From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1030892Ab2CPJsK (ORCPT ); Fri, 16 Mar 2012 05:48:10 -0400 Received: from www.linutronix.de ([62.245.132.108]:44894 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1030616Ab2CPJsI (ORCPT ); Fri, 16 Mar 2012 05:48:08 -0400 Date: Fri, 16 Mar 2012 10:48:02 +0100 (CET) From: Thomas Gleixner To: "H. Peter Anvin" cc: mingo@redhat.com, levinsasha928@gmail.com, linux-kernel@vger.kernel.org, linux-tip-commits@vger.kernel.org Subject: Re: [tip:timers/core] ntp: Fix integer overflow when setting time In-Reply-To: <4F62978A.7000009@zytor.com> Message-ID: References: <1331829374-31543-2-git-send-email-levinsasha928@gmail.com> <4F62978A.7000009@zytor.com> User-Agent: Alpine 2.02 (LFD 1266 2009-07-14) 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 Thu, 15 Mar 2012, H. Peter Anvin wrote: > On 03/15/2012 02:53 PM, tip-bot for Sasha Levin wrote: > > Commit-ID: a078c6d0e6288fad6d83fb6d5edd91ddb7b6ab33 > > Gitweb: http://git.kernel.org/tip/a078c6d0e6288fad6d83fb6d5edd91ddb7b6ab33 > > Author: Sasha Levin > > AuthorDate: Thu, 15 Mar 2012 12:36:14 -0400 > > Committer: Thomas Gleixner > > CommitDate: Thu, 15 Mar 2012 21:41:34 +0100 > > > > ntp: Fix integer overflow when setting time > > > > 'long secs' is passed as divisor to div_s64, which accepts a 32bit > > divisor. On 64bit machines that value is trimmed back from 8 bytes > > back to 4, causing a divide by zero when the number is bigger than > > (1 << 32) - 1 and all 32 lower bits are 0. > > > > Use div64_long() instead. > > > > Perhaps we should use the same kind of multiply-and-shift tricks we're > doing for jiffies conversion? If nothing else it ought to perform better. It's not a hotpath where performance matters, but divide by zero does :)