linux_kernel/include/linux/sched/idle.h

#ifndef _LINUX_SCHED_IDLE_H
#define _LINUX_SCHED_IDLE_H

#include <linux/sched.h>

enum cpu_idle_type {
	CPU_IDLE,
	CPU_NOT_IDLE,
	CPU_NEWLY_IDLE,
	CPU_MAX_IDLE_TYPES
};

extern void wake_up_if_idle(int cpu);

/*
 * Idle thread specific functions to determine the need_resched
 * polling state.
 */
#ifdef TIF_POLLING_NRFLAG
static inline int tsk_is_polling(struct task_struct *p)
{
	return test_tsk_thread_flag(p, TIF_POLLING_NRFLAG);
}

static inline void __current_set_polling(void)
{
	set_thread_flag(TIF_POLLING_NRFLAG);
}

static inline bool __must_check current_set_polling_and_test(void)
{
	__current_set_polling();

	/*
	 * Polling state must be visible before we test NEED_RESCHED,
	 * paired by resched_curr()
	 */
	smp_mb__after_atomic();

	return unlikely(tif_need_resched());
}

static inline void __current_clr_polling(void)
{
	clear_thread_flag(TIF_POLLING_NRFLAG);
}

static inline bool __must_check current_clr_polling_and_test(void)
{
	__current_clr_polling();

	/*
	 * Polling state must be visible before we test NEED_RESCHED,
	 * paired by resched_curr()
	 */
	smp_mb__after_atomic();

	return unlikely(tif_need_resched());
}

#else
static inline int tsk_is_polling(struct task_struct *p) { return 0; }
static inline void __current_set_polling(void) { }
static inline void __current_clr_polling(void) { }

static inline bool __must_check current_set_polling_and_test(void)
{
	return unlikely(tif_need_resched());
}
static inline bool __must_check current_clr_polling_and_test(void)
{
	return unlikely(tif_need_resched());
}
#endif

static inline void current_clr_polling(void)
{
	__current_clr_polling();

	/*
	 * Ensure we check TIF_NEED_RESCHED after we clear the polling bit.
	 * Once the bit is cleared, we'll get IPIs with every new
	 * TIF_NEED_RESCHED and the IPI handler, scheduler_ipi(), will also
	 * fold.
	 */
	smp_mb(); /* paired with resched_curr() */

	preempt_fold_need_resched();
}

#endif /* _LINUX_SCHED_IDLE_H */