1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * Copyright (C) 2010 Red Hat, Inc., Peter Zijlstra
4 *
5 * Provides a framework for enqueueing and running callbacks from hardirq
6 * context. The enqueueing is NMI-safe.
7 */
8
9#include <linux/bug.h>
10#include <linux/kernel.h>
11#include <linux/export.h>
12#include <linux/irq_work.h>
13#include <linux/percpu.h>
14#include <linux/hardirq.h>
15#include <linux/irqflags.h>
16#include <linux/sched.h>
17#include <linux/tick.h>
18#include <linux/cpu.h>
19#include <linux/notifier.h>
20#include <linux/smp.h>
21#include <linux/smpboot.h>
22#include <asm/processor.h>
23#include <linux/kasan.h>
24
25#include <trace/events/ipi.h>
26
27static DEFINE_PER_CPU(struct llist_head, raised_list);
28static DEFINE_PER_CPU(struct llist_head, lazy_list);
29static DEFINE_PER_CPU(struct task_struct *, irq_workd);
30
31static void wake_irq_workd(void)
32{
33	struct task_struct *tsk = __this_cpu_read(irq_workd);
34
35	if (!llist_empty(this_cpu_ptr(&lazy_list)) && tsk)
36		wake_up_process(tsk);
37}
38
39#ifdef CONFIG_SMP
40static void irq_work_wake(struct irq_work *entry)
41{
42	wake_irq_workd();
43}
44
45static DEFINE_PER_CPU(struct irq_work, irq_work_wakeup) =
46	IRQ_WORK_INIT_HARD(irq_work_wake);
47#endif
48
49static int irq_workd_should_run(unsigned int cpu)
50{
51	return !llist_empty(this_cpu_ptr(&lazy_list));
52}
53
54/*
55 * Claim the entry so that no one else will poke at it.
56 */
57static bool irq_work_claim(struct irq_work *work)
58{
59	int oflags;
60
61	oflags = atomic_fetch_or(IRQ_WORK_CLAIMED | CSD_TYPE_IRQ_WORK, &work->node.a_flags);
62	/*
63	 * If the work is already pending, no need to raise the IPI.
64	 * The pairing smp_mb() in irq_work_single() makes sure
65	 * everything we did before is visible.
66	 */
67	if (oflags & IRQ_WORK_PENDING)
68		return false;
69	return true;
70}
71
72void __weak arch_irq_work_raise(void)
73{
74	/*
75	 * Lame architectures will get the timer tick callback
76	 */
77}
78
79static __always_inline void irq_work_raise(struct irq_work *work)
80{
81	if (trace_ipi_send_cpu_enabled() && arch_irq_work_has_interrupt())
82		trace_ipi_send_cpu(smp_processor_id(), _RET_IP_, work->func);
83
84	arch_irq_work_raise();
85}
86
87/* Enqueue on current CPU, work must already be claimed and preempt disabled */
88static void __irq_work_queue_local(struct irq_work *work)
89{
90	struct llist_head *list;
91	bool rt_lazy_work = false;
92	bool lazy_work = false;
93	int work_flags;
94
95	work_flags = atomic_read(&work->node.a_flags);
96	if (work_flags & IRQ_WORK_LAZY)
97		lazy_work = true;
98	else if (IS_ENABLED(CONFIG_PREEMPT_RT) &&
99		 !(work_flags & IRQ_WORK_HARD_IRQ))
100		rt_lazy_work = true;
101
102	if (lazy_work || rt_lazy_work)
103		list = this_cpu_ptr(&lazy_list);
104	else
105		list = this_cpu_ptr(&raised_list);
106
107	if (!llist_add(&work->node.llist, list))
108		return;
109
110	/* If the work is "lazy", handle it from next tick if any */
111	if (!lazy_work || tick_nohz_tick_stopped())
112		irq_work_raise(work);
113}
114
115/* Enqueue the irq work @work on the current CPU */
116bool irq_work_queue(struct irq_work *work)
117{
118	/* Only queue if not already pending */
119	if (!irq_work_claim(work))
120		return false;
121
122	/* Queue the entry and raise the IPI if needed. */
123	preempt_disable();
124	__irq_work_queue_local(work);
125	preempt_enable();
126
127	return true;
128}
129EXPORT_SYMBOL_GPL(irq_work_queue);
130
131/*
132 * Enqueue the irq_work @work on @cpu unless it's already pending
133 * somewhere.
134 *
135 * Can be re-enqueued while the callback is still in progress.
136 */
137bool irq_work_queue_on(struct irq_work *work, int cpu)
138{
139#ifndef CONFIG_SMP
140	return irq_work_queue(work);
141
142#else /* CONFIG_SMP: */
143	/* All work should have been flushed before going offline */
144	WARN_ON_ONCE(cpu_is_offline(cpu));
145
146	/* Only queue if not already pending */
147	if (!irq_work_claim(work))
148		return false;
149
150	kasan_record_aux_stack_noalloc(work);
151
152	preempt_disable();
153	if (cpu != smp_processor_id()) {
154		/* Arch remote IPI send/receive backend aren't NMI safe */
155		WARN_ON_ONCE(in_nmi());
156
157		/*
158		 * On PREEMPT_RT the items which are not marked as
159		 * IRQ_WORK_HARD_IRQ are added to the lazy list and a HARD work
160		 * item is used on the remote CPU to wake the thread.
