From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752707Ab2GTOhS (ORCPT ); Fri, 20 Jul 2012 10:37:18 -0400 Received: from e35.co.us.ibm.com ([32.97.110.153]:43489 "EHLO e35.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752019Ab2GTOhQ (ORCPT ); Fri, 20 Jul 2012 10:37:16 -0400 Date: Fri, 20 Jul 2012 07:36:57 -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: <20120720143657.GC2721@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <5007F8FA.7000203@linux.vnet.ibm.com> <20120719171550.GL2507@linux.vnet.ibm.com> <500935BC.4040405@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <500935BC.4040405@linux.vnet.ibm.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-Content-Scanned: Fidelis XPS MAILER x-cbid: 12072014-6148-0000-0000-000007D3CC0F Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jul 20, 2012 at 04:11:00PM +0530, Srivatsa S. Bhat wrote: > On 07/19/2012 10:45 PM, Paul E. McKenney wrote: > > 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? > > Yes, that fixed it, thanks! :-) > Sorry for the noise... May I add your Tested-by? Thanx, Paul > Regards, > Srivatsa S. Bhat > > > > > ------------------------------------------------------------------------ > > > > 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; > > } > >