Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Wed, 31 Oct 2001 13:41:12 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Wed, 31 Oct 2001 13:41:03 -0500 Received: from [63.231.122.81] ([63.231.122.81]:61799 "EHLO lynx.adilger.int") by vger.kernel.org with ESMTP id ; Wed, 31 Oct 2001 13:40:56 -0500 Date: Wed, 31 Oct 2001 11:40:02 -0700 From: Andreas Dilger To: Tim Schmielau Cc: "Richard B. Johnson" , vda , linux-kernel@vger.kernel.org Subject: Re: [Patch] Re: Nasty suprise with uptime Message-ID: <20011031114002.H16554@lynx.no> Mail-Followup-To: Tim Schmielau , "Richard B. Johnson" , vda , linux-kernel@vger.kernel.org In-Reply-To:

Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.2.4i In-Reply-To: ; from tim@physik3.uni-rostock.de on Wed, Oct 31, 2001 at 07:16:44PM +0100 X-GPG-Key: 1024D/0D35BED6 X-GPG-Fingerprint: 7A37 5D79 BF1B CECA D44F 8A29 A488 39F5 0D35 BED6 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Oct 31, 2001 19:16 +0100, Tim Schmielau wrote: > The idea was that all drivers that use the 32 bit jiffies counter have to > be aware of the wraparound anyways, and won't see a difference. Agreed. I also like the change that you initialize jiffies to a pre-wrap value, so the jiffies wrap bugs can more easily be found/fixed. > The race only happens for 64 bit accesses to jiffies, but hey, without > the patch these values come out wrong _every_ time, so I believed a > tiny window for a single wrong display of uptime every 497.1 days to be > acceptable. I would say that the race is so rare that it should not be handled, especially since it adds extra code in the timer interrupt. > + /* We need to make sure jiffies_high does not change while > + * reading jiffies and jiffies_high */ > + do { > + jiffies_high_tmp = jiffies_high_shadow; > + barrier(); > + jiffies_tmp = jiffies; > + barrier(); > + } while (jiffies_high != jiffies_high_tmp); Maybe this could be condensed into a macro/inline, so that people don't screw it up (and it looks cleaner). Like get_jiffies64() or so, for those few places that really care about the full value and can't stand a miniscule chance of a race (i.e. uptime output is not a candidate). Cheers, Andreas -- Andreas Dilger http://sourceforge.net/projects/ext2resize/ http://www-mddsp.enel.ucalgary.ca/People/adilger/ - 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/