Release 4.15 include/linux/osq_lock.h

/* 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);
}

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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;
}

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#endif
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Directory: include/linux

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