drm: introduce drm_gem_object_[handle_]unreference_unlocked

This patch introduces the drm_gem_object_unreference_unlocked
and drm_gem_object_handle_unreference_unlocked functions that
do not require holding struct_mutex.

drm_gem_object_unreference_unlocked calls the new
->gem_free_object_unlocked entry point if available, and
otherwise just takes struct_mutex and just calls ->gem_free_object
Signed-off-by: Luca Barbieri <luca@luca-barbieri.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/drm_gem.c

@@ -411,8 +411,19 @@ drm_gem_release(struct drm_device *dev, struct drm_file *file_private)
 	mutex_unlock(&dev->struct_mutex);
 }
 
+static void
+drm_gem_object_free_common(struct drm_gem_object *obj)
+{
+	struct drm_device *dev = obj->dev;
+	fput(obj->filp);
+	atomic_dec(&dev->object_count);
+	atomic_sub(obj->size, &dev->object_memory);
+	kfree(obj);
+}
+
 /**
  * Called after the last reference to the object has been lost.
+ * Must be called holding struct_ mutex
  *
  * Frees the object
  */
@@ -427,13 +438,39 @@ drm_gem_object_free(struct kref *kref)
 	if (dev->driver->gem_free_object != NULL)
 		dev->driver->gem_free_object(obj);
 
-	fput(obj->filp);
-	atomic_dec(&dev->object_count);
-	atomic_sub(obj->size, &dev->object_memory);
-	kfree(obj);
+	drm_gem_object_free_common(obj);
 }
 EXPORT_SYMBOL(drm_gem_object_free);
 
+/**
+ * Called after the last reference to the object has been lost.
+ * Must be called without holding struct_mutex
+ *
+ * Frees the object
+ */
+void
+drm_gem_object_free_unlocked(struct kref *kref)
+{
+	struct drm_gem_object *obj = (struct drm_gem_object *) kref;
+	struct drm_device *dev = obj->dev;
+
+	if (dev->driver->gem_free_object_unlocked != NULL)
+		dev->driver->gem_free_object_unlocked(obj);
+	else if (dev->driver->gem_free_object != NULL) {
+		mutex_lock(&dev->struct_mutex);
+		dev->driver->gem_free_object(obj);
+		mutex_unlock(&dev->struct_mutex);
+	}
+
+	drm_gem_object_free_common(obj);
+}
+EXPORT_SYMBOL(drm_gem_object_free_unlocked);
+
+static void drm_gem_object_ref_bug(struct kref *list_kref)
+{
+	BUG();
+}
+
 /**
  * Called after the last handle to the object has been closed
  *
@@ -458,8 +495,10 @@ drm_gem_object_handle_free(struct kref *kref)
 		/*
 		 * The object name held a reference to this object, drop
 		 * that now.
+		*
+		* This cannot be the last reference, since the handle holds one too.
 		 */
-		drm_gem_object_unreference(obj);
+		kref_put(&obj->refcount, drm_gem_object_ref_bug);
 	} else
 		spin_unlock(&dev->object_name_lock);
 

include/drm/drmP.h

@@ -801,6 +801,7 @@ struct drm_driver {
 	 */
 	int (*gem_init_object) (struct drm_gem_object *obj);
 	void (*gem_free_object) (struct drm_gem_object *obj);
+	void (*gem_free_object_unlocked) (struct drm_gem_object *obj);
 
 	/* vga arb irq handler */
 	void (*vgaarb_irq)(struct drm_device *dev, bool state);
@@ -1427,6 +1428,7 @@ extern void drm_sysfs_connector_remove(struct drm_connector *connector);
 int drm_gem_init(struct drm_device *dev);
 void drm_gem_destroy(struct drm_device *dev);
 void drm_gem_object_free(struct kref *kref);
+void drm_gem_object_free_unlocked(struct kref *kref);
 struct drm_gem_object *drm_gem_object_alloc(struct drm_device *dev,
 					    size_t size);
 void drm_gem_object_handle_free(struct kref *kref);
@@ -1443,12 +1445,17 @@ drm_gem_object_reference(struct drm_gem_object *obj)
 static inline void
 drm_gem_object_unreference(struct drm_gem_object *obj)
 {
-	if (obj == NULL)
-		return;
-
+	if (obj != NULL)
 		kref_put(&obj->refcount, drm_gem_object_free);
 }
 
+static inline void
+drm_gem_object_unreference_unlocked(struct drm_gem_object *obj)
+{
+	if (obj != NULL)
+		kref_put(&obj->refcount, drm_gem_object_free_unlocked);
+}
+
 int drm_gem_handle_create(struct drm_file *file_priv,
 			  struct drm_gem_object *obj,
 			  u32 *handlep);
@@ -1475,6 +1482,21 @@ drm_gem_object_handle_unreference(struct drm_gem_object *obj)
 	drm_gem_object_unreference(obj);
 }
 
+static inline void
+drm_gem_object_handle_unreference_unlocked(struct drm_gem_object *obj)
+{
+	if (obj == NULL)
+		return;
+
+	/*
+	* Must bump handle count first as this may be the last
+	* ref, in which case the object would disappear before we
+	* checked for a name
+	*/
+	kref_put(&obj->handlecount, drm_gem_object_handle_free);
+	drm_gem_object_unreference_unlocked(obj);
+}
+
 struct drm_gem_object *drm_gem_object_lookup(struct drm_device *dev,
 					     struct drm_file *filp,
 					     u32 handle);