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1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * Generic entry points for the idle threads and
4 * implementation of the idle task scheduling class.
5 *
6 * (NOTE: these are not related to SCHED_IDLE batch scheduled
7 * tasks which are handled in sched/fair.c )
8 */
9
10/* Linker adds these: start and end of __cpuidle functions */
11extern char __cpuidle_text_start[], __cpuidle_text_end[];
12
13/**
14 * sched_idle_set_state - Record idle state for the current CPU.
15 * @idle_state: State to record.
16 */
17void sched_idle_set_state(struct cpuidle_state *idle_state)
18{
19 idle_set_state(this_rq(), idle_state);
20}
21
22static int __read_mostly cpu_idle_force_poll;
23
24void cpu_idle_poll_ctrl(bool enable)
25{
26 if (enable) {
27 cpu_idle_force_poll++;
28 } else {
29 cpu_idle_force_poll--;
30 WARN_ON_ONCE(cpu_idle_force_poll < 0);
31 }
32}
33
34#ifdef CONFIG_GENERIC_IDLE_POLL_SETUP
35static int __init cpu_idle_poll_setup(char *__unused)
36{
37 cpu_idle_force_poll = 1;
38
39 return 1;
40}
41__setup("nohlt", cpu_idle_poll_setup);
42
43static int __init cpu_idle_nopoll_setup(char *__unused)
44{
45 cpu_idle_force_poll = 0;
46
47 return 1;
48}
49__setup("hlt", cpu_idle_nopoll_setup);
50#endif
51
52static noinline int __cpuidle cpu_idle_poll(void)
53{
54 trace_cpu_idle(0, smp_processor_id());
55 stop_critical_timings();
56 ct_idle_enter();
57 local_irq_enable();
58
59 while (!tif_need_resched() &&
60 (cpu_idle_force_poll || tick_check_broadcast_expired()))
61 cpu_relax();
62
63 ct_idle_exit();
64 start_critical_timings();
65 trace_cpu_idle(PWR_EVENT_EXIT, smp_processor_id());
66
67 return 1;
68}
69
70/* Weak implementations for optional arch specific functions */
71void __weak arch_cpu_idle_prepare(void) { }
72void __weak arch_cpu_idle_enter(void) { }
73void __weak arch_cpu_idle_exit(void) { }
74void __weak arch_cpu_idle_dead(void) { }
75void __weak arch_cpu_idle(void)
76{
77 cpu_idle_force_poll = 1;
78 raw_local_irq_enable();
79}
80
81/**
82 * default_idle_call - Default CPU idle routine.
83 *
84 * To use when the cpuidle framework cannot be used.
85 */
86void __cpuidle default_idle_call(void)
87{
88 if (current_clr_polling_and_test()) {
89 local_irq_enable();
90 } else {
91
92 trace_cpu_idle(1, smp_processor_id());
93 stop_critical_timings();
94
95 /*
96 * arch_cpu_idle() is supposed to enable IRQs, however
97 * we can't do that because of RCU and tracing.
98 *
99 * Trace IRQs enable here, then switch off RCU, and have
100 * arch_cpu_idle() use raw_local_irq_enable(). Note that
101 * ct_idle_enter() relies on lockdep IRQ state, so switch that
102 * last -- this is very similar to the entry code.
103 */
104 trace_hardirqs_on_prepare();
105 lockdep_hardirqs_on_prepare();
106 ct_idle_enter();
107 lockdep_hardirqs_on(_THIS_IP_);
108
109 arch_cpu_idle();
110
111 /*
112 * OK, so IRQs are enabled here, but RCU needs them disabled to
113 * turn itself back on.. funny thing is that disabling IRQs
114 * will cause tracing, which needs RCU. Jump through hoops to
115 * make it 'work'.
