LXR linux/kernel/irq

   1/*
   2 * Copyright (C) 2010 Red Hat, Inc., Peter Zijlstra <pzijlstr@redhat.com>
   3 *
   4 * Provides a framework for enqueueing and running callbacks from hardirq
   5 * context. The enqueueing is NMI-safe.
   6 */
   7
   8#include <linux/kernel.h>
   9#include <linux/export.h>
  10#include <linux/irq_work.h>
  11#include <linux/percpu.h>
  12#include <linux/hardirq.h>
  13#include <asm/processor.h>
  14
  15/*
  16 * An entry can be in one of four states:
  17 *
  18 * free      NULL, 0 -> {claimed}       : free to be used
  19 * claimed   NULL, 3 -> {pending}       : claimed to be enqueued
  20 * pending   next, 3 -> {busy}          : queued, pending callback
  21 * busy      NULL, 2 -> {free, claimed} : callback in progress, can be claimed
  22 */
  23
  24#define IRQ_WORK_PENDING        1UL
  25#define IRQ_WORK_BUSY           2UL
  26#define IRQ_WORK_FLAGS          3UL
  27
  28static DEFINE_PER_CPU(struct llist_head, irq_work_list);
  29
  30/*
  31 * Claim the entry so that no one else will poke at it.
  32 */
  33static bool irq_work_claim(struct irq_work *work)
  34{
  35        unsigned long flags, nflags;
  36
  37        for (;;) {
  38                flags = work->flags;
  39                if (flags & IRQ_WORK_PENDING)
  40                        return false;
  41                nflags = flags | IRQ_WORK_FLAGS;
  42                if (cmpxchg(&work->flags, flags, nflags) == flags)
  43                        break;
  44                cpu_relax();
  45        }
  46
  47        return true;
  48}
  49
  50void __weak arch_irq_work_raise(void)
  51{
  52        /*
  53         * Lame architectures will get the timer tick callback
  54         */
  55}
  56
  57/*
  58 * Queue the entry and raise the IPI if needed.
  59 */
  60static void __irq_work_queue(struct irq_work *work)
  61{
  62        bool empty;
  63
  64        preempt_disable();
  65
  66        empty = llist_add(&work->llnode, &__get_cpu_var(irq_work_list));
  67        /* The list was empty, raise self-interrupt to start processing. */
  68        if (empty)
  69                arch_irq_work_raise();
  70
  71        preempt_enable();
  72}
  73
  74/*
  75 * Enqueue the irq_work @entry, returns true on success, failure when the
  76 * @entry was already enqueued by someone else.
  77 *
  78 * Can be re-enqueued while the callback is still in progress.
  79 */
  80bool irq_work_queue(struct irq_work *work)
  81{
  82        if (!irq_work_claim(work)) {
  83                /*
  84                 * Already enqueued, can't do!
  85                 */
  86                return false;
  87        }
  88
  89        __irq_work_queue(work);
  90        return true;
  91}
  92EXPORT_SYMBOL_GPL(irq_work_queue);
  93
  94/*
  95 * Run the irq_work entries on this cpu. Requires to be ran from hardirq
  96 * context with local IRQs disabled.
  97 */
  98void irq_work_run(void)
  99{
 100        struct irq_work *work;
 101        struct llist_head *this_list;
 102        struct llist_node *llnode;
 103
 104        this_list = &__get_cpu_var(irq_work_list);
 105        if (llist_empty(this_list))
 106                return;
 107
 108        BUG_ON(!in_irq());
 109        BUG_ON(!irqs_disabled());
 110
 111        llnode = llist_del_all(this_list);
 112        while (llnode != NULL) {
 113                work = llist_entry(llnode, struct irq_work, llnode);
 114
 115                llnode = llist_next(llnode);
 116
 117                /*
 118                 * Clear the PENDING bit, after this point the @work
 119                 * can be re-used.
 120                 */
 121                work->flags = IRQ_WORK_BUSY;
 122                work->func(work);
 123                /*
 124                 * Clear the BUSY bit and return to the free state if
 125                 * no-one else claimed it meanwhile.
 126                 */
 127                (void)cmpxchg(&work->flags, IRQ_WORK_BUSY, 0);
 128        }
 129}
 130EXPORT_SYMBOL_GPL(irq_work_run);
 131
 132/*
 133 * Synchronize against the irq_work @entry, ensures the entry is not
 134 * currently in use.
 135 */
 136void irq_work_sync(struct irq_work *work)
 137{
 138        WARN_ON_ONCE(irqs_disabled());
 139
 140        while (work->flags & IRQ_WORK_BUSY)
 141                cpu_relax();
 142}
 143EXPORT_SYMBOL_GPL(irq_work_sync);
 144