// SPDX-License-Identifier: GPL-2.0-only
/*
 * 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>
#include <linux/kasan.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)
{
        int oflags;

        oflags = atomic_fetch_or(IRQ_WORK_CLAIMED | CSD_TYPE_IRQ_WORK, &work->node.a_flags);
        /*
         * If the work is already pending, no need to raise the IPI.
         * The pairing smp_mb() in irq_work_single() makes sure
         * everything we did before is visible.
         */
        if (oflags & IRQ_WORK_PENDING)
                return false;
        return true;
}

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

/* Enqueue on current CPU, work must already be claimed and preempt disabled */
static void __irq_work_queue_local(struct irq_work *work)
{
        /* If the work is "lazy", handle it from next tick if any */
        if (atomic_read(&work->node.a_flags) & IRQ_WORK_LAZY) {
                if (llist_add(&work->node.llist, this_cpu_ptr(&lazy_list)) &&
                    tick_nohz_tick_stopped())
                        arch_irq_work_raise();
        } else {
                if (llist_add(&work->node.llist, this_cpu_ptr(&raised_list)))
                        arch_irq_work_raise();
        }
}

/* 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();
        __irq_work_queue_local(work);
        preempt_enable();

        return true;
}
EXPORT_SYMBOL_GPL(irq_work_queue);

/*
 * 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)
{
#ifndef CONFIG_SMP
        return irq_work_queue(work);

#else /* CONFIG_SMP: */
        /* All work should have been flushed before going offline */
        WARN_ON_ONCE(cpu_is_offline(cpu));

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

        kasan_record_aux_stack(work);

        preempt_disable();
        if (cpu != smp_processor_id()) {
                /* Arch remote IPI send/receive backend aren't NMI safe */
                WARN_ON_ONCE(in_nmi());
                __smp_call_single_queue(cpu, &work->node.llist);
        } else {
                __irq_work_queue_local(work);
        }
        preempt_enable();

        return true;
#endif /* CONFIG_SMP */
}


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;
}

void irq_work_single(void *arg)
{
        struct irq_work *work = arg;
        int flags;

        /*
         * Clear the PENDING bit, after this point the @work can be re-used.
         * The PENDING bit acts as a lock, and we own it, so we can clear it
         * without atomic ops.
         */
        flags = atomic_read(&work->node.a_flags);
        flags &= ~IRQ_WORK_PENDING;
        atomic_set(&work->node.a_flags, flags);

        /*
         * See irq_work_claim().
         */
        smp_mb();

        lockdep_irq_work_enter(flags);
        work->func(work);
        lockdep_irq_work_exit(flags);

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

static void irq_work_run_list(struct llist_head *list)
{
        struct irq_work *work, *tmp;
        struct llist_node *llnode;

        BUG_ON(!irqs_disabled());

        if (llist_empty(list))
                return;

        llnode = llist_del_all(list);
        llist_for_each_entry_safe(work, tmp, llnode, node.llist)
                irq_work_single(work);
}

/*
 * 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)
{
        lockdep_assert_irqs_enabled();

        while (irq_work_is_busy(work))
                cpu_relax();
}
EXPORT_SYMBOL_GPL(irq_work_sync);