drm/virtio: add virtio_gpu_cmd_unref_resource error handling

Usually we wait for the host to complete the unref request, then cleanup
the guest-side state of the object in the completion callback.  When
submitting the unref command failed the completion callback will not be
called though, so cleanup right away.

Fixes a WARN on stale mm entries on driver shutdown.
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Gurchetan Singh <gurchetansingh@chromium.org>
Link: http://patchwork.freedesktop.org/patch/msgid/20200908070723.6394-4-kraxel@redhat.com

drivers/gpu/drm/virtio/virtgpu_vq.c

@@ -536,6 +536,7 @@ void virtio_gpu_cmd_unref_resource(struct virtio_gpu_device *vgdev,
 {
 	struct virtio_gpu_resource_unref *cmd_p;
 	struct virtio_gpu_vbuffer *vbuf;
+	int ret;
 
 	cmd_p = virtio_gpu_alloc_cmd_cb(vgdev, &vbuf, sizeof(*cmd_p),
 					virtio_gpu_cmd_unref_cb);
@@ -545,7 +546,9 @@ void virtio_gpu_cmd_unref_resource(struct virtio_gpu_device *vgdev,
 	cmd_p->resource_id = cpu_to_le32(bo->hw_res_handle);
 
 	vbuf->resp_cb_data = bo;
-	virtio_gpu_queue_ctrl_buffer(vgdev, vbuf);
+	ret = virtio_gpu_queue_ctrl_buffer(vgdev, vbuf);
+	if (ret < 0)
+		virtio_gpu_cleanup_object(bo);
 }
 
 void virtio_gpu_cmd_set_scanout(struct virtio_gpu_device *vgdev,