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 
10 struct 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 
osq_lock_init(struct optimistic_spin_queue * lock)23 static inline void osq_lock_init(struct optimistic_spin_queue *lock)
24 {
25 	atomic_set(&lock->tail, OSQ_UNLOCKED_VAL);
26 }
27 
28 extern bool osq_lock(struct optimistic_spin_queue *lock);
29 extern void osq_unlock(struct optimistic_spin_queue *lock);
30 
osq_is_locked(struct optimistic_spin_queue * lock)31 static inline bool osq_is_locked(struct optimistic_spin_queue *lock)
32 {
33 	return atomic_read(&lock->tail) != OSQ_UNLOCKED_VAL;
34 }
35 
36 #endif
37