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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 | |
22 | static DEFINE_PER_CPU(struct llist_head, irq_work_list); |
23 | static DEFINE_PER_CPU(int, irq_work_raised); |
24 | |
25 | /* |
26 | * Claim the entry so that no one else will poke at it. |
27 | */ |
28 | static 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 | |
51 | void __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 | */ |
64 | void irq_work_queue(struct irq_work *work) |
65 | { |
66 | /* Only queue if not already pending */ |
67 | if (!irq_work_claim(work)) |
68 | return; |
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 | EXPORT_SYMBOL_GPL(irq_work_queue); |
88 | |
89 | bool irq_work_needs_cpu(void) |
90 | { |
91 | struct llist_head *this_list; |
92 | |
93 | this_list = &__get_cpu_var(irq_work_list); |
94 | if (llist_empty(this_list)) |
95 | return false; |
96 | |
97 | /* All work should have been flushed before going offline */ |
98 | WARN_ON_ONCE(cpu_is_offline(smp_processor_id())); |
99 | |
100 | return true; |
101 | } |
102 | |
103 | static void __irq_work_run(void) |
104 | { |
105 | unsigned long flags; |
106 | struct irq_work *work; |
107 | struct llist_head *this_list; |
108 | struct llist_node *llnode; |
109 | |
110 | |
111 | /* |
112 | * Reset the "raised" state right before we check the list because |
113 | * an NMI may enqueue after we find the list empty from the runner. |
114 | */ |
115 | __this_cpu_write(irq_work_raised, 0); |
116 | barrier(); |
117 | |
118 | this_list = &__get_cpu_var(irq_work_list); |
119 | if (llist_empty(this_list)) |
120 | return; |
121 | |
122 | BUG_ON(!irqs_disabled()); |
123 | |
124 | llnode = llist_del_all(this_list); |
125 | while (llnode != NULL) { |
126 | work = llist_entry(llnode, struct irq_work, llnode); |
127 | |
128 | llnode = llist_next(llnode); |
129 | |
130 | /* |
131 | * Clear the PENDING bit, after this point the @work |
132 | * can be re-used. |
133 | * Make it immediately visible so that other CPUs trying |
134 | * to claim that work don't rely on us to handle their data |
135 | * while we are in the middle of the func. |
136 | */ |
137 | flags = work->flags & ~IRQ_WORK_PENDING; |
138 | xchg(&work->flags, flags); |
139 | |
140 | work->func(work); |
141 | /* |
142 | * Clear the BUSY bit and return to the free state if |
143 | * no-one else claimed it meanwhile. |
144 | */ |
145 | (void)cmpxchg(&work->flags, flags, flags & ~IRQ_WORK_BUSY); |
146 | } |
147 | } |
148 | |
149 | /* |
150 | * Run the irq_work entries on this cpu. Requires to be ran from hardirq |
151 | * context with local IRQs disabled. |
152 | */ |
153 | void irq_work_run(void) |
154 | { |
155 | BUG_ON(!in_irq()); |
156 | __irq_work_run(); |
157 | } |
158 | EXPORT_SYMBOL_GPL(irq_work_run); |
159 | |
160 | /* |
161 | * Synchronize against the irq_work @entry, ensures the entry is not |
162 | * currently in use. |
163 | */ |
164 | void irq_work_sync(struct irq_work *work) |
165 | { |
166 | WARN_ON_ONCE(irqs_disabled()); |
167 | |
168 | while (work->flags & IRQ_WORK_BUSY) |
169 | cpu_relax(); |
170 | } |
171 | EXPORT_SYMBOL_GPL(irq_work_sync); |
172 | |
173 | #ifdef CONFIG_HOTPLUG_CPU |
174 | static int irq_work_cpu_notify(struct notifier_block *self, |
175 | unsigned long action, void *hcpu) |
176 | { |
177 | long cpu = (long)hcpu; |
178 | |
179 | switch (action) { |
180 | case CPU_DYING: |
181 | /* Called from stop_machine */ |
182 | if (WARN_ON_ONCE(cpu != smp_processor_id())) |
183 | break; |
184 | __irq_work_run(); |
185 | break; |
186 | default: |
187 | break; |
188 | } |
189 | return NOTIFY_OK; |
190 | } |
191 | |
192 | static struct notifier_block cpu_notify; |
193 | |
194 | static __init int irq_work_init_cpu_notifier(void) |
195 | { |
196 | cpu_notify.notifier_call = irq_work_cpu_notify; |
197 | cpu_notify.priority = 0; |
198 | register_cpu_notifier(&cpu_notify); |
199 | return 0; |
200 | } |
201 | device_initcall(irq_work_init_cpu_notifier); |
202 | |
203 | #endif /* CONFIG_HOTPLUG_CPU */ |
204 |
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