From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755295Ab2HaXwJ (ORCPT ); Fri, 31 Aug 2012 19:52:09 -0400 Received: from relay4-d.mail.gandi.net ([217.70.183.196]:44945 "EHLO relay4-d.mail.gandi.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752319Ab2HaXwG (ORCPT ); Fri, 31 Aug 2012 19:52:06 -0400 X-Originating-IP: 217.70.178.129 X-Originating-IP: 173.246.103.110 Date: Fri, 31 Aug 2012 16:51:57 -0700 From: Josh Triplett To: "Paul E. McKenney" 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, niv@us.ibm.com, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, Valdis.Kletnieks@vt.edu, dhowells@redhat.com, eric.dumazet@gmail.com, darren@dvhart.com, fweisbec@gmail.com, sbw@mit.edu, patches@linaro.org, Alessio Igor Bogani , Avi Kivity , Chris Metcalf , Christoph Lameter , Geoff Levand , Gilad Ben Yossef , Hakan Akkan , "H. Peter Anvin" , Ingo Molnar , Kevin Hilman , Max Krasnyansky , Stephen Hemminger , Sven-Thorsten Dietrich Subject: Re: [PATCH tip/core/rcu 10/26] rcu: Exit RCU extended QS on kernel preemption after irq/exception Message-ID: <20120831235157.GG11771@jtriplet-mobl1> References: <20120830210520.GA2824@linux.vnet.ibm.com> <1346360743-3628-1-git-send-email-paulmck@linux.vnet.ibm.com> <1346360743-3628-10-git-send-email-paulmck@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1346360743-3628-10-git-send-email-paulmck@linux.vnet.ibm.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Aug 30, 2012 at 02:05:27PM -0700, Paul E. McKenney wrote: > From: Frederic Weisbecker > > When an exception or an irq exits, and we are going to resume into > interrupted kernel code, the low level architecture code calls > preempt_schedule_irq() if there is a need to reschedule. > > If the interrupt/exception occured between a call to rcu_user_enter() > (from syscall exit, exception exit, do_notify_resume exit, ...) and > a real resume to userspace (iret,...), preempt_schedule_irq() can be > called whereas RCU thinks we are in userspace. But preempt_schedule_irq() > is going to run kernel code and may be some RCU read side critical > section. We must exit the userspace extended quiescent state before > we call it. > > To solve this, just call rcu_user_exit() in the beginning of > preempt_schedule_irq(). > > Signed-off-by: Frederic Weisbecker > Cc: Alessio Igor Bogani > Cc: Andrew Morton > Cc: Avi Kivity > Cc: Chris Metcalf > Cc: Christoph Lameter > Cc: Geoff Levand > Cc: Gilad Ben Yossef > Cc: Hakan Akkan > Cc: H. Peter Anvin > Cc: Ingo Molnar > Cc: Josh Triplett > Cc: Kevin Hilman > Cc: Max Krasnyansky > Cc: Peter Zijlstra > Cc: Stephen Hemminger > Cc: Steven Rostedt > Cc: Sven-Thorsten Dietrich > Cc: Thomas Gleixner > Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett > kernel/sched/core.c | 1 + > 1 files changed, 1 insertions(+), 0 deletions(-) > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index 07c6d9a..0bd599b 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -3564,6 +3564,7 @@ asmlinkage void __sched preempt_schedule_irq(void) > /* Catch callers which need to be fixed */ > BUG_ON(ti->preempt_count || !irqs_disabled()); > > + rcu_user_exit(); > do { > add_preempt_count(PREEMPT_ACTIVE); > local_irq_enable(); > -- > 1.7.8 >