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Message-ID: <86802c440904081503k545bf7b4n3d44aa3c9d101e0d@mail.gmail.com>
Date: Wed, 8 Apr 2009 15:03:49 -0700
From: Yinghai Lu <yhlu.kernel@...il.com>
To: Gary Hade <garyhade@...ibm.com>,
"Eric W. Biederman" <ebiederm@...ssion.com>
Cc: mingo@...e.hu, mingo@...hat.com, tglx@...utronix.de, hpa@...or.com,
x86@...nel.org, linux-kernel@...r.kernel.org, lcm@...ibm.com
Subject: Re: [PATCH 3/3] [BUGFIX] x86/x86_64: fix IRQ migration triggered
active device IRQ interrruption
On Wed, Apr 8, 2009 at 2:07 PM, Gary Hade <garyhade@...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@...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
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