summaryrefslogtreecommitdiff
path: root/include/linux/osq_lock.h
blob: 5581dbd3bd3407c6009b565fb935e0797585ab3b (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
/* SPDX-License-Identifier: GPL-2.0 */
#ifndef __LINUX_OSQ_LOCK_H
#define __LINUX_OSQ_LOCK_H

/*
 * An MCS like lock especially tailored for optimistic spinning for sleeping
 * lock implementations (mutex, rwsem, etc).
 */
struct optimistic_spin_node {
	struct optimistic_spin_node *next, *prev;
	int locked; /* 1 if lock acquired */
	int cpu; /* encoded CPU # + 1 value */
};

struct optimistic_spin_queue {
	/*
	 * Stores an encoded value of the CPU # of the tail node in the queue.
	 * If the queue is empty, then it's set to OSQ_UNLOCKED_VAL.
	 */
	atomic_t tail;
};

#define OSQ_UNLOCKED_VAL (0)

/* Init macro and function. */
#define OSQ_LOCK_UNLOCKED { ATOMIC_INIT(OSQ_UNLOCKED_VAL) }

static inline void osq_lock_init(struct optimistic_spin_queue *lock)
{
	atomic_set(&lock->tail, OSQ_UNLOCKED_VAL);
}

extern bool osq_lock(struct optimistic_spin_queue *lock);
extern void osq_unlock(struct optimistic_spin_queue *lock);

static inline bool osq_is_locked(struct optimistic_spin_queue *lock)
{
	return atomic_read(&lock->tail) != OSQ_UNLOCKED_VAL;
}

#endif