Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753380AbZCIPFQ (ORCPT ); Mon, 9 Mar 2009 11:05:16 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751914AbZCIPFA (ORCPT ); Mon, 9 Mar 2009 11:05:00 -0400 Received: from Cpsmtpm-eml107.kpnxchange.com ([195.121.3.11]:62331 "EHLO CPSMTPM-EML107.kpnxchange.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751903AbZCIPE7 (ORCPT ); Mon, 9 Mar 2009 11:04:59 -0400 From: Frans Pop To: linux-s390@vger.kernel.org Subject: Re: [BUG,2.6.28,s390] Fails to boot in Hercules S/390 emulator Date: Mon, 9 Mar 2009 16:04:53 +0100 User-Agent: KMail/1.9.9 Cc: Roman Zippel , John Stultz , Thomas Gleixner , Linux Kernel Mailing List References: <200903080230.10099.elendil@planet.nl> In-Reply-To: <200903080230.10099.elendil@planet.nl> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200903091604.56455.elendil@planet.nl> X-OriginalArrivalTime: 09 Mar 2009 15:04:57.0091 (UTC) FILETIME=[68EB1530:01C9A0C8] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1920 Lines: 49 On Sunday 08 March 2009, Frans Pop wrote: > Kernels after 2.6.27 fail to boot in the Hercules S/390 emulator, quite > early in the boot process: [...] > 0.141419! Initializing cgroup subsys ns > 0.141605! Initializing cgroup subsys cpuacct > 0.142009! Initializing cgroup subsys devices > 0.180403! cpu: 2 configured CPUs, 0 standby CPUs > > I've bisected this to the following commit: > commit 5cd1c9c5cf30d4b33df3d3f74d8142f278d536b7 > Author: Roman Zippel > Date: Mon Sep 22 14:42:43 2008 -0700 > timekeeping: fix rounding problem during clock update After staring at this commit for a while I decided to try the following patch: --- a/kernel/time/timekeeping.c +++ b/kernel/time/timekeeping.c @@ -547,5 +547,11 @@ void update_wall_time(void) * add the remainder to the error difference. */ xtime.tv_nsec = ((s64)clock->xtime_nsec >> clock->shift) + 1; + if (unlikely(clock->xtime_nsec < ((s64)xtime.tv_nsec << clock->shift))) { + printk("Negative result: %llu - %lld\n", + (unsigned long long)clock->xtime_nsec, + (long long)((s64)xtime.tv_nsec << clock->shift)); + BUG_ON(1); + } clock->xtime_nsec -= (s64)xtime.tv_nsec << clock->shift; clock->error += clock->xtime_nsec << (NTP_SCALE_SHIFT - clock->shift); And that resulted in: 0.004175! Negative result: 166039808000 - 166039808256 So we're trying to stuff a negative value into an unsigned field, and I keep seeing on these lists that's a bad idea. I'll leave it up to you how we get there, but could it possibly be the same kind of thing as corrected earlier today in Heiko Carsten's patch: http://lkml.org/lkml/2009/3/9/112 ? Cheers, FJP -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/