From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759227AbXKGX3R (ORCPT ); Wed, 7 Nov 2007 18:29:17 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753463AbXKGX3E (ORCPT ); Wed, 7 Nov 2007 18:29:04 -0500 Received: from smtp2.linux-foundation.org ([207.189.120.14]:37878 "EHLO smtp2.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753453AbXKGX3D (ORCPT ); Wed, 7 Nov 2007 18:29:03 -0500 Date: Wed, 7 Nov 2007 15:28:33 -0800 From: Andrew Morton To: David Brown Cc: linux-kernel@vger.kernel.org, Ulrich Drepper , Michael Kerrisk Subject: Re: compat_sys_times() bogus until jiffies >= 0. Message-Id: <20071107152833.6f302c2a.akpm@linux-foundation.org> In-Reply-To: <20071107224722.GA20204@old.davidb.org> References: <20071107224722.GA20204@old.davidb.org> X-Mailer: Sylpheed version 2.2.4 (GTK+ 2.8.19; i686-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org > On Wed, 7 Nov 2007 14:47:22 -0800 David Brown wrote: > compat_sys_times() has bogus return until jiffies is >= 0. I discovered > this running LTP within 5 minutes of booting. > > The return result > > return compat_jiffies_to_clock_t(jiffies); > > will return '-1' to user space and set the negated clock_t value to errno. > > I'm not sure what the correct fix for this is. I can come up with a patch > if anyone has ideas on how to fix it. > > At minimum, perhaps it should return a sane errno value. RETURN VALUE times() returns the number of clock ticks that have elapsed since an arbitrary point in the past. For Linux 2.4 and earlier this point is the moment the system was booted. Since Linux 2.6, this point is (2^32/HZ) - 300 (i.e., about 429 million) seconds before system boot time. The return value may overflow the possible range of type clock_t. On error, (clock_t) -1 is returned, and errno is set appro- priately. Perhaps this is a bug in glibc: it is interpreting the times() return value in the same way as other syscalls. It would have been sensible for us to add INITIAL_JIFFIES to the value instead of exposing this kernel-only detail to the world, although the problem will of course reoccur once jiffies hits 0x80000000. Unfortunately we've even gone and enshrined this bogon in the manpage. Proposed fix: - return compat_jiffies_to_clock_t(jiffies); + return compat_jiffies_to_clock_t((jiffies + INITIAL_JIFFIES) & + 0x7fffffff); ?