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 C630F6B0069 for ; Mon, 31 Oct 2011 13:20:00 -0400 (EDT) Message-ID: <4EAEAE3D.8070102@jp.fujitsu.com> Date: Mon, 31 Oct 2011 10:18:37 -0400 From: KOSAKI Motohiro MIME-Version: 1.0 Subject: Re: [PATCH v2] oom: fix integer overflow of points in oom_badness References: <1320048865-13175-1-git-send-email-fhrbata@redhat.com> <1320076569-23872-1-git-send-email-fhrbata@redhat.com> In-Reply-To: <1320076569-23872-1-git-send-email-fhrbata@redhat.com> Content-Type: text/plain; charset=ISO-2022-JP Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: fhrbata@redhat.com Cc: rientjes@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, akpm@linux-foundation.org, oleg@redhat.com, minchan.kim@gmail.com, stable@kernel.org, eteo@redhat.com, pmatouse@redhat.com (10/31/2011 11:56 AM), Frantisek Hrbata wrote: > An integer overflow will happen on 64bit archs if task's sum of rss, swapents > and nr_ptes exceeds (2^31)/1000 value. This was introduced by commit > > f755a04 oom: use pte pages in OOM score > > where the oom score computation was divided into several steps and it's no > longer computed as one expression in unsigned long(rss, swapents, nr_pte are > unsigned long), where the result value assigned to points(int) is in > range(1..1000). So there could be an int overflow while computing > > 176 points *= 1000; > > and points may have negative value. Meaning the oom score for a mem hog task > will be one. > > 196 if (points <= 0) > 197 return 1; > > For example: > [ 3366] 0 3366 35390480 24303939 5 0 0 oom01 > Out of memory: Kill process 3366 (oom01) score 1 or sacrifice child > > Here the oom1 process consumes more than 24303939(rss)*4096~=92GB physical > memory, but it's oom score is one. > > In this situation the mem hog task is skipped and oom killer kills another and > most probably innocent task with oom score greater than one. > > The points variable should be of type long instead of int to prevent the int > overflow. > > Signed-off-by: Frantisek Hrbata > --- > mm/oom_kill.c | 2 +- > 1 files changed, 1 insertions(+), 1 deletions(-) > > diff --git a/mm/oom_kill.c b/mm/oom_kill.c > index 626303b..e9a1785 100644 > --- a/mm/oom_kill.c > +++ b/mm/oom_kill.c > @@ -162,7 +162,7 @@ static bool oom_unkillable_task(struct task_struct *p, > unsigned int oom_badness(struct task_struct *p, struct mem_cgroup *mem, > const nodemask_t *nodemask, unsigned long totalpages) > { > - int points; > + long points; > > if (oom_unkillable_task(p, mem, nodemask)) > return 0; Good catch. Acked-by: KOSAKI Motohiro -- 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