From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757823AbbJIKjL (ORCPT ); Fri, 9 Oct 2015 06:39:11 -0400 Received: from www.linutronix.de ([62.245.132.108]:36824 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755876AbbJIKjJ (ORCPT ); Fri, 9 Oct 2015 06:39:09 -0400 Date: Fri, 9 Oct 2015 12:38:32 +0200 (CEST) From: Thomas Gleixner To: Miroslav Lichvar cc: Arnd Bergmann , linux-kernel@vger.kernel.org, y2038@lists.linaro.org, John Stultz , Prarit Bhargava , Richard Cochran Subject: Re: [PATCH] timekeeping: Limit system time to prevent 32-bit time_t overflow In-Reply-To: <20151009103421.GC2166@localhost> Message-ID: References: <1444224137-32510-1-git-send-email-mlichvar@redhat.com> <5753784.UXVo9jVTVp@wuerfel> <20151008062344.GO5778@localhost> <5836683.t4iPTifntz@wuerfel> <20151008093923.GQ5778@localhost> <20151009103421.GC2166@localhost> User-Agent: Alpine 2.11 (DEB 23 2013-08-11) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 9 Oct 2015, Miroslav Lichvar wrote: > On Fri, Oct 09, 2015 at 10:46:16AM +0100, Thomas Gleixner wrote: > > On Thu, 8 Oct 2015, Miroslav Lichvar wrote: > > > Applications are not allowed to rely on system time being sane? > > > To me the current behavior looks like the kernel is throwing the > > > applications off a cliff, while it's the only thing that can fly :). > > > > As Arnd said, you are creating a wrong sense of safety. They fall off > > the cliff with your changes as well. The fall is just different. Think > > about timeouts, user space overflows of time_t etc. > > I think vast majority of them won't fall. It doesn't prevent all > problems, but at least the userspace agrees with kernel on what the > current time it is, that looks to me like the most difficult one to > fix in applications. > > > We need to fix all of it, no matter what. > > Yeah, that would be nice, but I don't think it's realistic. > > Do you feel the same about preventing the time from reaching > KTIME_MAX? That's going to happen in ~500 years from now. Thanks, tglx