linux/kernel/irq_work.c
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   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/module.h>
  10#include <linux/irq_work.h>
  11#include <linux/hardirq.h>
  12
  13/*
  14 * An entry can be in one of four states:
  15 *
  16 * free      NULL, 0 -> {claimed}       : free to be used
  17 * claimed   NULL, 3 -> {pending}       : claimed to be enqueued
  18 * pending   next, 3 -> {busy}          : queued, pending callback
  19 * busy      NULL, 2 -> {free, claimed} : callback in progress, can be claimed
  20 *
  21 * We use the lower two bits of the next pointer to keep PENDING and BUSY
  22 * flags.
  23 */
  24
  25#define IRQ_WORK_PENDING        1UL
  26#define IRQ_WORK_BUSY           2UL
  27#define IRQ_WORK_FLAGS          3UL
  28
  29static inline bool irq_work_is_set(struct irq_work *entry, int flags)
  30{
  31        return (unsigned long)entry->next & flags;
  32}
  33
  34static inline struct irq_work *irq_work_next(struct irq_work *entry)
  35{
  36        unsigned long next = (unsigned long)entry->next;
  37        next &= ~IRQ_WORK_FLAGS;
  38        return (struct irq_work *)next;
  39}
  40
  41static inline struct irq_work *next_flags(struct irq_work *entry, int flags)
  42{
  43        unsigned long next = (unsigned long)entry;
  44        next |= flags;
  45        return (struct irq_work *)next;
  46}
  47
  48static DEFINE_PER_CPU(struct irq_work *, irq_work_list);
  49
  50/*
  51 * Claim the entry so that no one else will poke at it.
  52 */
  53static bool irq_work_claim(struct irq_work *entry)
  54{
  55        struct irq_work *next, *nflags;
  56
  57        do {
  58                next = entry->next;
  59                if ((unsigned long)next & IRQ_WORK_PENDING)
  60                        return false;
  61                nflags = next_flags(next, IRQ_WORK_FLAGS);
  62        } while (cmpxchg(&entry->next, next, nflags) != next);
  63
  64        return true;
  65}
  66
  67
  68void __weak arch_irq_work_raise(void)
  69{
  70        /*
  71         * Lame architectures will get the timer tick callback
  72         */
  73}
  74
  75/*
  76 * Queue the entry and raise the IPI if needed.
  77 */
  78static void __irq_work_queue(struct irq_work *entry)
  79{
  80        struct irq_work *next;
  81
  82        preempt_disable();
  83
  84        do {
  85                next = __this_cpu_read(irq_work_list);
  86                /* Can assign non-atomic because we keep the flags set. */
  87                entry->next = next_flags(next, IRQ_WORK_FLAGS);
  88        } while (this_cpu_cmpxchg(irq_work_list, next, entry) != next);
  89
  90        /* The list was empty, raise self-interrupt to start processing. */
  91        if (!irq_work_next(entry))
  92                arch_irq_work_raise();
  93
  94        preempt_enable();
  95}
  96
  97/*
  98 * Enqueue the irq_work @entry, returns true on success, failure when the
  99 * @entry was already enqueued by someone else.
 100 *
 101 * Can be re-enqueued while the callback is still in progress.
 102 */
 103bool irq_work_queue(struct irq_work *entry)
 104{
 105        if (!irq_work_claim(entry)) {
 106                /*
 107                 * Already enqueued, can't do!
 108                 */
 109                return false;
 110        }
 111
 112        __irq_work_queue(entry);
 113        return true;
 114}
 115EXPORT_SYMBOL_GPL(irq_work_queue);
 116
 117/*
 118 * Run the irq_work entries on this cpu. Requires to be ran from hardirq
 119 * context with local IRQs disabled.
 120 */
 121void irq_work_run(void)
 122{
 123        struct irq_work *list;
 124
 125        if (this_cpu_read(irq_work_list) == NULL)
 126                return;
 127
 128        BUG_ON(!in_irq());
 129        BUG_ON(!irqs_disabled());
 130
 131        list = this_cpu_xchg(irq_work_list, NULL);
 132
 133        while (list != NULL) {
 134                struct irq_work *entry = list;
 135
 136                list = irq_work_next(list);
 137
 138                /*
 139                 * Clear the PENDING bit, after this point the @entry
 140                 * can be re-used.
 141                 */
 142                entry->next = next_flags(NULL, IRQ_WORK_BUSY);
 143                entry->func(entry);
 144                /*
 145                 * Clear the BUSY bit and return to the free state if
 146                 * no-one else claimed it meanwhile.
 147                 */
 148                (void)cmpxchg(&entry->next,
 149                              next_flags(NULL, IRQ_WORK_BUSY),
 150                              NULL);
 151        }
 152}
 153EXPORT_SYMBOL_GPL(irq_work_run);
 154
 155/*
 156 * Synchronize against the irq_work @entry, ensures the entry is not
 157 * currently in use.
 158 */
 159void irq_work_sync(struct irq_work *entry)
 160{
 161        WARN_ON_ONCE(irqs_disabled());
 162
 163        while (irq_work_is_set(entry, IRQ_WORK_BUSY))
 164                cpu_relax();
 165}
 166EXPORT_SYMBOL_GPL(irq_work_sync);
 167
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