Re: [PATCH] irqchip/apple-aic: fix irq_disable from within irq handlers

[Hector Martin <marcan@marcan.st>]

*Puts on kernel maintainer hat again*

Sorry for the delay. I've been spending too much time on hardware RE 
recently...

On 12/08/2021 19.09, Sven Peter wrote:
> When disable_irq_nosync for an interrupt is called from within its
> interrupt handler, this interrupt is only marked as disabled with the
> intention to mask it when it triggers again.
> The AIC hardware however automatically masks the interrupt when it is read.
> aic_irq_eoi then unmasks it again if it's not disabled *and* not masked.
> This results in a state mismatch between the hardware state and the
> state kept in irq_data: The hardware interrupt is masked but
> IRQD_IRQ_MASKED is not set. Any further calls to unmask_irq will directly
> return and the interrupt can never be enabled again.
> 
> Fix this by keeping the hardware and irq_data state in sync by unmasking in
> aic_irq_eoi if and only if the irq_data state also assumes the interrupt to
> be unmasked.
> 
> Fixes: 76cde2639411 ("irqchip/apple-aic: Add support for the Apple Interrupt Controller")
> Signed-off-by: Sven Peter <sven@svenpeter.dev>
> ---
>   drivers/irqchip/irq-apple-aic.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/irqchip/irq-apple-aic.c b/drivers/irqchip/irq-apple-aic.c
> index b8c06bd8659e..6fc145aacaf0 100644
> --- a/drivers/irqchip/irq-apple-aic.c
> +++ b/drivers/irqchip/irq-apple-aic.c
> @@ -226,7 +226,7 @@ static void aic_irq_eoi(struct irq_data *d)
>   	 * Reading the interrupt reason automatically acknowledges and masks
>   	 * the IRQ, so we just unmask it here if needed.
>   	 */
> -	if (!irqd_irq_disabled(d) && !irqd_irq_masked(d))
> +	if (!irqd_irq_masked(d))
>   		aic_irq_unmask(d);
>   }
>   
> 

Looks good to me. I can't remember exactly where this code came from, 
but looking again at the irqchip code it's clear that the mask state and 
hardware mask always have to be in sync.

Acked-by: Hector Martin <marcan@marcan.st>

-- 
Hector Martin (marcan@marcan.st)
Public Key: https://mrcn.st/pub