From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail143.messagelabs.com (mail143.messagelabs.com [216.82.254.35]) by kanga.kvack.org (Postfix) with ESMTP id 8ADBD6B0071 for ; Mon, 7 Jun 2010 09:15:40 -0400 (EDT) Received: from d03relay04.boulder.ibm.com (d03relay04.boulder.ibm.com [9.17.195.106]) by e37.co.us.ibm.com (8.14.4/8.13.1) with ESMTP id o57DDtHs003190 for ; Mon, 7 Jun 2010 07:13:55 -0600 Received: from d03av04.boulder.ibm.com (d03av04.boulder.ibm.com [9.17.195.170]) by d03relay04.boulder.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id o57DFPRX100076 for ; Mon, 7 Jun 2010 07:15:26 -0600 Received: from d03av04.boulder.ibm.com (loopback [127.0.0.1]) by d03av04.boulder.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id o57DFKxF025667 for ; Mon, 7 Jun 2010 07:15:21 -0600 Date: Mon, 7 Jun 2010 18:28:28 +0530 From: Balbir Singh Subject: Re: [patch 02/18] oom: introduce find_lock_task_mm() to fix !mm false positives Message-ID: <20100607125828.GW4603@balbir.in.ibm.com> Reply-To: balbir@linux.vnet.ibm.com References: MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org To: David Rientjes Cc: Andrew Morton , Rik van Riel , Nick Piggin , Oleg Nesterov , KAMEZAWA Hiroyuki , KOSAKI Motohiro , linux-mm@kvack.org List-ID: * David Rientjes [2010-06-06 15:34:03]: > From: Oleg Nesterov > > Almost all ->mm == NUL checks in oom_kill.c are wrong. typo should be NULL > > The current code assumes that the task without ->mm has already > released its memory and ignores the process. However this is not > necessarily true when this process is multithreaded, other live > sub-threads can use this ->mm. > > - Remove the "if (!p->mm)" check in select_bad_process(), it is > just wrong. > > - Add the new helper, find_lock_task_mm(), which finds the live > thread which uses the memory and takes task_lock() to pin ->mm > > - change oom_badness() to use this helper instead of just checking > ->mm != NULL. > > - As David pointed out, select_bad_process() must never choose the > task without ->mm, but no matter what oom_badness() returns the > task can be chosen if nothing else has been found yet. > > Change oom_badness() to return int, change it to return -1 if > find_lock_task_mm() fails, and change select_bad_process() to > check points >= 0. > > Note! This patch is not enough, we need more changes. > > - oom_badness() was fixed, but oom_kill_task() still ignores > the task without ->mm > > - oom_forkbomb_penalty() should use find_lock_task_mm() too, > and it also needs other changes to actually find the first > first-descendant children > > This will be addressed later. > > [kosaki.motohiro@jp.fujitsu.com: use in badness(), __oom_kill_task()] > Signed-off-by: Oleg Nesterov > Signed-off-by: David Rientjes > --- > mm/oom_kill.c | 74 +++++++++++++++++++++++++++++++++------------------------ > 1 files changed, 43 insertions(+), 31 deletions(-) > > diff --git a/mm/oom_kill.c b/mm/oom_kill.c > --- a/mm/oom_kill.c > +++ b/mm/oom_kill.c > @@ -52,6 +52,20 @@ static int has_intersects_mems_allowed(struct task_struct *tsk) > return 0; > } > > +static struct task_struct *find_lock_task_mm(struct task_struct *p) > +{ > + struct task_struct *t = p; > + > + do { > + task_lock(t); > + if (likely(t->mm)) > + return t; > + task_unlock(t); > + } while_each_thread(p, t); > + > + return NULL; > +} > + Even if we miss this mm via p->mm, won't for_each_process actually catch it? Are you suggesting that the main thread could have detached the mm and a thread might still have it mapped? -- Three Cheers, Balbir -- 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