From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754277Ab1FOAkv (ORCPT ); Tue, 14 Jun 2011 20:40:51 -0400 Received: from e1.ny.us.ibm.com ([32.97.182.141]:52246 "EHLO e1.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752089Ab1FOAks (ORCPT ); Tue, 14 Jun 2011 20:40:48 -0400 Date: Tue, 14 Jun 2011 17:40:45 -0700 From: "Paul E. McKenney" To: Steven Rostedt Cc: linux-kernel@vger.kernel.org, Ingo Molnar , Andrew Morton , Peter Zijlstra , Andrew Theurer Subject: Re: [PATCH 2/2] sched: Check if lowest_mask is initialized in find_lowest_rq Message-ID: <20110615004045.GU2288@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20110614223623.876681637@goodmis.org> <20110614223657.824872966@goodmis.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20110614223657.824872966@goodmis.org> 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 Tue, Jun 14, 2011 at 06:36:25PM -0400, Steven Rostedt wrote: > From: Steven Rostedt > > On system boot up, the lowest_mask is initialized with early_initcall. > But RT tasks may wake up on other early_initcall callers before the > lowest_mask is initialized, causing a system crash. > > The commit d72bce0e67 rcu: Cure load woes > was the first commit to wake up RT tasks in early init. Before this > commit this bug should not happen. I never was able to reproduce this, but after adding Shaohua's patch, I need this one too on some systems. So: Tested-by: Paul E. McKenney > Cc: Peter Zijlstra > Cc: Paul McKenney > Reported-by: Andrew Theurer > Tested-by: Andrew Theurer > Link: http://lkml.kernel.org/r/1308014683.9218.107.camel@gandalf.stny.rr.com > Signed-off-by: Steven Rostedt > --- > kernel/sched_rt.c | 4 ++++ > 1 files changed, 4 insertions(+), 0 deletions(-) > > diff --git a/kernel/sched_rt.c b/kernel/sched_rt.c > index 9b8d5dc..10d0182 100644 > --- a/kernel/sched_rt.c > +++ b/kernel/sched_rt.c > @@ -1239,6 +1239,10 @@ static int find_lowest_rq(struct task_struct *task) > int this_cpu = smp_processor_id(); > int cpu = task_cpu(task); > > + /* Make sure the mask is initialized first */ > + if (unlikely(!lowest_mask)) > + return -1; > + > if (task->rt.nr_cpus_allowed == 1) > return -1; /* No other targets possible */ > > -- > 1.7.4.4 > >