Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754220Ab0DVM2I (ORCPT ); Thu, 22 Apr 2010 08:28:08 -0400 Received: from casper.infradead.org ([85.118.1.10]:41988 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754132Ab0DVM2G (ORCPT ); Thu, 22 Apr 2010 08:28:06 -0400 Subject: Re: [PATCH 4/5] freezer cgroup: Fix an RCU warning in cgroup_freezing_or_frozen() From: Peter Zijlstra To: Li Zefan Cc: LKML , "containers@lists.osdl.org" , "Paul E. McKenney" , Paul Menage , Andrew Morton , Matt Helsley , Cedric Le Goater In-Reply-To: <4BD01768.2020606@cn.fujitsu.com> References: <4BD016F4.8060108@cn.fujitsu.com> <4BD01768.2020606@cn.fujitsu.com> Content-Type: text/plain; charset="UTF-8" Date: Thu, 22 Apr 2010 14:27:55 +0200 Message-ID: <1271939275.1776.345.camel@laptop> Mime-Version: 1.0 X-Mailer: Evolution 2.28.3 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1537 Lines: 46 On Thu, 2010-04-22 at 17:31 +0800, Li Zefan wrote: > with CONFIG_PROVE_RCU, a warning can be triggered when we > resume from suspend: > > ... > include/linux/cgroup.h:533 invoked rcu_dereference_check() without protection! > ... > > task_freezer() calls task_subsys_state(), which needs to be > protected by rcu_read_lock or cgroup_mutex. > > Signed-off-by: Li Zefan > --- > kernel/cgroup_freezer.c | 2 ++ > 1 files changed, 2 insertions(+), 0 deletions(-) > > diff --git a/kernel/cgroup_freezer.c b/kernel/cgroup_freezer.c > index 5038f4c..ac76983 100644 > --- a/kernel/cgroup_freezer.c > +++ b/kernel/cgroup_freezer.c > @@ -53,6 +53,7 @@ int cgroup_freezing_or_frozen(struct task_struct *task) > struct freezer *freezer; > enum freezer_state state; > > + rcu_read_lock(); > task_lock(task); > freezer = task_freezer(task); > if (!freezer->css.cgroup->parent) > @@ -60,6 +61,7 @@ int cgroup_freezing_or_frozen(struct task_struct *task) > else > state = freezer->state; > task_unlock(task); > + rcu_read_unlock(); > > return (state == CGROUP_FREEZING) || (state == CGROUP_FROZEN); > } Hmm cgroup_attach_task() does hold task_lock() over setting tsk->cgroups, so doesn't that also pin the task to the cgroup and thus the cgroup itself? -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/