[PATCH v3 24/41] powerpc: add set_dec_or_work API for safely updating decrementer

[Alexey Kardashevskiy]

On 06/03/2021 02:06, Nicholas Piggin wrote:
> Decrementer updates must always check for new irq work to avoid an
> irq work decrementer interrupt being lost.
> 
> Add an API for this in the timer code so callers don't have to care
> about details.
> 
> Signed-off-by: Nicholas Piggin <npiggin at gmail.com>

Reviewed-by: Alexey Kardashevskiy <aik at ozlabs.ru>


> ---
>   arch/powerpc/include/asm/time.h |  9 +++++++++
>   arch/powerpc/kernel/time.c      | 20 +++++++++++---------
>   2 files changed, 20 insertions(+), 9 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/time.h b/arch/powerpc/include/asm/time.h
> index 0128cd9769bc..d62bde57bf02 100644
> --- a/arch/powerpc/include/asm/time.h
> +++ b/arch/powerpc/include/asm/time.h
> @@ -78,6 +78,15 @@ static inline void set_dec(u64 val)
>   		mtspr(SPRN_DEC, val - 1);
>   }
>   
> +#ifdef CONFIG_IRQ_WORK
> +void set_dec_or_work(u64 val);
> +#else
> +static inline void set_dec_or_work(u64 val)
> +{
> +	set_dec(val);
> +}
> +#endif
> +
>   static inline unsigned long tb_ticks_since(unsigned long tstamp)
>   {
>   	return mftb() - tstamp;
> diff --git a/arch/powerpc/kernel/time.c b/arch/powerpc/kernel/time.c
> index c5d524622c17..341cc8442e5e 100644
> --- a/arch/powerpc/kernel/time.c
> +++ b/arch/powerpc/kernel/time.c
> @@ -562,6 +562,15 @@ void arch_irq_work_raise(void)
>   	preempt_enable();
>   }
>   
> +void set_dec_or_work(u64 val)
> +{
> +	set_dec(val);
> +	/* We may have raced with new irq work */
> +	if (unlikely(test_irq_work_pending()))
> +		set_dec(1);
> +}
> +EXPORT_SYMBOL_GPL(set_dec_or_work);
> +
>   #else  /* CONFIG_IRQ_WORK */
>   
>   #define test_irq_work_pending()	0
> @@ -629,10 +638,7 @@ DEFINE_INTERRUPT_HANDLER_ASYNC(timer_interrupt)
>   	} else {
>   		now = *next_tb - now;
>   		if (now <= decrementer_max)
> -			set_dec(now);
> -		/* We may have raced with new irq work */
> -		if (test_irq_work_pending())
> -			set_dec(1);
> +			set_dec_or_work(now);
>   		__this_cpu_inc(irq_stat.timer_irqs_others);
>   	}
>   
> @@ -874,11 +880,7 @@ static int decrementer_set_next_event(unsigned long evt,
>   				      struct clock_event_device *dev)
>   {
>   	__this_cpu_write(decrementers_next_tb, get_tb() + evt);
> -	set_dec(evt);
> -
> -	/* We may have raced with new irq work */
> -	if (test_irq_work_pending())
> -		set_dec(1);
> +	set_dec_or_work(evt);
>   
>   	return 0;
>   }
> 

-- 
Alexey