116 */
117 raw_local_irq_disable();
118 lockdep_hardirqs_off(_THIS_IP_);
119 ct_idle_exit();
120 lockdep_hardirqs_on(_THIS_IP_);
121 raw_local_irq_enable();
122
123 start_critical_timings();
124 trace_cpu_idle(PWR_EVENT_EXIT, smp_processor_id());
125 }
126}
127
128static int call_cpuidle_s2idle(struct cpuidle_driver *drv,
129 struct cpuidle_device *dev)
130{
131 if (current_clr_polling_and_test())
132 return -EBUSY;
133
134 return cpuidle_enter_s2idle(drv, dev);
135}
136
137static int call_cpuidle(struct cpuidle_driver *drv, struct cpuidle_device *dev,
138 int next_state)
139{
140 /*
141 * The idle task must be scheduled, it is pointless to go to idle, just
142 * update no idle residency and return.
143 */
144 if (current_clr_polling_and_test()) {
145 dev->last_residency_ns = 0;
146 local_irq_enable();
147 return -EBUSY;
148 }
149
150 /*
151 * Enter the idle state previously returned by the governor decision.
152 * This function will block until an interrupt occurs and will take
153 * care of re-enabling the local interrupts
154 */
155 return cpuidle_enter(drv, dev, next_state);
156}
157
158/**
159 * cpuidle_idle_call - the main idle function
160 *
161 * NOTE: no locks or semaphores should be used here
162 *
163 * On architectures that support TIF_POLLING_NRFLAG, is called with polling
164 * set, and it returns with polling set. If it ever stops polling, it
165 * must clear the polling bit.
166 */
167static void cpuidle_idle_call(void)
168{
169 struct cpuidle_device *dev = cpuidle_get_device();
170 struct cpuidle_driver *drv = cpuidle_get_cpu_driver(dev);
171 int next_state, entered_state;
172
173 /*
174 * Check if the idle task must be rescheduled. If it is the
175 * case, exit the function after re-enabling the local irq.
176 */
177 if (need_resched()) {
178 local_irq_enable();
179 return;
180 }
181
182 /*
183 * The RCU framework needs to be told that we are entering an idle
184 * section, so no more rcu read side critical sections and one more
185 * step to the grace period
186 */
187
188 if (cpuidle_not_available(drv, dev)) {
189 tick_nohz_idle_stop_tick();
190
191 default_idle_call();
192 goto exit_idle;
193 }
194
195 /*
196 * Suspend-to-idle ("s2idle") is a system state in which all user space
197 * has been frozen, all I/O devices have been suspended and the only
198 * activity happens here and in interrupts (if any). In that case bypass
199 * the cpuidle governor and go straight for the deepest idle state
200 * available. Possibly also suspend the local tick and the entire
201 * timekeeping to prevent timer interrupts from kicking us out of idle
202 * until a proper wakeup interrupt happens.
203 */
204
205 if (idle_should_enter_s2idle() || dev->forced_idle_latency_limit_ns) {
206 u64 max_latency_ns;
207
208 if (idle_should_enter_s2idle()) {
209
210 entered_state = call_cpuidle_s2idle(drv, dev);
211 if (entered_state > 0)
212 goto exit_idle;
213
214 max_latency_ns = U64_MAX;
215 } else {
216 max_latency_ns = dev->forced_idle_latency_limit_ns;
217 }
218
219 tick_nohz_idle_stop_tick();
220
221 next_state = cpuidle_find_deepest_state(drv, dev, max_latency_ns);
222 call_cpuidle(drv, dev, next_state);
223 } else {
224 bool stop_tick = true;
225
226 /*
227 * Ask the cpuidle framework to choose a convenient idle state.
