include/linux/osq_lock.h

   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