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
irq_work_is_set(struct irq_work * entry,int flags)29 static inline bool irq_work_is_set(struct irq_work *entry, int flags)
30 {
31 return (unsigned long)entry->next & flags;
32 }
33
irq_work_next(struct irq_work * entry)34 static 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
next_flags(struct irq_work * entry,int flags)41 static 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
48 static 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 */
irq_work_claim(struct irq_work * entry)53 static 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
arch_irq_work_raise(void)68 void __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 */
__irq_work_queue(struct irq_work * entry)78 static 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 */
irq_work_queue(struct irq_work * entry)103 bool 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 }
115 EXPORT_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 */
irq_work_run(void)121 void 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 }
153 EXPORT_SYMBOL_GPL(irq_work_run);
154
155 /*
156 * Synchronize against the irq_work @entry, ensures the entry is not
157 * currently in use.
158 */
irq_work_sync(struct irq_work * entry)159 void 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 }
166 EXPORT_SYMBOL_GPL(irq_work_sync);
167