From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756823AbZDHXif (ORCPT ); Wed, 8 Apr 2009 19:38:35 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755946AbZDHXiE (ORCPT ); Wed, 8 Apr 2009 19:38:04 -0400 Received: from e9.ny.us.ibm.com ([32.97.182.139]:50628 "EHLO e9.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754535AbZDHXiD (ORCPT ); Wed, 8 Apr 2009 19:38:03 -0400 Date: Wed, 8 Apr 2009 16:37:58 -0700 From: Gary Hade To: Yinghai Lu Cc: Gary Hade , mingo@elte.hu, mingo@redhat.com, tglx@linutronix.de, hpa@zytor.com, x86@kernel.org, linux-kernel@vger.kernel.org, lcm@us.ibm.com Subject: Re: [PATCH 2/3] [BUGFIX] x86/x86_64: fix CPU offlining triggered inactive device IRQ interrruption Message-ID: <20090408233758.GB14412@us.ibm.com> References: <20090408210735.GD11159@us.ibm.com> <86802c440904081530i1b83e19ayddebd8b2f6d413af@mail.gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <86802c440904081530i1b83e19ayddebd8b2f6d413af@mail.gmail.com> User-Agent: Mutt/1.5.17+20080114 (2008-01-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Apr 08, 2009 at 03:30:15PM -0700, Yinghai Lu wrote: > On Wed, Apr 8, 2009 at 2:07 PM, Gary Hade wrote: > > Impact: Eliminates a race that can leave the system in an > >        unusable state > > > > During rapid offlining of multiple CPUs there is a chance > > that an IRQ affinity move destination CPU will be offlined > > before the IRQ affinity move initiated during the offlining > > of a previous CPU completes.  This can happen when the device > > is not very active and thus fails to generate the IRQ that is > > needed to complete the IRQ affinity move before the move > > destination CPU is offlined.  When this happens there is an > > -EBUSY return from __assign_irq_vector() during the offlining > > of the IRQ move destination CPU which prevents initiation of > > a new IRQ affinity move operation to an online CPU.  This > > leaves the IRQ affinity set to an offlined CPU. > > > > I have been able to reproduce the problem on some of our > > systems using the following script.  When the system is idle > > the problem often reproduces during the first CPU offlining > > sequence. > > > > #!/bin/sh > > > > SYS_CPU_DIR=/sys/devices/system/cpu > > VICTIM_IRQ=25 > > IRQ_MASK=f0 > > > > iteration=0 > > while true; do > >  echo $iteration > >  echo $IRQ_MASK > /proc/irq/$VICTIM_IRQ/smp_affinity > >  for cpudir in $SYS_CPU_DIR/cpu[1-9] $SYS_CPU_DIR/cpu??; do > >    echo 0 > $cpudir/online > >  done > >  for cpudir in $SYS_CPU_DIR/cpu[1-9] $SYS_CPU_DIR/cpu??; do > >    echo 1 > $cpudir/online > >  done > >  iteration=`expr $iteration + 1` > > done > > > > The proposed fix takes advantage of the fact that when all > > CPUs in the old domain are offline there is nothing to be done > > by send_cleanup_vector() during the affinity move completion. > > So, we simply avoid setting cfg->move_in_progress preventing > > the above mentioned -EBUSY return from __assign_irq_vector(). > > This allows initiation of a new IRQ affinity move to a CPU > > that is not going offline. > > > > Signed-off-by: Gary Hade > > > > --- > >  arch/x86/kernel/apic/io_apic.c |   11 ++++++++--- > >  1 file changed, 8 insertions(+), 3 deletions(-) > > > > Index: linux-2.6.30-rc1/arch/x86/kernel/apic/io_apic.c > > =================================================================== > > --- linux-2.6.30-rc1.orig/arch/x86/kernel/apic/io_apic.c        2009-04-08 09:23:00.000000000 -0700 > > +++ linux-2.6.30-rc1/arch/x86/kernel/apic/io_apic.c     2009-04-08 09:23:16.000000000 -0700 > > @@ -363,7 +363,8 @@ set_extra_move_desc(struct irq_desc *des > >        struct irq_cfg *cfg = desc->chip_data; > > > >        if (!cfg->move_in_progress) { > > -               /* it means that domain is not changed */ > > +               /* it means that domain has not changed or all CPUs > > +                * in old domain are offline */ > >                if (!cpumask_intersects(desc->affinity, mask)) > >                        cfg->move_desc_pending = 1; > >        } > > @@ -1262,8 +1263,11 @@ next: > >                current_vector = vector; > >                current_offset = offset; > >                if (old_vector) { > > -                       cfg->move_in_progress = 1; > >                        cpumask_copy(cfg->old_domain, cfg->domain); > > +                       if (cpumask_intersects(cfg->old_domain, > > +                                              cpu_online_mask)) { > > +                               cfg->move_in_progress = 1; > > +                       } > >                } > >                for_each_cpu_and(new_cpu, tmp_mask, cpu_online_mask) > >                        per_cpu(vector_irq, new_cpu)[vector] = irq; > > @@ -2492,7 +2496,8 @@ static void irq_complete_move(struct irq > >                if (likely(!cfg->move_desc_pending)) > >                        return; > > > > -               /* domain has not changed, but affinity did */ > > +               /* domain has not changed or all CPUs in old domain > > +                * are offline, but affinity changed */ > >                me = smp_processor_id(); > >                if (cpumask_test_cpu(me, desc->affinity)) { > >                        *descp = desc = move_irq_desc(desc, me); > > -- > > so you mean during __assign_irq_vector(), cpu_online_mask get updated? No, the CPU being offlined is removed from cpu_online_mask earlier via a call to remove_cpu_from_maps() from cpu_disable_common(). This happens just before fixup_irqs() is called. > with your patch, how about that it just happen right after you check > that second time. > > it seems we are missing some lock_vector_lock() on the remove cpu from > online mask. The remove_cpu_from_maps() call in cpu_disable_common() is vector lock protected: void cpu_disable_common(void) { < snip > /* It's now safe to remove this processor from the online map */ lock_vector_lock(); remove_cpu_from_maps(cpu); unlock_vector_lock(); fixup_irqs(); } Is this what you meant? Gary -- Gary Hade System x Enablement IBM Linux Technology Center 503-578-4503 IBM T/L: 775-4503 garyhade@us.ibm.com http://www.ibm.com/linux/ltc