linux-kernel - Re: [PATCH] genirq: Use irqd_get_trigger_type to compare the trigger type for shared IRQs

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Date:   Sat, 15 Apr 2017 14:30:58 +0100
From:   Marc Zyngier <marc.zyngier@....com>
To:     Hans de Goede <hdegoede@...hat.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>, <x86@...nel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] genirq: Use irqd_get_trigger_type to compare the trigger type for shared IRQs

On Sat, Apr 15 2017 at 11:08:31 am BST, Hans de Goede <hdegoede@...hat.com> wrote:
> When requesting a shared irq with IRQF_TRIGGER_NONE then the irqaction
> flags get filled with the trigger type from the irq_data:
>
>         if (!(new->flags & IRQF_TRIGGER_MASK))
>                 new->flags |= irqd_get_trigger_type(&desc->irq_data);
>
> On the first setup_irq() the trigger type in irq_data is NONE when the
> above code executes, then the irq is started up for the first time and
> then the actual trigger type gets established, but that's too late to fix
> up new->flags.
>
> When then a second user of the irq requests the irq with IRQF_TRIGGER_NONE
> its irqaction's triggertype gets set to the actual trigger type and the
> following check fails:
>
>         if (!((old->flags ^ new->flags) & IRQF_TRIGGER_MASK))
>
> Resulting in the request_irq failing with -EBUSY even though both
> users requested the irq with IRQF_SHARED | IRQF_TRIGGER_NONE
>
> This commit fixes this by comparing the new irqaction's trigger type
> to the trigger type stored in the irq_data which correctly reflects
> the actual trigger type being used for the irq.
>
> Suggested-by: Thomas Gleixner <tglx@...utronix.de>
> Signed-off-by: Hans de Goede <hdegoede@...hat.com>
> ---
>  kernel/irq/manage.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
> index a4afe5c..d63e91f 100644
> --- a/kernel/irq/manage.c
> +++ b/kernel/irq/manage.c
> @@ -1212,8 +1212,10 @@ __setup_irq(unsigned int irq, struct irq_desc *desc, struct irqaction *new)
>  		 * set the trigger type must match. Also all must
>  		 * agree on ONESHOT.
>  		 */
> +		unsigned int oldtype = irqd_get_trigger_type(&desc->irq_data);
> +
>  		if (!((old->flags & new->flags) & IRQF_SHARED) ||
> -		    ((old->flags ^ new->flags) & IRQF_TRIGGER_MASK) ||
> +		    (oldtype != (new->flags & IRQF_TRIGGER_MASK)) ||
>  		    ((old->flags ^ new->flags) & IRQF_ONESHOT))
>  			goto mismatch;

Looks sensible to me.

Acked-by: Marc Zyngier <marc.zyngier@....com>

	M.
-- 
Jazz is not dead, it just smell funny.