/*
 * Copyright (C) 2010 Red Hat, Inc., Peter Zijlstra <pzijlstr@redhat.com>
 *
 * Provides a framework for enqueueing and running callbacks from hardirq
 * context. The enqueueing is NMI-safe.
 */

#include <linux/bug.h>
#include <linux/kernel.h>
#include <linux/export.h>
#include <linux/irq_work.h>
#include <linux/percpu.h>
#include <linux/hardirq.h>
#include <linux/irqflags.h>
#include <linux/sched.h>
#include <linux/tick.h>
#include <linux/cpu.h>
#include <linux/notifier.h>
#include <asm/processor.h>


static DEFINE_PER_CPU(struct llist_head, irq_work_list);
static DEFINE_PER_CPU(int, irq_work_raised);

/*
 * Claim the entry so that no one else will poke at it.
 */
static bool irq_work_claim(struct irq_work *work)
{
        unsigned long flags, oflags, nflags;

        /*
         * Start with our best wish as a premise but only trust any
         * flag value after cmpxchg() result.
         */
        flags = work->flags & ~IRQ_WORK_PENDING;
        for (;;) {
                nflags = flags | IRQ_WORK_FLAGS;
                oflags = cmpxchg(&work->flags, flags, nflags);
                if (oflags == flags)
                        break;
                if (oflags & IRQ_WORK_PENDING)
                        return false;
                flags = oflags;
                cpu_relax();
        }

        return true;
}

void __weak arch_irq_work_raise(void)
{
        /*
         * Lame architectures will get the timer tick callback
         */
}

/*
 * Enqueue the irq_work @entry unless it's already pending
 * somewhere.
 *
 * Can be re-enqueued while the callback is still in progress.
 */
void irq_work_queue(struct irq_work *work)
{
        /* Only queue if not already pending */
        if (!irq_work_claim(work))
                return;

        /* Queue the entry and raise the IPI if needed. */
        preempt_disable();

        llist_add(&work->llnode, &__get_cpu_var(irq_work_list));

        /*
         * If the work is not "lazy" or the tick is stopped, raise the irq
         * work interrupt (if supported by the arch), otherwise, just wait
         * for the next tick.
         */
        if (!(work->flags & IRQ_WORK_LAZY) || tick_nohz_tick_stopped()) {
                if (!this_cpu_cmpxchg(irq_work_raised, 0, 1))
                        arch_irq_work_raise();
        }

        preempt_enable();
}
EXPORT_SYMBOL_GPL(irq_work_queue);

bool irq_work_needs_cpu(void)
{
        struct llist_head *this_list;

        this_list = &__get_cpu_var(irq_work_list);
        if (llist_empty(this_list))
                return false;

        /* All work should have been flushed before going offline */
        WARN_ON_ONCE(cpu_is_offline(smp_processor_id()));

        return true;
}

static void __irq_work_run(void)
{
        unsigned long flags;
        struct irq_work *work;
        struct llist_head *this_list;
        struct llist_node *llnode;


        /*
         * Reset the "raised" state right before we check the list because
         * an NMI may enqueue after we find the list empty from the runner.
         */
        __this_cpu_write(irq_work_raised, 0);
        barrier();

        this_list = &__get_cpu_var(irq_work_list);
        if (llist_empty(this_list))
                return;

        BUG_ON(!irqs_disabled());

        llnode = llist_del_all(this_list);
        while (llnode != NULL) {
                work = llist_entry(llnode, struct irq_work, llnode);

                llnode = llist_next(llnode);

                /*
                 * Clear the PENDING bit, after this point the @work
                 * can be re-used.
                 * Make it immediately visible so that other CPUs trying
                 * to claim that work don't rely on us to handle their data
                 * while we are in the middle of the func.
                 */
                flags = work->flags & ~IRQ_WORK_PENDING;
                xchg(&work->flags, flags);

                work->func(work);
                /*
                 * Clear the BUSY bit and return to the free state if
                 * no-one else claimed it meanwhile.
                 */
                (void)cmpxchg(&work->flags, flags, flags & ~IRQ_WORK_BUSY);
        }
}

/*
 * Run the irq_work entries on this cpu. Requires to be ran from hardirq
 * context with local IRQs disabled.
 */
void irq_work_run(void)
{
        BUG_ON(!in_irq());
        __irq_work_run();
}
EXPORT_SYMBOL_GPL(irq_work_run);

/*
 * Synchronize against the irq_work @entry, ensures the entry is not
 * currently in use.
 */
void irq_work_sync(struct irq_work *work)
{
        WARN_ON_ONCE(irqs_disabled());

        while (work->flags & IRQ_WORK_BUSY)
                cpu_relax();
}
EXPORT_SYMBOL_GPL(irq_work_sync);

#ifdef CONFIG_HOTPLUG_CPU
static int irq_work_cpu_notify(struct notifier_block *self,
                               unsigned long action, void *hcpu)
{
        long cpu = (long)hcpu;

        switch (action) {
        case CPU_DYING:
                /* Called from stop_machine */
                if (WARN_ON_ONCE(cpu != smp_processor_id()))
                        break;
                __irq_work_run();
                break;
        default:
                break;
        }
        return NOTIFY_OK;
}

static struct notifier_block cpu_notify;

static __init int irq_work_init_cpu_notifier(void)
{
        cpu_notify.notifier_call = irq_work_cpu_notify;
        cpu_notify.priority = 0;
        register_cpu_notifier(&cpu_notify);
        return 0;
}
device_initcall(irq_work_init_cpu_notifier);

#endif /* CONFIG_HOTPLUG_CPU */