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=-2.4 required=3.0 tests=DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,T_DKIM_INVALID, USER_AGENT_MUTT 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 E4064C28CF6 for ; Fri, 3 Aug 2018 15:20:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9E7B621775 for ; Fri, 3 Aug 2018 15:20:46 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=thunk.org header.i=@thunk.org header.b="SiF7cAwF" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9E7B621775 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=mit.edu 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 S1728171AbeHCRRb (ORCPT ); Fri, 3 Aug 2018 13:17:31 -0400 Received: from imap.thunk.org ([74.207.234.97]:34790 "EHLO imap.thunk.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726485AbeHCRRa (ORCPT ); Fri, 3 Aug 2018 13:17:30 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=thunk.org; s=ef5046eb; h=In-Reply-To:Content-Type:MIME-Version:References:Message-ID: Subject:Cc:To:From:Date:Sender:Reply-To:Content-Transfer-Encoding:Content-ID: Content-Description:Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc :Resent-Message-ID:List-Id:List-Help:List-Unsubscribe:List-Subscribe: List-Post:List-Owner:List-Archive; bh=gS6of1Wqx+Ga/Z6ewxwT1nDoWFudzhaHANCaL5kDyYM=; b=SiF7cAwFQy9rjIjWJXajYhZcs9 gMwvHAX4/Oc79SUrH4j1p3EkD57rchS5KjlnCmDK7Jbo9aFfW5T1oyKTN24JaKzSAgGJ8x7oudCyN UWwTSpbe2NTvefSt3B6NYdBGtrqbbu/ftRIY/CxlpNM5jAHLtzj03J0HlDTs3U3mZwpk=; Received: from root (helo=callcc.thunk.org) by imap.thunk.org with local-esmtp (Exim 4.89) (envelope-from ) id 1flbsZ-0002al-Ld; Fri, 03 Aug 2018 15:20:35 +0000 Received: by callcc.thunk.org (Postfix, from userid 15806) id C5D817A64C9; Fri, 3 Aug 2018 11:20:34 -0400 (EDT) Date: Fri, 3 Aug 2018 11:20:34 -0400 From: "Theodore Y. Ts'o" To: Mike Snitzer Cc: Linus Torvalds , Jens Axboe , Sagi Grimberg , Linux Kernel Mailing List , linux-block , dm-devel@redhat.com, Ilya Dryomov , wgh@torlan.ru, Zdenek Kabelac Subject: Re: [dm-devel] LVM snapshot broke between 4.14 and 4.16 Message-ID: <20180803152034.GD32066@thunk.org> Mail-Followup-To: "Theodore Y. Ts'o" , Mike Snitzer , Linus Torvalds , Jens Axboe , Sagi Grimberg , Linux Kernel Mailing List , linux-block , dm-devel@redhat.com, Ilya Dryomov , wgh@torlan.ru, Zdenek Kabelac References: <226835ba-2197-b850-6e5b-8ba14f7fd016@torlan.ru> <93bff248-6897-4867-841b-2dace11597de@torlan.ru> <1ec0a220-d5b0-1c27-e63b-c4d3f4ce9d77@torlan.ru> <20180803133102.GA3092@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180803133102.GA3092@redhat.com> User-Agent: Mutt/1.10.1 (2018-07-13) X-SA-Exim-Connect-IP: X-SA-Exim-Mail-From: tytso@thunk.org X-SA-Exim-Scanned: No (on imap.thunk.org); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Aug 03, 2018 at 09:31:03AM -0400, Mike Snitzer wrote: > > Debian is notorious for having a stale and/or custom lvm2. > Generally speaking, it is recommended that lvm2 not be older than the > kernel (but the opposite is fine). On Fri, Aug 03, 2018 at 03:31:18PM +0200, Zdenek Kabelac wrote: > IMHO (as the author of fixing lvm2 patch) user should not be upgrading > kernels and keep running older lvm2 user-land tool (and there are very good > reasons for this). I'm going to have to strenuously disagree. In *general* it's quite common for users to update their kernel without updating their userspace. For example, I as a *developer*, I am often running bleeding kernels (e.g., at the moment I am running something based on 4.18-rc6 on a Debian testing system; and it's not at all uncommon for users to run a newer kernel on older distribution). This is the *first* I've heard that I should be continuously updating lvm because I'm running bleeding edge kernels --- and I would claim that this is entirely unreasonable. I'll also note that very often users will update kernels while running distribution userspace. And if you are using Linode, very often *Linode* will offer a newer kernel to better take advantage of the Linode VM, and this is done without needing to install the Linode kernel into the userspace. It *used* to be the case that users running RHEL 2 or RHEL 3 could try updating to the latest upstream kernel, and everything would break and fall apart. This was universally considered to be a failure, and a Bad Thing. So if LVM2 is not backwards compatible, and breaks in the face of newer kernels running older distributions, that is a bug. If there is a fundamental bug in the userspace API, and it can't be fixed without a serious security bug, sometimes we need to have an exception to the "you can't mandate newer userspace" rule. But I don't think this falls into this category; how would a user "exploit" what people are calling a "security bug" to break root? - Ted