228 */
229 next_state = cpuidle_select(drv, dev, &stop_tick);
230
231 if (stop_tick || tick_nohz_tick_stopped())
232 tick_nohz_idle_stop_tick();
233 else
234 tick_nohz_idle_retain_tick();
235
236 entered_state = call_cpuidle(drv, dev, next_state);
237 /*
238 * Give the governor an opportunity to reflect on the outcome
239 */
240 cpuidle_reflect(dev, entered_state);
241 }
242
243exit_idle:
244 __current_set_polling();
245
246 /*
247 * It is up to the idle functions to reenable local interrupts
248 */
249 if (WARN_ON_ONCE(irqs_disabled()))
250 local_irq_enable();
251}
252
253/*
254 * Generic idle loop implementation
255 *
256 * Called with polling cleared.
257 */
258static void do_idle(void)
259{
260 int cpu = smp_processor_id();
261
262 /*
263 * Check if we need to update blocked load
264 */
265 nohz_run_idle_balance(cpu);
266
267 /*
268 * If the arch has a polling bit, we maintain an invariant:
269 *
270 * Our polling bit is clear if we're not scheduled (i.e. if rq->curr !=
271 * rq->idle). This means that, if rq->idle has the polling bit set,
272 * then setting need_resched is guaranteed to cause the CPU to
273 * reschedule.
274 */
275
276 __current_set_polling();
277 tick_nohz_idle_enter();
278
279 while (!need_resched()) {
280 rmb();
281
282 local_irq_disable();
283
284 if (cpu_is_offline(cpu)) {
285 tick_nohz_idle_stop_tick();
286 cpuhp_report_idle_dead();
287 arch_cpu_idle_dead();
288 }
289
290 arch_cpu_idle_enter();
291 rcu_nocb_flush_deferred_wakeup();
292
293 /*
294 * In poll mode we reenable interrupts and spin. Also if we
295 * detected in the wakeup from idle path that the tick
296 * broadcast device expired for us, we don't want to go deep
297 * idle as we know that the IPI is going to arrive right away.
298 */
299 if (cpu_idle_force_poll || tick_check_broadcast_expired()) {
300 tick_nohz_idle_restart_tick();
301 cpu_idle_poll();
302 } else {
303 cpuidle_idle_call();
304 }
305 arch_cpu_idle_exit();
306 }
307
308 /*
309 * Since we fell out of the loop above, we know TIF_NEED_RESCHED must
310 * be set, propagate it into PREEMPT_NEED_RESCHED.
311 *
312 * This is required because for polling idle loops we will not have had
313 * an IPI to fold the state for us.
314 */
315 preempt_set_need_resched();
316 tick_nohz_idle_exit();
317 __current_clr_polling();
318
319 /*
320 * We promise to call sched_ttwu_pending() and reschedule if
321 * need_resched() is set while polling is set. That means that clearing
322 * polling needs to be visible before doing these things.
323 */
324 smp_mb__after_atomic();
325
326 /*
327 * RCU relies on this call to be done outside of an RCU read-side
328 * critical section.
329 */
330 flush_smp_call_function_queue();
331 schedule_idle();
332
333 if (unlikely(klp_patch_pending(current)))
334 klp_update_patch_state(current);
335}
336
337bool cpu_in_idle(unsigned long pc)
338{
339 return pc >= (unsigned long)__cpuidle_text_start &&
340 pc < (unsigned long)__cpuidle_text_end;
341}
342
343struct idle_timer {
344 struct hrtimer timer;
345 int done;
346};
347
348static enum hrtimer_restart idle_inject_timer_fn(struct hrtimer *timer)
349{
350 struct idle_timer *it = container_of(timer, struct idle_timer, timer);
351
352 WRITE_ONCE(it->done, 1);
353 set_tsk_need_resched(current);
354
355 return HRTIMER_NORESTART;
356}
357
358void play_idle_precise(u64 duration_ns, u64 latency_ns)
359{
360 struct idle_timer it;
361
362 /*
363 * Only FIFO tasks can disable the tick since they don't need the forced
364 * preemption.
