From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759431Ab0FPXEq (ORCPT ); Wed, 16 Jun 2010 19:04:46 -0400 Received: from e6.ny.us.ibm.com ([32.97.182.146]:41021 "EHLO e6.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755354Ab0FPXEp (ORCPT ); Wed, 16 Jun 2010 19:04:45 -0400 Date: Wed, 16 Jun 2010 16:04:41 -0700 From: "Paul E. McKenney" To: Peter Zijlstra Cc: linux-kernel@vger.kernel.org, mingo@elte.hu, laijs@cn.fujitsu.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@polymtl.ca, josh@joshtriplett.org, dvhltc@us.ibm.com, niv@us.ibm.com, tglx@linutronix.de, rostedt@goodmis.org, Valdis.Kletnieks@vt.edu, dhowells@redhat.com, eric.dumazet@gmail.com, Daniel J Blueman Subject: Re: [PATCH tip/core/urgent 1/3] rcu: fix lockdep splat in wake_affine() Message-ID: <20100616230441.GK2457@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20100615222923.GA14571@linux.vnet.ibm.com> <1276640983-14641-1-git-send-email-paulmck@linux.vnet.ibm.com> <1276669391.1745.594.camel@laptop> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1276669391.1745.594.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 On Wed, Jun 16, 2010 at 08:23:11AM +0200, Peter Zijlstra wrote: > On Tue, 2010-06-15 at 15:29 -0700, Paul E. McKenney wrote: > > From: Daniel J Blueman > > > > With 2.6.35-rc1 and your patch in the context below, we still see > > "include/linux/cgroup.h:534 invoked rcu_dereference_check() without > > protection!", so need this additional patch: > > > > Acquire read-side RCU lock around task_group() calls, addressing > > "include/linux/cgroup.h:534 invoked rcu_dereference_check() without > > protection!" warning. > > Uhm,. this is all just slapping in rcu_read_lock() to make the warning > go away, without explanation of what and why. > > Its not obvious what the races is, nor how its handled. Please let me know if my explanation in a recent email covers this. If so, I will add it to the commit log. If not, well, back to the drawing board, I guess. ;-) Thanx, Paul > > Signed-off-by: Daniel J Blueman > > Signed-off-by: Paul E. McKenney > > --- > > kernel/sched_fair.c | 2 ++ > > 1 files changed, 2 insertions(+), 0 deletions(-) > > > > diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c > > index eed35ed..ca56133 100644 > > --- a/kernel/sched_fair.c > > +++ b/kernel/sched_fair.c > > @@ -1240,6 +1240,7 @@ static int wake_affine(struct sched_domain *sd, struct task_struct *p, int sync) > > * effect of the currently running task from the load > > * of the current CPU: > > */ > > + rcu_read_lock(); > > if (sync) { > > tg = task_group(current); > > weight = current->se.load.weight; > > @@ -1249,6 +1250,7 @@ static int wake_affine(struct sched_domain *sd, struct task_struct *p, int sync) > > } > > > > tg = task_group(p); > > + rcu_read_unlock(); > > weight = p->se.load.weight; > > > > /* > >