From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754768Ab1JBWuf (ORCPT ); Sun, 2 Oct 2011 18:50:35 -0400 Received: from mail-ww0-f42.google.com ([74.125.82.42]:32948 "EHLO mail-ww0-f42.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751693Ab1JBWu2 (ORCPT ); Sun, 2 Oct 2011 18:50:28 -0400 Date: Mon, 3 Oct 2011 00:50:22 +0200 From: Frederic Weisbecker To: "Paul E. McKenney" Cc: "Kirill A. Shutemov" , linux-kernel@vger.kernel.org, Dipankar Sarma , Thomas Gleixner , Ingo Molnar , Peter Zijlstra , Lai Jiangshan Subject: Re: linux-next-20110923: warning kernel/rcutree.c:1833 Message-ID: <20111002225019.GA1835@somewhere> References: <20110927180142.GD2335@linux.vnet.ibm.com> <20110928123116.GP18553@somewhere> <20110928184025.GF2383@linux.vnet.ibm.com> <20110928234633.GA3537@somewhere> <20110929005545.GT2383@linux.vnet.ibm.com> <20110929123040.GB3537@somewhere> <20110929171205.GA2362@linux.vnet.ibm.com> <20110930131105.GC19053@somewhere> <20110930152946.GA2397@linux.vnet.ibm.com> <20110930192438.GA7505@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20110930192438.GA7505@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 Fri, Sep 30, 2011 at 12:24:38PM -0700, Paul E. McKenney wrote: > @@ -328,11 +326,11 @@ static int rcu_implicit_offline_qs(struct rcu_data *rdp) > return 1; > } > > - /* If preemptible RCU, no point in sending reschedule IPI. */ > - if (rdp->preemptible) > - return 0; > - > - /* The CPU is online, so send it a reschedule IPI. */ > + /* > + * The CPU is online, so send it a reschedule IPI. This forces > + * it through the scheduler, and (inefficiently) also handles cases > + * where idle loops fail to inform RCU about the CPU being idle. > + */ If the idle loop forgets to call rcu_idle_enter() before going to sleep, I don't know if it's a good idea to try to cure that situation by forcing a quiescent state remotely. It may make the thing worse because we actually won't notice the lack of call to rcu_idle_enter() that the rcu stall detector would otherwise report to us. Also I don't think that works. If the task doesn't have TIF_RESCHED, it won't go through the scheduler on irq exit. smp_send_reschedule() doesn't set the flag. And also scheduler_ipi() returns right away if no wake up is pending. So, other than resuming the idle loop to sleep again, nothing may happen. Or am I missing something? > if (rdp->cpu != smp_processor_id()) > smp_send_reschedule(rdp->cpu); > else