linux-kernel - Re: [PATCH] counter: interrupt-cnt: Drop IRQF_NO

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Message-ID: <aRw4mIZpWdsr9exb@pengutronix.de>
Date: Tue, 18 Nov 2025 10:12:56 +0100
From: Oleksij Rempel <o.rempel@...gutronix.de>
To: "A. Sverdlin" <alexander.sverdlin@...mens.com>
Cc: Pengutronix Kernel Team <kernel@...gutronix.de>,
	linux-iio@...r.kernel.org, Ahmad Fatoum <a.fatoum@...gutronix.de>,
	"Paul E . McKenney" <paulmck@...nel.org>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	Jonathan Cameron <Jonathan.Cameron@...wei.com>,
	William Breathitt Gray <wbg@...nel.org>
Subject: Re: [PATCH] counter: interrupt-cnt: Drop IRQF_NO_THREAD flag

Hi Alexander,

On Tue, Nov 18, 2025 at 09:35:48AM +0100, A. Sverdlin wrote:
> From: Alexander Sverdlin <alexander.sverdlin@...mens.com>
> 
> An IRQ handler can either be IRQF_NO_THREAD or acquire spinlock_t, as
> CONFIG_PROVE_RAW_LOCK_NESTING warns:
> =============================
> [ BUG: Invalid wait context ]
> 6.18.0-rc1+git... #1
> -----------------------------
> some-user-space-process/1251 is trying to lock:
> (&counter->events_list_lock){....}-{3:3}, at: counter_push_event [counter]
> other info that might help us debug this:
> context-{2:2}
> no locks held by some-user-space-process/....
> stack backtrace:
> CPU: 0 UID: 0 PID: 1251 Comm: some-user-space-process 6.18.0-rc1+git... #1 PREEMPT
> Call trace:
>  show_stack (C)
>  dump_stack_lvl
>  dump_stack
>  __lock_acquire
>  lock_acquire
>  _raw_spin_lock_irqsave
>  counter_push_event [counter]
>  interrupt_cnt_isr [interrupt_cnt]
>  __handle_irq_event_percpu
>  handle_irq_event
>  handle_simple_irq
>  handle_irq_desc
>  generic_handle_domain_irq
>  gpio_irq_handler
>  handle_irq_desc
>  generic_handle_domain_irq
>  gic_handle_irq
>  call_on_irq_stack
>  do_interrupt_handler
>  el0_interrupt
>  __el0_irq_handler_common
>  el0t_64_irq_handler
>  el0t_64_irq
> 
> ... and Sebastian correctly points out. Remove IRQF_NO_THREAD as an
> alternative to switching to raw_spinlock_t, because the latter would limit
> all potential nested locks to raw_spinlock_t only.
> 
> Cc: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> Cc: stable@...r.kernel.org
> Link: https://lore.kernel.org/all/20251117151314.xwLAZrWY@linutronix.de/
> Fixes: a55ebd47f21f ("counter: add IRQ or GPIO based counter")
> Signed-off-by: Alexander Sverdlin <alexander.sverdlin@...mens.com>
> ---
>  drivers/counter/interrupt-cnt.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/drivers/counter/interrupt-cnt.c b/drivers/counter/interrupt-cnt.c
> index 6c0c1d2d7027d..e6100b5fb082e 100644
> --- a/drivers/counter/interrupt-cnt.c
> +++ b/drivers/counter/interrupt-cnt.c
> @@ -229,8 +229,7 @@ static int interrupt_cnt_probe(struct platform_device *pdev)
>  
>  	irq_set_status_flags(priv->irq, IRQ_NOAUTOEN);
>  	ret = devm_request_irq(dev, priv->irq, interrupt_cnt_isr,
> -			       IRQF_TRIGGER_RISING | IRQF_NO_THREAD,
> -			       dev_name(dev), counter);
> +			       IRQF_TRIGGER_RISING, dev_name(dev), counter);
>  	if (ret)
>  		return ret;
>  

Hm, I guess it will break the requirement to handle at least 10kHz
interrupts. May be we should move only counter_push_event() to the
thread? or using delayed worker?

Right now I do not have needed system for testing to come with better
proposal.

Best Regards,
Oleksij
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