From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752344AbaB0Ohn (ORCPT ); Thu, 27 Feb 2014 09:37:43 -0500 Received: from mail-qg0-f42.google.com ([209.85.192.42]:59884 "EHLO mail-qg0-f42.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751396AbaB0Ohl (ORCPT ); Thu, 27 Feb 2014 09:37:41 -0500 Date: Thu, 27 Feb 2014 09:37:37 -0500 From: Tejun Heo To: Li Zefan Cc: LKML , Cgroups Subject: Re: [PATCH 1/2] cpuset: fix a locking issue in cpuset_migrate_mm() Message-ID: <20140227143737.GA19178@htj.dyndns.org> References: <530F1117.1020605@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <530F1117.1020605@huawei.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Feb 27, 2014 at 06:19:03PM +0800, Li Zefan wrote: > I can trigger a lockdep warning: > > # mount -t cgroup -o cpuset xxx /cgroup > # mkdir /cgroup/cpuset > # mkdir /cgroup/tmp > # echo 0 > /cgroup/tmp/cpuset.cpus > # echo 0 > /cgroup/tmp/cpuset.mems > # echo 1 > /cgroup/tmp/cpuset.memory_migrate > # echo $$ > /cgroup/tmp/tasks > # echo 1 > /cgruop/tmp/cpuset.mems > > =============================== > [ INFO: suspicious RCU usage. ] > 3.14.0-rc1-0.1-default+ #32 Not tainted > ------------------------------- > include/linux/cgroup.h:682 suspicious rcu_dereference_check() usage! > ... > [] dump_stack+0x72/0x86 > [] lockdep_rcu_suspicious+0x101/0x140 > [] cpuset_migrate_mm+0xb1/0xe0 > ... > > We used to hold cgroup_mutex when calling cpuset_migrate_mm(), but now > we hold cpuset_mutex, which causes task_css() to complain. > > This is not a false-positive but a real issue. > > Holding cpuset_mutex won't prevent a task's cpuset from changing, and > it won't prevent the original task->cgroup from destroying during this > change. > > Fixes: 5d21cc2db040 (cpuset: replace cgroup_mutex locking with cpuset internal locking) > Cc: # 3.9+ > Signed-off-by: Li Zefan Applied to cgroup/for-3.14-fixes. Thanks. -- tejun