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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/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 | |
28 | static 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 | */ |
33 | static 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 | |
50 | void __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 | */ |
60 | static 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 | */ |
80 | bool 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 | } |
92 | EXPORT_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 | */ |
98 | void 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 | } |
130 | EXPORT_SYMBOL_GPL(irq_work_run); |
131 | |
132 | /* |
133 | * Synchronize against the irq_work @entry, ensures the entry is not |
134 | * currently in use. |
135 | */ |
136 | void 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 | } |
143 | EXPORT_SYMBOL_GPL(irq_work_sync); |
144 |
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