osq_lock.h

 1/* SPDX-License-Identifier: GPL-2.0 */
 2#ifndef __LINUX_OSQ_LOCK_H
 3#define __LINUX_OSQ_LOCK_H
 4
 5/*
 6 * An MCS like lock especially tailored for optimistic spinning for sleeping
 7 * lock implementations (mutex, rwsem, etc).
 8 */
 9
10struct optimistic_spin_queue {
11	/*
12	 * Stores an encoded value of the CPU # of the tail node in the queue.
13	 * If the queue is empty, then it's set to OSQ_UNLOCKED_VAL.
14	 */
15	atomic_t tail;
16};
17
18#define OSQ_UNLOCKED_VAL (0)
19
20/* Init macro and function. */
21#define OSQ_LOCK_UNLOCKED { ATOMIC_INIT(OSQ_UNLOCKED_VAL) }
22
23static inline void osq_lock_init(struct optimistic_spin_queue *lock)
24{
25	atomic_set(&lock->tail, OSQ_UNLOCKED_VAL);
26}
27
28extern bool osq_lock(struct optimistic_spin_queue *lock);
29extern void osq_unlock(struct optimistic_spin_queue *lock);
30
31static inline bool osq_is_locked(struct optimistic_spin_queue *lock)
32{
33	return atomic_read(&lock->tail) != OSQ_UNLOCKED_VAL;
34}
35
36#endif