Re: [RFC][4.1.15-rt17 PATCH] mm: swap: lru drain don't use workqueue with PREEMPT_RT_FULL

[Thomas Gleixner]

On Sun, 10 Jan 2016, l@xxxxxxxxxxx wrote:
> +#ifdef CONFIG_PREEMPT_RT_FULL
> +void lru_add_drain_all(void)
> +{
> +	static DEFINE_MUTEX(lock);
> +	int cpu;
> +
> +	mutex_lock(&lock);
> +	get_online_cpus();
> +
> +	for_each_online_cpu(cpu) {
> +		smp_call_function_single(cpu, lru_add_drain, NULL, 1);

How is that supposed to work on RT? Not at all, because lru_add_drain() takes
'sleeping' spinlocks and you cannot do that from hard interrupt context.

Enable lockdep (what you should have done before posting) and watch the
fireworks.

Thanks,

	tglx