Re: [PATCH 3/3] [BUGFIX] x86/x86_64: fix IRQ migration triggered active device IRQ interrruption

[Yinghai Lu <yhlu.kernel@gmail.com>]

On Wed, Apr 8, 2009 at 2:07 PM, Gary Hade <garyhade@us.ibm.com> wrote:
> Impact: Eliminates an issue that can leave the system in an
>        unusable state.
>
> This patch addresses an issue where device generated IRQs
> are no longer seen by the kernel following IRQ affinity
> migration while the device is generating IRQs at a high rate.
> We have seen this problem happen when IRQ affinities are
> adjusted in response to CPU offlining but I believe it
> could also happen in during user initiated IRQ affinity
> changes unrelated to CPU offlining. e.g. while the
> irqbalance daemon is adjusting IRQ affinities when the
> system is heavily loaded.
>
> I have been able to consistently reproduce the problem on
> some of our systems by running the following script (VICTIM_IRQ
> specifies the IRQ for the aic94xx device) while a single instance
> of the command
>  # while true; do find / -exec file {} \;; done
> is keeping the filesystem activity and IRQ rate reasonably high.
>
> #!/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 root cause is a known issue already addressed for some
> code paths [e.g. ack_apic_level() and the now obsolete
> migrate_irq_remapped_level_desc()] where the ioapic can
> misbehave when the I/O redirection table register is written
> while the Remote IRR bit is set.
>
> The proposed fix uses the same avoidance method and much
> of same code that the Interrupt Remapping code previously
> used to avoid the same problem.
>
> Signed-off-by: Gary Hade <garyhade@us.ibm.com>
>
> ---
>  arch/x86/kernel/apic/io_apic.c |   72 ++++++++++++++++++++++++++++++-
>  1 file changed, 71 insertions(+), 1 deletion(-)
>
> 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 09:24:11.000000000 -0700
> +++ linux-2.6.30-rc1/arch/x86/kernel/apic/io_apic.c     2009-04-08 09:24:23.000000000 -0700
> @@ -2331,7 +2331,8 @@ set_desc_affinity(struct irq_desc *desc,
>  }
>
>  static void
> -set_ioapic_affinity_irq_desc(struct irq_desc *desc, const struct cpumask *mask)
> +set_ioapic_irq_affinity_desc(struct irq_desc *desc,
> +                            const struct cpumask *mask)
>  {
>        struct irq_cfg *cfg;
>        unsigned long flags;
> @@ -2352,6 +2353,75 @@ set_ioapic_affinity_irq_desc(struct irq_
>  }
>
>  static void
> +delayed_irq_move(struct work_struct *work)
> +{
> +       unsigned int irq;
> +       struct irq_desc *desc;
> +
> +       for_each_irq_desc(irq, desc) {
> +               if (desc->status & IRQ_MOVE_PENDING) {
> +                       unsigned long flags;
> +
> +                       spin_lock_irqsave(&desc->lock, flags);
> +                       if (!desc->chip->set_affinity ||
> +                           !(desc->status & IRQ_MOVE_PENDING)) {
> +                               desc->status &= ~IRQ_MOVE_PENDING;
> +                               spin_unlock_irqrestore(&desc->lock, flags);
> +                               continue;
> +                       }
> +
> +                       desc->chip->set_affinity(irq, desc->pending_mask);
> +                       spin_unlock_irqrestore(&desc->lock, flags);
> +               }
> +       }
> +}
> +
> +static DECLARE_DELAYED_WORK(delayed_irq_move_work, delayed_irq_move);
> +
> +static void
> +set_ioapic_irq_affinity_level_desc(struct irq_desc *desc)
> +{
> +
> +       struct irq_cfg *cfg = desc->chip_data;
> +
> +       mask_IO_APIC_irq_desc(desc);
> +
> +       if (io_apic_level_ack_pending(cfg)) {
> +               /*
> +                * Interrupt in progress. Migrating irq now will change
> +                * the vector information in the IO-APIC RTE which will
> +                * confuse the EOI broadcast performed by cpu.
> +                * So, we delay the irq migration.
> +                */
> +               schedule_delayed_work(&delayed_irq_move_work, 1);
> +               goto unmask;
> +       }
> +
> +       /* Interrupt not in progress. we can change the vector
> +        * information in the IO-APIC RTE. */
> +       set_ioapic_irq_affinity_desc(desc, desc->pending_mask);
> +
> +       desc->status &= ~IRQ_MOVE_PENDING;
> +       cpumask_clear(desc->pending_mask);
> +
> +unmask:
> +       unmask_IO_APIC_irq_desc(desc);
> +}
> +
> +static void
> +set_ioapic_affinity_irq_desc(struct irq_desc *desc,
> +                            const struct cpumask *mask)
> +{
> +       if (desc->status & IRQ_LEVEL) {
> +               desc->status |= IRQ_MOVE_PENDING;
> +               cpumask_copy(desc->pending_mask, mask);
> +               set_ioapic_irq_affinity_level_desc(desc);
> +               return;
> +       }
> +       set_ioapic_irq_affinity_desc(desc, mask);
> +}
> +
> +static void
>  set_ioapic_affinity_irq(unsigned int irq, const struct cpumask *mask)
>  {
>        struct irq_desc *desc;
> --

it seems, ack_apic_level() already checked io_apic_level_ack_pending()

                cfg = desc->chip_data;
                if (!io_apic_level_ack_pending(cfg))
                        move_masked_irq(irq);
                unmask_IO_APIC_irq_desc(desc);

also calling path without irremap - for level triggered.
1. user use /proc/irq/xx/smp_affinity to set affinity
2. kernel/irq/manager.c::irq_set_affinity() is called, and
desc->pending_mask is changed
3a. one irq is arrived: arch/x86/kernel/irq.c::do_IRQ() is called,
hand_irq==>desc->handle_irq
    ==>kernel/irq/chip.c::handle_fasteoi_irq() ==> call desc->chip->eoi()
3b. desc->chip->eoi() aka
arch/x86/kernel/apic/io_apic.c::ack_apic_level() will call
mask_IO_APIC_irq_desc() and kernel/irq/migration.c::move_masked_irq()
3c. move_masked_irq will call desc->set_affinity(), vector and target
in io_apic controller and IDT are changed
    desc->affinity is changed at last. ( for desc moving,
move_in_progress and extra_move flag is set too.)
3d then ack_apic_level() will unmask the irq.
3e. finished other call in handle_fasteoi_irq()

YH