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