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