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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 | bool 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 | } |
89 | EXPORT_SYMBOL_GPL(irq_work_queue); |
90 | |
91 | bool 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 | |
105 | static 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 | */ |
155 | void irq_work_run(void) |
156 | { |
157 | BUG_ON(!in_irq()); |
158 | __irq_work_run(); |
159 | } |
160 | EXPORT_SYMBOL_GPL(irq_work_run); |
161 | |
162 | /* |
163 | * Synchronize against the irq_work @entry, ensures the entry is not |
164 | * currently in use. |
165 | */ |
166 | void 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 | } |
173 | EXPORT_SYMBOL_GPL(irq_work_sync); |
174 | |
175 | #ifdef CONFIG_HOTPLUG_CPU |
176 | static 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 | |
194 | static struct notifier_block cpu_notify; |
195 | |
196 | static __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 | } |
203 | device_initcall(irq_work_init_cpu_notifier); |
204 | |
205 | #endif /* CONFIG_HOTPLUG_CPU */ |
206 |
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