Re: [PATCH v3 2/3] genirq: Always limit the affinity to online CPUs

[Marek Szyprowski]

Hi Marc,

On 05.04.2022 20:50, Marc Zyngier wrote:
> When booting with maxcpus=<small number> (or even loading a driver
> while most CPUs are offline), it is pretty easy to observe managed
> affinities containing a mix of online and offline CPUs being passed
> to the irqchip driver.
>
> This means that the irqchip cannot trust the affinity passed down
> from the core code, which is a bit annoying and requires (at least
> in theory) all drivers to implement some sort of affinity narrowing.
>
> In order to address this, always limit the cpumask to the set of
> online CPUs.
>
> Signed-off-by: Marc Zyngier <maz@xxxxxxxxxx>

This patch landed in linux next-20220413 as commit 33de0aa4bae9 
("genirq: Always limit the affinity to online CPUs"). Unfortunately it 
breaks booting of most ARM 32bit Samsung Exynos based boards.

I don't see anything specific in the log, though. Booting just hangs at 
some point. The only Samsung Exynos boards that boot properly are those 
Exynos4412 based.

I assume that this is related to the Multi Core Timer IRQ configuration 
specific for that SoCs. Exynos4412 uses PPI interrupts, while all other 
Exynos SoCs have separate IRQ lines for each CPU.

Let me know how I can help debugging this issue.

> ---
>   kernel/irq/manage.c | 25 +++++++++++++++++--------
>   1 file changed, 17 insertions(+), 8 deletions(-)
>
> diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
> index c03f71d5ec10..f71ecc100545 100644
> --- a/kernel/irq/manage.c
> +++ b/kernel/irq/manage.c
> @@ -222,11 +222,16 @@ int irq_do_set_affinity(struct irq_data *data, const struct cpumask *mask,
>   {
>   	struct irq_desc *desc = irq_data_to_desc(data);
>   	struct irq_chip *chip = irq_data_get_irq_chip(data);
> +	const struct cpumask  *prog_mask;
>   	int ret;
>   
> +	static DEFINE_RAW_SPINLOCK(tmp_mask_lock);
> +	static struct cpumask tmp_mask;
> +
>   	if (!chip || !chip->irq_set_affinity)
>   		return -EINVAL;
>   
> +	raw_spin_lock(&tmp_mask_lock);
>   	/*
>   	 * If this is a managed interrupt and housekeeping is enabled on
>   	 * it check whether the requested affinity mask intersects with
> @@ -248,24 +253,28 @@ int irq_do_set_affinity(struct irq_data *data, const struct cpumask *mask,
>   	 */
>   	if (irqd_affinity_is_managed(data) &&
>   	    housekeeping_enabled(HK_TYPE_MANAGED_IRQ)) {
> -		const struct cpumask *hk_mask, *prog_mask;
> -
> -		static DEFINE_RAW_SPINLOCK(tmp_mask_lock);
> -		static struct cpumask tmp_mask;
> +		const struct cpumask *hk_mask;
>   
>   		hk_mask = housekeeping_cpumask(HK_TYPE_MANAGED_IRQ);
>   
> -		raw_spin_lock(&tmp_mask_lock);
>   		cpumask_and(&tmp_mask, mask, hk_mask);
>   		if (!cpumask_intersects(&tmp_mask, cpu_online_mask))
>   			prog_mask = mask;
>   		else
>   			prog_mask = &tmp_mask;
> -		ret = chip->irq_set_affinity(data, prog_mask, force);
> -		raw_spin_unlock(&tmp_mask_lock);
>   	} else {
> -		ret = chip->irq_set_affinity(data, mask, force);
> +		prog_mask = mask;
>   	}
> +
> +	/* Make sure we only provide online CPUs to the irqchip */
> +	cpumask_and(&tmp_mask, prog_mask, cpu_online_mask);
> +	if (!cpumask_empty(&tmp_mask))
> +		ret = chip->irq_set_affinity(data, &tmp_mask, force);
> +	else
> +		ret = -EINVAL;
> +
> +	raw_spin_unlock(&tmp_mask_lock);
> +
>   	switch (ret) {
>   	case IRQ_SET_MASK_OK:
>   	case IRQ_SET_MASK_OK_DONE:

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland