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