Re: [PATCH v3 5/5] watchdog: qcom: Register pretimeout interrupt as NMI

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] Level-triggered bark interrupts will cause an infinite NMI storm and hard-lock the CPU.
--

commit 8f544329ecb4910dd7e00b39c0aabc3e32909823
Author: Mayank Rungta <mrungta@google.com>
Subject: watchdog: qcom: Register pretimeout interrupt as NMI

This commit modifies the qcom-wdt driver to attempt registering the watchdog
pretimeout bark interrupt as an NMI using request_nmi(). If NMI registration
is unsupported on the platform, it gracefully falls back to a standard
interrupt request.

> diff --git a/drivers/watchdog/qcom-wdt.c b/drivers/watchdog/qcom-wdt.c
> index 4eb1bf9790125..2849dcb1f717c 100644
> --- a/drivers/watchdog/qcom-wdt.c
> +++ b/drivers/watchdog/qcom-wdt.c

[ ... ]

> @@ -311,10 +321,25 @@ static int qcom_wdt_probe(struct platform_device *pdev)
>  		if (irq < 0 && irq != -ENXIO)
>  			return irq;
>  		if (irq > 0) {
> -			ret = devm_request_irq(dev, irq, qcom_wdt_isr, 0,
> -					       "wdt_bark", &wdt->wdd);
> -			if (ret)
> -				return ret;
> +			wdt->irq = irq;
> +			irq_flags = IRQF_PERCPU | IRQF_NOBALANCING |
> +				    IRQF_NO_AUTOEN | IRQF_NO_THREAD;
> +
> +			ret = request_nmi(irq, qcom_wdt_isr, irq_flags,
> +					  "wdt_bark", &wdt->wdd);

[Severity: High]
Does requesting this interrupt as an NMI risk an infinite NMI storm on 
platforms where the bark interrupt is level-triggered (e.g., QCS615 'talos',
QCM2290 'agatti', or 'shikra')?

Looking at qcom_wdt_isr(), the handler simply notifies the pretimeout and 
returns without acknowledging or clearing the hardware interrupt line:

static irqreturn_t qcom_wdt_isr(int irq, void *arg)
{
	struct watchdog_device *wdd = arg;

	watchdog_notify_pretimeout(wdd);

	return IRQ_HANDLED;
}

Since NMI handlers bypass the generic IRQ spurious interrupt protection that 
would normally mask an unhandled level-triggered interrupt, will this cause
an immediate re-trigger upon return and hard-lock the CPU when the 
pretimeout is reached?

[ ... ]

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260902-qcom-wdt-nmi-series-v3-0-f3999362a9ea@google.com?part=5