From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757068AbbCRVgF (ORCPT ); Wed, 18 Mar 2015 17:36:05 -0400 Received: from mx2.parallels.com ([199.115.105.18]:52269 "EHLO mx2.parallels.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755796AbbCRVgB (ORCPT ); Wed, 18 Mar 2015 17:36:01 -0400 Message-ID: <5509EF82.60900@parallels.com> Date: Thu, 19 Mar 2015 00:34:58 +0300 From: Pavel Emelyanov User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.5.0 MIME-Version: 1.0 To: Andy Lutomirski , Oleg Nesterov CC: Andrey Wagin , Cyrill Gorcunov , Andy Lutomirski , Ingo Molnar , Andi Kleen , "H. Peter Anvin" , Al Viro , X86 ML , LKML , Linus Torvalds , Borislav Petkov , Pavel Emelyanov Subject: Re: [PATCH v3 1/2] x86_64,signal: Fix SS handling for signals delivered to 64-bit programs References: <405594361340a2ec32f8e2b115c142df0e180d8e.1426193719.git.luto@kernel.org> <20150318174843.GA32238@redhat.com> <20150318181306.GF2255@moon> <20150318183133.GB1832@redhat.com> <20150318185027.GB17491@moon> <20150318200247.GA6355@redhat.com> In-Reply-To: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-Originating-IP: [89.169.95.100] X-ClientProxiedBy: US-EXCH.sw.swsoft.com (10.255.249.47) To US-EXCH.sw.swsoft.com (10.255.249.47) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 03/19/2015 12:26 AM, Andy Lutomirski wrote: > On Wed, Mar 18, 2015 at 1:02 PM, Oleg Nesterov wrote: >> On 03/18, Andrey Wagin wrote: >>> >>> This patch fixes the problem. Oleg, could you send this path in the >>> criu maillist? >> >> Sure, will do. > > We still haven't answered one question: what's the kernel's position > on ABI stability wrt CRIU? We clearly shouldn't make changes that > break the principle of CRIU, but CRIU encodes so many tricky > assumptions about the inner workings of the kernel that it's really > tough to avoid breaking old CRIU versions. Well, we try hard to use only documented kernel API-s. Isn't the sigframe considered to be some sort of "stable API"? I mean -- it's visible by the userspace, nobody prevents glibc or gdb from messing with this stuff just by reading it from memory. If it's "parse-able" e.g. like VDSO is, but we don't do it in CRIU -- then it's definitely a CRIU BUG to be fixed. > So... do we introduce somewhat nasty code into the kernel to keep old > CRIU versions working, or do we require that users who want to restore > onto new kernels use new CRIU? It's OK (I think) to require newer versions of CRIU, it's easy to update one unlike the kernel ;) But if "old" version of CRIU just crash the restored processes on "new" kernels and there's no way to detect this properly -- that's the problem. > (It seems clear to me that CRIU should apply the patch regardless of > what the kernel does. It will enable CRIU to work on the same class > of programs that are fixed by the kernel change that started this > thread.) > > --Andy > . > Thanks, Pavel