Re: [PATCH 3/3] irqchip: renesas-rzg2l: Fix irq storm with edge trigger detection for TINT

[Marc Zyngier <maz@kernel.org>]

On Mon, 18 Sep 2023 13:24:11 +0100,
Biju Das <biju.das.jz@bp.renesas.com> wrote:
> 
> In case of edge trigger detection, enabling the TINT source causes a
> phantum interrupt that leads to irq storm. So clear the phantum interrupt
> in rzg2l_irqc_irq_enable().
> 
> This issue is observed when the irq handler disables the interrupts using
> disable_irq_nosync() and scheduling a work queue and in the work queue,
> re-enabling the interrupt with enable_irq().
> 
> Fixes: 3fed09559cd8 ("irqchip: Add RZ/G2L IA55 Interrupt Controller driver")
> Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
> Tested-by: Claudiu Beznea <claudiu.beznea.uj@bp.renesas.com>
> ---
>  drivers/irqchip/irq-renesas-rzg2l.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/irqchip/irq-renesas-rzg2l.c b/drivers/irqchip/irq-renesas-rzg2l.c
> index 33a22bafedcd..78a9e90512a6 100644
> --- a/drivers/irqchip/irq-renesas-rzg2l.c
> +++ b/drivers/irqchip/irq-renesas-rzg2l.c
> @@ -144,6 +144,12 @@ static void rzg2l_irqc_irq_enable(struct irq_data *d)
>  		reg = readl_relaxed(priv->base + TSSR(tssr_index));
>  		reg |= (TIEN | tint) << TSSEL_SHIFT(tssr_offset);
>  		writel_relaxed(reg, priv->base + TSSR(tssr_index));
> +		/*
> +		 * In case of edge trigger detection, enabling the TINT source
> +		 * cause a phantum interrupt that leads to irq storm. So clear
> +		 * the phantum interrupt.
> +		 */
> +		rzg2l_tint_eoi(d);

This looks incredibly unsafe. disable_irq()+enable_irq() with an
interrupt being made pending in the middle, and you've lost that
interrupt.

What prevents this scenario?

	M.

-- 
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