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 <linux/smp.h>
20#include <asm/processor.h>
21
22
23static DEFINE_PER_CPU(struct llist_head, raised_list);
24static DEFINE_PER_CPU(struct llist_head, lazy_list);
25
26/*
27 * Claim the entry so that no one else will poke at it.
28 */
29static 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
52void __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 */
66bool 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}
83EXPORT_SYMBOL_GPL(irq_work_queue_on);
84#endif
85
86/* Enqueue the irq work @work on the current CPU */
87bool 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}
110EXPORT_SYMBOL_GPL(irq_work_queue);
111
112bool 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
129static 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 */
169void 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}
174EXPORT_SYMBOL_GPL(irq_work_run);
175
176void 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 */
189void 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}
196EXPORT_SYMBOL_GPL(irq_work_sync);
197