/*
 * Copyright (C) 2010 Red Hat, Inc., Peter Zijlstra
 *
 * 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 <linux/smp.h>
#include <asm/processor.h>


static DEFINE_PER_CPU(struct llist_head, raised_list);
static DEFINE_PER_CPU(struct llist_head, lazy_list);

/*
 * 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
         */
}

#ifdef CONFIG_SMP
/*
 * Enqueue the irq_work @work on @cpu unless it's already pending
 * somewhere.
 *
 * Can be re-enqueued while the callback is still in progress.
 */
bool irq_work_queue_on(struct irq_work *work, int cpu)
{
        /* All work should have been flushed before going offline */
        WARN_ON_ONCE(cpu_is_offline(cpu));

        /* Arch remote IPI send/receive backend aren't NMI safe */
        WARN_ON_ONCE(in_nmi());

        /* Only queue if not already pending */
        if (!irq_work_claim(work))
                return false;

        if (llist_add(&work->llnode, &per_cpu(raised_list, cpu)))
                arch_send_call_function_single_ipi(cpu);

        return true;
}
EXPORT_SYMBOL_GPL(irq_work_queue_on);
#endif

/* Enqueue the irq work @work on the current CPU */
bool irq_work_queue(struct irq_work *work)
{
        /* Only queue if not already pending */
        if (!irq_work_claim(work))
                return false;

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

        /* If the work is "lazy", handle it from next tick if any */
        if (work->flags & IRQ_WORK_LAZY) {
                if (llist_add(&work->llnode, this_cpu_ptr(&lazy_list)) &&
                    tick_nohz_tick_stopped())
                        arch_irq_work_raise();
        } else {
                if (llist_add(&work->llnode, this_cpu_ptr(&raised_list)))
                        arch_irq_work_raise();
        }

        preempt_enable();

        return true;
}
EXPORT_SYMBOL_GPL(irq_work_queue);

bool irq_work_needs_cpu(void)
{
        struct llist_head *raised, *lazy;

        raised = this_cpu_ptr(&raised_list);
        lazy = this_cpu_ptr(&lazy_list);

        if (llist_empty(raised) || arch_irq_work_has_interrupt())
                if (llist_empty(lazy))
                        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_list(struct llist_head *list)
{
        unsigned long flags;
        struct irq_work *work;
        struct llist_node *llnode;

        BUG_ON(!irqs_disabled());

        if (llist_empty(list))
                return;

        llnode = llist_del_all(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);
        }
}

/*
 * hotplug calls this through:
 *  hotplug_cfd() -> flush_smp_call_function_queue()
 */
void irq_work_run(void)
{
        irq_work_run_list(this_cpu_ptr(&raised_list));
        irq_work_run_list(this_cpu_ptr(&lazy_list));
}
EXPORT_SYMBOL_GPL(irq_work_run);

void irq_work_tick(void)
{
        struct llist_head *raised = this_cpu_ptr(&raised_list);

        if (!llist_empty(raised) && !arch_irq_work_has_interrupt())
                irq_work_run_list(raised);
        irq_work_run_list(this_cpu_ptr(&lazy_list));
}

/*
 * 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);