365 */
366 WARN_ON_ONCE(current->policy != SCHED_FIFO);
367 WARN_ON_ONCE(current->nr_cpus_allowed != 1);
368 WARN_ON_ONCE(!(current->flags & PF_KTHREAD));
369 WARN_ON_ONCE(!(current->flags & PF_NO_SETAFFINITY));
370 WARN_ON_ONCE(!duration_ns);
371 WARN_ON_ONCE(current->mm);
372
373 rcu_sleep_check();
374 preempt_disable();
375 current->flags |= PF_IDLE;
376 cpuidle_use_deepest_state(latency_ns);
377
378 it.done = 0;
379 hrtimer_init_on_stack(&it.timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL_HARD);
380 it.timer.function = idle_inject_timer_fn;
381 hrtimer_start(&it.timer, ns_to_ktime(duration_ns),
382 HRTIMER_MODE_REL_PINNED_HARD);
383
384 while (!READ_ONCE(it.done))
385 do_idle();
386
387 cpuidle_use_deepest_state(0);
388 current->flags &= ~PF_IDLE;
389
390 preempt_fold_need_resched();
391 preempt_enable();
392}
393EXPORT_SYMBOL_GPL(play_idle_precise);
394
395void cpu_startup_entry(enum cpuhp_state state)
396{
397 arch_cpu_idle_prepare();
398 cpuhp_online_idle(state);
399 while (1)
400 do_idle();
401}
402
403/*
404 * idle-task scheduling class.
405 */
406
407#ifdef CONFIG_SMP
408static int
409select_task_rq_idle(struct task_struct *p, int cpu, int flags)
410{
411 return task_cpu(p); /* IDLE tasks as never migrated */
412}
413
414static int
415balance_idle(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
416{
417 return WARN_ON_ONCE(1);
418}
419#endif
420
421/*
422 * Idle tasks are unconditionally rescheduled:
423 */
424static void check_preempt_curr_idle(struct rq *rq, struct task_struct *p, int flags)
425{
426 resched_curr(rq);
427}
428
429static void put_prev_task_idle(struct rq *rq, struct task_struct *prev)
430{
431}
432
433static void set_next_task_idle(struct rq *rq, struct task_struct *next, bool first)
434{
435 update_idle_core(rq);
436 schedstat_inc(rq->sched_goidle);
437}
438
439#ifdef CONFIG_SMP
440static struct task_struct *pick_task_idle(struct rq *rq)
441{
442 return rq->idle;
443}
444#endif
445
446struct task_struct *pick_next_task_idle(struct rq *rq)
447{
448 struct task_struct *next = rq->idle;
449
450 set_next_task_idle(rq, next, true);
451
452 return next;
453}
454
455/*
456 * It is not legal to sleep in the idle task - print a warning
457 * message if some code attempts to do it:
458 */
459static void
460dequeue_task_idle(struct rq *rq, struct task_struct *p, int flags)
461{
462 raw_spin_rq_unlock_irq(rq);
463 printk(KERN_ERR "bad: scheduling from the idle thread!\n");
464 dump_stack();
465 raw_spin_rq_lock_irq(rq);
466}
467
468/*
469 * scheduler tick hitting a task of our scheduling class.
470 *
471 * NOTE: This function can be called remotely by the tick offload that
472 * goes along full dynticks. Therefore no local assumption can be made
473 * and everything must be accessed through the @rq and @curr passed in
474 * parameters.
