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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);
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/kernel.h>
9#include <linux/module.h>
10#include <linux/irq_work.h>
11#include <linux/hardirq.h>
12
13/*
14 * An entry can be in one of four states:
15 *
16 * free NULL, 0 -> {claimed} : free to be used
17 * claimed NULL, 3 -> {pending} : claimed to be enqueued
18 * pending next, 3 -> {busy} : queued, pending callback
19 * busy NULL, 2 -> {free, claimed} : callback in progress, can be claimed
20 *
21 * We use the lower two bits of the next pointer to keep PENDING and BUSY
22 * flags.
23 */
24
25#define IRQ_WORK_PENDING 1UL
26#define IRQ_WORK_BUSY 2UL
27#define IRQ_WORK_FLAGS 3UL
28
29static inline bool irq_work_is_set(struct irq_work *entry, int flags)
30{
31 return (unsigned long)entry->next & flags;
32}
33
34static inline struct irq_work *irq_work_next(struct irq_work *entry)
35{
36 unsigned long next = (unsigned long)entry->next;
37 next &= ~IRQ_WORK_FLAGS;
38 return (struct irq_work *)next;
39}
40
41static inline struct irq_work *next_flags(struct irq_work *entry, int flags)
42{
43 unsigned long next = (unsigned long)entry;
44 next |= flags;
45 return (struct irq_work *)next;
46}
47
48static DEFINE_PER_CPU(struct irq_work *, irq_work_list);
49
50/*
51 * Claim the entry so that no one else will poke at it.
52 */
53static bool irq_work_claim(struct irq_work *entry)
54{
55 struct irq_work *next, *nflags;
56
57 do {
58 next = entry->next;
59 if ((unsigned long)next & IRQ_WORK_PENDING)
60 return false;
61 nflags = next_flags(next, IRQ_WORK_FLAGS);
62 } while (cmpxchg(&entry->next, next, nflags) != next);
63
64 return true;
65}
66
67
68void __weak arch_irq_work_raise(void)
69{
70 /*
71 * Lame architectures will get the timer tick callback
72 */
73}
74
75/*
76 * Queue the entry and raise the IPI if needed.
77 */
78static void __irq_work_queue(struct irq_work *entry)
79{
80 struct irq_work *next;
81
82 preempt_disable();
83
84 do {
85 next = __this_cpu_read(irq_work_list);
86 /* Can assign non-atomic because we keep the flags set. */
87 entry->next = next_flags(next, IRQ_WORK_FLAGS);
88 } while (this_cpu_cmpxchg(irq_work_list, next, entry) != next);
89
90 /* The list was empty, raise self-interrupt to start processing. */
91 if (!irq_work_next(entry))
92 arch_irq_work_raise();
93
94 preempt_enable();
95}
96
97/*
98 * Enqueue the irq_work @entry, returns true on success, failure when the
99 * @entry was already enqueued by someone else.
100 *
101 * Can be re-enqueued while the callback is still in progress.
102 */
103bool irq_work_queue(struct irq_work *entry)
104{
105 if (!irq_work_claim(entry)) {
106 /*
107 * Already enqueued, can't do!
108 */
109 return false;
110 }
111
112 __irq_work_queue(entry);
113 return true;
114}
115EXPORT_SYMBOL_GPL(irq_work_queue);
116
117/*
118 * Run the irq_work entries on this cpu. Requires to be ran from hardirq
119 * context with local IRQs disabled.
120 */
121void irq_work_run(void)
122{
123 struct irq_work *list;
124
125 if (this_cpu_read(irq_work_list) == NULL)
126 return;
127
128 BUG_ON(!in_irq());
129 BUG_ON(!irqs_disabled());
130
131 list = this_cpu_xchg(irq_work_list, NULL);
132
133 while (list != NULL) {
134 struct irq_work *entry = list;
135
136 list = irq_work_next(list);
137
138 /*
139 * Clear the PENDING bit, after this point the @entry
140 * can be re-used.
141 */
142 entry->next = next_flags(NULL, IRQ_WORK_BUSY);
143 entry->func(entry);
144 /*
145 * Clear the BUSY bit and return to the free state if
146 * no-one else claimed it meanwhile.
147 */
148 (void)cmpxchg(&entry->next,
149 next_flags(NULL, IRQ_WORK_BUSY),
150 NULL);
151 }
152}
153EXPORT_SYMBOL_GPL(irq_work_run);
154
155/*
156 * Synchronize against the irq_work @entry, ensures the entry is not
157 * currently in use.
158 */
159void irq_work_sync(struct irq_work *entry)
160{
161 WARN_ON_ONCE(irqs_disabled());
162
163 while (irq_work_is_set(entry, IRQ_WORK_BUSY))
164 cpu_relax();
165}
166EXPORT_SYMBOL_GPL(irq_work_sync);