From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753570AbaEHKRz (ORCPT ); Thu, 8 May 2014 06:17:55 -0400 Received: from fgwmail5.fujitsu.co.jp ([192.51.44.35]:33181 "EHLO fgwmail5.fujitsu.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751513AbaEHKRx (ORCPT ); Thu, 8 May 2014 06:17:53 -0400 Message-ID: <536B59A1.3000602@jp.fujitsu.com> Date: Thu, 8 May 2014 19:17:05 +0900 From: Masayoshi Mizuma User-Agent: Mozilla/5.0 (X11; Linux i686; rv:24.0) Gecko/20100101 Thunderbird/24.2.0 MIME-Version: 1.0 To: Rik van Riel CC: Andrew Morton , Michal Hocko , , , , , , , , 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> In-Reply-To: <20140430164255.7a753a8e@cuia.bos.redhat.com> Content-Type: text/plain; charset="ISO-2022-JP" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.124.101.151] X-SecurityPolicyCheck-GC: OK by FENCE-Mail Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Rik, 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 :) > > Masayoshi-san, does the bug still happen with this version, or does > this fix the problem? I applied the v5 patch and the divide error did not happen when I ran the test. Thank you for fixing it! Thanks, Masayoshi Mizuma > > ---8<--- > > Subject: mm,writeback: fix divide by zero in pos_ratio_polynom > > It is possible for "limit - setpoint + 1" to equal zero, after > getting truncated to a 32 bit variable, and resulting in a divide > by zero error. > > Using the fully 64 bit divide functions avoids this problem. > > Also uninline pos_ratio_polynom, at Andrew's request. > > Signed-off-by: Rik van Riel > --- > mm/page-writeback.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/mm/page-writeback.c b/mm/page-writeback.c > index ef41349..a4317da 100644 > --- a/mm/page-writeback.c > +++ b/mm/page-writeback.c > @@ -593,14 +593,14 @@ unsigned long bdi_dirty_limit(struct backing_dev_info *bdi, unsigned long dirty) > * (5) the closer to setpoint, the smaller |df/dx| (and the reverse) > * => fast response on large errors; small oscillation near setpoint > */ > -static inline long long pos_ratio_polynom(unsigned long setpoint, > +static long long pos_ratio_polynom(unsigned long setpoint, > unsigned long dirty, > unsigned long limit) > { > long long pos_ratio; > long x; > > - x = div_s64(((s64)setpoint - (s64)dirty) << RATELIMIT_CALC_SHIFT, > + x = div64_s64(((s64)setpoint - (s64)dirty) << RATELIMIT_CALC_SHIFT, > limit - setpoint + 1); > pos_ratio = x; > pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT; > @@ -842,7 +842,7 @@ static unsigned long bdi_position_ratio(struct backing_dev_info *bdi, > x_intercept = bdi_setpoint + span; > > if (bdi_dirty < x_intercept - span / 4) { > - pos_ratio = div_u64(pos_ratio * (x_intercept - bdi_dirty), > + pos_ratio = div64_u64(pos_ratio * (x_intercept - bdi_dirty), > x_intercept - bdi_setpoint + 1); > } else > pos_ratio /= 4; > > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to majordomo@kvack.org. For more info on Linux MM, > see: http://www.linux-mm.org/ . > Don't email: email@kvack.org >