Comment 5 for bug 1789828

@hopem, yeah, I think you're totally right, all the places calling RBDVolumeProxy should have the same problem. This is a problem caused by the mix of green thread and local thread, the race between _get_usage_info and delete_volume is just one of them, so thank you very much to amend my previous title from 'racy between _get_usage_info and delete_volume' to 'race between threaded rbd operations' to react more closely to practical problem.