LXR linux/include/linux/osq

   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 */
   9struct 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
  15struct 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
  28static inline void osq_lock_init(struct optimistic_spin_queue *lock)
  29{
  30        atomic_set(&lock->tail, OSQ_UNLOCKED_VAL);
  31}
  32
  33extern bool osq_lock(struct optimistic_spin_queue *lock);
  34extern void osq_unlock(struct optimistic_spin_queue *lock);
  35
  36static 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