text: // SPDX-License-Identifier: GPL-2.0-only
  /*
   * Generic entry points for the idle threads and
   * implementation of the idle task scheduling class.
   *
   * (NOTE: these are not related to SCHED_IDLE batch scheduled
   *        tasks which are handled in sched/fair.c )
   */
  #include "sched.h"
  
  #include <trace/events/power.h>
  
  /* Linker adds these: start and end of __cpuidle functions */
  extern char __cpuidle_text_start[], __cpuidle_text_end[];
  
  /**
   * sched_idle_set_state - Record idle state for the current CPU.
   * @idle_state: State to record.
   */
  void sched_idle_set_state(struct cpuidle_state *idle_state)
  {
  	idle_set_state(this_rq(), idle_state);
  }
  
  static int __read_mostly cpu_idle_force_poll;
  
  void cpu_idle_poll_ctrl(bool enable)
  {
  	if (enable) {
  		cpu_idle_force_poll++;
  	} else {
  		cpu_idle_force_poll--;
  		WARN_ON_ONCE(cpu_idle_force_poll < 0);
  	}
  }
  
  #ifdef CONFIG_GENERIC_IDLE_POLL_SETUP
  static int __init cpu_idle_poll_setup(char *__unused)
  {
  	cpu_idle_force_poll = 1;
  
  	return 1;
  }
  __setup("nohlt", cpu_idle_poll_setup);
  
  static int __init cpu_idle_nopoll_setup(char *__unused)
  {
  	cpu_idle_force_poll = 0;
  
  	return 1;
  }
  __setup("hlt", cpu_idle_nopoll_setup);
  #endif
  
  static noinline int __cpuidle cpu_idle_poll(void)
  {
  	trace_cpu_idle(0, smp_processor_id());
  	stop_critical_timings();
  	rcu_idle_enter();
  	local_irq_enable();
  
  	while (!tif_need_resched() &&
  	       (cpu_idle_force_poll || tick_check_broadcast_expired()))
  		cpu_relax();
  
  	rcu_idle_exit();
  	start_critical_timings();
  	trace_cpu_idle(PWR_EVENT_EXIT, smp_processor_id());
  
  	return 1;
  }
  
  /* Weak implementations for optional arch specific functions */
  void __weak arch_cpu_idle_prepare(void) { }
  void __weak arch_cpu_idle_enter(void) { }
  void __weak arch_cpu_idle_exit(void) { }
  void __weak arch_cpu_idle_dead(void) { }
  void __weak arch_cpu_idle(void)
  {
  	cpu_idle_force_poll = 1;
  	raw_local_irq_enable();
  }
  
  /**
   * default_idle_call - Default CPU idle routine.
   *
   * To use when the cpuidle framework cannot be used.
   */
  void __cpuidle default_idle_call(void)
  {
  	if (current_clr_polling_and_test()) {
  		local_irq_enable();
  	} else {
  
  		trace_cpu_idle(1, smp_processor_id());
  		stop_critical_timings();
  
  		/*
  		 * arch_cpu_idle() is supposed to enable IRQs, however
  		 * we can't do that because of RCU and tracing.
  		 *
  		 * Trace IRQs enable here, then switch off RCU, and have
  		 * arch_cpu_idle() use raw_local_irq_enable(). Note that
  		 * rcu_idle_enter() relies on lockdep IRQ state, so switch that
  		 * last -- this is very similar to the entry code.
  		 */
  		trace_hardirqs_on_prepare();
  		lockdep_hardirqs_on_prepare(_THIS_IP_);
  		rcu_idle_enter();
  		lockdep_hardirqs_on(_THIS_IP_);
  
  		arch_cpu_idle();
  
