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_unlock_wait - wait until the _current_ lock holder releases the lock
  26  * @lock : Pointer to queued spinlock structure
  27  *
  28  * There is a very slight possibility of live-lock if the lockers keep coming
  29  * and the waiter is just unfortunate enough to not see any unlock state.
  30  */
  31 #ifndef queued_spin_unlock_wait
  32 extern void queued_spin_unlock_wait(struct qspinlock *lock);
  33 #endif
  34
  35 /**
  36  * queued_spin_is_locked - is the spinlock locked?
  37  * @lock: Pointer to queued spinlock structure
  38  * Return: 1 if it is locked, 0 otherwise
  39  */
  40 #ifndef queued_spin_is_locked
  41 static __always_inline int queued_spin_is_locked(struct qspinlock *lock)
  42 {
  43         /*
  44          * See queued_spin_unlock_wait().
  45          *
  46          * Any !0 state indicates it is locked, even if _Q_LOCKED_VAL
  47          * isn't immediately observable.
  48          */
  49         return atomic_read(&lock->val);
  50 }
  51 #endif
  52
  53 /**
  54  * queued_spin_value_unlocked - is the spinlock structure unlocked?
  55  * @lock: queued spinlock structure
  56  * Return: 1 if it is unlocked, 0 otherwise
  57  *
  58  * N.B. Whenever there are tasks waiting for the lock, it is considered
  59  *      locked wrt the lockref code to avoid lock stealing by the lockref
  60  *      code and change things underneath the lock. This also allows some
  61  *      optimizations to be applied without conflict with lockref.
  62  */
  63 static __always_inline int queued_spin_value_unlocked(struct qspinlock lock)
  64 {
  65         return !atomic_read(&lock.val);
  66 }
  67
  68 /**
  69  * queued_spin_is_contended - check if the lock is contended
  70  * @lock : Pointer to queued spinlock structure
  71  * Return: 1 if lock contended, 0 otherwise
  72  */
  73 static __always_inline int queued_spin_is_contended(struct qspinlock *lock)
  74 {
  75         return atomic_read(&lock->val) & ~_Q_LOCKED_MASK;
  76 }
  77 /**
  78  * queued_spin_trylock - try to acquire the queued spinlock
  79  * @lock : Pointer to queued spinlock structure
  80  * Return: 1 if lock acquired, 0 if failed
  81  */
  82 static __always_inline int queued_spin_trylock(struct qspinlock *lock)
  83 {
  84         if (!atomic_read(&lock->val) &&
  85            (atomic_cmpxchg_acquire(&lock->val, 0, _Q_LOCKED_VAL) == 0))
  86                 return 1;
  87         return 0;
  88 }
  89
  90 extern void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val);
  91
  92 /**
  93  * queued_spin_lock - acquire a queued spinlock
  94  * @lock: Pointer to queued spinlock structure
  95  */
  96 static __always_inline void queued_spin_lock(struct qspinlock *lock)
  97 {
  98         u32 val;
  99
 100         val = atomic_cmpxchg_acquire(&lock->val, 0, _Q_LOCKED_VAL);
 101         if (likely(val == 0))
 102                 return;
 103         queued_spin_lock_slowpath(lock, val);
 104 }
 105
 106 #ifndef queued_spin_unlock
 107 /**
 108  * queued_spin_unlock - release a queued spinlock
 109  * @lock : Pointer to queued spinlock structure
 110  */
 111 static __always_inline void queued_spin_unlock(struct qspinlock *lock)
 112 {
 113         /*
 114          * unlock() needs release semantics:
 115          */
 116         (void)atomic_sub_return_release(_Q_LOCKED_VAL, &lock->val);
 117 }
 118 #endif
 119
 120 #ifndef virt_spin_lock
 121 static __always_inline bool virt_spin_lock(struct qspinlock *lock)
 122 {
 123         return false;
 124 }
 125 #endif
 126
 127 /*
 128  * Remapping spinlock architecture specific functions to the corresponding
 129  * queued spinlock functions.
 130  */
 131 #define arch_spin_is_locked(l)          queued_spin_is_locked(l)
 132 #define arch_spin_is_contended(l)       queued_spin_is_contended(l)
 133 #define arch_spin_value_unlocked(l)     queued_spin_value_unlocked(l)
 134 #define arch_spin_lock(l)               queued_spin_lock(l)
 135 #define arch_spin_trylock(l)            queued_spin_trylock(l)
 136 #define arch_spin_unlock(l)             queued_spin_unlock(l)
 137 #define arch_spin_lock_flags(l, f)      queued_spin_lock(l)
 138 #define arch_spin_unlock_wait(l)        queued_spin_unlock_wait(l)
 139
 140 #endif /* __ASM_GENERIC_QSPINLOCK_H */