LXR linux/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 */
  29static __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 */
  44static __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 */
  54static __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 */
  63static __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
  71extern 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 */
  77static __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 */
  92static __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 */
 109static 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
 116static __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 */
 136