Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751185Ab0DUDOP (ORCPT ); Tue, 20 Apr 2010 23:14:15 -0400 Received: from e6.ny.us.ibm.com ([32.97.182.146]:49180 "EHLO e6.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750910Ab0DUDON (ORCPT ); Tue, 20 Apr 2010 23:14:13 -0400 Date: Tue, 20 Apr 2010 20:14:10 -0700 From: "Paul E. McKenney" To: Li Zefan Cc: Eric Paris , Peter Zijlstra , Eric Paris , Miles Lane , LKML Subject: Re: INFO: suspicious rcu_dereference_check() usage - include/linux/cgroup.h:492 invoked rcu_dereference_check() without protection! Message-ID: <20100421031410.GB2613@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20100311032843.GE6767@linux.vnet.ibm.com> <1271098032.4807.137.camel@twins> <1271242058.32749.19.camel@laptop> <1271701612.2972.5.camel@dhcp231-113.rdu.redhat.com> <20100419230136.GA16856@linux.vnet.ibm.com> <4BCE4F6E.10301@cn.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4BCE4F6E.10301@cn.fujitsu.com> 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: 1692 Lines: 44 On Wed, Apr 21, 2010 at 09:05:50AM +0800, Li Zefan wrote: > > commit 2836f18139267ea918ed2cf39023fb0eb38c4361 > > Author: Paul E. McKenney > > Date: Mon Apr 19 15:59:50 2010 -0700 > > > > rcu: fix RCU lockdep splat on freezer_fork path > > > > Add an RCU read-side critical section to suppress this false positive. > > > > Located-by: Eric Paris > > Signed-off-by: Paul E. McKenney > > > > diff --git a/kernel/cgroup_freezer.c b/kernel/cgroup_freezer.c > > index da5e139..e5c0244 100644 > > --- a/kernel/cgroup_freezer.c > > +++ b/kernel/cgroup_freezer.c > > @@ -205,9 +205,12 @@ static void freezer_fork(struct cgroup_subsys *ss, struct task_struct *task) > > * No lock is needed, since the task isn't on tasklist yet, > > * so it can't be moved to another cgroup, which means the > > * freezer won't be removed and will be valid during this > > - * function call. > > + * function call. Nevertheless, apply RCU read-side critical > > + * section to suppress RCU lockdep false positives. > > */ > > It was me that added the original comment. > > > + rcu_read_lock(); > > freezer = task_freezer(task); > > + rcu_read_unlock(); > > > > /* > > * The root cgroup is non-freezable, so we can skip the > > Acked-by: Li Zefan Thank you, Li! I have added your Acked-by. 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/