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 X-Spam-Level: X-Spam-Status: No, score=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 344B6C433FF for ; Mon, 12 Aug 2019 18:08:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 101D12067D for ; Mon, 12 Aug 2019 18:08:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726776AbfHLSIO (ORCPT ); Mon, 12 Aug 2019 14:08:14 -0400 Received: from imap1.codethink.co.uk ([176.9.8.82]:48853 "EHLO imap1.codethink.co.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726185AbfHLSIN (ORCPT ); Mon, 12 Aug 2019 14:08:13 -0400 Received: from [167.98.27.226] (helo=xylophone) by imap1.codethink.co.uk with esmtpsa (Exim 4.84_2 #1 (Debian)) id 1hxELt-0001w2-Ar; Mon, 12 Aug 2019 18:43:25 +0100 Message-ID: <7edb5c85c29a46cf5edb6fe5033b07884fd068ae.camel@codethink.co.uk> Subject: Re: [Y2038] [PATCH 04/20] mount: Add mount warning for impending timestamp expiry From: Ben Hutchings To: Deepa Dinamani , Arnd Bergmann Cc: Alexander Viro , Linux Kernel Mailing List , Linux FS-devel Mailing List , y2038 Mailman List Date: Mon, 12 Aug 2019 18:43:24 +0100 In-Reply-To: References: <20190730014924.2193-1-deepa.kernel@gmail.com> <20190730014924.2193-5-deepa.kernel@gmail.com> <53df9d81bfb4ee7ec64fabf1089f91d80dceb491.camel@codethink.co.uk> Organization: Codethink Ltd. Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.30.5-1.1 MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 2019-08-12 at 09:15 -0700, Deepa Dinamani wrote: > On Mon, Aug 12, 2019 at 9:09 AM Deepa Dinamani wrote: > > On Mon, Aug 12, 2019 at 7:11 AM Arnd Bergmann wrote: > > > On Mon, Aug 12, 2019 at 3:25 PM Ben Hutchings > > > wrote: > > > > On Sat, 2019-08-10 at 13:44 -0700, Deepa Dinamani wrote: > > > > > On Mon, Aug 5, 2019 at 7:14 AM Ben Hutchings > > > > > wrote: > > > > > > On Mon, 2019-07-29 at 18:49 -0700, Deepa Dinamani wrote: > > > > > > > The warning reuses the uptime max of 30 years used by the > > > > > > > setitimeofday(). > > > > > > > > > > > > > > Note that the warning is only added for new filesystem mounts > > > > > > > through the mount syscall. Automounts do not have the same warning. > > > > > > [...] > > > > > > > > > > > > Another thing - perhaps this warning should be suppressed for read-only > > > > > > mounts? > > > > > > > > > > Many filesystems support read only mounts only. We do fill in right > > > > > granularities and limits for these filesystems as well. In keeping > > > > > with the trend, I have added the warning accordingly. I don't think I > > > > > have a preference either way. But, not warning for the red only mounts > > > > > adds another if case. If you have a strong preference, I could add it > > > > > in. > > > > > > > > It seems to me that the warning is needed if there is a possibility of > > > > data loss (incorrect timestamps, potentially leading to incorrect > > > > decisions about which files are newer). This can happen only when a > > > > filesystem is mounted read-write, or when a filesystem image is > > > > created. > > > > > > > > I think that warning for read-only mounts would be an annoyance to > > > > users retrieving files from old filesystems. > > > > > > I agree, the warning is not helpful for read-only mounts. An earlier > > > plan was to completely disallow writable mounts that might risk an > > > overflow (in some configurations at least). The warning replaces that > > > now, and I think it should also just warn for the cases that would > > > otherwise have been dangerous. > > > > Ok, I will make the change to exclude new read only mounts. I will use > > __mnt_is_readonly() so that it also exculdes filesystems that are > > readonly also. > > The diff looks like below: > > > > - if (!error && sb->s_time_max && > > + if (!error && !__mnt_is_readonly(mnt) && > > (ktime_get_real_seconds() + TIME_UPTIME_SEC_MAX > sb->s_time_max)) { > > > > Note that we can get rid of checking for non zero sb->s_time_max now. > > One more thing, we will probably have to add a second warning for when > the filesystem is re-mounted rw after the initial readonly mount. Indeed, there would need to be a check for remount-read-write. I didn't check whether remount uses this same code path. Ben. -- Ben Hutchings, Software Developer Codethink Ltd https://www.codethink.co.uk/ Dale House, 35 Dale Street Manchester, M1 2HF, United Kingdom