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 */
11 extern 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  */
sched_idle_set_state(struct cpuidle_state * idle_state)17 void sched_idle_set_state(struct cpuidle_state *idle_state)
18 {
19 	idle_set_state(this_rq(), idle_state);
20 }
21 
22 static int __read_mostly cpu_idle_force_poll;
23 
cpu_idle_poll_ctrl(bool enable)24 void 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
cpu_idle_poll_setup(char * __unused)35 static 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 
cpu_idle_nopoll_setup(char * __unused)43 static 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 
cpu_idle_poll(void)52 static noinline int __cpuidle cpu_idle_poll(void)
53 {
54 	trace_cpu_idle(0, smp_processor_id());
55 	stop_critical_timings();
56 	rcu_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 	rcu_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 */
arch_cpu_idle_prepare(void)71 void __weak arch_cpu_idle_prepare(void) { }
arch_cpu_idle_enter(void)72 void __weak arch_cpu_idle_enter(void) { }
arch_cpu_idle_exit(void)73 void __weak arch_cpu_idle_exit(void) { }
arch_cpu_idle_dead(void)74 void __weak arch_cpu_idle_dead(void) { }
arch_cpu_idle(void)75 void __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  */
default_idle_call(void)86 void __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 		 * rcu_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 		rcu_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 		rcu_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 
call_cpuidle_s2idle(struct cpuidle_driver * drv,struct cpuidle_device * dev)128 static 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 
call_cpuidle(struct cpuidle_driver * drv,struct cpuidle_device * dev,int next_state)137 static 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  */
cpuidle_idle_call(void)167 static 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 
243 exit_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  */
do_idle(void)258 static 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 
cpu_in_idle(unsigned long pc)337 bool cpu_in_idle(unsigned long pc)
338 {
339 	return pc >= (unsigned long)__cpuidle_text_start &&
340 		pc < (unsigned long)__cpuidle_text_end;
341 }
342 
343 struct idle_timer {
344 	struct hrtimer timer;
345 	int done;
346 };
347 
idle_inject_timer_fn(struct hrtimer * timer)348 static 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 
play_idle_precise(u64 duration_ns,u64 latency_ns)358 void 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 }
393 EXPORT_SYMBOL_GPL(play_idle_precise);
394 
cpu_startup_entry(enum cpuhp_state state)395 void 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
408 static int
select_task_rq_idle(struct task_struct * p,int cpu,int flags)409 select_task_rq_idle(struct task_struct *p, int cpu, int flags)
410 {
411 	return task_cpu(p); /* IDLE tasks as never migrated */
412 }
413 
414 static int
balance_idle(struct rq * rq,struct task_struct * prev,struct rq_flags * rf)415 balance_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  */
check_preempt_curr_idle(struct rq * rq,struct task_struct * p,int flags)424 static void check_preempt_curr_idle(struct rq *rq, struct task_struct *p, int flags)
425 {
426 	resched_curr(rq);
427 }
428 
put_prev_task_idle(struct rq * rq,struct task_struct * prev)429 static void put_prev_task_idle(struct rq *rq, struct task_struct *prev)
430 {
431 }
432 
set_next_task_idle(struct rq * rq,struct task_struct * next,bool first)433 static 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
pick_task_idle(struct rq * rq)440 static struct task_struct *pick_task_idle(struct rq *rq)
441 {
442 	return rq->idle;
443 }
444 #endif
445 
pick_next_task_idle(struct rq * rq)446 struct 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  */
459 static void
dequeue_task_idle(struct rq * rq,struct task_struct * p,int flags)460 dequeue_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  */
task_tick_idle(struct rq * rq,struct task_struct * curr,int queued)476 static void task_tick_idle(struct rq *rq, struct task_struct *curr, int queued)
477 {
478 }
479 
switched_to_idle(struct rq * rq,struct task_struct * p)480 static void switched_to_idle(struct rq *rq, struct task_struct *p)
481 {
482 	BUG();
483 }
484 
485 static void
prio_changed_idle(struct rq * rq,struct task_struct * p,int oldprio)486 prio_changed_idle(struct rq *rq, struct task_struct *p, int oldprio)
487 {
488 	BUG();
489 }
490 
update_curr_idle(struct rq * rq)491 static void update_curr_idle(struct rq *rq)
492 {
493 }
494 
495 /*
496  * Simple, special scheduling class for the per-CPU idle tasks:
497  */
498 DEFINE_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 };
524