Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757862Ab0DVT7V (ORCPT ); Thu, 22 Apr 2010 15:59:21 -0400 Received: from e6.ny.us.ibm.com ([32.97.182.146]:42788 "EHLO e6.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757787Ab0DVT7P (ORCPT ); Thu, 22 Apr 2010 15:59:15 -0400 Date: Thu, 22 Apr 2010 12:59:11 -0700 From: "Paul E. McKenney" To: Peter Zijlstra Cc: Li Zefan , LKML , "containers@lists.osdl.org" , Paul Menage , Andrew Morton , Matt Helsley , Cedric Le Goater Subject: Re: [PATCH 4/5] freezer cgroup: Fix an RCU warning in cgroup_freezing_or_frozen() Message-ID: <20100422195911.GN2524@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <4BD016F4.8060108@cn.fujitsu.com> <4BD01768.2020606@cn.fujitsu.com> <1271939275.1776.345.camel@laptop> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1271939275.1776.345.camel@laptop> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1787 Lines: 51 On Thu, Apr 22, 2010 at 02:27:55PM +0200, Peter Zijlstra wrote: > 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? So you are advocating for the rcu_dereference check including the task lock, correct? Thanx, Paul -- 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/