int select_task_rq(struct task_struct *p, int cpu, int sd_flags, int wake_flags)
{
	lockdep_assert_held(&p->pi_lock);

	if (p->nr_cpus_allowed > 1)
		cpu = p->sched_class->select_task_rq(p, cpu, sd_flags, wake_flags);

	/*
	 * In order not to call set_task_cpu() on a blocking task we need
	 * to rely on ttwu() to place the task on a valid ->cpus_allowed
	 * cpu.
	 *
	 * Since this is common to all placement strategies, this lives here.
	 *
	 * [ this allows ->select_task() to simply return task_cpu(p) and
	 *   not worry about this generic constraint ]
	 */
	if (unlikely(!cpumask_test_cpu(cpu, tsk_cpus_allowed(p)) ||
		     !cpu_online(cpu)))
		cpu = select_fallback_rq(task_cpu(p), p);

	return cpu;
}
Unknown