From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758080AbZDIWiV (ORCPT ); Thu, 9 Apr 2009 18:38:21 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752946AbZDIWiI (ORCPT ); Thu, 9 Apr 2009 18:38:08 -0400 Received: from rv-out-0506.google.com ([209.85.198.235]:51647 "EHLO rv-out-0506.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752922AbZDIWiH convert rfc822-to-8bit (ORCPT ); Thu, 9 Apr 2009 18:38:07 -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=kOkl893KkM195vOhCsLp/hgGeDquwOMgDlezhQDr1UIxeisEpWIjQVx5NgRE4gOAJe gTtEAq6TZFrvqQB2UP2w3PU6geRQzo0JgEBp7TDUnTcScKvl9MVu/jZVLY2NRERoXidc wTgCHLK4I//1AjCtDZsvPaC6NqX80cU/aKGLo= MIME-Version: 1.0 In-Reply-To: <20090409191707.GA7247@us.ibm.com> References: <20090408210735.GD11159@us.ibm.com> <86802c440904081530i1b83e19ayddebd8b2f6d413af@mail.gmail.com> <20090408233758.GB14412@us.ibm.com> <86802c440904081658v4d8a3a80jdd51e27e0f8e0a6d@mail.gmail.com> <86802c440904081659l1ec30838l99fcb9c693363d00@mail.gmail.com> <20090409191707.GA7247@us.ibm.com> Date: Thu, 9 Apr 2009 15:38:04 -0700 Message-ID: <86802c440904091538m70de6f4y901dbcbb97ceb70f@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 , "Eric W. Biederman" 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 Thu, Apr 9, 2009 at 12:17 PM, Gary Hade wrote: > On Wed, Apr 08, 2009 at 04:59:35PM -0700, Yinghai Lu wrote: >> On Wed, Apr 8, 2009 at 4:58 PM, Yinghai Lu wrote: >> > On Wed, Apr 8, 2009 at 4:37 PM, Gary Hade wrote: >> >> 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(); >> >> } >> > >> > >> > __assign_irq_vector always has vector_lock locked... > > OK, I see the 'vector_lock' spin_lock_irqsave/spin_unlock_irqrestore > surrounding the __assign_irq_vector call in assign_irq_vector. > >> > so cpu_online_mask will not changed during, > > I understand that this 'vector_lock' acquisition prevents > multiple simultaneous executions of __assign_irq_vector but > does that really prevent another thread executing outside > __assign_irq_vector (or outside other 'vector_lock' serialized > code) from modifying cpu_online_mask? > > Isn't it really 'cpu_add_remove_lock' (also held when > __assign_irq_vector() is called in the context of a CPU add > or remove) that is used for this purpose? > >> > why do you need to check that again in __assign_irq_vector ? > > Because that is where the cfg->move_in_progress flag was > being set. > > Is there some reason that the content of cpu_online_mask > cannot be trusted at this location? > > If all the CPUs in the old domain are offline doesn't > that imply that we got to that location in response to > a CPU offline request? > >> > >> looks like you need to clear move_in_progress in fixup_irqs() > > This would be a difficult since I believe the code is > currently partitioned in a manner that prevents access to > irq_cfg records from functions defined in arch/x86/kernel/irq_32.c > and arch/x86/kernel/irq_64.c.  It also doesn't feel right to > allow cfg->move_in_progress to be set in __assign_irq_vector > and then clear it in fixup_irqs(). it looks before fixup_irqs() cpu_online_mask get updated, and before irq_complete_move get called. so we could fixup_irqs to clear move_in_progress and cleanup percpu vector_irq ... YH