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 */
14 extern 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  */
sched_idle_set_state(struct cpuidle_state * idle_state)20 void sched_idle_set_state(struct cpuidle_state *idle_state)
21 {
22 	idle_set_state(this_rq(), idle_state);
23 }
24 
25 static int __read_mostly cpu_idle_force_poll;
26 
cpu_idle_poll_ctrl(bool enable)27 void 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
cpu_idle_poll_setup(char * __unused)38 static 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 
cpu_idle_nopoll_setup(char * __unused)46 static 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 
cpu_idle_poll(void)55 static noinline int __cpuidle cpu_idle_poll(void)
56 {
57 	trace_cpu_idle(0, smp_processor_id());
58 	stop_critical_timings();
59 	rcu_idle_enter();
60 	local_irq_enable();
61 
62 	while (!tif_need_resched() &&
63 	       (cpu_idle_force_poll || tick_check_broadcast_expired()))
64 		cpu_relax();
65 
66 	rcu_idle_exit();
67 	start_critical_timings();
68 	trace_cpu_idle(PWR_EVENT_EXIT, smp_processor_id());
69 
70 	return 1;
71 }
72 
73 /* Weak implementations for optional arch specific functions */
arch_cpu_idle_prepare(void)74 void __weak arch_cpu_idle_prepare(void) { }
arch_cpu_idle_enter(void)75 void __weak arch_cpu_idle_enter(void) { }
arch_cpu_idle_exit(void)76 void __weak arch_cpu_idle_exit(void) { }
arch_cpu_idle_dead(void)77 void __weak arch_cpu_idle_dead(void) { }
arch_cpu_idle(void)78 void __weak arch_cpu_idle(void)
79 {
80 	cpu_idle_force_poll = 1;
81 	raw_local_irq_enable();
82 }
83 
84 /**
85  * default_idle_call - Default CPU idle routine.
86  *
87  * To use when the cpuidle framework cannot be used.
88  */
default_idle_call(void)89 void __cpuidle default_idle_call(void)
90 {
91 	if (current_clr_polling_and_test()) {
92 		local_irq_enable();
93 	} else {
94 
95 		trace_cpu_idle(1, smp_processor_id());
96 		stop_critical_timings();
97 
98 		/*
99 		 * arch_cpu_idle() is supposed to enable IRQs, however
100 		 * we can't do that because of RCU and tracing.
101 		 *
102 		 * Trace IRQs enable here, then switch off RCU, and have
103 		 * arch_cpu_idle() use raw_local_irq_enable(). Note that
104 		 * rcu_idle_enter() relies on lockdep IRQ state, so switch that
105 		 * last -- this is very similar to the entry code.
106 		 */
107 		trace_hardirqs_on_prepare();
108 		lockdep_hardirqs_on_prepare(_THIS_IP_);
109 		rcu_idle_enter();
110 		lockdep_hardirqs_on(_THIS_IP_);
111 
112 		arch_cpu_idle();
113 
114 		/*
115 		 * OK, so IRQs are enabled here, but RCU needs them disabled to
116 		 * turn itself back on.. funny thing is that disabling IRQs
117 		 * will cause tracing, which needs RCU. Jump through hoops to
118 		 * make it 'work'.
119 		 */
120 		raw_local_irq_disable();
121 		lockdep_hardirqs_off(_THIS_IP_);
122 		rcu_idle_exit();
123 		lockdep_hardirqs_on(_THIS_IP_);
124 		raw_local_irq_enable();
125 
126 		start_critical_timings();
127 		trace_cpu_idle(PWR_EVENT_EXIT, smp_processor_id());
128 	}
129 }
130 
call_cpuidle_s2idle(struct cpuidle_driver * drv,struct cpuidle_device * dev)131 static int call_cpuidle_s2idle(struct cpuidle_driver *drv,
132 			       struct cpuidle_device *dev)
133 {
134 	if (current_clr_polling_and_test())
135 		return -EBUSY;
136 
137 	return cpuidle_enter_s2idle(drv, dev);
138 }
139 
call_cpuidle(struct cpuidle_driver * drv,struct cpuidle_device * dev,int next_state)140 static int call_cpuidle(struct cpuidle_driver *drv, struct cpuidle_device *dev,
141 		      int next_state)
142 {
143 	/*
144 	 * The idle task must be scheduled, it is pointless to go to idle, just
145 	 * update no idle residency and return.
146 	 */
147 	if (current_clr_polling_and_test()) {
148 		dev->last_residency_ns = 0;
149 		local_irq_enable();
150 		return -EBUSY;
151 	}
152 
153 	/*
154 	 * Enter the idle state previously returned by the governor decision.
