drm/prime: fix error path deadlock fail

There were a couple messed up things about this fail path.
(1) it would drop object_name_lock twice
(2) drm_gem_handle_delete() (in drm_gem_remove_prime_handles())
    needs to grab prime_lock

Reported-by: Alex Deucher <alexdeucher@gmail.com>
Signed-off-by: Rob Clark <robdclark@gmail.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1465500559-17873-1-git-send-email-robdclark@gmail.com

drivers/gpu/drm/drm_prime.c

@@ -593,7 +593,7 @@ int drm_gem_prime_fd_to_handle(struct drm_device *dev,
 		get_dma_buf(dma_buf);
 	}
 
-	/* drm_gem_handle_create_tail unlocks dev->object_name_lock. */
+	/* _handle_create_tail unconditionally unlocks dev->object_name_lock. */
 	ret = drm_gem_handle_create_tail(file_priv, obj, handle);
 	drm_gem_object_unreference_unlocked(obj);
 	if (ret)
@@ -601,11 +601,10 @@ int drm_gem_prime_fd_to_handle(struct drm_device *dev,
 
 	ret = drm_prime_add_buf_handle(&file_priv->prime,
 			dma_buf, *handle);
+	mutex_unlock(&file_priv->prime.lock);
 	if (ret)
 		goto fail;
 
-	mutex_unlock(&file_priv->prime.lock);
-
 	dma_buf_put(dma_buf);
 
 	return 0;
@@ -615,11 +614,14 @@ fail:
 	 * to detach.. which seems ok..
 	 */
 	drm_gem_handle_delete(file_priv, *handle);
+	dma_buf_put(dma_buf);
+	return ret;
+
 out_unlock:
 	mutex_unlock(&dev->object_name_lock);
 out_put:
-	dma_buf_put(dma_buf);
 	mutex_unlock(&file_priv->prime.lock);
+	dma_buf_put(dma_buf);
 	return ret;
 }
 EXPORT_SYMBOL(drm_gem_prime_fd_to_handle);