Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S935575AbZDITRZ (ORCPT ); Thu, 9 Apr 2009 15:17:25 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1762092AbZDITRP (ORCPT ); Thu, 9 Apr 2009 15:17:15 -0400 Received: from e5.ny.us.ibm.com ([32.97.182.145]:56011 "EHLO e5.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1761630AbZDITRO (ORCPT ); Thu, 9 Apr 2009 15:17:14 -0400 Date: Thu, 9 Apr 2009 12:17:08 -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: <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> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <86802c440904081659l1ec30838l99fcb9c693363d00@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 Content-Length: 7541 Lines: 178 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(). 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/