DM_DEFERRED_REMOVE
if (r == -EBUSY && param->flags & DM_DEFERRED_REMOVE) {
param->flags &= ~DM_DEFERRED_REMOVE;
dm_hash_remove_all(true, !!(param->flags & DM_DEFERRED_REMOVE), false);
param->flags |= DM_DEFERRED_REMOVE;
r = dm_lock_for_deletion(md, !!(param->flags & DM_DEFERRED_REMOVE), false);