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#include <linux/atomic.h>
  15
  16#ifndef queued_spin_is_locked
  17/**
  18 * queued_spin_is_locked - is the spinlock locked?
  19 * @lock: Pointer to queued spinlock structure
  20 * Return: 1 if it is locked, 0 otherwise
  21 */
  22static __always_inline int queued_spin_is_locked(struct qspinlock *lock)
  23{
  24        /*
  25         * Any !0 state indicates it is locked, even if _Q_LOCKED_VAL
  26         * isn't immediately observable.
  27         */
  28        return atomic_read(&lock->val);
  29}
  30#endif
  31
  32/**
  33 * queued_spin_value_unlocked - is the spinlock structure unlocked?
  34 * @lock: queued spinlock structure
  35 * Return: 1 if it is unlocked, 0 otherwise
  36 *
  37 * N.B. Whenever there are tasks waiting for the lock, it is considered
  38 *      locked wrt the lockref code to avoid lock stealing by the lockref
  39 *      code and change things underneath the lock. This also allows some
  40 *      optimizations to be applied without conflict with lockref.
  41 */
  42static __always_inline int queued_spin_value_unlocked(struct qspinlock lock)
  43{
  44        return !atomic_read(&lock.val);
  45}
  46
  47/**
  48 * queued_spin_is_contended - check if the lock is contended
  49 * @lock : Pointer to queued spinlock structure
  50 * Return: 1 if lock contended, 0 otherwise
  51 */
  52static __always_inline int queued_spin_is_contended(struct qspinlock *lock)
  53{
  54        return atomic_read(&lock->val) & ~_Q_LOCKED_MASK;
  55}
  56/**
  57 * queued_spin_trylock - try to acquire the queued spinlock
  58 * @lock : Pointer to queued spinlock structure
  59 * Return: 1 if lock acquired, 0 if failed
  60 */
  61static __always_inline int queued_spin_trylock(struct qspinlock *lock)
  62{
  63        int val = atomic_read(&lock->val);
  64
  65        if (unlikely(val))
  66                return 0;
  67
  68        return likely(atomic_try_cmpxchg_acquire(&lock->val, &val, _Q_LOCKED_VAL));
  69}
  70
  71extern void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val);
  72
  73#ifndef queued_spin_lock
  74/**
  75 * queued_spin_lock - acquire a queued spinlock
  76 * @lock: Pointer to queued spinlock structure
  77 */
  78static __always_inline void queued_spin_lock(struct qspinlock *lock)
  79{
  80        int val = 0;
  81
  82        if (likely(atomic_try_cmpxchg_acquire(&lock->val, &val, _Q_LOCKED_VAL)))
  83                return;
  84
  85        queued_spin_lock_slowpath(lock, val);
  86}
  87#endif
  88
  89#ifndef queued_spin_unlock
  90/**
  91 * queued_spin_unlock - release a queued spinlock
  92 * @lock : Pointer to queued spinlock structure
  93 */
  94static __always_inline void queued_spin_unlock(struct qspinlock *lock)
  95{
  96        /*
  97         * unlock() needs release semantics:
  98         */
  99        smp_store_release(&lock->locked, 0);
 100}
 101#endif
 102
 103#ifndef virt_spin_lock
 104static __always_inline bool virt_spin_lock(struct qspinlock *lock)
 105{
 106        return false;
 107}
 108#endif
 109
 110/*
 111 * Remapping spinlock architecture specific functions to the corresponding
 112 * queued spinlock functions.
 113 */
 114#define arch_spin_is_locked(l)          queued_spin_is_locked(l)
 115#define arch_spin_is_contended(l)       queued_spin_is_contended(l)
 116#define arch_spin_value_unlocked(l)     queued_spin_value_unlocked(l)
 117#define arch_spin_lock(l)               queued_spin_lock(l)
 118#define arch_spin_trylock(l)            queued_spin_trylock(l)
 119#define arch_spin_unlock(l)             queued_spin_unlock(l)
 120
 121#endif /* __ASM_GENERIC_QSPINLOCK_H */
 122