!1012 [sync] PR-924: dm: add disk before alloc dax

Merge Pull Request from: @openeuler-sync-bot 
 

Origin pull request: 
https://gitee.com/openeuler/kernel/pulls/924 
 
PR sync from:  Li Lingfeng <lilingfeng3@huawei.com>
 https://mailweb.openeuler.org/hyperkitty/list/kernel@openeuler.org/thread/KP2DRRZQIPU5IM7FF4GECWSW5466QLFH/ 
 
 
Link:https://gitee.com/openeuler/kernel/pulls/1012 

Reviewed-by: zhangyi (F) <yi.zhang@huawei.com> 
Signed-off-by: Jialin Zhang <zhangjialin11@huawei.com> 

drivers/md/dm.c

@@ -1883,6 +1883,8 @@ static struct mapped_device *alloc_dev(int minor)
 	md->disk->private_data = md;
 	sprintf(md->disk->disk_name, "dm-%d", minor);
 
+	add_disk_no_queue_reg(md->disk);
+
 	if (IS_ENABLED(CONFIG_DAX_DRIVER)) {
 		md->dax_dev = alloc_dax(md, md->disk->disk_name,
 					&dm_dax_ops, 0);
@@ -1892,7 +1894,6 @@ static struct mapped_device *alloc_dev(int minor)
 		}
 	}
 
-	add_disk_no_queue_reg(md->disk);
 	format_dev_t(md->name, MKDEV(_major, minor));
 
 	md->wq = alloc_workqueue("kdmflush", WQ_MEM_RECLAIM, 0);