475 */
476static void task_tick_idle(struct rq *rq, struct task_struct *curr, int queued)
477{
478}
479
480static void switched_to_idle(struct rq *rq, struct task_struct *p)
481{
482 BUG();
483}
484
485static void
486prio_changed_idle(struct rq *rq, struct task_struct *p, int oldprio)
487{
488 BUG();
489}
490
491static void update_curr_idle(struct rq *rq)
492{
493}
494
495/*
496 * Simple, special scheduling class for the per-CPU idle tasks:
497 */
498DEFINE_SCHED_CLASS(idle) = {
499
500 /* no enqueue/yield_task for idle tasks */
501
502 /* dequeue is not valid, we print a debug message there: */
503 .dequeue_task = dequeue_task_idle,
504
505 .check_preempt_curr = check_preempt_curr_idle,
506
507 .pick_next_task = pick_next_task_idle,
508 .put_prev_task = put_prev_task_idle,
509 .set_next_task = set_next_task_idle,
510
511#ifdef CONFIG_SMP
512 .balance = balance_idle,
513 .pick_task = pick_task_idle,
514 .select_task_rq = select_task_rq_idle,
515 .set_cpus_allowed = set_cpus_allowed_common,
516#endif
517
518 .task_tick = task_tick_idle,
519
520 .prio_changed = prio_changed_idle,
521 .switched_to = switched_to_idle,
522 .update_curr = update_curr_idle,
523};
1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * Generic entry points for the idle threads and
4 * implementation of the idle task scheduling class.
5 *
6 * (NOTE: these are not related to SCHED_IDLE batch scheduled
7 * tasks which are handled in sched/fair.c )
8 */
9#include "sched.h"
10
11#include <trace/events/power.h>
12
13/* Linker adds these: start and end of __cpuidle functions */
14extern char __cpuidle_text_start[], __cpuidle_text_end[];
15
16/**
17 * sched_idle_set_state - Record idle state for the current CPU.
18 * @idle_state: State to record.
19 */
20void sched_idle_set_state(struct cpuidle_state *idle_state)
21{
22 idle_set_state(this_rq(), idle_state);
23}
24
25static int __read_mostly cpu_idle_force_poll;
26
27void cpu_idle_poll_ctrl(bool enable)
28{
29 if (enable) {
30 cpu_idle_force_poll++;
31 } else {
32 cpu_idle_force_poll--;
33 WARN_ON_ONCE(cpu_idle_force_poll < 0);
34 }
35}
36
37#ifdef CONFIG_GENERIC_IDLE_POLL_SETUP
38static int __init cpu_idle_poll_setup(char *__unused)
39{
40 cpu_idle_force_poll = 1;
41
42 return 1;
43}
44__setup("nohlt", cpu_idle_poll_setup);
45
46static int __init cpu_idle_nopoll_setup(char *__unused)
47{
48 cpu_idle_force_poll = 0;
49
50 return 1;
51}
52__setup("hlt", cpu_idle_nopoll_setup);
53#endif
54
55static noinline int __cpuidle cpu_idle_poll(void)
56{
57 rcu_idle_enter();
58 trace_cpu_idle_rcuidle(0, smp_processor_id());
59 local_irq_enable();
60 stop_critical_timings();
61
62 while (!tif_need_resched() &&
63 (cpu_idle_force_poll || tick_check_broadcast_expired()))
64 cpu_relax();
65 start_critical_timings();
66 trace_cpu_idle_rcuidle(PWR_EVENT_EXIT, smp_processor_id());
67 rcu_idle_exit();
68
69 return 1;
70}
71
72/* Weak implementations for optional arch specific functions */
73void __weak arch_cpu_idle_prepare(void) { }
74void __weak arch_cpu_idle_enter(void) { }
75void __weak arch_cpu_idle_exit(void) { }
76void __weak arch_cpu_idle_dead(void) { }
77void __weak arch_cpu_idle(void)
78{
79 cpu_idle_force_poll = 1;
80 local_irq_enable();
81}
82
83/**
84 * default_idle_call - Default CPU idle routine.
85 *
86 * To use when the cpuidle framework cannot be used.
87 */
88void __cpuidle default_idle_call(void)
89{
90 if (current_clr_polling_and_test()) {
91 local_irq_enable();
92 } else {
93 stop_critical_timings();
94 arch_cpu_idle();
95 start_critical_timings();
96 }
97}
98
99static int call_cpuidle(struct cpuidle_driver *drv, struct cpuidle_device *dev,
100 int next_state)
101{
102 /*
103 * The idle task must be scheduled, it is pointless to go to idle, just
104 * update no idle residency and return.
