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SubjectRe: [PATCH V2] genirq/affinity: Handle affinity setting on inactive interrupts correctly
Hi,

On Fri, 17 Jul 2020 18:00:02 +0200
Thomas Gleixner <tglx@linutronix.de> wrote:

> Setting interrupt affinity on inactive interrupts is inconsistent when
> hierarchical irq domains are enabled. The core code should just store the
> affinity and not call into the irq chip driver for inactive interrupts
> because the chip drivers may not be in a state to handle such requests.
>
> X86 has a hacky workaround for that but all other irq chips have not which
> causes problems e.g. on GIC V3 ITS.
>
> Instead of adding more ugly hacks all over the place, solve the problem in
> the core code. If the affinity is set on an inactive interrupt then:
>
> - Store it in the irq descriptors affinity mask
> - Update the effective affinity to reflect that so user space has
> a consistent view
> - Don't call into the irq chip driver
>
> This is the core equivalent of the X86 workaround and works correctly
> because the affinity setting is established in the irq chip when the
> interrupt is activated later on.
>
> Note, that this is only effective when hierarchical irq domains are enabled
> by the architecture. Doing it unconditionally would break legacy irq chip
> implementations.
>
> For hierarchial irq domains this works correctly as none of the drivers can
> have a dependency on affinity setting in inactive state by design.
>
> Remove the X86 workaround as it is not longer required.
>
> Fixes: 02edee152d6e ("x86/apic/vector: Ignore set_affinity call for inactive interrupts")
> Reported-by: Ali Saidi <alisaidi@amazon.com>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> Cc: stable@vger.kernel.org
> Link: https://lore.kernel.org/r/20200529015501.15771-1-alisaidi@amazon.com
> ---
> V2: Fix the fallout for CONFIG_GENERIC_IRQ_EFFECTIVE_AFF_MASK=n (0day)

It seems that this patch breaks perf events on RK3288 because the PMU
interrupts that should be per-cpu are now all on CPU0 so no events are
collected from CPUs 1-3 and those interrupts are killed as spurious
after a few seconds.

I'm seeing this on 4.19.134 and 5.4.53 but as far as I can tell the
relevant code hasn't changed through to next-20200723. Reverting the
backport of this change fixes the problem.

It looks like what happens is that because the interrupts are not
per-CPU in the hardware, armpmu_request_irq() calls irq_force_affinity()
while the interrupt is deactivated and then request_irq() with
IRQF_PERCPU | IRQF_NOBALANCING.

Now when irq_startup() runs with IRQ_STARTUP_NORMAL, it calls
irq_setup_affinity() which returns early because IRQF_PERCPU and
IRQF_NOBALANCING are set, leaving the interrupt on its original CPU.

At this point /proc/interrupts clearly shows the interrupts occurring on
CPU0 despite /proc/irq/N/effective_affinity and /proc/irq/N/smp_affinity
showing them spread across the cores as expected.

I don't think I understand what's meant to happen well enough to propose
a patch, but hopefully the above explanation explains the problem.


