[PATCH v5 1/7] drm: fix drmm_mutex_init()

[Matthew Auld]

In mutex_init() lockdep seems to identify a lock by defining a static
key for each lock class. However if we wrap the whole thing in a
function the static key will be the same for everything calling that
function, which looks to be the case for drmm_mutex_init(). This then
results in impossible lockdep splats since lockdep thinks completely
unrelated locks are the same lock class. The other issue is that when
looking at splats we lose the actual lock name, where instead of seeing
something like xe->mem_access.lock for the name, we just see something
generic like lock#8.

Attempt to fix this by converting drmm_mutex_init() into a macro, which
should ensure that mutex_init() behaves as expected.

Reported-by: Thomas Hellström <thomas.hellstrom at linux.intel.com>
Fixes: e13f13e039dc ("drm: Add DRM-managed mutex_init()")
Cc: Thomas Zimmermann <tzimmermann at suse.de>
Cc: Jocelyn Falempe <jfalempe at redhat.com>
Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
Cc: dri-devel at lists.freedesktop.org
Signed-off-by: Matthew Auld <matthew.auld at intel.com>
---
 drivers/gpu/drm/drm_managed.c | 26 --------------------------
 include/drm/drm_managed.h     | 23 ++++++++++++++++++++++-
 2 files changed, 22 insertions(+), 27 deletions(-)

diff --git a/drivers/gpu/drm/drm_managed.c b/drivers/gpu/drm/drm_managed.c
index 4cf214de50c4..71c49819a7a2 100644
--- a/drivers/gpu/drm/drm_managed.c
+++ b/drivers/gpu/drm/drm_managed.c
@@ -263,29 +263,3 @@ void drmm_kfree(struct drm_device *dev, void *data)
 	free_dr(dr_match);
 }
 EXPORT_SYMBOL(drmm_kfree);
-
-static void drmm_mutex_release(struct drm_device *dev, void *res)
-{
-	struct mutex *lock = res;
-
-	mutex_destroy(lock);
-}
-
-/**
- * drmm_mutex_init - &drm_device-managed mutex_init()
- * @dev: DRM device
- * @lock: lock to be initialized
- *
- * Returns:
- * 0 on success, or a negative errno code otherwise.
- *
- * This is a &drm_device-managed version of mutex_init(). The initialized
- * lock is automatically destroyed on the final drm_dev_put().
- */
-int drmm_mutex_init(struct drm_device *dev, struct mutex *lock)
-{
-	mutex_init(lock);
-
-	return drmm_add_action_or_reset(dev, drmm_mutex_release, lock);
-}
-EXPORT_SYMBOL(drmm_mutex_init);
diff --git a/include/drm/drm_managed.h b/include/drm/drm_managed.h
index 359883942612..01f977e91933 100644
--- a/include/drm/drm_managed.h
+++ b/include/drm/drm_managed.h
@@ -105,6 +105,27 @@ char *drmm_kstrdup(struct drm_device *dev, const char *s, gfp_t gfp);
 
 void drmm_kfree(struct drm_device *dev, void *data);
 
-int drmm_mutex_init(struct drm_device *dev, struct mutex *lock);
+static inline void __drmm_mutex_release(struct drm_device *dev, void *res)
+{
+	struct mutex *lock = res;
+
+	mutex_destroy(lock);
+}
+
+/**
+ * drmm_mutex_init - &drm_device-managed mutex_init()
+ * @dev: DRM device
+ * @lock: lock to be initialized
+ *
+ * Returns:
+ * 0 on success, or a negative errno code otherwise.
+ *
+ * This is a &drm_device-managed version of mutex_init(). The initialized
+ * lock is automatically destroyed on the final drm_dev_put().
+ */
+#define drmm_mutex_init(dev, lock) ({					     \
+	mutex_init(lock);						     \
+	drmm_add_action_or_reset(dev, __drmm_mutex_release, lock);	     \
+})									     \
 
 #endif
-- 
2.40.1