kernel/irq/cpuhotplug.c

/*
 * Generic cpu hotunplug interrupt migration code copied from the
 * arch/arm implementation
 *
 * Copyright (C) Russell King
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 */
#include <linux/interrupt.h>
#include <linux/ratelimit.h>
#include <linux/irq.h>
#include <linux/cpumask.h>

#include "internals.h"

static bool migrate_one_irq(struct irq_desc *desc)
{
	struct irq_data *d = irq_desc_get_irq_data(desc);
	const struct cpumask *affinity = d->common->affinity;
	struct irq_chip *c;
	bool ret = false;
	struct cpumask available_cpus;

	/*
	 * If this is a per-CPU interrupt, or the affinity does not
	 * include this CPU, then we have nothing to do.
	 */
	if (irqd_is_per_cpu(d) ||
	    !cpumask_test_cpu(smp_processor_id(), affinity))
		return false;

	cpumask_copy(&available_cpus, affinity);
	cpumask_andnot(&available_cpus, &available_cpus, cpu_isolated_mask);
	affinity = &available_cpus;

	if (cpumask_any_and(affinity, cpu_online_mask) >= nr_cpu_ids) {
		const struct cpumask *default_affinity;

		default_affinity = desc->affinity_hint ? : irq_default_affinity;

		/*
		 * The order of preference for selecting a fallback CPU is
		 *
		 * (1) online and un-isolated CPU from default affinity
		 * (2) online and un-isolated CPU
		 * (3) online CPU
		 */
		cpumask_andnot(&available_cpus, cpu_online_mask,
							cpu_isolated_mask);
		if (cpumask_intersects(&available_cpus, default_affinity))
			cpumask_and(&available_cpus, &available_cpus,
							default_affinity);
		else if (cpumask_empty(&available_cpus))
			affinity = cpu_online_mask;

		/*
		 * We are overriding the affinity with all online and
		 * un-isolated cpus. irq_set_affinity_locked() call
		 * below notify this mask to PM QOS affinity listener.
		 * That results in applying the CPU_DMA_LATENCY QOS
		 * to all the CPUs specified in the mask. But the low
		 * level irqchip driver sets the affinity of an irq
		 * to only one CPU. So pick only one CPU from the
		 * prepared mask while overriding the user affinity.
		 */
		affinity = cpumask_of(cpumask_any(affinity));
		ret = true;
	}

	c = irq_data_get_irq_chip(d);
	if (!c->irq_set_affinity) {
		pr_debug("IRQ%u: unable to set affinity\n", d->irq);
	} else {
		int r = irq_set_affinity_locked(d, affinity, false);
		if (r)
			pr_warn_ratelimited("IRQ%u: set affinity failed(%d).\n",
					    d->irq, r);
	}

	return ret;
}

/**
 * irq_migrate_all_off_this_cpu - Migrate irqs away from offline cpu
 *
 * The current CPU has been marked offline.  Migrate IRQs off this CPU.
 * If the affinity settings do not allow other CPUs, force them onto any
 * available CPU.
 *
 * Note: we must iterate over all IRQs, whether they have an attached
 * action structure or not, as we need to get chained interrupts too.
 */
void irq_migrate_all_off_this_cpu(void)
{
	unsigned int irq;
	struct irq_desc *desc;
	unsigned long flags;

	local_irq_save(flags);

	for_each_active_irq(irq) {
		bool affinity_broken;

		desc = irq_to_desc(irq);
		if (!desc)
			continue;

		raw_spin_lock(&desc->lock);
		affinity_broken = migrate_one_irq(desc);
		raw_spin_unlock(&desc->lock);

		if (affinity_broken)
			pr_warn_ratelimited("IRQ%u no longer affine to CPU%u\n",
					    irq, smp_processor_id());
	}

	local_irq_restore(flags);
}