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 struct 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
  15 struct 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
  28 static inline void osq_lock_init(struct optimistic_spin_queue *lock)
  29 {
  30         atomic_set(&lock->tail, OSQ_UNLOCKED_VAL);
  31 }
  32
  33 extern bool osq_lock(struct optimistic_spin_queue *lock);
  34 extern void osq_unlock(struct optimistic_spin_queue *lock);
  35
  36 static inline bool osq_is_locked(struct optimistic_spin_queue *lock)
  37 {
  38         return atomic_read(&lock->tail) != OSQ_UNLOCKED_VAL;
  39 }
  40
  41 #endif