Re: [PATCH] clocksource/i8253: Acquire the lock disabled interrupts.

[Thomas Gleixner <tglx@linutronix.de>]

On Fri, Apr 04 2025 at 15:31, Sebastian Andrzej Siewior wrote:
> On x86 during boot, clockevent_i8253_disable() can be invoked via
> x86_late_time_init -> hpet_time_init() -> pit_timer_init() which happens
> with enabled interrupts.
> If some of the old i8253 hardware is actually used then lockdep will
> notice that i8253_lock is used in hardirq context. This causes lockdep
> to complain because it observed the lock being acquired with enabled
> interrupts and in hardirq context.
>
> Make clockevent_i8253_disable() acquire the lock with disabled
> interrupts.

This sentence does not make sense. I'll fix it up...

> Fixes: c8c4076723dac ("x86/timer: Skip PIT initialization on modern chipsets")
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> ---
>  drivers/clocksource/i8253.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/clocksource/i8253.c b/drivers/clocksource/i8253.c
> index 39f7c2d736d16..67dcd9c8f1875 100644
> --- a/drivers/clocksource/i8253.c
> +++ b/drivers/clocksource/i8253.c
> @@ -103,8 +103,9 @@ int __init clocksource_i8253_init(void)
>  #ifdef CONFIG_CLKEVT_I8253
>  void clockevent_i8253_disable(void)
>  {
> -	raw_spin_lock(&i8253_lock);
> +	unsigned long flags;
>  
> +	raw_spin_lock_irqsave(&i8253_lock, flags);
>  	/*
>  	 * Writing the MODE register should stop the counter, according to
>  	 * the datasheet. This appears to work on real hardware (well, on
> @@ -133,7 +134,7 @@ void clockevent_i8253_disable(void)
>  
>  	outb_p(0x30, PIT_MODE);
>  
> -	raw_spin_unlock(&i8253_lock);
> +	raw_spin_unlock_irqrestore(&i8253_lock, flags);
>  }
>  
>  static int pit_shutdown(struct clock_event_device *evt)