Root/kernel/irq_work.c

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

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