drm/virtio: Don't return invalid caps on timeout

If the wait timeouts, the caps are probably invalid and we shouldn't be
passing them to userspace.

Signed-off-by: Tomeu Vizoso <tomeu.vizoso@collabora.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20171127142126.25765-1-tomeu.vizoso@collabora.com
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

drivers/gpu/drm/virtio/virtgpu_ioctl.c

@@ -518,6 +518,8 @@ static int virtio_gpu_get_caps_ioctl(struct drm_device *dev,
 
 	ret = wait_event_timeout(vgdev->resp_wq,
 				 atomic_read(&cache_ent->is_valid), 5 * HZ);
+	if (!ret)
+		return -EBUSY;
 
 	ptr = cache_ent->caps_cache;