Re: [PATCH] Input: gpio-keys - fix a sleep while atomic with PREEMPT_RT

[Sebastian Andrzej Siewior <bigeasy@linutronix.de>]

On 2025-05-26 15:56:29 [+0200], Gatien Chevallier wrote:
> From: Fabrice Gasnier <fabrice.gasnier@foss.st.com>
> 
> When enabling PREEMPT_RT, the gpio_keys_irq_timer() callback runs in
> hard irq context, but the input_event() takes a spin_lock, which isn't
> allowed there as it is converted to a rt_spin_lock().
> 
> [ 4054.289999] BUG: sleeping function called from invalid context at kernel/locking/spinlock_rt.c:48
> [ 4054.290028] in_atomic(): 1, irqs_disabled(): 1, non_block: 0, pid: 0, name: swapper/0
> ...
> [ 4054.290195]  __might_resched+0x13c/0x1f4
> [ 4054.290209]  rt_spin_lock+0x54/0x11c
> [ 4054.290219]  input_event+0x48/0x80
> [ 4054.290230]  gpio_keys_irq_timer+0x4c/0x78
> [ 4054.290243]  __hrtimer_run_queues+0x1a4/0x438
> [ 4054.290257]  hrtimer_interrupt+0xe4/0x240
> [ 4054.290269]  arch_timer_handler_phys+0x2c/0x44
> [ 4054.290283]  handle_percpu_devid_irq+0x8c/0x14c
> [ 4054.290297]  handle_irq_desc+0x40/0x58
> [ 4054.290307]  generic_handle_domain_irq+0x1c/0x28
> [ 4054.290316]  gic_handle_irq+0x44/0xcc
> 
> Considering the gpio_keys_irq_isr() can run in any context, e.g. it can
> be threaded, it seems there's no point in requesting the timer isr to
> run in hard irq context.
> 
> So relax the hrtimer not to use the hard context. This requires the
> spin_lock to be added back in gpio_keys_irq_timer().

Why does it? This needs to be explained or it deserves an independent
patch/ fix. This flag change makes not difference on !PREEMPT_RT and so
should be the requirements for locking here.

> Fixes: 019002f20cb5 ("Input: gpio-keys - use hrtimer for release timer")
> Suggested-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> Signed-off-by: Fabrice Gasnier <fabrice.gasnier@foss.st.com>
> Signed-off-by: Gatien Chevallier <gatien.chevallier@foss.st.com>

Sebastian