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
27 static DEFINE_PER_CPU(struct llist_head, raised_list);
28 static DEFINE_PER_CPU(struct llist_head, lazy_list);
29 static DEFINE_PER_CPU(struct task_struct *, irq_workd);
30
wake_irq_workd(void)31 static 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
irq_work_wake(struct irq_work * entry)40 static void irq_work_wake(struct irq_work *entry)
41 {
42 wake_irq_workd();
43 }
44
45 static DEFINE_PER_CPU(struct irq_work, irq_work_wakeup) =
46 IRQ_WORK_INIT_HARD(irq_work_wake);
47 #endif
48
irq_workd_should_run(unsigned int cpu)49 static 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 */
irq_work_claim(struct irq_work * work)57 static 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
arch_irq_work_raise(void)72 void __weak arch_irq_work_raise(void)
73 {
74 /*
75 * Lame architectures will get the timer tick callback
76 */
77 }
78
irq_work_raise(struct irq_work * work)79 static __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 */
__irq_work_queue_local(struct irq_work * work)88 static 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 */
irq_work_queue(struct irq_work * work)116 bool 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 }
129 EXPORT_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 */
irq_work_queue_on(struct irq_work * work,int cpu)137 bool 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 }
177 out:
178 preempt_enable();
179
180 return true;
181 #endif /* CONFIG_SMP */
182 }
183
irq_work_needs_cpu(void)184 bool 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
irq_work_single(void * arg)201 void 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
irq_work_run_list(struct llist_head * list)235 static 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 */
irq_work_run(void)259 void 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 }
267 EXPORT_SYMBOL_GPL(irq_work_run);
268
irq_work_tick(void)269 void 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 */
irq_work_sync(struct irq_work * work)286 void 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 }
301 EXPORT_SYMBOL_GPL(irq_work_sync);
302
run_irq_workd(unsigned int cpu)303 static void run_irq_workd(unsigned int cpu)
304 {
305 irq_work_run_list(this_cpu_ptr(&lazy_list));
306 }
307
irq_workd_setup(unsigned int cpu)308 static void irq_workd_setup(unsigned int cpu)
309 {
310 sched_set_fifo_low(current);
311 }
312
313 static 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
irq_work_init_threads(void)321 static __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 }
327 early_initcall(irq_work_init_threads);
328