105 */
106 if (current_clr_polling_and_test()) {
107 dev->last_residency = 0;
108 local_irq_enable();
109 return -EBUSY;
110 }
111
112 /*
113 * Enter the idle state previously returned by the governor decision.
114 * This function will block until an interrupt occurs and will take
115 * care of re-enabling the local interrupts
116 */
117 return cpuidle_enter(drv, dev, next_state);
118}
119
120/**
121 * cpuidle_idle_call - the main idle function
122 *
123 * NOTE: no locks or semaphores should be used here
124 *
125 * On archs that support TIF_POLLING_NRFLAG, is called with polling
126 * set, and it returns with polling set. If it ever stops polling, it
127 * must clear the polling bit.
128 */
129static void cpuidle_idle_call(void)
130{
131 struct cpuidle_device *dev = cpuidle_get_device();
132 struct cpuidle_driver *drv = cpuidle_get_cpu_driver(dev);
133 int next_state, entered_state;
134
135 /*
136 * Check if the idle task must be rescheduled. If it is the
137 * case, exit the function after re-enabling the local irq.
138 */
139 if (need_resched()) {
140 local_irq_enable();
141 return;
142 }
143
144 /*
145 * The RCU framework needs to be told that we are entering an idle
146 * section, so no more rcu read side critical sections and one more
147 * step to the grace period
148 */
149
150 if (cpuidle_not_available(drv, dev)) {
151 tick_nohz_idle_stop_tick();
152 rcu_idle_enter();
153
154 default_idle_call();
155 goto exit_idle;
156 }
157
158 /*
159 * Suspend-to-idle ("s2idle") is a system state in which all user space
160 * has been frozen, all I/O devices have been suspended and the only
161 * activity happens here and in iterrupts (if any). In that case bypass
162 * the cpuidle governor and go stratight for the deepest idle state
163 * available. Possibly also suspend the local tick and the entire
164 * timekeeping to prevent timer interrupts from kicking us out of idle
165 * until a proper wakeup interrupt happens.
166 */
167
168 if (idle_should_enter_s2idle() || dev->use_deepest_state) {
169 if (idle_should_enter_s2idle()) {
170 rcu_idle_enter();
171
172 entered_state = cpuidle_enter_s2idle(drv, dev);
173 if (entered_state > 0) {
174 local_irq_enable();
175 goto exit_idle;
176 }
177
178 rcu_idle_exit();
179 }
180
181 tick_nohz_idle_stop_tick();
182 rcu_idle_enter();
183
184 next_state = cpuidle_find_deepest_state(drv, dev);
185 call_cpuidle(drv, dev, next_state);
186 } else {
187 bool stop_tick = true;
188
189 /*
190 * Ask the cpuidle framework to choose a convenient idle state.
191 */
192 next_state = cpuidle_select(drv, dev, &stop_tick);
193
194 if (stop_tick || tick_nohz_tick_stopped())
195 tick_nohz_idle_stop_tick();
196 else
197 tick_nohz_idle_retain_tick();
198
199 rcu_idle_enter();
200
201 entered_state = call_cpuidle(drv, dev, next_state);
202 /*
203 * Give the governor an opportunity to reflect on the outcome
204 */
205 cpuidle_reflect(dev, entered_state);
206 }
207
208exit_idle:
209 __current_set_polling();
210
211 /*
212 * It is up to the idle functions to reenable local interrupts
213 */
214 if (WARN_ON_ONCE(irqs_disabled()))
215 local_irq_enable();
216
217 rcu_idle_exit();
218}
219
220/*
221 * Generic idle loop implementation
222 *
223 * Called with polling cleared.
