From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753700AbZDHWa3 (ORCPT ); Wed, 8 Apr 2009 18:30:29 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751676AbZDHWaS (ORCPT ); Wed, 8 Apr 2009 18:30:18 -0400 Received: from rv-out-0506.google.com ([209.85.198.235]:33790 "EHLO rv-out-0506.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750908AbZDHWaQ convert rfc822-to-8bit (ORCPT ); Wed, 8 Apr 2009 18:30:16 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type:content-transfer-encoding; b=lWU37MscFXHI3rC5jQWr4iYu5mD+ODqjj2IBxwLiKcGkuMQyFBwdFbOQDgwJ130rKB ZqJ+3ANU/6g8O0mF+QhZzFWPQUEaL3BQw19M+JabI6O38HEa1Dr23+7ccPfCTfF3Erdy 7HXNq9pI+/6Ph6RwlYew3D+1lk7G6NuNc2YfA= MIME-Version: 1.0 In-Reply-To: <20090408210735.GD11159@us.ibm.com> References: <20090408210735.GD11159@us.ibm.com> Date: Wed, 8 Apr 2009 15:30:15 -0700 Message-ID: <86802c440904081530i1b83e19ayddebd8b2f6d413af@mail.gmail.com> Subject: Re: [PATCH 2/3] [BUGFIX] x86/x86_64: fix CPU offlining triggered inactive device IRQ interrruption From: Yinghai Lu To: Gary Hade Cc: mingo@elte.hu, mingo@redhat.com, tglx@linutronix.de, hpa@zytor.com, x86@kernel.org, linux-kernel@vger.kernel.org, lcm@us.ibm.com Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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? 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. YH