144 строки
3.8 KiB
C
144 строки
3.8 KiB
C
/* SPDX-License-Identifier: GPL-2.0-or-later */
|
|
/*
|
|
* Queue read/write lock
|
|
*
|
|
* (C) Copyright 2013-2014 Hewlett-Packard Development Company, L.P.
|
|
*
|
|
* Authors: Waiman Long <waiman.long@hp.com>
|
|
*/
|
|
#ifndef __ASM_GENERIC_QRWLOCK_H
|
|
#define __ASM_GENERIC_QRWLOCK_H
|
|
|
|
#include <linux/atomic.h>
|
|
#include <asm/barrier.h>
|
|
#include <asm/processor.h>
|
|
|
|
#include <asm-generic/qrwlock_types.h>
|
|
|
|
/* Must be included from asm/spinlock.h after defining arch_spin_is_locked. */
|
|
|
|
/*
|
|
* Writer states & reader shift and bias.
|
|
*/
|
|
#define _QW_WAITING 0x100 /* A writer is waiting */
|
|
#define _QW_LOCKED 0x0ff /* A writer holds the lock */
|
|
#define _QW_WMASK 0x1ff /* Writer mask */
|
|
#define _QR_SHIFT 9 /* Reader count shift */
|
|
#define _QR_BIAS (1U << _QR_SHIFT)
|
|
|
|
/*
|
|
* External function declarations
|
|
*/
|
|
extern void queued_read_lock_slowpath(struct qrwlock *lock);
|
|
extern void queued_write_lock_slowpath(struct qrwlock *lock);
|
|
|
|
/**
|
|
* queued_read_trylock - try to acquire read lock of a queue rwlock
|
|
* @lock : Pointer to queue rwlock structure
|
|
* Return: 1 if lock acquired, 0 if failed
|
|
*/
|
|
static inline int queued_read_trylock(struct qrwlock *lock)
|
|
{
|
|
int cnts;
|
|
|
|
cnts = atomic_read(&lock->cnts);
|
|
if (likely(!(cnts & _QW_WMASK))) {
|
|
cnts = (u32)atomic_add_return_acquire(_QR_BIAS, &lock->cnts);
|
|
if (likely(!(cnts & _QW_WMASK)))
|
|
return 1;
|
|
atomic_sub(_QR_BIAS, &lock->cnts);
|
|
}
|
|
return 0;
|
|
}
|
|
|
|
/**
|
|
* queued_write_trylock - try to acquire write lock of a queue rwlock
|
|
* @lock : Pointer to queue rwlock structure
|
|
* Return: 1 if lock acquired, 0 if failed
|
|
*/
|
|
static inline int queued_write_trylock(struct qrwlock *lock)
|
|
{
|
|
int cnts;
|
|
|
|
cnts = atomic_read(&lock->cnts);
|
|
if (unlikely(cnts))
|
|
return 0;
|
|
|
|
return likely(atomic_try_cmpxchg_acquire(&lock->cnts, &cnts,
|
|
_QW_LOCKED));
|
|
}
|
|
/**
|
|
* queued_read_lock - acquire read lock of a queue rwlock
|
|
* @lock: Pointer to queue rwlock structure
|
|
*/
|
|
static inline void queued_read_lock(struct qrwlock *lock)
|
|
{
|
|
int cnts;
|
|
|
|
cnts = atomic_add_return_acquire(_QR_BIAS, &lock->cnts);
|
|
if (likely(!(cnts & _QW_WMASK)))
|
|
return;
|
|
|
|
/* The slowpath will decrement the reader count, if necessary. */
|
|
queued_read_lock_slowpath(lock);
|
|
}
|
|
|
|
/**
|
|
* queued_write_lock - acquire write lock of a queue rwlock
|
|
* @lock : Pointer to queue rwlock structure
|
|
*/
|
|
static inline void queued_write_lock(struct qrwlock *lock)
|
|
{
|
|
int cnts = 0;
|
|
/* Optimize for the unfair lock case where the fair flag is 0. */
|
|
if (likely(atomic_try_cmpxchg_acquire(&lock->cnts, &cnts, _QW_LOCKED)))
|
|
return;
|
|
|
|
queued_write_lock_slowpath(lock);
|
|
}
|
|
|
|
/**
|
|
* queued_read_unlock - release read lock of a queue rwlock
|
|
* @lock : Pointer to queue rwlock structure
|
|
*/
|
|
static inline void queued_read_unlock(struct qrwlock *lock)
|
|
{
|
|
/*
|
|
* Atomically decrement the reader count
|
|
*/
|
|
(void)atomic_sub_return_release(_QR_BIAS, &lock->cnts);
|
|
}
|
|
|
|
/**
|
|
* queued_write_unlock - release write lock of a queue rwlock
|
|
* @lock : Pointer to queue rwlock structure
|
|
*/
|
|
static inline void queued_write_unlock(struct qrwlock *lock)
|
|
{
|
|
smp_store_release(&lock->wlocked, 0);
|
|
}
|
|
|
|
/**
|
|
* queued_rwlock_is_contended - check if the lock is contended
|
|
* @lock : Pointer to queue rwlock structure
|
|
* Return: 1 if lock contended, 0 otherwise
|
|
*/
|
|
static inline int queued_rwlock_is_contended(struct qrwlock *lock)
|
|
{
|
|
return arch_spin_is_locked(&lock->wait_lock);
|
|
}
|
|
|
|
/*
|
|
* Remapping rwlock architecture specific functions to the corresponding
|
|
* queue rwlock functions.
|
|
*/
|
|
#define arch_read_lock(l) queued_read_lock(l)
|
|
#define arch_write_lock(l) queued_write_lock(l)
|
|
#define arch_read_trylock(l) queued_read_trylock(l)
|
|
#define arch_write_trylock(l) queued_write_trylock(l)
|
|
#define arch_read_unlock(l) queued_read_unlock(l)
|
|
#define arch_write_unlock(l) queued_write_unlock(l)
|
|
#define arch_rwlock_is_contended(l) queued_rwlock_is_contended(l)
|
|
|
|
#endif /* __ASM_GENERIC_QRWLOCK_H */
|