irq_work.c

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/*
 * Copyright (C) 2010 Red Hat, Inc., Peter Zijlstra <[email protected]>
 *
 * 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 <asm/processor.h>

/*
 * An entry can be in one of four states:
 *
 * free      NULL, 0 -> {claimed}       : free to be used
 * claimed   NULL, 3 -> {pending}       : claimed to be enqueued
 * pending   next, 3 -> {busy}          : queued, pending callback
 * busy      NULL, 2 -> {free, claimed} : callback in progress, can be claimed
 */

#define IRQ_WORK_PENDING    1UL
#define IRQ_WORK_BUSY       2UL
#define IRQ_WORK_FLAGS      3UL

static DEFINE_PER_CPU(struct llist_head, irq_work_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, nflags;

    for (;;) {
        flags = work->flags;
        if (flags & IRQ_WORK_PENDING)
            return false;
        nflags = flags | IRQ_WORK_FLAGS;
        if (cmpxchg(&work->flags, flags, nflags) == flags)
            break;
        cpu_relax();
    }

    return true;
}

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

/*
 * Queue the entry and raise the IPI if needed.
 */
static void __irq_work_queue(struct irq_work *work)
{
    bool empty;

    preempt_disable();

    empty = llist_add(&work->llnode, &__get_cpu_var(irq_work_list));
    /* The list was empty, raise self-interrupt to start processing. */
    if (empty)
        arch_irq_work_raise();

    preempt_enable();
}

/*
 * Enqueue the irq_work @entry, returns true on success, failure when the
 * @entry was already enqueued by someone else.
 *
 * Can be re-enqueued while the callback is still in progress.
 */
bool irq_work_queue(struct irq_work *work)
{
    if (!irq_work_claim(work)) {
        /*
         * Already enqueued, can't do!
         */
        return false;
    }

    __irq_work_queue(work);
    return true;
}
EXPORT_SYMBOL_GPL(irq_work_queue);

/*
 * Run the irq_work entries on this cpu. Requires to be ran from hardirq
 * context with local IRQs disabled.
 */
void irq_work_run(void)
{
    struct irq_work *work;
    struct llist_head *this_list;
    struct llist_node *llnode;

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

    BUG_ON(!in_irq());
    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.
         */
        work->flags = IRQ_WORK_BUSY;
        work->func(work);
        /*
         * Clear the BUSY bit and return to the free state if
         * no-one else claimed it meanwhile.
         */
        (void)cmpxchg(&work->flags, IRQ_WORK_BUSY, 0);
    }
}
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);