From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pd0-f177.google.com (mail-pd0-f177.google.com [209.85.192.177]) by kanga.kvack.org (Postfix) with ESMTP id A40A76B0035 for ; Tue, 29 Apr 2014 18:53:56 -0400 (EDT) Received: by mail-pd0-f177.google.com with SMTP id v10so834113pde.36 for ; Tue, 29 Apr 2014 15:53:56 -0700 (PDT) Received: from mail.linuxfoundation.org (mail.linuxfoundation.org. [140.211.169.12]) by mx.google.com with ESMTP id yb4si14520161pab.349.2014.04.29.15.53.55 for ; Tue, 29 Apr 2014 15:53:55 -0700 (PDT) Date: Tue, 29 Apr 2014 15:53:53 -0700 From: Andrew Morton Subject: Re: [PATCH] mm,writeback: fix divide by zero in pos_ratio_polynom Message-Id: <20140429155353.8fe070101d3b4faa0c825d99@linux-foundation.org> In-Reply-To: <53602C2B.50604@redhat.com> References: <20140429151910.53f740ef@annuminas.surriel.com> <20140429153936.49a2710c0c2bba4d233032f2@linux-foundation.org> <53602C2B.50604@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Rik van Riel Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, sandeen@redhat.com, jweiner@redhat.com, kosaki.motohiro@jp.fujitsu.com, mhocko@suse.cz, fengguang.wu@intel.com, mpatlasov@parallels.com On Tue, 29 Apr 2014 18:48:11 -0400 Rik van Riel wrote: > On 04/29/2014 06:39 PM, Andrew Morton wrote: > > On Tue, 29 Apr 2014 15:19:10 -0400 Rik van Riel wrote: > > > >> It is possible for "limit - setpoint + 1" to equal zero, leading to a > >> divide by zero error. Blindly adding 1 to "limit - setpoint" is not > >> working, so we need to actually test the divisor before calling div64. > >> > >> ... > >> > >> --- a/mm/page-writeback.c > >> +++ b/mm/page-writeback.c > >> @@ -597,11 +597,16 @@ static inline long long pos_ratio_polynom(unsigned long setpoint, > >> unsigned long dirty, > >> unsigned long limit) > >> { > >> + unsigned int divisor; > > > > I'm thinking this would be better as a ulong so I don't have to worry > > my pretty head over truncation things? > > I looked at div_*64, and the second argument is a 32 bit > variable. I guess a long would be ok, since if we are > dividing by more than 4 billion we don't really care :) > > static inline s64 div_s64(s64 dividend, s32 divisor) ah, good point. Switching to ulong is perhaps a bit misleading then. -- 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