- /* allocate new elevator */
- e = elevator_alloc(q, new_e);
- if (!e)
- return -ENOMEM;
+ /*
+ * Turn on BYPASS and drain all requests w/ elevator private data.
+ * Block layer doesn't call into a quiesced elevator - all requests
+ * are directly put on the dispatch list without elevator data
+ * using INSERT_BACK. All requests have SOFTBARRIER set and no
+ * merge happens either.
+ */
+ blk_queue_bypass_start(q);
+
+ /* unregister and clear all auxiliary data of the old elevator */
+ if (registered)
+ elv_unregister_queue(q);
+
+ spin_lock_irq(q->queue_lock);
+ ioc_clear_queue(q);
+ spin_unlock_irq(q->queue_lock);