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  *
  16  * Authors: Waiman Long <waiman.long@hp.com>
  17  */
  18 #ifndef __ASM_GENERIC_QSPINLOCK_H
  19 #define __ASM_GENERIC_QSPINLOCK_H
  20
  21 #include <asm-generic/qspinlock_types.h>
  22
  23 /**
  24  * queued_spin_is_locked - is the spinlock locked?
  25  * @lock: Pointer to queued spinlock structure
  26  * Return: 1 if it is locked, 0 otherwise
  27  */
  28 static __always_inline int queued_spin_is_locked(struct qspinlock *lock)
  29 {
  30         return atomic_read(&lock->val);
  31 }
  32
  33 /**
  34  * queued_spin_value_unlocked - is the spinlock structure unlocked?
  35  * @lock: queued spinlock structure
  36  * Return: 1 if it is unlocked, 0 otherwise
  37  *
  38  * N.B. Whenever there are tasks waiting for the lock, it is considered
  39  *      locked wrt the lockref code to avoid lock stealing by the lockref
  40  *      code and change things underneath the lock. This also allows some
  41  *      optimizations to be applied without conflict with lockref.
  42  */
  43 static __always_inline int queued_spin_value_unlocked(struct qspinlock lock)
  44 {
  45         return !atomic_read(&lock.val);
  46 }
  47
  48 /**
  49  * queued_spin_is_contended - check if the lock is contended
  50  * @lock : Pointer to queued spinlock structure
  51  * Return: 1 if lock contended, 0 otherwise
  52  */
  53 static __always_inline int queued_spin_is_contended(struct qspinlock *lock)
  54 {
  55         return atomic_read(&lock->val) & ~_Q_LOCKED_MASK;
  56 }
  57 /**
  58  * queued_spin_trylock - try to acquire the queued spinlock
  59  * @lock : Pointer to queued spinlock structure
  60  * Return: 1 if lock acquired, 0 if failed
  61  */
  62 static __always_inline int queued_spin_trylock(struct qspinlock *lock)
  63 {
  64         if (!atomic_read(&lock->val) &&
  65            (atomic_cmpxchg(&lock->val, 0, _Q_LOCKED_VAL) == 0))
  66                 return 1;
  67         return 0;
  68 }
  69
  70 extern void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val);
  71
  72 /**
  73  * queued_spin_lock - acquire a queued spinlock
  74  * @lock: Pointer to queued spinlock structure
  75  */
  76 static __always_inline void queued_spin_lock(struct qspinlock *lock)
  77 {
  78         u32 val;
  79
  80         val = atomic_cmpxchg(&lock->val, 0, _Q_LOCKED_VAL);
  81         if (likely(val == 0))
  82                 return;
  83         queued_spin_lock_slowpath(lock, val);
  84 }
  85
  86 #ifndef queued_spin_unlock
  87 /**
  88  * queued_spin_unlock - release a queued spinlock
  89  * @lock : Pointer to queued spinlock structure
  90  */
  91 static __always_inline void queued_spin_unlock(struct qspinlock *lock)
  92 {
  93         /*
  94          * smp_mb__before_atomic() in order to guarantee release semantics
  95          */
  96         smp_mb__before_atomic_dec();
  97         atomic_sub(_Q_LOCKED_VAL, &lock->val);
  98 }
  99 #endif
 100
 101 /**
 102  * queued_spin_unlock_wait - wait until current lock holder releases the lock
 103  * @lock : Pointer to queued spinlock structure
 104  *
 105  * There is a very slight possibility of live-lock if the lockers keep coming
 106  * and the waiter is just unfortunate enough to not see any unlock state.
 107  */
 108 static inline void queued_spin_unlock_wait(struct qspinlock *lock)
 109 {
 110         while (atomic_read(&lock->val) & _Q_LOCKED_MASK)
 111                 cpu_relax();
 112 }
 113
 114 /*
 115  * Initializier
 116  */
 117 #define __ARCH_SPIN_LOCK_UNLOCKED       { ATOMIC_INIT(0) }
 118
 119 /*
 120  * Remapping spinlock architecture specific functions to the corresponding
 121  * queued spinlock functions.
 122  */
 123 #define arch_spin_is_locked(l)          queued_spin_is_locked(l)
 124 #define arch_spin_is_contended(l)       queued_spin_is_contended(l)
 125 #define arch_spin_value_unlocked(l)     queued_spin_value_unlocked(l)
 126 #define arch_spin_lock(l)               queued_spin_lock(l)
 127 #define arch_spin_trylock(l)            queued_spin_trylock(l)
 128 #define arch_spin_unlock(l)             queued_spin_unlock(l)
 129 #define arch_spin_lock_flags(l, f)      queued_spin_lock(l)
 130 #define arch_spin_unlock_wait(l)        queued_spin_unlock_wait(l)
 131
 132 #endif /* __ASM_GENERIC_QSPINLOCK_H */