224 */
225static void do_idle(void)
226{
227 int cpu = smp_processor_id();
228 /*
229 * If the arch has a polling bit, we maintain an invariant:
230 *
231 * Our polling bit is clear if we're not scheduled (i.e. if rq->curr !=
232 * rq->idle). This means that, if rq->idle has the polling bit set,
233 * then setting need_resched is guaranteed to cause the CPU to
234 * reschedule.
235 */
236
237 __current_set_polling();
238 tick_nohz_idle_enter();
239
240 while (!need_resched()) {
241 rmb();
242
243 local_irq_disable();
244
245 if (cpu_is_offline(cpu)) {
246 tick_nohz_idle_stop_tick();
247 cpuhp_report_idle_dead();
248 arch_cpu_idle_dead();
249 }
250
251 arch_cpu_idle_enter();
252
253 /*
254 * In poll mode we reenable interrupts and spin. Also if we
255 * detected in the wakeup from idle path that the tick
256 * broadcast device expired for us, we don't want to go deep
257 * idle as we know that the IPI is going to arrive right away.
258 */
259 if (cpu_idle_force_poll || tick_check_broadcast_expired()) {
260 tick_nohz_idle_restart_tick();
261 cpu_idle_poll();
262 } else {
263 cpuidle_idle_call();
264 }
265 arch_cpu_idle_exit();
266 }
267
268 /*
269 * Since we fell out of the loop above, we know TIF_NEED_RESCHED must
270 * be set, propagate it into PREEMPT_NEED_RESCHED.
271 *
272 * This is required because for polling idle loops we will not have had
273 * an IPI to fold the state for us.
274 */
275 preempt_set_need_resched();
276 tick_nohz_idle_exit();
277 __current_clr_polling();
278
279 /*
280 * We promise to call sched_ttwu_pending() and reschedule if
281 * need_resched() is set while polling is set. That means that clearing
282 * polling needs to be visible before doing these things.
283 */
284 smp_mb__after_atomic();
285
286 sched_ttwu_pending();
287 schedule_idle();
288
289 if (unlikely(klp_patch_pending(current)))
290 klp_update_patch_state(current);
291}
292
293bool cpu_in_idle(unsigned long pc)
294{
295 return pc >= (unsigned long)__cpuidle_text_start &&
296 pc < (unsigned long)__cpuidle_text_end;
297}
298
299struct idle_timer {
300 struct hrtimer timer;
301 int done;
302};
303
304static enum hrtimer_restart idle_inject_timer_fn(struct hrtimer *timer)
305{
306 struct idle_timer *it = container_of(timer, struct idle_timer, timer);
307
308 WRITE_ONCE(it->done, 1);
309 set_tsk_need_resched(current);
310
311 return HRTIMER_NORESTART;
312}
313
314void play_idle(unsigned long duration_us)
315{
316 struct idle_timer it;
317
318 /*
319 * Only FIFO tasks can disable the tick since they don't need the forced
320 * preemption.
321 */
322 WARN_ON_ONCE(current->policy != SCHED_FIFO);
323 WARN_ON_ONCE(current->nr_cpus_allowed != 1);
324 WARN_ON_ONCE(!(current->flags & PF_KTHREAD));
325 WARN_ON_ONCE(!(current->flags & PF_NO_SETAFFINITY));
326 WARN_ON_ONCE(!duration_us);
327
328 rcu_sleep_check();
329 preempt_disable();
330 current->flags |= PF_IDLE;
331 cpuidle_use_deepest_state(true);
332
333 it.done = 0;
334 hrtimer_init_on_stack(&it.timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
335 it.timer.function = idle_inject_timer_fn;
336 hrtimer_start(&it.timer, ns_to_ktime(duration_us * NSEC_PER_USEC),
337 HRTIMER_MODE_REL_PINNED);
338
339 while (!READ_ONCE(it.done))
340 do_idle();
341
342 cpuidle_use_deepest_state(false);
343 current->flags &= ~PF_IDLE;
344
345 preempt_fold_need_resched();
346 preempt_enable();
347}
348EXPORT_SYMBOL_GPL(play_idle);
349
350void cpu_startup_entry(enum cpuhp_state state)
351{
352 arch_cpu_idle_prepare();
353 cpuhp_online_idle(state);
354 while (1)
355 do_idle();
356}
357
358/*
359 * idle-task scheduling class.
