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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