From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752431Ab2GSR0h (ORCPT ); Thu, 19 Jul 2012 13:26:37 -0400 Received: from e9.ny.us.ibm.com ([32.97.182.139]:40095 "EHLO e9.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751281Ab2GSR0f (ORCPT ); Thu, 19 Jul 2012 13:26:35 -0400 Date: Thu, 19 Jul 2012 10:15:51 -0700 From: "Paul E. McKenney" To: "Srivatsa S. Bhat" Cc: "linux-kernel@vger.kernel.org" Subject: Re: WARNING: at kernel/rcutree.c:1550 __rcu_process_callbacks+0x46f/0x4b0() Message-ID: <20120719171550.GL2507@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <5007F8FA.7000203@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5007F8FA.7000203@linux.vnet.ibm.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-Content-Scanned: Fidelis XPS MAILER x-cbid: 12071917-7182-0000-0000-0000020820FF Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jul 19, 2012 at 05:39:30PM +0530, Srivatsa S. Bhat wrote: > Hi Paul, > > While running a CPU hotplug stress test on v3.5-rc7+ > (mainline commit 8a7298b7805ab) I hit this warning. > I haven't tried to debug this yet... > > Line number 1550 maps to: > > WARN_ON_ONCE(cpu_is_offline(smp_processor_id())); > > inside rcu_do_batch(). Hello, Srivatsa, I believe that you need commit a16b7a69 (Prevent __call_rcu() from invoking RCU core on offline CPUs), which is currently in -tip, queued for 3.6. Please see below for the patch. Does this help? Thanx, Paul ------------------------------------------------------------------------ rcu: Prevent __call_rcu() from invoking RCU core on offline CPUs The __call_rcu() function will invoke the RCU core, for example, if it detects that the current CPU has too many callbacks. However, this can happen on an offline CPU that is on its way to the idle loop, in which case it is an error to invoke the RCU core, and the excess callbacks will be adopted in any case. This commit therefore adds checks to __call_rcu() for running on an offline CPU, refraining from invoking the RCU core in this case. Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett diff --git a/kernel/rcutree.c b/kernel/rcutree.c index a4a9c91..ceaa959 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -1904,11 +1904,11 @@ __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu), * If called from an extended quiescent state, invoke the RCU * core in order to force a re-evaluation of RCU's idleness. */ - if (rcu_is_cpu_idle()) + if (rcu_is_cpu_idle() && cpu_online(smp_processor_id())) invoke_rcu_core(); - /* If interrupts were disabled, don't dive into RCU core. */ - if (irqs_disabled_flags(flags)) { + /* If interrupts were disabled or CPU offline, don't invoke RCU core. */ + if (irqs_disabled_flags(flags) || cpu_is_offline(smp_processor_id())) { local_irq_restore(flags); return; }