rbd: complete notifies before cleaning up osd_client and rbd_dev

To ensure rbd_dev is not used after it's released, flush all pending
notify callbacks before calling rbd_dev_image_release(). No new
notifies can be added to the queue at this point because the watch has
already be unregistered with the osd_client.

Signed-off-by: Josh Durgin <josh.durgin@inktank.com>
Reviewed-by: Alex Elder <elder@linaro.org>

drivers/block/rbd.c

@@ -5163,6 +5163,13 @@ static ssize_t rbd_remove(struct bus_type *bus,
 	ret = rbd_dev_header_watch_sync(rbd_dev, false);
 	if (ret)
 		rbd_warn(rbd_dev, "failed to cancel watch event (%d)\n", ret);
+
+	/*
+	 * flush remaining watch callbacks - these must be complete
+	 * before the osd_client is shutdown
+	 */
+	dout("%s: flushing notifies", __func__);
+	ceph_osdc_flush_notifies(&rbd_dev->rbd_client->client->osdc);
 	rbd_dev_image_release(rbd_dev);
 	module_put(THIS_MODULE);