include/asm-generic/qspinlock.h

   1 /* SPDX-License-Identifier: GPL-2.0-or-later */
   2 /*
   3  * Queued spinlock
   4  *
   5  * (C) Copyright 2013-2015 Hewlett-Packard Development Company, L.P.
   6  * (C) Copyright 2015 Hewlett-Packard Enterprise Development LP
   7  *
   8  * Authors: Waiman Long <waiman.long@hpe.com>
   9  */
  10 #ifndef __ASM_GENERIC_QSPINLOCK_H
  11 #define __ASM_GENERIC_QSPINLOCK_H
  12
  13 #include <asm-generic/qspinlock_types.h>
  14 #include <linux/atomic.h>
  15
  16 #ifndef queued_spin_is_locked
  17 /**
  18  * queued_spin_is_locked - is the spinlock locked?
  19  * @lock: Pointer to queued spinlock structure
  20  * Return: 1 if it is locked, 0 otherwise
  21  */
  22 static __always_inline int queued_spin_is_locked(struct qspinlock *lock)
  23 {
  24         /*
  25          * Any !0 state indicates it is locked, even if _Q_LOCKED_VAL
  26          * isn't immediately observable.
  27          */
  28         return atomic_read(&lock->val);
  29 }
  30 #endif
  31
  32 /**
  33  * queued_spin_value_unlocked - is the spinlock structure unlocked?
  34  * @lock: queued spinlock structure
  35  * Return: 1 if it is unlocked, 0 otherwise
  36  *
  37  * N.B. Whenever there are tasks waiting for the lock, it is considered
  38  *      locked wrt the lockref code to avoid lock stealing by the lockref
  39  *      code and change things underneath the lock. This also allows some
  40  *      optimizations to be applied without conflict with lockref.
  41  */
  42 static __always_inline int queued_spin_value_unlocked(struct qspinlock lock)
  43 {
  44         return !atomic_read(&lock.val);
  45 }
  46
  47 /**
  48  * queued_spin_is_contended - check if the lock is contended
  49  * @lock : Pointer to queued spinlock structure
  50  * Return: 1 if lock contended, 0 otherwise
  51  */
  52 static __always_inline int queued_spin_is_contended(struct qspinlock *lock)
  53 {
  54         return atomic_read(&lock->val) & ~_Q_LOCKED_MASK;
  55 }
  56 /**
  57  * queued_spin_trylock - try to acquire the queued spinlock
  58  * @lock : Pointer to queued spinlock structure
  59  * Return: 1 if lock acquired, 0 if failed
  60  */
  61 static __always_inline int queued_spin_trylock(struct qspinlock *lock)
  62 {
  63         int val = atomic_read(&lock->val);
  64
  65         if (unlikely(val))
  66                 return 0;
  67
  68         return likely(atomic_try_cmpxchg_acquire(&lock->val, &val, _Q_LOCKED_VAL));
  69 }
  70
  71 extern void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val);
  72
  73 #ifndef queued_spin_lock
  74 /**
  75  * queued_spin_lock - acquire a queued spinlock
  76  * @lock: Pointer to queued spinlock structure
  77  */
  78 static __always_inline void queued_spin_lock(struct qspinlock *lock)
  79 {
  80         int val = 0;
  81
  82         if (likely(atomic_try_cmpxchg_acquire(&lock->val, &val, _Q_LOCKED_VAL)))
  83                 return;
  84
  85         queued_spin_lock_slowpath(lock, val);
  86 }
  87 #endif
  88
  89 #ifndef queued_spin_unlock
  90 /**
  91  * queued_spin_unlock - release a queued spinlock
  92  * @lock : Pointer to queued spinlock structure
  93  */
  94 static __always_inline void queued_spin_unlock(struct qspinlock *lock)
  95 {
  96         /*
  97          * unlock() needs release semantics:
  98          */
  99         smp_store_release(&lock->locked, 0);
 100 }
 101 #endif
 102
 103 #ifndef virt_spin_lock
 104 static __always_inline bool virt_spin_lock(struct qspinlock *lock)
 105 {
 106         return false;
 107 }
 108 #endif
 109
 110 /*
 111  * Remapping spinlock architecture specific functions to the corresponding
 112  * queued spinlock functions.
 113  */
 114 #define arch_spin_is_locked(l)          queued_spin_is_locked(l)
 115 #define arch_spin_is_contended(l)       queued_spin_is_contended(l)
 116 #define arch_spin_value_unlocked(l)     queued_spin_value_unlocked(l)
 117 #define arch_spin_lock(l)               queued_spin_lock(l)
 118 #define arch_spin_trylock(l)            queued_spin_trylock(l)
 119 #define arch_spin_unlock(l)             queued_spin_unlock(l)
 120
 121 #endif /* __ASM_GENERIC_QSPINLOCK_H */