From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail137.messagelabs.com (mail137.messagelabs.com [216.82.249.19]) by kanga.kvack.org (Postfix) with SMTP id 9477A6B0069 for ; Mon, 31 Oct 2011 11:49:50 -0400 (EDT) Date: Mon, 31 Oct 2011 16:49:42 +0100 From: Frantisek Hrbata Subject: Re: [PATCH] oom: fix integer overflow of points in oom_badness Message-ID: <20111031154942.GB2280@dhcp-26-164.brq.redhat.com> Reply-To: Frantisek Hrbata References: <1320048865-13175-1-git-send-email-fhrbata@redhat.com> <20111031152833.GA31904@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20111031152833.GA31904@redhat.com> Sender: owner-linux-mm@kvack.org List-ID: To: Oleg Nesterov Cc: rientjes@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, akpm@linux-foundation.org, kosaki.motohiro@jp.fujitsu.com, minchan.kim@gmail.com, stable@kernel.org, eteo@redhat.com, pmatouse@redhat.com On Mon, Oct 31, 2011 at 04:28:33PM +0100, Oleg Nesterov wrote: > On 10/31, Frantisek Hrbata wrote: > > > > My understanding is that we may just change the type of points variable from int > > to long and keep the current imho clearer(better readable) computation. There > > should not be an overflow on 32bit and there is a plenty of space for 64bit. > > If you like this solution better I will post the patch as v2. > > Up to maintainer, but personally I think the simple s/int/long/ looks better. > Everything like get_mm_*/nr_ptes returns long. Agreed. I will post v2 with the int => long change. > > Anyway good catch. Imho stable needs the fix too. > > Cosmetic nit, > > > - points = get_mm_rss(p->mm) + p->mm->nr_ptes; > > - points += get_mm_counter(p->mm, MM_SWAPENTS); > > + points = (int)((get_mm_rss(p->mm) + get_mm_counter(p->mm, MM_SWAPENTS) + > ^^^^^ > > Why do we need the explicit typecast? It buys nothing and looks a bit confusing. You are right, it's not needed. I just wanted to make the cast more visible, but some kind of comment would be probably better here. > > And, if you prefer "int", perhaps something like > > - points *= 1000; > - points /= totalpages; > + /* avoid the possible overflow */ > + points = points * 1000L / totalpages; > > looks a bit more readable with the same effect. But I won't insist, this is > up to you and David. Sure, this looks much better than the one line expression in the patch I sent. If David or others decide to not go with the int=>long change I think we should use this. > > Oleg. > Many thanks Oleg. -- Frantisek Hrbata -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org