root/include/asm-generic/qspinlock.h

INCLUDED FROM

DEFINITIONS

1. queued_spin_is_locked
2. queued_spin_value_unlocked
3. queued_spin_is_contended
4. queued_spin_trylock
5. queued_spin_lock
6. queued_spin_unlock
7. virt_spin_lock

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