drm/gem: support BO freeing without dev->struct_mutex

Finally all the core gem and a lot of drivers are entirely free of
dev->struct_mutex depencies, and we can start to have an entirely
lockless unref path.

To make sure that no one who touches the core code accidentally breaks
existing drivers which still require dev->struct_mutex I've made the
might_lock check unconditional.

While at it de-inline the ref/unref functions, they've become a bit
too big.

v2: Make it not leak like a sieve.

v3: Review from Lucas:
- drop != NULL in pointer checks.
- fixup copypasted kerneldoc to actually match the functions.

v4:
Add __drm_gem_object_unreference as a fastpath helper for drivers who
abolished dev->struct_mutex, requested by Chris.

v5: Fix silly mistake in drm_gem_object_unreference_unlocked caught by
intel-gfx CI - I checked for gem_free_object instead of
gem_free_object_unlocked ...

Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Alex Deucher <alexdeucher@gmail.com>
Cc: Lucas Stach <l.stach@pengutronix.de>
Reviewed-by: Lucas Stach <l.stach@pengutronix.de> (v3)
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk> (v4)
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1462178451-1765-1-git-send-email-daniel.vetter@ffwll.ch

1 files changed, 12 insertions, 3 deletions

diff --git a/include/drm/drmP.h b/include/drm/drmP.h
index 7901768..360b2a7 100644
--- a/include/drm/drmP.h
+++ b/include/drm/drmP.h
@@ -580,12 +580,21 @@ struct drm_driver {
 	void (*debugfs_cleanup)(struct drm_minor *minor);
 
 	/**
-	 * Driver-specific constructor for drm_gem_objects, to set up
-	 * obj->driver_private.
+	 * @gem_free_object: deconstructor for drm_gem_objects
 	 *
-	 * Returns 0 on success.
+	 * This is deprecated and should not be used by new drivers. Use
+	 * @gem_free_object_unlocked instead.
 	 */
 	void (*gem_free_object) (struct drm_gem_object *obj);
+
+	/**
+	 * @gem_free_object_unlocked: deconstructor for drm_gem_objects
+	 *
+	 * This is for drivers which are not encumbered with dev->struct_mutex
+	 * legacy locking schemes. Use this hook instead of @gem_free_object.
+	 */
+	void (*gem_free_object_unlocked) (struct drm_gem_object *obj);
+
 	int (*gem_open_object) (struct drm_gem_object *, struct drm_file *);
 	void (*gem_close_object) (struct drm_gem_object *, struct drm_file *);