Re: [PATCH 2/3] x86/irq: Use irq_chip_retrigger_hierarchy() in fixup_irqs()

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] The patch replaces the direct invocation of the outermost chip's irq_retrigger() callback with irq_chip_retrigger_hierarchy(). However, irq_chip_retrigger_hierarchy() initializes its loop with `data = data->parent_data`, completely skipping the outermost chip. This breaks interrupt retriggering for flat domains (like native lapic_controller) and any hierarchical domain where the outermost chip directly implements the retrigger callback.
--

--- Patch [2]: [PATCH 2/3] x86/irq: Use irq_chip_retrigger_hierarchy() in fixup_irqs() ---
commit f97e883de2f6626561de48c426194caa41c3e062
Author: Naman Jain <namjain@linux.microsoft.com>
x86/irq: Use irq_chip_retrigger_hierarchy() in fixup_irqs()

This commit modifies fixup_irqs() to use irq_chip_retrigger_hierarchy()
instead of invoking the outermost domain chip's irq_retrigger() callback
directly. It also refactors the loop to use scoped guards for the irq
descriptor lock.

> diff --git a/arch/x86/kernel/irq.c b/arch/x86/kernel/irq.c
> index 30122f0b3af96..ef1bdd3c4659a 100644
> --- a/arch/x86/kernel/irq.c
> +++ b/arch/x86/kernel/irq.c
[ ... ]
> @@ -489,22 +484,18 @@ void fixup_irqs(void)
[ ... ]
> -	for (vector = FIRST_EXTERNAL_VECTOR; vector < NR_VECTORS; vector++) {
> -		if (IS_ERR_OR_NULL(__this_cpu_read(vector_irq[vector])))
> +	for (unsigned int vector = FIRST_EXTERNAL_VECTOR; vector < NR_VECTORS; vector++) {
> +		struct irq_desc *desc = __this_cpu_read(vector_irq[vector]);
> +
> +		if (IS_ERR_OR_NULL(desc))
>  			continue;
>  
>  		if (is_vector_pending(vector)) {
> -			desc = __this_cpu_read(vector_irq[vector]);
> -
> -			raw_spin_lock(&desc->lock);
> -			data = irq_desc_get_irq_data(desc);
> -			chip = irq_data_get_irq_chip(data);
> -			if (chip->irq_retrigger) {
> -				chip->irq_retrigger(data);
> +			guard(raw_spinlock)(&desc->lock);
> +			if (irq_chip_retrigger_hierarchy(&desc->irq_data))
[Severity: High]
Will this skip the outermost chip and cause a regression for flat domains?

Looking at kernel/irq/chip.c:irq_chip_retrigger_hierarchy(), the loop
initializes by immediately moving to the parent_data:

    int irq_chip_retrigger_hierarchy(struct irq_data *data)
    {
        for (data = data->parent_data; data; data = data->parent_data)
            if (data->chip && data->chip->irq_retrigger)
                return data->chip->irq_retrigger(data);

        return 0;
    }

By passing &desc->irq_data directly to this function, it seems any retrigger
callback on the outermost chip itself will be bypassed.

Could this lead to dropped hardware interrupts during CPU hot-unplug for
flat domains (like native lapic_controller) or any hierarchical domain where
the outermost chip implements the retrigger callback?

>  				__this_cpu_write(vector_irq[vector], VECTOR_RETRIGGERED);
> -			}
> -			raw_spin_unlock(&desc->lock);
>  		}

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260728135117.2888175-1-namjain@linux.microsoft.com?part=2