From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754122Ab3LCPqm (ORCPT ); Tue, 3 Dec 2013 10:46:42 -0500 Received: from mail-la0-f43.google.com ([209.85.215.43]:62178 "EHLO mail-la0-f43.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753279Ab3LCPqj (ORCPT ); Tue, 3 Dec 2013 10:46:39 -0500 Date: Tue, 3 Dec 2013 19:46:35 +0400 From: Sergey Dyasly To: Oleg Nesterov Cc: Andrew Morton , David Rientjes , Frederic Weisbecker , Mandeep Singh Baines , "Ma, Xindong" , Michal Hocko , Sameer Nanda , "Tu, Xiaobing" , linux-kernel@vger.kernel.org Subject: Re: [PATCH 0/2] initial while_each_thread() fixes Message-Id: <20131203194635.7be1c07ae042ee395bc83527@gmail.com> In-Reply-To: <20131202152423.GA10878@redhat.com> References: <20131202152423.GA10878@redhat.com> X-Mailer: Sylpheed 3.3.0 (GTK+ 2.24.17; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Oleg, I was waiting for this one! On Mon, 2 Dec 2013 16:24:23 +0100 Oleg Nesterov wrote: > 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. The race is very easy to catch if you have a process with several threads, all of which allocates memory simultaneously. This leads to: 1) OOMk selects and sends SIGKILL to one of the threads 2) another thread invokes OOMk and the first thread gets selected, but it gets unhashed before while_each_thread... > 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. The patches look correct and my test case no longer hangs, so Reviewed-and-Tested-by: Sergey Dyasly > > 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(-) > -- Sergey Dyasly