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From: Thomas Gleixner <tglx@kernel.org>
To: Mayank Rungta <mrungta@google.com>, Wim Van Sebroeck
 <wim@linux-watchdog.org>, Guenter Roeck <linux@roeck-us.net>, Radu Rendec
 <radu@rendec.net>
Cc: linux-watchdog@vger.kernel.org, linux-kernel@vger.kernel.org,
 linux-arm-msm@vger.kernel.org, "Kirill A. Shutemov" <kas@kernel.org>,
 Douglas Anderson <dianders@chromium.org>, Mayank Rungta
 <mrungta@google.com>, Marc Zyngier <maz@kernel.org>
Subject: Re: [PATCH v3 1/5] genirq: Synchronize in-flight handlers during
 NMI teardown
In-Reply-To: <20260902-qcom-wdt-nmi-series-v3-1-f3999362a9ea@google.com>
References: <20260902-qcom-wdt-nmi-series-v3-0-f3999362a9ea@google.com>
 <20260902-qcom-wdt-nmi-series-v3-1-f3999362a9ea@google.com>
Date: Fri, 04 Sep 2026 11:17:42 +0200
Message-ID: <87fqzp8jex.ffs@fw13>
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On Wed, Sep 02 2026 at 18:54, Mayank Rungta wrote:
> diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
> index 2fbff2618a1e..a9973b61163a 100644
> --- a/kernel/irq/manage.c
> +++ b/kernel/irq/manage.c
> @@ -1379,6 +1379,14 @@ static bool irq_supports_nmi(struct irq_desc *desc)
>  	if (d->chip->irq_bus_lock || d->chip->irq_bus_sync_unlock)
>  		return false;
>  
> +	/*
> +	 * NMIs cannot set IRQD_IRQ_INPROGRESS because they cannot acquire
> +	 * spinlocks. Synchronous disable and teardown require querying the
> +	 * hardware state via ->irq_get_irqchip_state().
> +	 */
> +	if (!d->chip->irq_get_irqchip_state)
> +		return false;
> +
>  	return d->chip->flags & IRQCHIP_SUPPORTS_NMI;
>  }
>  
> @@ -2034,11 +2042,20 @@ static const void *__cleanup_nmi(unsigned int irq, struct irq_desc *desc)
>  	struct irqaction *action = NULL;
>  	const char *devname = NULL;
>  
> +	guard(mutex)(&desc->request_mutex);
> +
>  	scoped_guard(raw_spinlock_irqsave, &desc->lock) {
> -		irq_nmi_teardown(desc);
> +		irq_settings_clr_disable_unlazy(desc);
> +		irq_shutdown(desc);
> +	}
>  
> -		desc->istate &= ~IRQS_NMI;
> +	/*
> +	 * Ensure all in-flight NMI handlers on other CPUs complete before
> +	 * clearing desc->action or tearing down NMI state.
> +	 */
> +	__synchronize_hardirq(desc, true);

NMIs are strictly per CPU interrupts. So how is this supposed to work
correctly when looking at irqchip_state(ACTIVE) ?

Marc?