Re: [PATCH v5 9/9] irqchip/al-fic: support per-child affinity via interrupt redirection

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] irqchip/al-fic: unconfigured level interrupts cause interrupt storm on redirection
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commit a2b0d194e9e91e226ae5163eb51d0cdf61945a75
Author: Eliav Farber <farbere@amazon.com>

irqchip/al-fic: support per-child affinity via interrupt redirection

This commit wires al-fic into the interrupt redirection infrastructure to
support per-child affinity control. It defers the handler execution to the
target CPU via irq_work while moving the ack (and masking for level
configured groups) into parent context using irq_pre_redirect.

> diff --git a/drivers/irqchip/irq-al-fic.c b/drivers/irqchip/irq-al-fic.c
> index 13a945a1d312a..77cff6308eba1 100644
> --- a/drivers/irqchip/irq-al-fic.c
> +++ b/drivers/irqchip/irq-al-fic.c

[ ... ]

> @@ -157,6 +163,32 @@ static int al_fic_irq_retrigger(struct irq_data *data)
>  	return 1;
>  }
>  
> +#ifdef CONFIG_SMP
> +/* The ack happens in al_fic_irq_pre_redirect() on both paths instead. */
> +static void al_fic_irq_noop(struct irq_data *data) { }
> +
> +/*
> + * Runs in the parent interrupt context on every dispatch, redirected or not.
> + * Clear the cause bit here: once the flow handler is deferred, the FIC keeps
> + * driving its output until the irq_work runs, and a level parent SPI re-fires.
> + *
> + * A level configured group is masked too, because its cause bit re-latches
> + * while the input stays asserted; the deferred handle_level_irq() unmasks
> + * when the handler is done. An edge configured group is only acked, since
> + * handle_edge_irq() never unmasks unconditionally and the mask would stay.
> + */
> +static void al_fic_irq_pre_redirect(struct irq_data *data)
> +{
> +	struct irq_chip_generic *gc = irq_data_get_irq_chip_data(data);
> +	struct al_fic *fic = gc->private;
> +
> +	if (fic->state == AL_FIC_CONFIGURED_LEVEL)
> +		irq_gc_mask_set_bit(data);

[Severity: High]
Could unconfigured level interrupts cause an interrupt storm on redirection
here?

If a driver requests a child interrupt without specifying a trigger type,
fic->state remains AL_FIC_UNCONFIGURED.

Since the generic chip defaults to handle_level_irq, when the interrupt
fires and its affinity excludes the current CPU,
generic_handle_demux_domain_irq() calls al_fic_irq_pre_redirect().

Because the state is unconfigured, the check for AL_FIC_CONFIGURED_LEVEL
fails and the interrupt is not masked.

The handler execution is then deferred to another CPU via irq_work.
However, because the hardware is level-triggered and was not masked, the
FIC continues asserting the parent SPI. This immediately re-triggers the
parent interrupt upon return, trapping the parent CPU in an infinite loop.

> +
> +	irq_gc_ack_clr_bit(data);
> +}
> +#endif /* CONFIG_SMP */

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261011050449.41903-1-farbere@amazon.com?part=9