Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1946018AbaD3VYJ (ORCPT ); Wed, 30 Apr 2014 17:24:09 -0400 Received: from mx1.redhat.com ([209.132.183.28]:16995 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965069AbaD3VYI (ORCPT ); Wed, 30 Apr 2014 17:24:08 -0400 Message-ID: <53616957.1020309@redhat.com> Date: Wed, 30 Apr 2014 17:21:27 -0400 From: Rik van Riel User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.2.0 MIME-Version: 1.0 To: Andrew Morton CC: Michal Hocko , Masayoshi Mizuma , linux-kernel@vger.kernel.org, linux-mm@kvack.org, sandeen@redhat.com, jweiner@redhat.com, kosaki.motohiro@jp.fujitsu.com, fengguang.wu@intel.com, mpatlasov@parallels.com, Motohiro.Kosaki@us.fujitsu.com Subject: Re: [PATCH v5] mm,writeback: fix divide by zero in pos_ratio_polynom References: <20140429151910.53f740ef@annuminas.surriel.com> <5360C9E7.6010701@jp.fujitsu.com> <20140430093035.7e7226f2@annuminas.surriel.com> <20140430134826.GH4357@dhcp22.suse.cz> <20140430104114.4bdc588e@cuia.bos.redhat.com> <20140430120001.b4b95061ac7252a976b8a179@linux-foundation.org> <53614F3C.8020009@redhat.com> <20140430123526.bc6a229c1ea4addad1fb483d@linux-foundation.org> <20140430160218.442863e0@cuia.bos.redhat.com> <20140430131353.fa9f49604ea39425bc93c24a@linux-foundation.org> <20140430164255.7a753a8e@cuia.bos.redhat.com> <20140430140057.7d2a6e984b2ec987182d2a4e@linux-foundation.org> In-Reply-To: <20140430140057.7d2a6e984b2ec987182d2a4e@linux-foundation.org> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 04/30/2014 05:00 PM, Andrew Morton wrote: > On Wed, 30 Apr 2014 16:42:55 -0400 Rik van Riel wrote: > >> On Wed, 30 Apr 2014 13:13:53 -0700 >> Andrew Morton wrote: >> >>> This was a consequence of 64->32 truncation and it can't happen any >>> more, can it? >> >> Andrew, this is cleaner indeed :) > > I'm starting to get worried about 32-bit wraparound in the patch > version number ;) > >> Masayoshi-san, does the bug still happen with this version, or does >> this fix the problem? >> > > We could put something like > > if (WARN_ON_ONCE(setpoint == limit)) > setpoint--; > > in there if we're not sure. But it's better to be sure! The more I look at the code, the more I am convinced that Michal is right, and we cannot actually hit the case that "limit - setpoint + 1 == 0". Setpoint always seems to be some in-between point. -- 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/