certainyl needs a comment to explain the subtleties.

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

diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index b9e9adec73e8..c8b0d292bf8e 100644
--- a/include/linux/lockdep.h
+++ 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)
 
-#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.c
+++ 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() */
 
        raw_local_irq_save(flags);
        check_flags(flags);