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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/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 <linux/sched.h>
16#include <linux/tick.h>
17#include <linux/cpu.h>
18#include <linux/notifier.h>
19#include <asm/processor.h>
20
21
22static DEFINE_PER_CPU(struct llist_head, irq_work_list);
23static DEFINE_PER_CPU(int, irq_work_raised);
24
25/*
26 * Claim the entry so that no one else will poke at it.
27 */
28static bool irq_work_claim(struct irq_work *work)
29{
30 unsigned long flags, oflags, nflags;
31
32 /*
33 * Start with our best wish as a premise but only trust any
34 * flag value after cmpxchg() result.
35 */
36 flags = work->flags & ~IRQ_WORK_PENDING;
37 for (;;) {
38 nflags = flags | IRQ_WORK_FLAGS;
39 oflags = cmpxchg(&work->flags, flags, nflags);
40 if (oflags == flags)
41 break;
42 if (oflags & IRQ_WORK_PENDING)
43 return false;
44 flags = oflags;
45 cpu_relax();
46 }
47
48 return true;
49}
50
51void __weak arch_irq_work_raise(void)
52{
53 /*
54 * Lame architectures will get the timer tick callback
55 */
56}
57
58/*
59 * Enqueue the irq_work @entry unless it's already pending
60 * somewhere.
61 *
62 * Can be re-enqueued while the callback is still in progress.
63 */
64bool irq_work_queue(struct irq_work *work)
65{
66 /* Only queue if not already pending */
67 if (!irq_work_claim(work))
68 return false;
69
70 /* Queue the entry and raise the IPI if needed. */
71 preempt_disable();
72
73 llist_add(&work->llnode, &__get_cpu_var(irq_work_list));
74
75 /*
76 * If the work is not "lazy" or the tick is stopped, raise the irq
77 * work interrupt (if supported by the arch), otherwise, just wait
78 * for the next tick.
79 */
80 if (!(work->flags & IRQ_WORK_LAZY) || tick_nohz_tick_stopped()) {
81 if (!this_cpu_cmpxchg(irq_work_raised, 0, 1))
82 arch_irq_work_raise();
83 }
84
85 preempt_enable();
86
87 return true;
88}
89EXPORT_SYMBOL_GPL(irq_work_queue);
90
91bool irq_work_needs_cpu(void)
92{
93 struct llist_head *this_list;
94
95 this_list = &__get_cpu_var(irq_work_list);
96 if (llist_empty(this_list))
97 return false;
98
99 /* All work should have been flushed before going offline */
100 WARN_ON_ONCE(cpu_is_offline(smp_processor_id()));
101
102 return true;
103}
104
105static void __irq_work_run(void)
106{
107 unsigned long flags;
108 struct irq_work *work;
109 struct llist_head *this_list;
110 struct llist_node *llnode;
111
112
113 /*
114 * Reset the "raised" state right before we check the list because
115 * an NMI may enqueue after we find the list empty from the runner.
116 */
117 __this_cpu_write(irq_work_raised, 0);
118 barrier();
119
120 this_list = &__get_cpu_var(irq_work_list);
121 if (llist_empty(this_list))
122 return;
123
124 BUG_ON(!irqs_disabled());
125
126 llnode = llist_del_all(this_list);
127 while (llnode != NULL) {
128 work = llist_entry(llnode, struct irq_work, llnode);
129
130 llnode = llist_next(llnode);
131
132 /*
133 * Clear the PENDING bit, after this point the @work
134 * can be re-used.
135 * Make it immediately visible so that other CPUs trying
136 * to claim that work don't rely on us to handle their data
137 * while we are in the middle of the func.
138 */
139 flags = work->flags & ~IRQ_WORK_PENDING;
140 xchg(&work->flags, flags);
141
142 work->func(work);
143 /*
144 * Clear the BUSY bit and return to the free state if
145 * no-one else claimed it meanwhile.
146 */
147 (void)cmpxchg(&work->flags, flags, flags & ~IRQ_WORK_BUSY);
148 }
149}
150
151/*
152 * Run the irq_work entries on this cpu. Requires to be ran from hardirq
153 * context with local IRQs disabled.
154 */
155void irq_work_run(void)
156{
157 BUG_ON(!in_irq());
158 __irq_work_run();
159}
160EXPORT_SYMBOL_GPL(irq_work_run);
161
162/*
163 * Synchronize against the irq_work @entry, ensures the entry is not
164 * currently in use.
165 */
166void irq_work_sync(struct irq_work *work)
167{
168 WARN_ON_ONCE(irqs_disabled());
169
170 while (work->flags & IRQ_WORK_BUSY)
171 cpu_relax();
172}
173EXPORT_SYMBOL_GPL(irq_work_sync);
174
175#ifdef CONFIG_HOTPLUG_CPU
176static int irq_work_cpu_notify(struct notifier_block *self,
177 unsigned long action, void *hcpu)
178{
179 long cpu = (long)hcpu;
180
181 switch (action) {
182 case CPU_DYING:
183 /* Called from stop_machine */
184 if (WARN_ON_ONCE(cpu != smp_processor_id()))
185 break;
186 __irq_work_run();
187 break;
188 default:
189 break;
190 }
191 return NOTIFY_OK;
192}
193
194static struct notifier_block cpu_notify;
195
196static __init int irq_work_init_cpu_notifier(void)
197{
198 cpu_notify.notifier_call = irq_work_cpu_notify;
199 cpu_notify.priority = 0;
200 register_cpu_notifier(&cpu_notify);
201 return 0;
202}
203device_initcall(irq_work_init_cpu_notifier);
204
205#endif /* CONFIG_HOTPLUG_CPU */
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);