360 */
361
362#ifdef CONFIG_SMP
363static int
364select_task_rq_idle(struct task_struct *p, int cpu, int sd_flag, int flags)
365{
366 return task_cpu(p); /* IDLE tasks as never migrated */
367}
368
369static int
370balance_idle(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
371{
372 return WARN_ON_ONCE(1);
373}
374#endif
375
376/*
377 * Idle tasks are unconditionally rescheduled:
378 */
379static void check_preempt_curr_idle(struct rq *rq, struct task_struct *p, int flags)
380{
381 resched_curr(rq);
382}
383
384static void put_prev_task_idle(struct rq *rq, struct task_struct *prev)
385{
386}
387
388static void set_next_task_idle(struct rq *rq, struct task_struct *next)
389{
390 update_idle_core(rq);
391 schedstat_inc(rq->sched_goidle);
392}
393
394static struct task_struct *
395pick_next_task_idle(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
396{
397 struct task_struct *next = rq->idle;
398
399 if (prev)
400 put_prev_task(rq, prev);
401
402 set_next_task_idle(rq, next);
403
404 return next;
405}
406
407/*
408 * It is not legal to sleep in the idle task - print a warning
409 * message if some code attempts to do it:
410 */
411static void
412dequeue_task_idle(struct rq *rq, struct task_struct *p, int flags)
413{
414 raw_spin_unlock_irq(&rq->lock);
415 printk(KERN_ERR "bad: scheduling from the idle thread!\n");
416 dump_stack();
417 raw_spin_lock_irq(&rq->lock);
418}
419
420/*
421 * scheduler tick hitting a task of our scheduling class.
422 *
423 * NOTE: This function can be called remotely by the tick offload that
424 * goes along full dynticks. Therefore no local assumption can be made
425 * and everything must be accessed through the @rq and @curr passed in
426 * parameters.
427 */
428static void task_tick_idle(struct rq *rq, struct task_struct *curr, int queued)
429{
430}
431
432static void switched_to_idle(struct rq *rq, struct task_struct *p)
433{
434 BUG();
435}
436
437static void
438prio_changed_idle(struct rq *rq, struct task_struct *p, int oldprio)
439{
440 BUG();
441}
442
443static unsigned int get_rr_interval_idle(struct rq *rq, struct task_struct *task)
444{
445 return 0;
446}
447
448static void update_curr_idle(struct rq *rq)
449{
450}
451
452/*
453 * Simple, special scheduling class for the per-CPU idle tasks:
454 */
455const struct sched_class idle_sched_class = {
456 /* .next is NULL */
457 /* no enqueue/yield_task for idle tasks */
458
459 /* dequeue is not valid, we print a debug message there: */
460 .dequeue_task = dequeue_task_idle,
461
462 .check_preempt_curr = check_preempt_curr_idle,
463
464 .pick_next_task = pick_next_task_idle,
465 .put_prev_task = put_prev_task_idle,
466 .set_next_task = set_next_task_idle,
467
468#ifdef CONFIG_SMP
469 .balance = balance_idle,
470 .select_task_rq = select_task_rq_idle,
471 .set_cpus_allowed = set_cpus_allowed_common,
472#endif
473
474 .task_tick = task_tick_idle,
475
476 .get_rr_interval = get_rr_interval_idle,
477
478 .prio_changed = prio_changed_idle,
479 .switched_to = switched_to_idle,
480 .update_curr = update_curr_idle,
481};