LXR linux/include/asm-generic/qspinlock.h

   1/* SPDX-License-Identifier: GPL-2.0-or-later */
   2/*
   3 * Queued spinlock
   4 *
   5 * (C) Copyright 2013-2015 Hewlett-Packard Development Company, L.P.
   6 * (C) Copyright 2015 Hewlett-Packard Enterprise Development LP
   7 *
   8 * Authors: Waiman Long <waiman.long@hpe.com>
   9 */
  10#ifndef __ASM_GENERIC_QSPINLOCK_H
  11#define __ASM_GENERIC_QSPINLOCK_H
  12
  13#include <asm-generic/qspinlock_types.h>
  14
  15/**
  16 * queued_spin_is_locked - is the spinlock locked?
  17 * @lock: Pointer to queued spinlock structure
  18 * Return: 1 if it is locked, 0 otherwise
  19 */
  20static __always_inline int queued_spin_is_locked(struct qspinlock *lock)
  21{
  22        /*
  23         * Any !0 state indicates it is locked, even if _Q_LOCKED_VAL
  24         * isn't immediately observable.
  25         */
  26        return atomic_read(&lock->val);
  27}
  28
  29/**
  30 * queued_spin_value_unlocked - is the spinlock structure unlocked?
  31 * @lock: queued spinlock structure
  32 * Return: 1 if it is unlocked, 0 otherwise
  33 *
  34 * N.B. Whenever there are tasks waiting for the lock, it is considered
  35 *      locked wrt the lockref code to avoid lock stealing by the lockref
  36 *      code and change things underneath the lock. This also allows some
  37 *      optimizations to be applied without conflict with lockref.
  38 */
  39static __always_inline int queued_spin_value_unlocked(struct qspinlock lock)
  40{
  41        return !atomic_read(&lock.val);
  42}
  43
  44/**
  45 * queued_spin_is_contended - check if the lock is contended
  46 * @lock : Pointer to queued spinlock structure
  47 * Return: 1 if lock contended, 0 otherwise
  48 */
  49static __always_inline int queued_spin_is_contended(struct qspinlock *lock)
  50{
  51        return atomic_read(&lock->val) & ~_Q_LOCKED_MASK;
  52}
  53/**
  54 * queued_spin_trylock - try to acquire the queued spinlock
  55 * @lock : Pointer to queued spinlock structure
  56 * Return: 1 if lock acquired, 0 if failed
  57 */
  58static __always_inline int queued_spin_trylock(struct qspinlock *lock)
  59{
  60        u32 val = atomic_read(&lock->val);
  61
  62        if (unlikely(val))
  63                return 0;
  64
  65        return likely(atomic_try_cmpxchg_acquire(&lock->val, &val, _Q_LOCKED_VAL));
  66}
  67
  68extern void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val);
  69
  70/**
  71 * queued_spin_lock - acquire a queued spinlock
  72 * @lock: Pointer to queued spinlock structure
  73 */
  74static __always_inline void queued_spin_lock(struct qspinlock *lock)
  75{
  76        u32 val = 0;
  77
  78        if (likely(atomic_try_cmpxchg_acquire(&lock->val, &val, _Q_LOCKED_VAL)))
  79                return;
  80
  81        queued_spin_lock_slowpath(lock, val);
  82}
  83
  84#ifndef queued_spin_unlock
  85/**
  86 * queued_spin_unlock - release a queued spinlock
  87 * @lock : Pointer to queued spinlock structure
  88 */
  89static __always_inline void queued_spin_unlock(struct qspinlock *lock)
  90{
  91        /*
  92         * unlock() needs release semantics:
  93         */
  94        smp_store_release(&lock->locked, 0);
  95}
  96#endif
  97
  98#ifndef virt_spin_lock
  99static __always_inline bool virt_spin_lock(struct qspinlock *lock)
 100{
 101        return false;
 102}
 103#endif
 104
 105/*
 106 * Remapping spinlock architecture specific functions to the corresponding
 107 * queued spinlock functions.
 108 */
 109#define arch_spin_is_locked(l)          queued_spin_is_locked(l)
 110#define arch_spin_is_contended(l)       queued_spin_is_contended(l)
 111#define arch_spin_value_unlocked(l)     queued_spin_value_unlocked(l)
 112#define arch_spin_lock(l)               queued_spin_lock(l)
 113#define arch_spin_trylock(l)            queued_spin_trylock(l)
 114#define arch_spin_unlock(l)             queued_spin_unlock(l)
 115
 116#endif /* __ASM_GENERIC_QSPINLOCK_H */
 117