// SPDX-License-Identifier: GPL-2.0

  /*
   * stop-task scheduling class.
   *
   * The stop task is the highest priority task in the system, it preempts
   * everything and will be preempted by nothing.
   *
   * See kernel/stop_machine.c
   */

  #include "sched.h"

  
  #ifdef CONFIG_SMP
  static int

  select_task_rq_stop(struct task_struct *p, int cpu, int sd_flag, int flags)

  {
  	return task_cpu(p); /* stop tasks as never migrate */
  }

  
  static int
  balance_stop(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
  {
  	return sched_stop_runnable(rq);
  }

  #endif /* CONFIG_SMP */
  
  static void
  check_preempt_curr_stop(struct rq *rq, struct task_struct *p, int flags)
  {

  	/* we're never preempted */

  }

  static void set_next_task_stop(struct rq *rq, struct task_struct *stop, bool first)

  {
  	stop->se.exec_start = rq_clock_task(rq);
  }

  static struct task_struct *pick_next_task_stop(struct rq *rq)

  {

  	if (!sched_stop_runnable(rq))

  		return NULL;

  	set_next_task_stop(rq, rq->stop, true);

  	return rq->stop;

  }
  
  static void
  enqueue_task_stop(struct rq *rq, struct task_struct *p, int flags)
  {

  	add_nr_running(rq, 1);

  }
  
  static void
  dequeue_task_stop(struct rq *rq, struct task_struct *p, int flags)
  {

  	sub_nr_running(rq, 1);

  }
  
  static void yield_task_stop(struct rq *rq)
  {
  	BUG(); /* the stop task should never yield, its pointless. */
  }

  static void put_prev_task_stop(struct rq *rq, struct task_struct *prev)

  {

  	struct task_struct *curr = rq->curr;
  	u64 delta_exec;

  	delta_exec = rq_clock_task(rq) - curr->se.exec_start;

  	if (unlikely((s64)delta_exec < 0))
  		delta_exec = 0;
  
  	schedstat_set(curr->se.statistics.exec_max,
  			max(curr->se.statistics.exec_max, delta_exec));
  
  	curr->se.sum_exec_runtime += delta_exec;
  	account_group_exec_runtime(curr, delta_exec);

  	curr->se.exec_start = rq_clock_task(rq);

  	cgroup_account_cputime(curr, delta_exec);

  }

  /*
   * 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_stop(struct rq *rq, struct task_struct *curr, int queued)
  {
  }

  static void switched_to_stop(struct rq *rq, struct task_struct *p)

  {
  	BUG(); /* its impossible to change to this class */
  }

  static void
  prio_changed_stop(struct rq *rq, struct task_struct *p, int oldprio)

  {
  	BUG(); /* how!?, what priority? */
  }

  static void update_curr_stop(struct rq *rq)
  {
  }

  /*
   * Simple, special scheduling class for the per-CPU stop tasks:
   */

  const struct sched_class stop_sched_class

  	__section("__stop_sched_class") = {

  
  	.enqueue_task		= enqueue_task_stop,
  	.dequeue_task		= dequeue_task_stop,
  	.yield_task		= yield_task_stop,
  
  	.check_preempt_curr	= check_preempt_curr_stop,
  
  	.pick_next_task		= pick_next_task_stop,
  	.put_prev_task		= put_prev_task_stop,

  	.set_next_task          = set_next_task_stop,

  
  #ifdef CONFIG_SMP

  	.balance		= balance_stop,

  	.select_task_rq		= select_task_rq_stop,

  	.set_cpus_allowed	= set_cpus_allowed_common,

  #endif

  	.task_tick		= task_tick_stop,

  	.prio_changed		= prio_changed_stop,
  	.switched_to		= switched_to_stop,

  	.update_curr		= update_curr_stop,

  };