155 	 * This function will block until an interrupt occurs and will take
156 	 * care of re-enabling the local interrupts
157 	 */
158 	return cpuidle_enter(drv, dev, next_state);
159 }
160 
161 /**
162  * cpuidle_idle_call - the main idle function
163  *
164  * NOTE: no locks or semaphores should be used here
165  *
166  * On architectures that support TIF_POLLING_NRFLAG, is called with polling
167  * set, and it returns with polling set.  If it ever stops polling, it
168  * must clear the polling bit.
169  */
cpuidle_idle_call(void)170 static void cpuidle_idle_call(void)
171 {
172 	struct cpuidle_device *dev = cpuidle_get_device();
173 	struct cpuidle_driver *drv = cpuidle_get_cpu_driver(dev);
174 	int next_state, entered_state;
175 
176 	/*
177 	 * Check if the idle task must be rescheduled. If it is the
178 	 * case, exit the function after re-enabling the local irq.
179 	 */
180 	if (need_resched()) {
181 		local_irq_enable();
182 		return;
183 	}
184 
185 	/*
186 	 * The RCU framework needs to be told that we are entering an idle
187 	 * section, so no more rcu read side critical sections and one more
188 	 * step to the grace period
189 	 */
190 
191 	if (cpuidle_not_available(drv, dev)) {
192 		tick_nohz_idle_stop_tick();
193 
194 		default_idle_call();
195 		goto exit_idle;
196 	}
197 
198 	/*
199 	 * Suspend-to-idle ("s2idle") is a system state in which all user space
200 	 * has been frozen, all I/O devices have been suspended and the only
201 	 * activity happens here and in interrupts (if any). In that case bypass
202 	 * the cpuidle governor and go straight for the deepest idle state
203 	 * available.  Possibly also suspend the local tick and the entire
204 	 * timekeeping to prevent timer interrupts from kicking us out of idle
205 	 * until a proper wakeup interrupt happens.
206 	 */
207 
208 	if (idle_should_enter_s2idle() || dev->forced_idle_latency_limit_ns) {
209 		u64 max_latency_ns;
210 
211 		if (idle_should_enter_s2idle()) {
212 
213 			entered_state = call_cpuidle_s2idle(drv, dev);
214 			if (entered_state > 0)
215 				goto exit_idle;
216 
217 			max_latency_ns = U64_MAX;
218 		} else {
219 			max_latency_ns = dev->forced_idle_latency_limit_ns;
220 		}
221 
222 		tick_nohz_idle_stop_tick();
223 
224 		next_state = cpuidle_find_deepest_state(drv, dev, max_latency_ns);
225 		call_cpuidle(drv, dev, next_state);
226 	} else {
227 		bool stop_tick = true;
228 
229 		/*
230 		 * Ask the cpuidle framework to choose a convenient idle state.
231 		 */
232 		next_state = cpuidle_select(drv, dev, &stop_tick);
233 
234 		if (stop_tick || tick_nohz_tick_stopped())
235 			tick_nohz_idle_stop_tick();
236 		else
237 			tick_nohz_idle_retain_tick();
238 
239 		entered_state = call_cpuidle(drv, dev, next_state);
240 		/*
241 		 * Give the governor an opportunity to reflect on the outcome
242 		 */
243 		cpuidle_reflect(dev, entered_state);
244 	}
245 
246 exit_idle:
247 	__current_set_polling();
248 
249 	/*
250 	 * It is up to the idle functions to reenable local interrupts
251 	 */
252 	if (WARN_ON_ONCE(irqs_disabled()))
253 		local_irq_enable();
254 }
255 
256 /*
257  * Generic idle loop implementation
258  *
259  * Called with polling cleared.
260  */
do_idle(void)261 static void do_idle(void)
262 {
263 	int cpu = smp_processor_id();
264 
265 	/*
266 	 * Check if we need to update blocked load
267 	 */
268 	nohz_run_idle_balance(cpu);
269 
270 	/*
271 	 * If the arch has a polling bit, we maintain an invariant:
272 	 *
273 	 * Our polling bit is clear if we're not scheduled (i.e. if rq->curr !=
274 	 * rq->idle). This means that, if rq->idle has the polling bit set,
275 	 * then setting need_resched is guaranteed to cause the CPU to
276 	 * reschedule.