161		 */
162		if (IS_ENABLED(CONFIG_PREEMPT_RT) &&
163		    !(atomic_read(&work->node.a_flags) & IRQ_WORK_HARD_IRQ)) {
164
165			if (!llist_add(&work->node.llist, &per_cpu(lazy_list, cpu)))
166				goto out;
167
168			work = &per_cpu(irq_work_wakeup, cpu);
169			if (!irq_work_claim(work))
170				goto out;
171		}
172
173		__smp_call_single_queue(cpu, &work->node.llist);
174	} else {
175		__irq_work_queue_local(work);
176	}
177out:
178	preempt_enable();
179
180	return true;
181#endif /* CONFIG_SMP */
182}
183
184bool irq_work_needs_cpu(void)
185{
186	struct llist_head *raised, *lazy;
187
188	raised = this_cpu_ptr(&raised_list);
189	lazy = this_cpu_ptr(&lazy_list);
190
191	if (llist_empty(raised) || arch_irq_work_has_interrupt())
192		if (llist_empty(lazy))
193			return false;
194
195	/* All work should have been flushed before going offline */
196	WARN_ON_ONCE(cpu_is_offline(smp_processor_id()));
197
198	return true;
199}
200
201void irq_work_single(void *arg)
202{
203	struct irq_work *work = arg;
204	int flags;
205
206	/*
207	 * Clear the PENDING bit, after this point the @work can be re-used.
208	 * The PENDING bit acts as a lock, and we own it, so we can clear it
209	 * without atomic ops.
210	 */
211	flags = atomic_read(&work->node.a_flags);
212	flags &= ~IRQ_WORK_PENDING;
213	atomic_set(&work->node.a_flags, flags);
214
215	/*
216	 * See irq_work_claim().
217	 */
218	smp_mb();
219
220	lockdep_irq_work_enter(flags);
221	work->func(work);
222	lockdep_irq_work_exit(flags);
223
224	/*
225	 * Clear the BUSY bit, if set, and return to the free state if no-one
226	 * else claimed it meanwhile.
227	 */
228	(void)atomic_cmpxchg(&work->node.a_flags, flags, flags & ~IRQ_WORK_BUSY);
229
230	if ((IS_ENABLED(CONFIG_PREEMPT_RT) && !irq_work_is_hard(work)) ||
231	    !arch_irq_work_has_interrupt())
232		rcuwait_wake_up(&work->irqwait);
233}
234
235static void irq_work_run_list(struct llist_head *list)
236{
237	struct irq_work *work, *tmp;
238	struct llist_node *llnode;
239
240	/*
241	 * On PREEMPT_RT IRQ-work which is not marked as HARD will be processed
242	 * in a per-CPU thread in preemptible context. Only the items which are
243	 * marked as IRQ_WORK_HARD_IRQ will be processed in hardirq context.
244	 */
245	BUG_ON(!irqs_disabled() && !IS_ENABLED(CONFIG_PREEMPT_RT));
246
247	if (llist_empty(list))
248		return;
249
250	llnode = llist_del_all(list);
251	llist_for_each_entry_safe(work, tmp, llnode, node.llist)
252		irq_work_single(work);
253}
254
255/*
256 * hotplug calls this through:
257 *  hotplug_cfd() -> flush_smp_call_function_queue()
258 */
259void irq_work_run(void)
260{
261	irq_work_run_list(this_cpu_ptr(&raised_list));
262	if (!IS_ENABLED(CONFIG_PREEMPT_RT))
263		irq_work_run_list(this_cpu_ptr(&lazy_list));
264	else
265		wake_irq_workd();
266}
267EXPORT_SYMBOL_GPL(irq_work_run);
268
269void irq_work_tick(void)
270{
271	struct llist_head *raised = this_cpu_ptr(&raised_list);
272
273	if (!llist_empty(raised) && !arch_irq_work_has_interrupt())
274		irq_work_run_list(raised);
275
276	if (!IS_ENABLED(CONFIG_PREEMPT_RT))
277		irq_work_run_list(this_cpu_ptr(&lazy_list));
278	else
279		wake_irq_workd();
280}
281
282/*
283 * Synchronize against the irq_work @entry, ensures the entry is not
284 * currently in use.
285 */
286void irq_work_sync(struct irq_work *work)
287{
288	lockdep_assert_irqs_enabled();
289	might_sleep();
290
291	if ((IS_ENABLED(CONFIG_PREEMPT_RT) && !irq_work_is_hard(work)) ||
292	    !arch_irq_work_has_interrupt()) {
293		rcuwait_wait_event(&work->irqwait, !irq_work_is_busy(work),
294				   TASK_UNINTERRUPTIBLE);
295		return;
296	}
297
298	while (irq_work_is_busy(work))
299		cpu_relax();
300}
301EXPORT_SYMBOL_GPL(irq_work_sync);
302
303static void run_irq_workd(unsigned int cpu)
304{
305	irq_work_run_list(this_cpu_ptr(&lazy_list));
306}
307
308static void irq_workd_setup(unsigned int cpu)
309{
310	sched_set_fifo_low(current);
311}
312
313static struct smp_hotplug_thread irqwork_threads = {
314	.store                  = &irq_workd,
315	.setup			= irq_workd_setup,
316	.thread_should_run      = irq_workd_should_run,
317	.thread_fn              = run_irq_workd,
318	.thread_comm            = "irq_work/%u",
319};
320
321static __init int irq_work_init_threads(void)
322{
323	if (IS_ENABLED(CONFIG_PREEMPT_RT))
324		BUG_ON(smpboot_register_percpu_thread(&irqwork_threads));
325	return 0;
326}
327early_initcall(irq_work_init_threads);
328