Commit c21f11d1 authored May 19, 2023 by Matthew Auld Committed by Thomas Zimmermann May 22, 2023

drm: fix drmm_mutex_init()



In mutex_init() lockdep identifies a lock by defining a special static
key for each lock class. However if we wrap the macro in a function,
like in drmm_mutex_init(), we end up generating:

int drmm_mutex_init(struct drm_device *dev, struct mutex *lock)
{
      static struct lock_class_key __key;

      __mutex_init((lock), "lock", &__key);
      ....
}

The static __key here is what lockdep uses to identify the lock class,
however since this is just a normal function the key here will be
created once, where all callers then use the same key. In effect the
mutex->depmap.key will be the same pointer for different
drmm_mutex_init() callers. This then results in impossible lockdep
splats since lockdep thinks completely unrelated locks are the same lock
class.

To fix this turn drmm_mutex_init() into a macro such that it generates a
different "static struct lock_class_key __key" for each invocation,
which looks to be inline with what mutex_init() wants.

v2:
  - Revamp the commit message with clearer explanation of the issue.
  - Rather export __drmm_mutex_release() than static inline.

Reported-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reported-by: Sarah Walker <sarah.walker@imgtec.com>
Fixes: e13f13e0 ("drm: Add DRM-managed mutex_init()")
Cc: Stanislaw Gruszka <stanislaw.gruszka@linux.intel.com>
Cc: Boris Brezillon <boris.brezillon@collabora.com>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Jocelyn Falempe <jfalempe@redhat.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: dri-devel@lists.freedesktop.org
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Stanislaw Gruszka <stanislaw.gruszka@linux.intel.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20230519090733.489019-1-matthew.auld@intel.com

parent aa8bf931

drivers/gpu/drm/drm_managed.c

+2 −20

Original line number	Diff line number	Diff line
		@@ -264,28 +264,10 @@ void drmm_kfree(struct drm_device dev, void data)
		}
		EXPORT_SYMBOL(drmm_kfree);

		static void drmm_mutex_release(struct drm_device dev, void res)
		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);
		EXPORT_SYMBOL(__drmm_mutex_release);

include/drm/drm_managed.h

+17 −1

Original line number	Diff line number	Diff line
		@@ -105,6 +105,22 @@ 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);
		void __drmm_mutex_release(struct drm_device dev, void res);

		/**
		* 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