Messages in this thread | | | Date | Wed, 8 Apr 2009 16:37:58 -0700 | From | Gary Hade <> | Subject | Re: [PATCH 2/3] [BUGFIX] x86/x86_64: fix CPU offlining triggered inactive device IRQ interrruption |
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On Wed, Apr 08, 2009 at 03:30:15PM -0700, Yinghai Lu wrote: > On Wed, Apr 8, 2009 at 2:07 PM, Gary Hade <garyhade@us.ibm.com> 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 <garyhade@us.ibm.com> > > > > --- > > 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
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