include/asm-generic/qspinlock.h

   1 /*
   2  * Queued spinlock
   3  *
   4  * This program is free software; you can redistribute it and/or modify
   5  * it under the terms of the GNU General Public License as published by
   6  * the Free Software Foundation; either version 2 of the License, or
   7  * (at your option) any later version.
   8  *
   9  * This program is distributed in the hope that it will be useful,
  10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12  * GNU General Public License for more details.
  13  *
  14  * (C) Copyright 2013-2015 Hewlett-Packard Development Company, L.P.
  15  * (C) Copyright 2015 Hewlett-Packard Enterprise Development LP
  16  *
  17  * Authors: Waiman Long <waiman.long@hpe.com>
  18  */
  19 #ifndef __ASM_GENERIC_QSPINLOCK_H
  20 #define __ASM_GENERIC_QSPINLOCK_H
  21
  22 #include <asm-generic/qspinlock_types.h>
  23
  24 /**
  25  * queued_spin_is_locked - is the spinlock locked?
  26  * @lock: Pointer to queued spinlock structure
  27  * Return: 1 if it is locked, 0 otherwise
  28  */
  29 static __always_inline int queued_spin_is_locked(struct qspinlock *lock)
  30 {
  31         /*
  32          * Any !0 state indicates it is locked, even if _Q_LOCKED_VAL
  33          * isn't immediately observable.
  34          */
  35         return atomic_read(&lock->val);
  36 }
  37
  38 /**
  39  * queued_spin_value_unlocked - is the spinlock structure unlocked?
  40  * @lock: queued spinlock structure
  41  * Return: 1 if it is unlocked, 0 otherwise
  42  *
  43  * N.B. Whenever there are tasks waiting for the lock, it is considered
  44  *      locked wrt the lockref code to avoid lock stealing by the lockref
  45  *      code and change things underneath the lock. This also allows some
  46  *      optimizations to be applied without conflict with lockref.
  47  */
  48 static __always_inline int queued_spin_value_unlocked(struct qspinlock lock)
  49 {
  50         return !atomic_read(&lock.val);
  51 }
  52
  53 /**
  54  * queued_spin_is_contended - check if the lock is contended
  55  * @lock : Pointer to queued spinlock structure
  56  * Return: 1 if lock contended, 0 otherwise
  57  */
  58 static __always_inline int queued_spin_is_contended(struct qspinlock *lock)
  59 {
  60         return atomic_read(&lock->val) & ~_Q_LOCKED_MASK;
  61 }
  62 /**
  63  * queued_spin_trylock - try to acquire the queued spinlock
  64  * @lock : Pointer to queued spinlock structure
  65  * Return: 1 if lock acquired, 0 if failed
  66  */
  67 static __always_inline int queued_spin_trylock(struct qspinlock *lock)
  68 {
  69         u32 val = atomic_read(&lock->val);
  70
  71         if (unlikely(val))
  72                 return 0;
  73
  74         return likely(atomic_try_cmpxchg_acquire(&lock->val, &val, _Q_LOCKED_VAL));
  75 }
  76
  77 extern void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val);
  78
  79 /**
  80  * queued_spin_lock - acquire a queued spinlock
  81  * @lock: Pointer to queued spinlock structure
  82  */
  83 static __always_inline void queued_spin_lock(struct qspinlock *lock)
  84 {
  85         u32 val = 0;
  86
  87         if (likely(atomic_try_cmpxchg_acquire(&lock->val, &val, _Q_LOCKED_VAL)))
  88                 return;
  89
  90         queued_spin_lock_slowpath(lock, val);
  91 }
  92
  93 #ifndef queued_spin_unlock
  94 /**
  95  * queued_spin_unlock - release a queued spinlock
  96  * @lock : Pointer to queued spinlock structure
  97  */
  98 static __always_inline void queued_spin_unlock(struct qspinlock *lock)
  99 {
 100         /*
 101          * unlock() needs release semantics:
 102          */
 103         smp_store_release(&lock->locked, 0);
 104 }
 105 #endif
 106
 107 #ifndef virt_spin_lock
 108 static __always_inline bool virt_spin_lock(struct qspinlock *lock)
 109 {
 110         return false;
 111 }
 112 #endif
 113
 114 /*
 115  * Remapping spinlock architecture specific functions to the corresponding
 116  * queued spinlock functions.
 117  */
 118 #define arch_spin_is_locked(l)          queued_spin_is_locked(l)
 119 #define arch_spin_is_contended(l)       queued_spin_is_contended(l)
 120 #define arch_spin_value_unlocked(l)     queued_spin_value_unlocked(l)
 121 #define arch_spin_lock(l)               queued_spin_lock(l)
 122 #define arch_spin_trylock(l)            queued_spin_trylock(l)
 123 #define arch_spin_unlock(l)             queued_spin_unlock(l)
 124
 125 #endif /* __ASM_GENERIC_QSPINLOCK_H */