linux-kernel - Re: [PATCH] Input: gpio-keys - fix a sleep while atomic with PREEMPT

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Message-ID: <20250527144159.Dcstk83c@linutronix.de>
Date: Tue, 27 May 2025 16:41:59 +0200
From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To: Gatien CHEVALLIER <gatien.chevallier@...s.st.com>
Cc: Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Clark Williams <clrkwllms@...nel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Paul Cercueil <paul@...pouillou.net>, linux-input@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-rt-devel@...ts.linux.dev,
	Fabrice Gasnier <fabrice.gasnier@...s.st.com>
Subject: Re: [PATCH] Input: gpio-keys - fix a sleep while atomic with
 PREEMPT_RT

On 2025-05-27 15:36:37 [+0200], Gatien CHEVALLIER wrote:
> Hello Sebastian,
Hello Gatien,

> Can you elaborate on "This flag change makes not difference on
> !PREEMPT_RT" please? IIUC,this makes the callback not run in hard IRQ
> context, even in !PREEMPT_RT, no?

If you set
- HRTIMER_MODE_REL_HARD
  then the callback runs in
  - hardirq context on !PREEMPT_RT
  - hardirq context on PREEMPT_RT.

- HRTIMER_MODE_REL
  then the callback runs in
  - hardirq context on !PREEMPT_RT
  - preemptible softirq on PREEMPT_RT.

- HRTIMER_MODE_REL_SOFT
  then the callback runs in
  - softirq context on !PREEMPT_RT
  - preemptible softirq on PREEMPT_RT.

Therefore if you switch HRTIMER_MODE_REL_HARD -> HRTIMER_MODE_REL then
it is a nop on !PREEMPT_RT.

> Regarding the need of the spin_lock: gpio_keys_irq_timer() and
> gpio_keys_irq_isr() appear to access the same resources. Can't we
> have a concurrent access on it from:
> HR timer interrupt // GPIO interrupt?

Yes, it could.

> But looking back at the patch, this situation does not depend on
> the HRTIMER_MODE_REL_HARD flag. So maybe it should be addressed
> separately.

Yes, please.

> On the other hand, I should use the new
> guard(spinlock_irqsave)(&bdata->lock);

Yes, please. The other instance already does so.

Sebastian