277 	 */
278 
279 	__current_set_polling();
280 	tick_nohz_idle_enter();
281 
282 	while (!need_resched()) {
283 		rmb();
284 
285 		local_irq_disable();
286 
287 		if (cpu_is_offline(cpu)) {
288 			tick_nohz_idle_stop_tick();
289 			cpuhp_report_idle_dead();
290 			arch_cpu_idle_dead();
291 		}
292 
293 		arch_cpu_idle_enter();
294 		rcu_nocb_flush_deferred_wakeup();
295 
296 		/*
297 		 * In poll mode we reenable interrupts and spin. Also if we
298 		 * detected in the wakeup from idle path that the tick
299 		 * broadcast device expired for us, we don't want to go deep
300 		 * idle as we know that the IPI is going to arrive right away.
301 		 */
302 		if (cpu_idle_force_poll || tick_check_broadcast_expired()) {
303 			tick_nohz_idle_restart_tick();
304 			cpu_idle_poll();
305 		} else {
306 			cpuidle_idle_call();
307 		}
308 		arch_cpu_idle_exit();
309 	}
310 
311 	/*
312 	 * Since we fell out of the loop above, we know TIF_NEED_RESCHED must
313 	 * be set, propagate it into PREEMPT_NEED_RESCHED.
314 	 *
315 	 * This is required because for polling idle loops we will not have had
316 	 * an IPI to fold the state for us.
317 	 */
318 	preempt_set_need_resched();
319 	tick_nohz_idle_exit();
320 	__current_clr_polling();
321 
322 	/*
323 	 * We promise to call sched_ttwu_pending() and reschedule if
324 	 * need_resched() is set while polling is set. That means that clearing
325 	 * polling needs to be visible before doing these things.
326 	 */
327 	smp_mb__after_atomic();
328 
329 	/*
330 	 * RCU relies on this call to be done outside of an RCU read-side
331 	 * critical section.
332 	 */
333 	flush_smp_call_function_from_idle();
334 	schedule_idle();
335 
336 	if (unlikely(klp_patch_pending(current)))
337 		klp_update_patch_state(current);
338 }
339 
cpu_in_idle(unsigned long pc)340 bool cpu_in_idle(unsigned long pc)
341 {
342 	return pc >= (unsigned long)__cpuidle_text_start &&
343 		pc < (unsigned long)__cpuidle_text_end;
344 }
345 
346 struct idle_timer {
347 	struct hrtimer timer;
348 	int done;
349 };
350 
idle_inject_timer_fn(struct hrtimer * timer)351 static enum hrtimer_restart idle_inject_timer_fn(struct hrtimer *timer)
352 {
353 	struct idle_timer *it = container_of(timer, struct idle_timer, timer);
354 
355 	WRITE_ONCE(it->done, 1);
356 	set_tsk_need_resched(current);
357 
358 	return HRTIMER_NORESTART;
359 }
360 
play_idle_precise(u64 duration_ns,u64 latency_ns)361 void play_idle_precise(u64 duration_ns, u64 latency_ns)
362 {
363 	struct idle_timer it;
364 
365 	/*
366 	 * Only FIFO tasks can disable the tick since they don't need the forced
367 	 * preemption.
368 	 */
369 	WARN_ON_ONCE(current->policy != SCHED_FIFO);
370 	WARN_ON_ONCE(current->nr_cpus_allowed != 1);
371 	WARN_ON_ONCE(!(current->flags & PF_KTHREAD));
372 	WARN_ON_ONCE(!(current->flags & PF_NO_SETAFFINITY));
373 	WARN_ON_ONCE(!duration_ns);
374 	WARN_ON_ONCE(current->mm);
375 
376 	rcu_sleep_check();
377 	preempt_disable();
378 	current->flags |= PF_IDLE;
379 	cpuidle_use_deepest_state(latency_ns);
380 
381 	it.done = 0;
382 	hrtimer_init_on_stack(&it.timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL_HARD);
383 	it.timer.function = idle_inject_timer_fn;
384 	hrtimer_start(&it.timer, ns_to_ktime(duration_ns),
385 		      HRTIMER_MODE_REL_PINNED_HARD);
386 
387 	while (!READ_ONCE(it.done))
388 		do_idle();
389 
390 	cpuidle_use_deepest_state(0);
391 	current->flags &= ~PF_IDLE;
392 
393 	preempt_fold_need_resched();
394 	preempt_enable();
395 }
396 EXPORT_SYMBOL_GPL(play_idle_precise);
397 
cpu_startup_entry(enum cpuhp_state state)398 void cpu_startup_entry(enum cpuhp_state state)
399 {
400 	arch_cpu_idle_prepare();
401 	cpuhp_online_idle(state);
402 	while (1)
403 		do_idle();
404 }
405 
406 /*
407  * idle-task scheduling class.
