RE: [PATCH v3 2/3] x86/irq: Fall back to irq_chip_retrigger_hierarchy() in fixup_irqs()

[Michael Kelley]

From: Naman Jain <namjain@xxxxxxxxxxxxxxxxxxx> Sent: Sunday, September 6, 2026 11:51 PM
> 
> fixup_irqs() re-injects a pending interrupt on its new target CPU by
> looking at the outermost domain chip and invoking its irq_retrigger()
> callback directly. When the outermost chip does not implement
> irq_retrigger(), the pending interrupt is silently dropped, which can
> lead to lost interrupts on CPU hot-unplug.
> 
> Keep calling the outermost chip's irq_retrigger() when it is present,
> but fall back to irq_chip_retrigger_hierarchy() otherwise, which walks
> up the interrupt hierarchy until it finds a chip that implements
> irq_retrigger().
> 
> While at it, use a scoped guard for desc->lock. VECTOR_RETRIGGERED is
> now set only when the retrigger succeeds instead of unconditionally,
> which is harmless today since apic_retrigger_irq() always returns 1.
> 
> Suggested-by: Thomas Gleixner <tglx@xxxxxxxxxx>
> Reviewed-by: Shradha Gupta <shradhagupta@xxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Naman Jain <namjain@xxxxxxxxxxxxxxxxxxx>

Reviewed-by: Michael Kelley <mhklinux@xxxxxxxxxxx>

> ---
>  arch/x86/kernel/irq.c | 19 +++++++++++--------
>  1 file changed, 11 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/x86/kernel/irq.c b/arch/x86/kernel/irq.c
> index 30122f0b3af96..e0163f7ac7368 100644
> --- a/arch/x86/kernel/irq.c
> +++ b/arch/x86/kernel/irq.c
> @@ -470,6 +470,7 @@ void fixup_irqs(void)
>  	struct irq_desc *desc;
>  	struct irq_data *data;
>  	struct irq_chip *chip;
> +	int ret;
> 
>  	irq_migrate_all_off_this_cpu();
> 
> @@ -490,21 +491,23 @@ void fixup_irqs(void)
>  	 * nothing else will touch it.
>  	 */
>  	for (vector = FIRST_EXTERNAL_VECTOR; vector < NR_VECTORS; vector++) {
> -		if (IS_ERR_OR_NULL(__this_cpu_read(vector_irq[vector])))
> +		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);
> +			guard(raw_spinlock)(&desc->lock);
>  			data = irq_desc_get_irq_data(desc);
>  			chip = irq_data_get_irq_chip(data);
> -			if (chip->irq_retrigger) {
> -				chip->irq_retrigger(data);
> +			if (chip->irq_retrigger)
> +				ret = chip->irq_retrigger(data);
> +			else
> +				ret = irq_chip_retrigger_hierarchy(data);
> +			if (ret)
>  				__this_cpu_write(vector_irq[vector], VECTOR_RETRIGGERED);
> -			}
> -			raw_spin_unlock(&desc->lock);
>  		}
> +
>  		if (__this_cpu_read(vector_irq[vector]) != VECTOR_RETRIGGERED)
>  			__this_cpu_write(vector_irq[vector], VECTOR_UNUSED);
>  	}
> --
> 2.43.0
>