Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S936326Ab3DIHIN (ORCPT ); Tue, 9 Apr 2013 03:08:13 -0400 Received: from mail1.sysgo.com ([176.9.26.183]:36684 "EHLO mail1.sysgo.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932600Ab3DIHIK (ORCPT ); Tue, 9 Apr 2013 03:08:10 -0400 Message-ID: <5163BE58.3090206@sysgo.com> Date: Tue, 09 Apr 2013 09:08:08 +0200 From: David Engraf User-Agent: Mozilla/5.0 (X11; Linux i686; rv:17.0) Gecko/20130308 Thunderbird/17.0.4 MIME-Version: 1.0 To: John Stultz CC: Thomas Gleixner , linux-kernel@vger.kernel.org Subject: Re: [PATCH] ktime_add_ns() may overflow on 32bit architectures References: <51485A43.4020600@sysgo.com> <51632673.8030603@linaro.org> In-Reply-To: <51632673.8030603@linaro.org> Content-Type: text/plain; charset=ISO-8859-15; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1633 Lines: 46 Am 08.04.2013 22:20, schrieb John Stultz: > On 03/19/2013 05:29 AM, David Engraf wrote: >> Hello, >> >> I've triggered an overflow when using ktime_add_ns() on a 32bit >> architecture not supporting CONFIG_KTIME_SCALAR. >> >> When passing a very high value for u64 nsec, e.g. 7881299347898368000 >> the do_div() function converts this value to seconds (7881299347) >> which is still to high to pass to the ktime_set() function as long. >> The result in my case is a negative value. >> >> The problem on my system occurs in the tick-sched.c, >> tick_nohz_stop_sched_tick() when time_delta is set to >> timekeeping_max_deferment(). The check for time_delta < KTIME_MAX is >> valid, thus ktime_add_ns() is called with a too large value resulting >> in a negative expire value. This leads to an endless loop in the >> ticker code: >> >> time_delta: 7881299347898368000 >> expires = ktime_add_ns(last_update, time_delta) >> expires: negative value >> >> This error doesn't occurs on 64bit or architectures supporting >> CONFIG_KTIME_SCALAR (e.g. ARM, x86-32). > > Sorry, this fell through the cracks. I see Andrew caught it, but I've > queued for 3.10 in my tree as well. > > This should be tagged for -stable as well, no? Yes, please tag it for -stable as well because I had the problem with kernel 3.0 and it can overflow on all current version. Best regards - David > thanks > -john > -- 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/