1 /*
2 * Copyright (C) 2010 Red Hat, Inc., Peter Zijlstra
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 <linux/smp.h>
20 #include <asm/processor.h>
21
22
23 static DEFINE_PER_CPU(struct llist_head, raised_list);
24 static DEFINE_PER_CPU(struct llist_head, lazy_list);
25
26 /*
27 * Claim the entry so that no one else will poke at it.
28 */
irq_work_claim(struct irq_work * work)29 static bool irq_work_claim(struct irq_work *work)
30 {
31 unsigned long flags, oflags, nflags;
32
33 /*
34 * Start with our best wish as a premise but only trust any
35 * flag value after cmpxchg() result.
36 */
37 flags = work->flags & ~IRQ_WORK_PENDING;
38 for (;;) {
39 nflags = flags | IRQ_WORK_FLAGS;
40 oflags = cmpxchg(&work->flags, flags, nflags);
41 if (oflags == flags)
42 break;
43 if (oflags & IRQ_WORK_PENDING)
44 return false;
45 flags = oflags;
46 cpu_relax();
47 }
48
49 return true;
50 }
51
arch_irq_work_raise(void)52 void __weak arch_irq_work_raise(void)
53 {
54 /*
55 * Lame architectures will get the timer tick callback
56 */
57 }
58
59 #ifdef CONFIG_SMP
60 /*
61 * Enqueue the irq_work @work on @cpu unless it's already pending
62 * somewhere.
63 *
64 * Can be re-enqueued while the callback is still in progress.
65 */
irq_work_queue_on(struct irq_work * work,int cpu)66 bool irq_work_queue_on(struct irq_work *work, int cpu)
67 {
68 /* All work should have been flushed before going offline */
69 WARN_ON_ONCE(cpu_is_offline(cpu));
70
71 /* Arch remote IPI send/receive backend aren't NMI safe */
72 WARN_ON_ONCE(in_nmi());
73
74 /* Only queue if not already pending */
75 if (!irq_work_claim(work))
76 return false;
77
78 if (llist_add(&work->llnode, &per_cpu(raised_list, cpu)))
79 arch_send_call_function_single_ipi(cpu);
80
81 return true;
82 }
83 EXPORT_SYMBOL_GPL(irq_work_queue_on);
84 #endif
85
86 /* Enqueue the irq work @work on the current CPU */
irq_work_queue(struct irq_work * work)87 bool irq_work_queue(struct irq_work *work)
88 {
89 /* Only queue if not already pending */
90 if (!irq_work_claim(work))
91 return false;
92
93 /* Queue the entry and raise the IPI if needed. */
94 preempt_disable();
95
96 /* If the work is "lazy", handle it from next tick if any */
97 if (work->flags & IRQ_WORK_LAZY) {
98 if (llist_add(&work->llnode, this_cpu_ptr(&lazy_list)) &&
99 tick_nohz_tick_stopped())
100 arch_irq_work_raise();
101 } else {
102 if (llist_add(&work->llnode, this_cpu_ptr(&raised_list)))
103 arch_irq_work_raise();
104 }
105
106 preempt_enable();
107
108 return true;
109 }
110 EXPORT_SYMBOL_GPL(irq_work_queue);
111
irq_work_needs_cpu(void)112 bool irq_work_needs_cpu(void)
113 {
114 struct llist_head *raised, *lazy;
115
116 raised = this_cpu_ptr(&raised_list);
117 lazy = this_cpu_ptr(&lazy_list);
118
119 if (llist_empty(raised) || arch_irq_work_has_interrupt())
120 if (llist_empty(lazy))
121 return false;
122
123 /* All work should have been flushed before going offline */
124 WARN_ON_ONCE(cpu_is_offline(smp_processor_id()));
125
126 return true;
127 }
128
irq_work_run_list(struct llist_head * list)129 static void irq_work_run_list(struct llist_head *list)
130 {
131 unsigned long flags;
132 struct irq_work *work;
133 struct llist_node *llnode;
134
135 BUG_ON(!irqs_disabled());
136
137 if (llist_empty(list))
138 return;
139
140 llnode = llist_del_all(list);
141 while (llnode != NULL) {
142 work = llist_entry(llnode, struct irq_work, llnode);
143
144 llnode = llist_next(llnode);
145
146 /*
147 * Clear the PENDING bit, after this point the @work
148 * can be re-used.
149 * Make it immediately visible so that other CPUs trying
150 * to claim that work don't rely on us to handle their data
151 * while we are in the middle of the func.
152 */
153 flags = work->flags & ~IRQ_WORK_PENDING;
154 xchg(&work->flags, flags);
155
156 work->func(work);
157 /*
158 * Clear the BUSY bit and return to the free state if
159 * no-one else claimed it meanwhile.
160 */
161 (void)cmpxchg(&work->flags, flags, flags & ~IRQ_WORK_BUSY);
162 }
163 }
164
165 /*
166 * hotplug calls this through:
167 * hotplug_cfd() -> flush_smp_call_function_queue()
168 */
irq_work_run(void)169 void irq_work_run(void)
170 {
171 irq_work_run_list(this_cpu_ptr(&raised_list));
172 irq_work_run_list(this_cpu_ptr(&lazy_list));
173 }
174 EXPORT_SYMBOL_GPL(irq_work_run);
175
irq_work_tick(void)176 void irq_work_tick(void)
177 {
178 struct llist_head *raised = this_cpu_ptr(&raised_list);
179
180 if (!llist_empty(raised) && !arch_irq_work_has_interrupt())
181 irq_work_run_list(raised);
182 irq_work_run_list(this_cpu_ptr(&lazy_list));
183 }
184
185 /*
186 * Synchronize against the irq_work @entry, ensures the entry is not
187 * currently in use.
188 */
irq_work_sync(struct irq_work * work)189 void irq_work_sync(struct irq_work *work)
190 {
191 WARN_ON_ONCE(irqs_disabled());
192
193 while (work->flags & IRQ_WORK_BUSY)
194 cpu_relax();
195 }
196 EXPORT_SYMBOL_GPL(irq_work_sync);
197