408  */
409 
410 #ifdef CONFIG_SMP
411 static int
select_task_rq_idle(struct task_struct * p,int cpu,int flags)412 select_task_rq_idle(struct task_struct *p, int cpu, int flags)
413 {
414 	return task_cpu(p); /* IDLE tasks as never migrated */
415 }
416 
417 static int
balance_idle(struct rq * rq,struct task_struct * prev,struct rq_flags * rf)418 balance_idle(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
419 {
420 	return WARN_ON_ONCE(1);
421 }
422 #endif
423 
424 /*
425  * Idle tasks are unconditionally rescheduled:
426  */
check_preempt_curr_idle(struct rq * rq,struct task_struct * p,int flags)427 static void check_preempt_curr_idle(struct rq *rq, struct task_struct *p, int flags)
428 {
429 	resched_curr(rq);
430 }
431 
put_prev_task_idle(struct rq * rq,struct task_struct * prev)432 static void put_prev_task_idle(struct rq *rq, struct task_struct *prev)
433 {
434 }
435 
set_next_task_idle(struct rq * rq,struct task_struct * next,bool first)436 static void set_next_task_idle(struct rq *rq, struct task_struct *next, bool first)
437 {
438 	update_idle_core(rq);
439 	schedstat_inc(rq->sched_goidle);
440 	queue_core_balance(rq);
441 }
442 
443 #ifdef CONFIG_SMP
pick_task_idle(struct rq * rq)444 static struct task_struct *pick_task_idle(struct rq *rq)
445 {
446 	return rq->idle;
447 }
448 #endif
449 
pick_next_task_idle(struct rq * rq)450 struct task_struct *pick_next_task_idle(struct rq *rq)
451 {
452 	struct task_struct *next = rq->idle;
453 
454 	set_next_task_idle(rq, next, true);
455 
456 	return next;
457 }
458 
459 /*
460  * It is not legal to sleep in the idle task - print a warning
461  * message if some code attempts to do it:
462  */
463 static void
dequeue_task_idle(struct rq * rq,struct task_struct * p,int flags)464 dequeue_task_idle(struct rq *rq, struct task_struct *p, int flags)
465 {
466 	raw_spin_rq_unlock_irq(rq);
467 	printk(KERN_ERR "bad: scheduling from the idle thread!\n");
468 	dump_stack();
469 	raw_spin_rq_lock_irq(rq);
470 }
471 
472 /*
473  * scheduler tick hitting a task of our scheduling class.
474  *
475  * NOTE: This function can be called remotely by the tick offload that
476  * goes along full dynticks. Therefore no local assumption can be made
477  * and everything must be accessed through the @rq and @curr passed in
478  * parameters.
479  */
task_tick_idle(struct rq * rq,struct task_struct * curr,int queued)480 static void task_tick_idle(struct rq *rq, struct task_struct *curr, int queued)
481 {
482 }
483 
switched_to_idle(struct rq * rq,struct task_struct * p)484 static void switched_to_idle(struct rq *rq, struct task_struct *p)
485 {
486 	BUG();
487 }
488 
489 static void
prio_changed_idle(struct rq * rq,struct task_struct * p,int oldprio)490 prio_changed_idle(struct rq *rq, struct task_struct *p, int oldprio)
491 {
492 	BUG();
493 }
494 
update_curr_idle(struct rq * rq)495 static void update_curr_idle(struct rq *rq)
496 {
497 }
498 
499 /*
500  * Simple, special scheduling class for the per-CPU idle tasks:
501  */
502 DEFINE_SCHED_CLASS(idle) = {
503 
504 	/* no enqueue/yield_task for idle tasks */
505 
506 	/* dequeue is not valid, we print a debug message there: */
507 	.dequeue_task		= dequeue_task_idle,
508 
509 	.check_preempt_curr	= check_preempt_curr_idle,
510 
511 	.pick_next_task		= pick_next_task_idle,
512 	.put_prev_task		= put_prev_task_idle,
513 	.set_next_task          = set_next_task_idle,
514 
515 #ifdef CONFIG_SMP
516 	.balance		= balance_idle,
517 	.pick_task		= pick_task_idle,
518 	.select_task_rq		= select_task_rq_idle,
519 	.set_cpus_allowed	= set_cpus_allowed_common,
520 #endif
521 
522 	.task_tick		= task_tick_idle,
523 
524 	.prio_changed		= prio_changed_idle,
525 	.switched_to		= switched_to_idle,
526 	.update_curr		= update_curr_idle,
527 };
528