  		/*
  		 * OK, so IRQs are enabled here, but RCU needs them disabled to
  		 * turn itself back on.. funny thing is that disabling IRQs
  		 * will cause tracing, which needs RCU. Jump through hoops to
  		 * make it 'work'.
  		 */
  		raw_local_irq_disable();
  		lockdep_hardirqs_off(_THIS_IP_);
  		rcu_idle_exit();
  		lockdep_hardirqs_on(_THIS_IP_);
  		raw_local_irq_enable();
  
  		start_critical_timings();
  		trace_cpu_idle(PWR_EVENT_EXIT, smp_processor_id());
  	}
  }
  
  static int call_cpuidle_s2idle(struct cpuidle_driver *drv,
  			       struct cpuidle_device *dev)
  {
  	if (current_clr_polling_and_test())
  		return -EBUSY;
  
  	return cpuidle_enter_s2idle(drv, dev);
  }
  
  static int call_cpuidle(struct cpuidle_driver *drv, struct cpuidle_device *dev,
  		      int next_state)
  {
  	/*
  	 * The idle task must be scheduled, it is pointless to go to idle, just
  	 * update no idle residency and return.
  	 */
  	if (current_clr_polling_and_test()) {
  		dev->last_residency_ns = 0;
  		local_irq_enable();
  		return -EBUSY;
  	}
  
  	/*
  	 * Enter the idle state previously returned by the governor decision.
  	 * This function will block until an interrupt occurs and will take
  	 * care of re-enabling the local interrupts
  	 */
  	return cpuidle_enter(drv, dev, next_state);
  }
  
  /**
   * cpuidle_idle_call - the main idle function
   *
   * NOTE: no locks or semaphores should be used here
   *
   * On architectures that support TIF_POLLING_NRFLAG, is called with polling
   * set, and it returns with polling set.  If it ever stops polling, it
   * must clear the polling bit.
   */
  static void cpuidle_idle_call(void)
  {
  	struct cpuidle_device *dev = cpuidle_get_device();
  	struct cpuidle_driver *drv = cpuidle_get_cpu_driver(dev);
  	int next_state, entered_state;
  
  	/*
  	 * Check if the idle task must be rescheduled. If it is the
  	 * case, exit the function after re-enabling the local irq.
  	 */
  	if (need_resched()) {
  		local_irq_enable();
  		return;
  	}
  
  	/*
  	 * The RCU framework needs to be told that we are entering an idle
  	 * section, so no more rcu read side critical sections and one more
  	 * step to the grace period
  	 */
  
  	if (cpuidle_not_available(drv, dev)) {
  		tick_nohz_idle_stop_tick();
  
  		default_idle_call();
  		goto exit_idle;
  	}
  
  	/*
  	 * Suspend-to-idle ("s2idle") is a system state in which all user space
  	 * has been frozen, all I/O devices have been suspended and the only
  	 * activity happens here and in interrupts (if any). In that case bypass
  	 * the cpuidle governor and go straight for the deepest idle state
  	 * available.  Possibly also suspend the local tick and the entire
  	 * timekeeping to prevent timer interrupts from kicking us out of idle
  	 * until a proper wakeup interrupt happens.
  	 */
  
  	if (idle_should_enter_s2idle() || dev->forced_idle_latency_limit_ns) {
  		u64 max_latency_ns;
  
  		if (idle_should_enter_s2idle()) {
  
  			entered_state = call_cpuidle_s2idle(drv, dev);
  			if (entered_state > 0)
  				goto exit_idle;
  
  			max_latency_ns = U64_MAX;
  		} else {
  			max_latency_ns = dev->forced_idle_latency_limit_ns;
  		}
  
  		tick_nohz_idle_stop_tick();
  
  		next_state = cpuidle_find_deepest_state(drv, dev, max_latency_ns);
  		call_cpuidle(drv, dev, next_state);
  	} else {
  		bool stop_tick = true;
  
  		/*
  		 * Ask the cpuidle framework to choose a convenient idle state.
  		 */
  		next_state = cpuidle_select(drv, dev, &stop_tick);
  
  		if (stop_tick || tick_nohz_tick_stopped())
  			tick_nohz_idle_stop_tick();
  		else
  			tick_nohz_idle_retain_tick();
  
  		entered_state = call_cpuidle(drv, dev, next_state);
  		/*
  		 * Give the governor an opportunity to reflect on the outcome
  		 */
  		cpuidle_reflect(dev, entered_state);
  	}
  
  exit_idle:
  	__current_set_polling();
  
  	/*
  	 * It is up to the idle functions to reenable local interrupts
  	 */
  	if (WARN_ON_ONCE(irqs_disabled()))
  		local_irq_enable();
  }
  
