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_CLAIMED;
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 /*
60 * Enqueue the irq_work @work on @cpu unless it's already pending
61 * somewhere.
62 *
63 * Can be re-enqueued while the callback is still in progress.
64 */
irq_work_queue_on(struct irq_work * work,int cpu)65 bool irq_work_queue_on(struct irq_work *work, int cpu)
66 {
67 /* All work should have been flushed before going offline */
68 WARN_ON_ONCE(cpu_is_offline(cpu));
69
70 #ifdef CONFIG_SMP
71
72 /* Arch remote IPI send/receive backend aren't NMI safe */
73 WARN_ON_ONCE(in_nmi());
74
75 /* Only queue if not already pending */
76 if (!irq_work_claim(work))
77 return false;
78
79 if (llist_add(&work->llnode, &per_cpu(raised_list, cpu)))
80 arch_send_call_function_single_ipi(cpu);
81
82 #else /* #ifdef CONFIG_SMP */
83 irq_work_queue(work);
84 #endif /* #else #ifdef CONFIG_SMP */
85
86 return true;
87 }
88
89 /* Enqueue the irq work @work on the current CPU */
irq_work_queue(struct irq_work * work)90 bool irq_work_queue(struct irq_work *work)
91 {
92 /* Only queue if not already pending */
93 if (!irq_work_claim(work))
94 return false;
95
96 /* Queue the entry and raise the IPI if needed. */
97 preempt_disable();
98
99 /* If the work is "lazy", handle it from next tick if any */
100 if (work->flags & IRQ_WORK_LAZY) {
101 if (llist_add(&work->llnode, this_cpu_ptr(&lazy_list)) &&
102 tick_nohz_tick_stopped())
103 arch_irq_work_raise();
104 } else {
105 if (llist_add(&work->llnode, this_cpu_ptr(&raised_list)))
106 arch_irq_work_raise();
107 }
108
109 preempt_enable();
110
111 return true;
112 }
113 EXPORT_SYMBOL_GPL(irq_work_queue);
114
irq_work_needs_cpu(void)115 bool irq_work_needs_cpu(void)
116 {
117 struct llist_head *raised, *lazy;
118
119 raised = this_cpu_ptr(&raised_list);
120 lazy = this_cpu_ptr(&lazy_list);
121
122 if (llist_empty(raised) || arch_irq_work_has_interrupt())
123 if (llist_empty(lazy))
124 return false;
125
126 /* All work should have been flushed before going offline */
127 WARN_ON_ONCE(cpu_is_offline(smp_processor_id()));
128
129 return true;
130 }
131
irq_work_run_list(struct llist_head * list)132 static void irq_work_run_list(struct llist_head *list)
133 {
134 struct irq_work *work, *tmp;
135 struct llist_node *llnode;
136 unsigned long flags;
137
138 BUG_ON(!irqs_disabled());
139
140 if (llist_empty(list))
141 return;
142
143 llnode = llist_del_all(list);
144 llist_for_each_entry_safe(work, tmp, llnode, llnode) {
145 /*
146 * Clear the PENDING bit, after this point the @work
147 * can be re-used.
148 * Make it immediately visible so that other CPUs trying
149 * to claim that work don't rely on us to handle their data
150 * while we are in the middle of the func.
151 */
152 flags = work->flags & ~IRQ_WORK_PENDING;
153 xchg(&work->flags, flags);
154
155 work->func(work);
156 /*
157 * Clear the BUSY bit and return to the free state if
158 * no-one else claimed it meanwhile.
159 */
160 (void)cmpxchg(&work->flags, flags, flags & ~IRQ_WORK_BUSY);
161 }
162 }
163
164 /*
165 * hotplug calls this through:
166 * hotplug_cfd() -> flush_smp_call_function_queue()
167 */
irq_work_run(void)168 void irq_work_run(void)
169 {
170 irq_work_run_list(this_cpu_ptr(&raised_list));
171 irq_work_run_list(this_cpu_ptr(&lazy_list));
172 }
173 EXPORT_SYMBOL_GPL(irq_work_run);
174
irq_work_tick(void)175 void irq_work_tick(void)
176 {
177 struct llist_head *raised = this_cpu_ptr(&raised_list);
178
179 if (!llist_empty(raised) && !arch_irq_work_has_interrupt())
180 irq_work_run_list(raised);
181 irq_work_run_list(this_cpu_ptr(&lazy_list));
182 }
183
184 /*
185 * Synchronize against the irq_work @entry, ensures the entry is not
186 * currently in use.
187 */
irq_work_sync(struct irq_work * work)188 void irq_work_sync(struct irq_work *work)
189 {
190 lockdep_assert_irqs_enabled();
191
192 while (work->flags & IRQ_WORK_BUSY)
193 cpu_relax();
194 }
195 EXPORT_SYMBOL_GPL(irq_work_sync);
196
