Re: 3.18.7-rt2: NOHZ_FULL warning at boot

[Carsten Emde <C.Emde@osadl.org>]

On 03/06/2015 07:13 PM, Sebastian Andrzej Siewior wrote:
> * Luis Claudio R. Goncalves | 2015-02-26 17:05:47 [-0300]:
>
>> I have been seeing the warning below at boot time on 3.18.7-rt2. Anybody
>> else seeing it?
>
> This should fix it.
>
> diff --git a/kernel/irq_work.c b/kernel/irq_work.c
> index 19c363a..0c64912 100644
> --- a/kernel/irq_work.c
> +++ b/kernel/irq_work.c
> @@ -71,6 +71,8 @@ void __weak arch_irq_work_raise(void)
>    */
>   bool irq_work_queue_on(struct irq_work *work, int cpu)
>   {
> +	bool raise_irqwork;
> +
>   	/* All work should have been flushed before going offline */
>   	WARN_ON_ONCE(cpu_is_offline(cpu));
>
> @@ -81,7 +83,19 @@ bool irq_work_queue_on(struct irq_work *work, int cpu)
>   	if (!irq_work_claim(work))
>   		return false;
>
> -	if (llist_add(&work->llnode, &per_cpu(raised_list, cpu)))
> +#ifdef CONFIG_PREEMPT_RT_FULL
> +	if (work->flags & IRQ_WORK_HARD_IRQ)
> +		raise_irqwork = llist_add(&work->llnode,
> +					  &per_cpu(hirq_work_list, cpu));
> +	else
> +		raise_irqwork = llist_add(&work->llnode,
> +					  &per_cpu(lazy_list, cpu));
> +#else
> +		raise_irqwork = llist_add(&work->llnode,
> +					  &per_cpu(raised_list, cpu));
> +#endif
> +
> +	if (raise_irqwork)
>   		arch_send_call_function_single_ipi(cpu);
>
>   	return true;
> @@ -101,19 +115,14 @@ bool irq_work_queue(struct irq_work *work)
>
>   #ifdef CONFIG_PREEMPT_RT_FULL
>   	if (work->flags & IRQ_WORK_HARD_IRQ) {
> -		if (llist_add(&work->llnode, this_cpu_ptr(&hirq_work_list))) {
> -			if (work->flags & IRQ_WORK_LAZY) {
> -				if (tick_nohz_tick_stopped())
> -					arch_irq_work_raise();
> -			} else {
> -				arch_irq_work_raise();
> -			}
> -		}
> -	/* If the work is "lazy", handle it from next tick if any */
> -	} else if (work->flags & IRQ_WORK_LAZY) {
> +		if (llist_add(&work->llnode, this_cpu_ptr(&hirq_work_list)))
> +			arch_irq_work_raise();
> +	} else {
> +		if (llist_add(&work->llnode, this_cpu_ptr(&lazy_list)))
> +			arch_irq_work_raise();
> +	}
>   #else
>   	if (work->flags & IRQ_WORK_LAZY) {
> -#endif
>   		if (llist_add(&work->llnode, this_cpu_ptr(&lazy_list)) &&
>   		    tick_nohz_tick_stopped())
>   			arch_irq_work_raise();
> @@ -121,6 +130,7 @@ bool irq_work_queue(struct irq_work *work)
>   		if (llist_add(&work->llnode, this_cpu_ptr(&raised_list)))
>   			arch_irq_work_raise();
>   	}
> +#endif
>
>   	preempt_enable();
>
> @@ -137,7 +147,8 @@ bool irq_work_needs_cpu(void)
>
>   	if (llist_empty(raised))
>   		if (llist_empty(lazy))
> -			return false;
> +			if (llist_empty(this_cpu_ptr(&hirq_work_list)))
> +				return false;
>
>   	/* All work should have been flushed before going offline */
>   	WARN_ON_ONCE(cpu_is_offline(smp_processor_id()));

I can confirm that the warning is no longer issued when this patch is 
applied.

Thanks,
	-Carsten.