  /*
   * Generic idle loop implementation
   *
   * Called with polling cleared.
   */
  static void do_idle(void)
  {
  	int cpu = smp_processor_id();
  
  	/*
  	 * Check if we need to update blocked load
  	 */
  	nohz_run_idle_balance(cpu);
  
  	/*
  	 * If the arch has a polling bit, we maintain an invariant:
  	 *
  	 * Our polling bit is clear if we're not scheduled (i.e. if rq->curr !=
  	 * rq->idle). This means that, if rq->idle has the polling bit set,
  	 * then setting need_resched is guaranteed to cause the CPU to
  	 * reschedule.
  	 */
  
  	__current_set_polling();
  	tick_nohz_idle_enter();
  
  	while (!need_resched()) {
  		rmb();
  
  		local_irq_disable();
  
  		if (cpu_is_offline(cpu)) {
  			tick_nohz_idle_stop_tick();
  			cpuhp_report_idle_dead();
  			arch_cpu_idle_dead();
  		}
  
  		arch_cpu_idle_enter();
  		rcu_nocb_flush_deferred_wakeup();
  
  		/*
  		 * In poll mode we reenable interrupts and spin. Also if we
  		 * detected in the wakeup from idle path that the tick
  		 * broadcast device expired for us, we don't want to go deep
  		 * idle as we know that the IPI is going to arrive right away.
  		 */
  		if (cpu_idle_force_poll || tick_check_broadcast_expired()) {
  			tick_nohz_idle_restart_tick();
  			cpu_idle_poll();
  		} else {
  			cpuidle_idle_call();
  		}
  		arch_cpu_idle_exit();
  	}
  
  	/*
  	 * Since we fell out of the loop above, we know TIF_NEED_RESCHED must
  	 * be set, propagate it into PREEMPT_NEED_RESCHED.
  	 *
  	 * This is required because for polling idle loops we will not have had
  	 * an IPI to fold the state for us.
  	 */
  	preempt_set_need_resched();
  	tick_nohz_idle_exit();
  	__current_clr_polling();
  
  	/*
  	 * We promise to call sched_ttwu_pending() and reschedule if
  	 * need_resched() is set while polling is set. That means that clearing
  	 * polling needs to be visible before doing these things.
  	 */
  	smp_mb__after_atomic();
  
  	/*
  	 * RCU relies on this call to be done outside of an RCU read-side
  	 * critical section.
  	 */
  	flush_smp_call_function_from_idle();
  	schedule_idle();
  
  	if (unlikely(klp_patch_pending(current)))
  		klp_update_patch_state(current);
  }
  
  bool cpu_in_idle(unsigned long pc)
  {
  	return pc >= (unsigned long)__cpuidle_text_start &&
  		pc < (unsigned long)__cpuidle_text_end;
  }
  
  struct idle_timer {
  	struct hrtimer timer;
  	int done;
  };
  
  static enum hrtimer_restart idle_inject_timer_fn(struct hrtimer *timer)
  {
  	struct idle_timer *it = container_of(timer, struct idle_timer, timer);
  
  	WRITE_ONCE(it->done, 1);
  	set_tsk_need_resched(current);
  
  	return HRTIMER_NORESTART;
  }
  
  void play_idle_precise(u64 duration_ns, u64 latency_ns)
  {
  	struct idle_timer it;
  
  	/*
  	 * Only FIFO tasks can disable the tick since they don't need the forced
  	 * preemption.
  	 */
  	WARN_ON_ONCE(current->policy != SCHED_FIFO);
  	WARN_ON_ONCE(current->nr_cpus_allowed != 1);
  	WARN_ON_ONCE(!(current->flags & PF_KTHREAD));
  	WARN_ON_ONCE(!(current->flags & PF_NO_SETAFFINITY));
  	WARN_ON_ONCE(!duration_ns);
  	WARN_ON_ONCE(current->mm);
  
  	rcu_sleep_check();
  	preempt_disable();
  	current->flags |= PF_IDLE;
  	cpuidle_use_deepest_state(latency_ns);
  
