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
30 static 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 */
irq_work_claim(struct irq_work * work)35 static 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
arch_irq_work_raise(void)52 void __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 */
__irq_work_queue(struct irq_work * work)62 static 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 */
irq_work_queue(struct irq_work * work)82 bool 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 }
94 EXPORT_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 */
irq_work_run(void)100 void 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 }
132 EXPORT_SYMBOL_GPL(irq_work_run);
133
134 /*
135 * Synchronize against the irq_work @entry, ensures the entry is not
136 * currently in use.
137 */
irq_work_sync(struct irq_work * work)138 void 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 }
145 EXPORT_SYMBOL_GPL(irq_work_sync);
146