From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752682Ab3LBPX1 (ORCPT ); Mon, 2 Dec 2013 10:23:27 -0500 Received: from mx1.redhat.com ([209.132.183.28]:61262 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752000Ab3LBPXW (ORCPT ); Mon, 2 Dec 2013 10:23:22 -0500 Date: Mon, 2 Dec 2013 16:24:23 +0100 From: Oleg Nesterov To: Andrew Morton Cc: David Rientjes , Frederic Weisbecker , Mandeep Singh Baines , "Ma, Xindong" , Michal Hocko , Sameer Nanda , Sergey Dyasly , "Tu, Xiaobing" , linux-kernel@vger.kernel.org Subject: [PATCH 0/2] initial while_each_thread() fixes Message-ID: <20131202152423.GA10878@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello. This was reported several times, I believe the first report is http://marc.info/?l=linux-kernel&m=127688978121665. Hmm, 3 years ago. The lockless while_each_thread() is racy and broken, almost every user can loop forever. Recently people started to report they actually hit this problem in oom_kill.c. This doesn't really matter and I can be wrong, but in fact I do not think they really hit this race, it is very unlikely. Another problem with while_each_thread() is that it is very easy to use it wrongly, and oom_kill.c is the good example. I came to conclusion that it is practically impossible to send a single series which fixes all problems, too many different users. So 1/2 adds the new for_each_thread() interface, and 2/2 fixes oom kill as an example. We obviously need a lot more changes like 2/2 before we can kill while_each_thread() and task_struct->thread_group, but I hope they will be straighforward. And in fact I hope that task->thread_group can go away before we change all users of while_each_thread(). David, et al, I din't actually test 2/2, I do not know how. Please review, although it looks simple. Oleg. include/linux/init_task.h | 2 ++ include/linux/sched.h | 12 ++++++++++++ kernel/exit.c | 1 + kernel/fork.c | 7 +++++++ mm/oom_kill.c | 37 ++++++++++++++++++++----------------- 5 files changed, 42 insertions(+), 17 deletions(-)