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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS autolearn=ham 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 49D3BC43142 for ; Thu, 2 Aug 2018 21:39:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 035142157F for ; Thu, 2 Aug 2018 21:39:29 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 035142157F Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=torlan.ru Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732171AbeHBXc0 (ORCPT ); Thu, 2 Aug 2018 19:32:26 -0400 Received: from forward103j.mail.yandex.net ([5.45.198.246]:33105 "EHLO forward103j.mail.yandex.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731366AbeHBXc0 (ORCPT ); Thu, 2 Aug 2018 19:32:26 -0400 Received: from mxback2o.mail.yandex.net (mxback2o.mail.yandex.net [IPv6:2a02:6b8:0:1a2d::1c]) by forward103j.mail.yandex.net (Yandex) with ESMTP id 4CC0534C47E8; Fri, 3 Aug 2018 00:39:23 +0300 (MSK) Received: from smtp3p.mail.yandex.net (smtp3p.mail.yandex.net [2a02:6b8:0:1472:2741:0:8b6:8]) by mxback2o.mail.yandex.net (nwsmtp/Yandex) with ESMTP id vnSIHLm7qY-dM7GTsQZ; Fri, 03 Aug 2018 00:39:23 +0300 Received: by smtp3p.mail.yandex.net (nwsmtp/Yandex) with ESMTPSA id 0wFCcvwoHc-dM8CDJ4l; Fri, 03 Aug 2018 00:39:22 +0300 (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (Client certificate not present) Subject: Re: LVM snapshot broke between 4.14 and 4.16 From: WGH To: Linus Torvalds , Ilya Dryomov Cc: Jens Axboe , linux-block , Linux Kernel Mailing List , Sagi Grimberg , Mike Snitzer , dm-devel@redhat.com References: <226835ba-2197-b850-6e5b-8ba14f7fd016@torlan.ru> <93bff248-6897-4867-841b-2dace11597de@torlan.ru> Openpgp: preference=signencrypt Message-ID: <1ec0a220-d5b0-1c27-e63b-c4d3f4ce9d77@torlan.ru> Date: Fri, 3 Aug 2018 00:39:22 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 08/03/2018 12:32 AM, WGH wrote: > On 08/02/2018 09:32 PM, Linus Torvalds wrote: >> WGH (sorry, no idea what your real name is) - what's the source of the >> script that broke? Was it some system script you got from outside and >> likely to affect others too? >> >> Or was it just some local thing you wrote yourself and was >> unintentionally buggy and nobody else is likely to hit this? >> >> Because if the latter, if you can work around it and you're the only >> user this hits, we might just be able to ignore it. > The script in question is written by me and contains literally two lines: > >     lvcreate --size 5G --snapshot --name snap0 --permission r > /dev/mapper/vg0-lvol_rootfs >     mount /dev/mapper/vg0-snap0 /mnt/rootfs_snapshot > > The script is not buggy (I think), it was written under simple > assumption that --permission r works. And it does - unless you happen to > have combination of kernel >=4.16 and lvm2 <2.02.178. > > The commit in question appeared only in 4.16, and this kernel version is > not widespread yet. You have to be running both recent kernel and > not-so-recent lvm2 to be bitten by this. This probably explains why no > one else reported this problem. > > Workaround certainly exists: I can just create read-write snapshot, but > mount it read-only. The reason why I didn't discover the workaround > earlier is that after unsuccessful read-only snapshot creation system > ends up in some weird state where read-write snapshots are also failing > with the same error (until reboot). So I got a wrong impression that > read-write snapshots were broken as well. > I've just found one public report of this bug, though: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=900442