fs/bcachefs/two_state_shared_lock.h

   1 /* SPDX-License-Identifier: GPL-2.0 */
   2 #ifndef _BCACHEFS_TWO_STATE_LOCK_H
   3 #define _BCACHEFS_TWO_STATE_LOCK_H
   4
   5 #include <linux/atomic.h>
   6 #include <linux/sched.h>
   7 #include <linux/wait.h>
   8
   9 #include "util.h"
  10
  11 /*
  12  * Two-state lock - can be taken for add or block - both states are shared,
  13  * like read side of rwsem, but conflict with other state:
  14  */
  15 typedef struct {
  16         atomic_long_t           v;
  17         wait_queue_head_t       wait;
  18 } two_state_lock_t;
  19
  20 static inline void two_state_lock_init(two_state_lock_t *lock)
  21 {
  22         atomic_long_set(&lock->v, 0);
  23         init_waitqueue_head(&lock->wait);
  24 }
  25
  26 static inline void bch2_two_state_unlock(two_state_lock_t *lock, int s)
  27 {
  28         long i = s ? 1 : -1;
  29
  30         EBUG_ON(atomic_long_read(&lock->v) == 0);
  31
  32         if (atomic_long_sub_return_release(i, &lock->v) == 0)
  33                 wake_up_all(&lock->wait);
  34 }
  35
  36 static inline bool bch2_two_state_trylock(two_state_lock_t *lock, int s)
  37 {
  38         long i = s ? 1 : -1;
  39         long old;
  40
  41         old = atomic_long_read(&lock->v);
  42         do {
  43                 if (i > 0 ? old < 0 : old > 0)
  44                         return false;
  45         } while (!atomic_long_try_cmpxchg_acquire(&lock->v, &old, old + i));
  46
  47         return true;
  48 }
  49
  50 void __bch2_two_state_lock(two_state_lock_t *, int);
  51
  52 static inline void bch2_two_state_lock(two_state_lock_t *lock, int s)
  53 {
  54         if (!bch2_two_state_trylock(lock, s))
  55                 __bch2_two_state_lock(lock, s);
  56 }
  57
  58 #endif /* _BCACHEFS_TWO_STATE_LOCK_H */