RE: [PATCH 1/2] genirq: Allow an interrupt to be marked as 'naked'

[David Laight <David.Laight@ACULAB.COM>]

From: Marc Zyngier
> Sent: 01 November 2020 13:14
> 
> Some interrupts (such as the rescheduling IPI) rely on not going through
> the irq_enter()/irq_exit() calls. To distinguish such interrupts, add
> a new IRQ flag that allows the low-level handling code to sidestep the
> enter()/exit() calls.
> 
> Only the architecture code is expected to use this. It will do the wrong
> thing on normal interrupts.
> 
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> ---
>  include/linux/irq.h   |  4 +++-
>  kernel/irq/debugfs.c  |  1 +
>  kernel/irq/irqdesc.c  | 17 ++++++++++++-----
>  kernel/irq/settings.h |  7 +++++++
>  4 files changed, 23 insertions(+), 6 deletions(-)
> 
...
> diff --git a/kernel/irq/irqdesc.c b/kernel/irq/irqdesc.c
> index 1a7723604399..c08a1c19d061 100644
> --- a/kernel/irq/irqdesc.c
> +++ b/kernel/irq/irqdesc.c
> @@ -667,10 +667,9 @@ int __handle_domain_irq(struct irq_domain *domain, unsigned int hwirq,
>  {
>  	struct pt_regs *old_regs = set_irq_regs(regs);
>  	unsigned int irq = hwirq;
> +	struct irq_desc *desc;
>  	int ret = 0;
> 
> -	irq_enter();
> -
>  #ifdef CONFIG_IRQ_DOMAIN
>  	if (lookup)
>  		irq = irq_find_mapping(domain, hwirq);
> @@ -680,14 +679,22 @@ int __handle_domain_irq(struct irq_domain *domain, unsigned int hwirq,
>  	 * Some hardware gives randomly wrong interrupts.  Rather
>  	 * than crashing, do something sensible.
>  	 */
> -	if (unlikely(!irq || irq >= nr_irqs)) {
> +	desc = irq_to_desc(irq);
> +	if (unlikely(!desc || irq >= nr_irqs)) {

Should those tests be in the other order?
Probably as:
	if (unlikely(irq >= nr_irqs || !(desc = irq_to_desc(irq))) {
		...

	David

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