From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5DF5EC4167B for ; Fri, 8 Dec 2023 05:36:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232893AbjLHFgf (ORCPT ); Fri, 8 Dec 2023 00:36:35 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60832 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229476AbjLHFgc (ORCPT ); Fri, 8 Dec 2023 00:36:32 -0500 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 73F3D1718 for ; Thu, 7 Dec 2023 21:36:38 -0800 (PST) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9013DC433C7; Fri, 8 Dec 2023 05:36:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1702013798; bh=mVdL+hSiaypb7UZGEHfzAERRsf1Q9lNQPKgfGI436YM=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=Lcp0z1Qb7IPGjoLbqhT/1+AY8NP2B3KEY8SYOxcERtQmtI3oawnnpVLkFoQ4PBXAh 9qo8WOkKvDm2pTlX3UJVEcgKyUwejH+tOcUTOeZMmfhk3nSXk0OmMbIgKRtoxauHJf 1EurDlePYZ96dK4qUPLbXUiDsnM4mW+ULyWE2vdg= Date: Fri, 8 Dec 2023 06:36:35 +0100 From: Greg KH To: Yafang Shao Cc: jejb@linux.ibm.com, martin.petersen@oracle.com, rafael@kernel.org, linux-kernel@vger.kernel.org, linux-scsi@vger.kernel.org Subject: Re: [PATCH] drivers: base: Introduce a new kernel parameter driver_sync_probe= Message-ID: <2023120856-empathy-debtless-06b2@gregkh> References: <20231206115355.4319-1-laoar.shao@gmail.com> <2023120644-pry-worried-22a2@gregkh> <2023120724-overstep-gesture-75be@gregkh> <2023120704-conducive-junkman-2e3f@gregkh> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Dec 07, 2023 at 08:36:56PM +0800, Yafang Shao wrote: > On Thu, Dec 7, 2023 at 8:12 PM Greg KH wrote: > > > > On Thu, Dec 07, 2023 at 07:59:03PM +0800, Yafang Shao wrote: > > > On Thu, Dec 7, 2023 at 6:19 PM Greg KH wrote: > > > > > > > > On Wed, Dec 06, 2023 at 10:08:40PM +0800, Yafang Shao wrote: > > > > > On Wed, Dec 6, 2023 at 9:31 PM Greg KH wrote: > > > > > > > > > > > > On Wed, Dec 06, 2023 at 11:53:55AM +0000, Yafang Shao wrote: > > > > > > > After upgrading our kernel from version 4.19 to 6.1, certain regressions > > > > > > > occurred due to the driver's asynchronous probe behavior. Specifically, > > > > > > > the SCSI driver transitioned to an asynchronous probe by default, resulting > > > > > > > in a non-fixed root disk behavior. In the prior 4.19 kernel, the root disk > > > > > > > was consistently identified as /dev/sda. However, with kernel 6.1, the root > > > > > > > disk can be any of /dev/sdX, leading to issues for applications reliant on > > > > > > > /dev/sda, notably impacting monitoring systems monitoring the root disk. > > > > > > > > > > > > Device names are never guaranteed to be stable, ALWAYS use a persistant > > > > > > names like a filesystem label or other ways. Look at /dev/disk/ for the > > > > > > needed ways to do this properly. > > > > > > > > > > The root disk is typically identified as /dev/sda or /dev/vda, right? > > > > > > > > Depends on your system. It can also be identified, in the proper way, > > > > as /dev/disk/by-uuid/eef0abc1-4039-4c3f-a123-81fc99999993 if you want > > > > (note, fake uuid, use your own disk uuid please.) > > > > > > > > Why not do that? That's the most stable and recommended way of doing > > > > things. > > > > > > Adapting to this change isn't straightforward, especially for a large > > > fleet of servers. Our monitoring system needs to accommodate and > > > adjust accordingly. > > > > Agreed, that can be rough. But as this is an issue that was caused by a > > scsi core change, perhaps the scsi developers can describe why it's ok. > > > > But really, device naming has ALWAYS been known to not be > > deterministic, which is why Pat and I did all the driver core work 20+ > > years ago so that you have the ability to properly name your devices in > > a way that is deterministic. Using the kernel name like sda is NOT > > using that functionality, so while it has been nice to see that it has > > been stable for you for a while, you are playing with fire here and will > > get burned one day when the firmware in your devices decide to change > > response times. > > I agree that using UUID is a better approach. However, it's worth > noting that the widely used IO monitoring tool 'iostat' faces > challenges when working with UUIDs. This indicates that there's a > significant amount of work ahead of us in this aspect. That indicates that iostat needs to be fixed as this has been an option that people rely on for 20+ years now. Or use a better tool :) thanks, greg k-h