From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754350AbbHMXff (ORCPT ); Thu, 13 Aug 2015 19:35:35 -0400 Received: from mail-pa0-f45.google.com ([209.85.220.45]:35676 "EHLO mail-pa0-f45.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752212AbbHMXfd (ORCPT ); Thu, 13 Aug 2015 19:35:33 -0400 Subject: Re: [regression] x86/signal/64: Fix SS handling for signals delivered to 64-bit programs breaks dosemu To: Linus Torvalds References: <55CA90B4.2010205@list.ru> <55CCD921.4040301@list.ru> <20150813200823.GS2059@uranus> <55CD0F29.4070604@gmail.com> <55CD13A0.8060403@gmail.com> Cc: Cyrill Gorcunov , Andy Lutomirski , Pavel Emelyanov , Stas Sergeev , Linux kernel From: Raymond Jennings Message-ID: <55CD29C2.7060901@gmail.com> Date: Thu, 13 Aug 2015 16:35:30 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.1.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 08/13/15 16:18, Linus Torvalds wrote: > On Thu, Aug 13, 2015 at 4:05 PM, Linus Torvalds > wrote: >> The _only_ thing that matters is that something broke. > To clarify: things like test programs etc don't matter. Real > applications, used by real users. That's what regressions cover. If > you have a workflow that isn't just some random kernel test thing, and > you depend on it, and we break it, the kernel is supposed to fix it. > > There are some (very few) exceptions. > > If it's a security issue, we may not be able to "fix" it, because > other concerns can obviously take precedence. > > Also, sometimes the reports come in way too late - if you were running > some stable distro kernel for several years, and updated, and notice a > change that happened four years ago and modern applications now rely > on the _new_ behavior, we may not be able to fix the regression any > more. > > But no, "it was an unintentional kernel bug and clearly just stupid > crap code, and we fixed it and now the kernel is much better and > cleaner" is not a valid reason for regressions. We'll go back to the > stupid and crap code if necessary, however much that may annoy us. > > For an example of the kind of things we may have to do, see commits > > 64f371bc3107 autofs: make the autofsv5 packet file descriptor use > a packetized pipe > 9883035ae7ed pipes: add a "packetized pipe" mode for writing > > and just wonder at the insanity. That's the kinds of things that > happen when one application had actively worked around a bug in > compatibility handling, and then trying to "fix" that bug just caused > another application to break instead. > > Linus Is there a way to temporally confine the bad crap code just to the applications that depend on it, or does a userspace app latching onto bad behavior effectively lock down the abi for the future? I know that some features in the kernel get deprecated over a process (devfs for example) once userspace is given an alternative...would there be a process like that to deal with userspace code that is pinning a piece of crap in the kernel?