  	it.done = 0;
  	hrtimer_init_on_stack(&it.timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL_HARD);
  	it.timer.function = idle_inject_timer_fn;
  	hrtimer_start(&it.timer, ns_to_ktime(duration_ns),
  		      HRTIMER_MODE_REL_PINNED_HARD);
  
  	while (!READ_ONCE(it.done))
  		do_idle();
  
  	cpuidle_use_deepest_state(0);
  	current->flags &= ~PF_IDLE;
  
  	preempt_fold_need_resched();
  	preempt_enable();
  }
  EXPORT_SYMBOL_GPL(play_idle_precise);
  
  void cpu_startup_entry(enum cpuhp_state state)
  {
  	arch_cpu_idle_prepare();
  	cpuhp_online_idle(state);
  	while (1)
  		do_idle();
  }
  
  /*
   * idle-task scheduling class.
   */
  
  #ifdef CONFIG_SMP
  static int
  select_task_rq_idle(struct task_struct *p, int cpu, int flags)
  {
  	return task_cpu(p); /* IDLE tasks as never migrated */
  }
  
  static int
  balance_idle(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
  {
  	return WARN_ON_ONCE(1);
  }
  #endif
  
  /*
   * Idle tasks are unconditionally rescheduled:
   */
  static void check_preempt_curr_idle(struct rq *rq, struct task_struct *p, int flags)
  {
  	resched_curr(rq);
  }
  
  static void put_prev_task_idle(struct rq *rq, struct task_struct *prev)
  {
  }
  
  static void set_next_task_idle(struct rq *rq, struct task_struct *next, bool first)
  {
  	update_idle_core(rq);
  	schedstat_inc(rq->sched_goidle);
  	queue_core_balance(rq);
  }
  
  #ifdef CONFIG_SMP
  static struct task_struct *pick_task_idle(struct rq *rq)
  {
  	return rq->idle;
  }
  #endif
  
  struct task_struct *pick_next_task_idle(struct rq *rq)
  {
  	struct task_struct *next = rq->idle;
  
  	set_next_task_idle(rq, next, true);
  
  	return next;
  }
  
  /*
   * It is not legal to sleep in the idle task - print a warning
   * message if some code attempts to do it:
   */
  static void
  dequeue_task_idle(struct rq *rq, struct task_struct *p, int flags)
  {
  	raw_spin_rq_unlock_irq(rq);
  	printk(KERN_ERR "bad: scheduling from the idle thread!\n");
  	dump_stack();
  	raw_spin_rq_lock_irq(rq);
  }
  
  /*
   * scheduler tick hitting a task of our scheduling class.
   *
   * NOTE: This function can be called remotely by the tick offload that
   * goes along full dynticks. Therefore no local assumption can be made
   * and everything must be accessed through the @rq and @curr passed in
   * parameters.
   */
  static void task_tick_idle(struct rq *rq, struct task_struct *curr, int queued)
  {
  }
  
  static void switched_to_idle(struct rq *rq, struct task_struct *p)
  {
  	BUG();
  }
  
  static void
  prio_changed_idle(struct rq *rq, struct task_struct *p, int oldprio)
  {
  	BUG();
  }
  
  static void update_curr_idle(struct rq *rq)
  {
  }
  
  /*
   * Simple, special scheduling class for the per-CPU idle tasks:
   */
  DEFINE_SCHED_CLASS(idle) = {
  
  	/* no enqueue/yield_task for idle tasks */
  
  	/* dequeue is not valid, we print a debug message there: */
  	.dequeue_task		= dequeue_task_idle,
  
  	.check_preempt_curr	= check_preempt_curr_idle,
  
  	.pick_next_task		= pick_next_task_idle,
  	.put_prev_task		= put_prev_task_idle,
  	.set_next_task          = set_next_task_idle,
  
  #ifdef CONFIG_SMP
  	.balance		= balance_idle,
  	.pick_task		= pick_task_idle,
  	.select_task_rq		= select_task_rq_idle,
  	.set_cpus_allowed	= set_cpus_allowed_common,
  #endif
  
  	.task_tick		= task_tick_idle,
  
  	.prio_changed		= prio_changed_idle,
  	.switched_to		= switched_to_idle,
  	.update_curr		= update_curr_idle,
  };
  