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
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
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
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