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

[Wei Liu <wei.liu@kernel.org>]

On Tue, Jul 28, 2026 at 01:51:16PM +0000, Naman Jain wrote:
> 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. That only works when the outermost chip happens to
> install an irq_retrigger() callback, which is not guaranteed for every
> irqchip and could lead to lost interrupts on CPU hot-unplug.
> 
> Use irq_chip_retrigger_hierarchy() instead, which walks up the interrupt
> hierarchy until it finds a chip that implements irq_retrigger().
> 
> While at it, move the loop-local variables into the loop scope and use a
> scoped guard for desc->lock.
> 
> No functional change intended for chips which already provide an
> irq_retrigger() callback on the outermost domain.
> 
> Suggested-by: Thomas Gleixner <tglx@kernel.org>
> Signed-off-by: Naman Jain <namjain@linux.microsoft.com>

I can pick this up as part of this series but this requires an ack from
Thomas.

Wei

> ---
>  arch/x86/kernel/irq.c | 23 +++++++----------------
>  1 file changed, 7 insertions(+), 16 deletions(-)
> 
> 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
> @@ -466,11 +466,6 @@ DEFINE_IDTENTRY_SYSVEC(sysvec_posted_msi_notification)
>  /* A cpu has been removed from cpu_online_mask.  Reset irq affinities. */
>  void fixup_irqs(void)
>  {
> -	unsigned int vector;
> -	struct irq_desc *desc;
> -	struct irq_data *data;
> -	struct irq_chip *chip;
> -
>  	irq_migrate_all_off_this_cpu();
>  
>  	/*
> @@ -489,22 +484,18 @@ void fixup_irqs(void)
>  	 * vector_lock because the cpu is already marked !online, so
>  	 * 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])))
> +	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))
>  				__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
> 
>