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

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Message-ID: <20251118103022.1FY-iKhs@linutronix.de>
Date: Tue, 18 Nov 2025 11:30:22 +0100
From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To: "A. Sverdlin" <alexander.sverdlin@...mens.com>
Cc: Oleksij Rempel <o.rempel@...gutronix.de>,
	Pengutronix Kernel Team <kernel@...gutronix.de>,
	linux-iio@...r.kernel.org, William Breathitt Gray <wbg@...nel.org>,
	Jonathan Cameron <Jonathan.Cameron@...wei.com>,
	Ahmad Fatoum <a.fatoum@...gutronix.de>,
	linux-kernel@...r.kernel.org,
	"Paul E . McKenney" <paulmck@...nel.org>, stable@...r.kernel.org
Subject: Re: [PATCH] counter: interrupt-cnt: Drop IRQF_NO_THREAD flag

On 2025-11-18 09:35:48 [+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

I would recommend to trim the commit message to what is required in
terms of describing the problem you faced. This backtrace contains a lot
noise and is not relevant.
The problem is that IRQF_NO_THREAD does not allow threading the
interrupt handler. Using spinlock_t in non-threaded (atomic) context is
not allowed and is reported by lockdep.

> ... 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.
Correct.

Reviewed-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>

> 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>

Sebastian