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 struct optimistic_spin_node {
10 	struct optimistic_spin_node *next, *prev;
11 	int locked; /* 1 if lock acquired */
12 	int cpu; /* encoded CPU # + 1 value */
13 };
14 
15 struct optimistic_spin_queue {
16 	/*
17 	 * Stores an encoded value of the CPU # of the tail node in the queue.
18 	 * If the queue is empty, then it's set to OSQ_UNLOCKED_VAL.
19 	 */
20 	atomic_t tail;
21 };
22 
23 #define OSQ_UNLOCKED_VAL (0)
24 
25 /* Init macro and function. */
26 #define OSQ_LOCK_UNLOCKED { ATOMIC_INIT(OSQ_UNLOCKED_VAL) }
27 
osq_lock_init(struct optimistic_spin_queue * lock)28 static inline void osq_lock_init(struct optimistic_spin_queue *lock)
29 {
30 	atomic_set(&lock->tail, OSQ_UNLOCKED_VAL);
31 }
32 
33 extern bool osq_lock(struct optimistic_spin_queue *lock);
34 extern void osq_unlock(struct optimistic_spin_queue *lock);
35 
osq_is_locked(struct optimistic_spin_queue * lock)36 static inline bool osq_is_locked(struct optimistic_spin_queue *lock)
37 {
38 	return atomic_read(&lock->tail) != OSQ_UNLOCKED_VAL;
39 }
40 
41 #endif
42