Regards,
John

> ---
> arch/x86/kernel/apic/vector.c | 22 +++++-----------------
> kernel/irq/manage.c | 37 +++++++++++++++++++++++++++++++++++--
> 2 files changed, 40 insertions(+), 19 deletions(-)
>
> --- a/arch/x86/kernel/apic/vector.c
> +++ b/arch/x86/kernel/apic/vector.c
> @@ -446,12 +446,10 @@ static int x86_vector_activate(struct ir
> trace_vector_activate(irqd->irq, apicd->is_managed,
> apicd->can_reserve, reserve);
>
> - /* Nothing to do for fixed assigned vectors */
> - if (!apicd->can_reserve && !apicd->is_managed)
> - return 0;
> -
> raw_spin_lock_irqsave(&vector_lock, flags);
> - if (reserve || irqd_is_managed_and_shutdown(irqd))
> + if (!apicd->can_reserve && !apicd->is_managed)
> + assign_irq_vector_any_locked(irqd);
> + else if (reserve || irqd_is_managed_and_shutdown(irqd))
> vector_assign_managed_shutdown(irqd);
> else if (apicd->is_managed)
> ret = activate_managed(irqd);
> @@ -775,20 +773,10 @@ void lapic_offline(void)
> static int apic_set_affinity(struct irq_data *irqd,
> const struct cpumask *dest, bool force)
> {
> - struct apic_chip_data *apicd = apic_chip_data(irqd);
> int err;
>
> - /*
> - * Core code can call here for inactive interrupts. For inactive
> - * interrupts which use managed or reservation mode there is no
> - * point in going through the vector assignment right now as the
> - * activation will assign a vector which fits the destination
> - * cpumask. Let the core code store the destination mask and be
> - * done with it.
> - */
> - if (!irqd_is_activated(irqd) &&
> - (apicd->is_managed || apicd->can_reserve))
> - return IRQ_SET_MASK_OK;
> + if (WARN_ON_ONCE(!irqd_is_activated(irqd)))
> + return -EIO;
>
> raw_spin_lock(&vector_lock);
> cpumask_and(vector_searchmask, dest, cpu_online_mask);
> --- a/kernel/irq/manage.c
> +++ b/kernel/irq/manage.c
> @@ -195,9 +195,9 @@ void irq_set_thread_affinity(struct irq_
> set_bit(IRQTF_AFFINITY, &action->thread_flags);
> }
>
> +#ifdef CONFIG_GENERIC_IRQ_EFFECTIVE_AFF_MASK
> static void irq_validate_effective_affinity(struct irq_data *data)
> {
> -#ifdef CONFIG_GENERIC_IRQ_EFFECTIVE_AFF_MASK
> const struct cpumask *m = irq_data_get_effective_affinity_mask(data);
> struct irq_chip *chip = irq_data_get_irq_chip(data);
>
> @@ -205,9 +205,19 @@ static void irq_validate_effective_affin
> return;
> pr_warn_once("irq_chip %s did not update eff. affinity mask of irq %u\n",
> chip->name, data->irq);
> -#endif
> }
>
> +static inline void irq_init_effective_affinity(struct irq_data *data,
> + const struct cpumask *mask)
> +{
> + cpumask_copy(irq_data_get_effective_affinity_mask(data), mask);
> +}
> +#else
> +static inline void irq_validate_effective_affinity(struct irq_data *data) { }
> +static inline void irq_init_effective_affinity(struct irq_data *data,
> + const struct cpumask *mask) { }
> +#endif
> +
> int irq_do_set_affinity(struct irq_data *data, const struct cpumask *mask,
> bool force)
> {
> @@ -304,6 +314,26 @@ static int irq_try_set_affinity(struct i
> return ret;
> }
>
> +static bool irq_set_affinity_deactivated(struct irq_data *data,
> + const struct cpumask *mask, bool force)
> +{
> + struct irq_desc *desc = irq_data_to_desc(data);
> +
> + /*
> + * If the interrupt is not yet activated, just store the affinity
> + * mask and do not call the chip driver at all. On activation the
> + * driver has to make sure anyway that the interrupt is in a
> + * useable state so startup works.
> + */
> + if (!IS_ENABLED(CONFIG_IRQ_DOMAIN_HIERARCHY) || irqd_is_activated(data))
> + return false;
> +
> + cpumask_copy(desc->irq_common_data.affinity, mask);
> + irq_init_effective_affinity(data, mask);
> + irqd_set(data, IRQD_AFFINITY_SET);
> + return true;
> +}
> +
> int irq_set_affinity_locked(struct irq_data *data, const struct cpumask *mask,
> bool force)
> {
> @@ -314,6 +344,9 @@ int irq_set_affinity_locked(struct irq_d
> if (!chip || !chip->irq_set_affinity)
> return -EINVAL;
>
> + if (irq_set_affinity_deactivated(data, mask, force))
> + return 0;
> +
> if (irq_can_move_pcntxt(data) && !irqd_is_setaffinity_pending(data)) {
> ret = irq_try_set_affinity(data, mask, force);
> } else {

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