include/linux/osq_lock.h

   1 #ifndef __LINUX_OSQ_LOCK_H
   2 #define __LINUX_OSQ_LOCK_H
   3
   4 /*
   5  * An MCS like lock especially tailored for optimistic spinning for sleeping
   6  * lock implementations (mutex, rwsem, etc).
   7  */
   8 struct optimistic_spin_node {
   9         struct optimistic_spin_node *next, *prev;
  10         int locked; /* 1 if lock acquired */
  11         int cpu; /* encoded CPU # + 1 value */
  12 };
  13
  14 struct optimistic_spin_queue {
  15         /*
  16          * Stores an encoded value of the CPU # of the tail node in the queue.
  17          * If the queue is empty, then it's set to OSQ_UNLOCKED_VAL.
  18          */
  19         atomic_t tail;
  20 };
  21
  22 #define OSQ_UNLOCKED_VAL (0)
  23
  24 /* Init macro and function. */
  25 #define OSQ_LOCK_UNLOCKED { ATOMIC_INIT(OSQ_UNLOCKED_VAL) }
  26
  27 static inline void osq_lock_init(struct optimistic_spin_queue *lock)
  28 {
  29         atomic_set(&lock->tail, OSQ_UNLOCKED_VAL);
  30 }
  31
  32 extern bool osq_lock(struct optimistic_spin_queue *lock);
  33 extern void osq_unlock(struct optimistic_spin_queue *lock);
  34
  35 static inline bool osq_is_locked(struct optimistic_spin_queue *lock)
  36 {
  37         return atomic_read(&lock->tail) != OSQ_UNLOCKED_VAL;
  38 }
  39
  40 #endif