Current File : //usr/src/kernels/3.10.0-1160.81.1.el7.centos.plus.x86_64/include/asm-generic/qrwlock.h
/*
* Queue read/write lock
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* (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>
/*
* Writer states & reader shift and bias
*/
#define _QW_WAITING 1 /* A writer is waiting */
#define _QW_LOCKED 0xff /* A writer holds the lock */
#define _QW_WMASK 0xff /* Writer mask */
#define _QR_SHIFT 8 /* Reader count shift */
#define _QR_BIAS (1U << _QR_SHIFT)
/*
* External function declarations
*/
extern void queued_read_lock_slowpath(struct qrwlock *lock, u32 cnts);
extern void queued_write_lock_slowpath(struct qrwlock *lock);
/**
* queued_read_can_lock- would read_trylock() succeed?
* @lock: Pointer to queue rwlock structure
*/
static inline int queued_read_can_lock(struct qrwlock *lock)
{
return !(atomic_read(&lock->cnts) & _QW_WMASK);
}
/**
* queued_write_can_lock- would write_trylock() succeed?
* @lock: Pointer to queue rwlock structure
*/
static inline int queued_write_can_lock(struct qrwlock *lock)
{
return !atomic_read(&lock->cnts);
}
/**
* 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)
{
u32 cnts;
cnts = atomic_read(&lock->cnts);
if (likely(!(cnts & _QW_WMASK))) {
cnts = (u32)atomic_add_return(_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)
{
u32 cnts;
cnts = atomic_read(&lock->cnts);
if (unlikely(cnts))
return 0;
return likely(atomic_cmpxchg(&lock->cnts,
cnts, cnts | _QW_LOCKED) == cnts);
}
/**
* 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)
{
u32 cnts;
cnts = atomic_add_return(_QR_BIAS, &lock->cnts);
if (likely(!(cnts & _QW_WMASK)))
return;
/* The slowpath will decrement the reader count, if necessary. */
queued_read_lock_slowpath(lock, cnts);
}
/**
* queued_read_lock_unfair - unfairly acquire read lock of a queue rwlock
* @lock : Pointer to queue rwlock structure
*
* This function should only be used sparingly to avoid lock starvation.
*/
static inline void queued_read_lock_unfair(struct qrwlock *lock)
{
u32 cnts;
cnts = atomic_add_return(_QR_BIAS, &lock->cnts);
while ((cnts & _QW_WMASK) == _QW_LOCKED) {
/* Wait until the writer goes away */
cpu_relax();
cnts = atomic_read_acquire(&lock->cnts);
}
}
/**
* 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)
{
/* Optimize for the unfair lock case where the fair flag is 0. */
if (atomic_cmpxchg(&lock->cnts, 0, _QW_LOCKED) == 0)
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
*/
smp_mb__before_atomic();
atomic_sub(_QR_BIAS, &lock->cnts);
}
#ifndef queued_write_unlock
/**
* 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)
{
/*
* If the writer field is atomic, it can be cleared directly.
* Otherwise, an atomic subtraction will be used to clear it.
*/
smp_mb__before_atomic();
atomic_sub(_QW_LOCKED, &lock->cnts);
}
#endif
/*
* Remapping rwlock architecture specific functions to the corresponding
* queue rwlock functions.
*/
#define arch_qread_can_lock(l) queued_read_can_lock(l)
#define arch_qwrite_can_lock(l) queued_write_can_lock(l)
#define arch_qread_lock(l) queued_read_lock(l)
#define arch_qwrite_lock(l) queued_write_lock(l)
#define arch_qread_trylock(l) queued_read_trylock(l)
#define arch_qwrite_trylock(l) queued_write_trylock(l)
#define arch_qread_unlock(l) queued_read_unlock(l)
#define arch_qwrite_unlock(l) queued_write_unlock(l)
#define arch_qread_lock_flags(lock, flags) arch_qread_lock(lock)
#define arch_qwrite_lock_flags(lock, flags) arch_qwrite_lock(lock)
#define qread_lock_unfair(lock) do { \
preempt_disable(); \
rwlock_acquire_read(&(lock)->dep_map, 0, 0, _RET_IP_); \
queued_read_lock_unfair(&(lock)->raw_lock); \
} while (0)
#endif /* __ASM_GENERIC_QRWLOCK_H */
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