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

[Gary Hade <garyhade@us.ibm.com>]

On Wed, Apr 08, 2009 at 03:03:49PM -0700, Yinghai Lu wrote:
> 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);

Yes, I have actually observed instances where the command
   `echo $IRQ_MASK > /proc/irq/$VICTIM_IRQ/smp_affinity`
in the above test script failed to modify the affinity due to
a debug printk confirmed non-zero return from io_apic_level_ack_pending()
at this location.  However, this is definitely not catching all the cases.
This was confirmed this with a printk in __target_IO_APIC_irq() that would
sometimes shows the Remote IRR bit set before the io_apic_modify() call.
e.g.
__target_IO_APIC_irq: XXX before io_apic_modify irq=25 vector=0xd9 reg=0x1e0d9

> 
> 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()

Need to think about this.  I'll get back to you.

Thanks!

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