xref: /openbmc/linux/kernel/irq_work.c (revision e23feb16)
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