From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Fri, 7 Mar 2003 07:12:05 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Fri, 7 Mar 2003 07:12:05 -0500 Received: from ns.virtualhost.dk ([195.184.98.160]:39120 "EHLO virtualhost.dk") by vger.kernel.org with ESMTP id ; Fri, 7 Mar 2003 07:12:04 -0500 Date: Fri, 7 Mar 2003 14:20:48 +0100 From: Jens Axboe To: Andrew Morton Cc: tim@physik3.uni-rostock.de, linux-kernel@vger.kernel.org Subject: Re: 2.5.64 and jiffies wrap Message-ID: <20030307132048.GC903@suse.de> References: <20030307130504.GA903@suse.de> <20030307041558.6112425c.akpm@digeo.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20030307041558.6112425c.akpm@digeo.com> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Mar 07 2003, Andrew Morton wrote: > Jens Axboe wrote: > > > > Hi, > > > > The patch doesn't look right, why is INITIAL_JIFFIES being cast to > > unsigned int? This breaks x86_64 at least. > > > > ... > > -#define INITIAL_JIFFIES ((unsigned int) (-300*HZ)) > > This sets the initial jiffies value to 0x00000000fffb6c20, which can trigger > 32-bit wraparound bugs: if some random jiffy counter wraps from > 0x00000000ffffffff to 0x0000000000000000 then things fail. > > davem was bitten by at least one such bug in the qlogicfc driver. It would > have caused 64-bit machines to fail after 49 days. > > It turns out that it is more valuable to test for this than to test for > 64-bit wraparound bugs. Ok makes sense, I thought the point was just to test for jiffies wrap. Anyways, the patch breaks boot on x86_64 here. -- Jens Axboe