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         if (!atomic_read(&lock->val) &&
  70            (atomic_cmpxchg_acquire(&lock->val, 0, _Q_LOCKED_VAL) == 0))
  71                 return 1;
  72         return 0;
  73 }
  74
  75 extern void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val);
  76
  77 /**
  78  * queued_spin_lock - acquire a queued spinlock
  79  * @lock: Pointer to queued spinlock structure
  80  */
  81 static __always_inline void queued_spin_lock(struct qspinlock *lock)
  82 {
  83         u32 val;
  84
  85         val = atomic_cmpxchg_acquire(&lock->val, 0, _Q_LOCKED_VAL);
  86         if (likely(val == 0))
  87                 return;
  88         queued_spin_lock_slowpath(lock, val);
  89 }
  90
  91 #ifndef queued_spin_unlock
  92 /**
  93  * queued_spin_unlock - release a queued spinlock
  94  * @lock : Pointer to queued spinlock structure
  95  */
  96 static __always_inline void queued_spin_unlock(struct qspinlock *lock)
  97 {
  98         /*
  99          * unlock() needs release semantics:
 100          */
 101         smp_store_release(&lock->locked, 0);
 102 }
 103 #endif
 104
 105 #ifndef virt_spin_lock
 106 static __always_inline bool virt_spin_lock(struct qspinlock *lock)
 107 {
 108         return false;
 109 }
 110 #endif
 111
 112 /*
 113  * Remapping spinlock architecture specific functions to the corresponding
 114  * queued spinlock functions.
 115  */
 116 #define arch_spin_is_locked(l)          queued_spin_is_locked(l)
 117 #define arch_spin_is_contended(l)       queued_spin_is_contended(l)
 118 #define arch_spin_value_unlocked(l)     queued_spin_value_unlocked(l)
 119 #define arch_spin_lock(l)               queued_spin_lock(l)
 120 #define arch_spin_trylock(l)            queued_spin_trylock(l)
 121 #define arch_spin_unlock(l)             queued_spin_unlock(l)
 122
 123 #endif /* __ASM_GENERIC_QSPINLOCK_H */