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

From	Thomas Gleixner <tglx@linutronix.de>
Newsgroups	linux.kernel
Subject	Re: [RFC][4.1.15-rt17 PATCH] mm: swap: lru drain don't use workqueue with PREEMPT_RT_FULL
Date	2016-01-12 13:10 +0100
Message-ID	<qQ5VT-FV-1@gated-at.bofh.it> (permalink)
References	<qPyQh-3dt-3@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On Sun, 10 Jan 2016, l@dorileo.org 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

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[RFC][4.1.15-rt17 PATCH] mm: swap: lru drain don't use workqueue with PREEMPT_RT_FULL l@dorileo.org - 2016-01-11 01:50 +0100
  Re: [RFC][4.1.15-rt17 PATCH] mm: swap: lru drain don't use workqueue  with PREEMPT_RT_FULL Thomas Gleixner <tglx@linutronix.de> - 2016-01-12 13:10 +0100

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