139 lines
3.8 KiB
C
139 lines
3.8 KiB
C
/*
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* Queue read/write lock
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* (C) Copyright 2013-2014 Hewlett-Packard Development Company, L.P.
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*
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* Authors: Waiman Long <waiman.long@hp.com>
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*/
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#ifndef __ASM_GENERIC_QRWLOCK_H
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#define __ASM_GENERIC_QRWLOCK_H
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#include <linux/atomic.h>
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#include <asm/barrier.h>
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#include <asm/processor.h>
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#include <asm-generic/qrwlock_types.h>
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/*
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* Writer states & reader shift and bias.
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*/
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#define _QW_WAITING 0x100 /* A writer is waiting */
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#define _QW_LOCKED 0x0ff /* A writer holds the lock */
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#define _QW_WMASK 0x1ff /* Writer mask */
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#define _QR_SHIFT 9 /* Reader count shift */
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#define _QR_BIAS (1U << _QR_SHIFT)
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/*
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* External function declarations
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*/
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extern void queued_read_lock_slowpath(struct qrwlock *lock);
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extern void queued_write_lock_slowpath(struct qrwlock *lock);
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/**
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* queued_read_trylock - try to acquire read lock of a queue rwlock
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* @lock : Pointer to queue rwlock structure
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* Return: 1 if lock acquired, 0 if failed
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*/
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static inline int queued_read_trylock(struct qrwlock *lock)
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{
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u32 cnts;
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cnts = atomic_read(&lock->cnts);
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if (likely(!(cnts & _QW_WMASK))) {
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cnts = (u32)atomic_add_return_acquire(_QR_BIAS, &lock->cnts);
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if (likely(!(cnts & _QW_WMASK)))
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return 1;
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atomic_sub(_QR_BIAS, &lock->cnts);
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}
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return 0;
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}
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/**
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* queued_write_trylock - try to acquire write lock of a queue rwlock
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* @lock : Pointer to queue rwlock structure
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* Return: 1 if lock acquired, 0 if failed
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*/
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static inline int queued_write_trylock(struct qrwlock *lock)
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{
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u32 cnts;
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cnts = atomic_read(&lock->cnts);
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if (unlikely(cnts))
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return 0;
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return likely(atomic_cmpxchg_acquire(&lock->cnts,
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cnts, cnts | _QW_LOCKED) == cnts);
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}
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/**
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* queued_read_lock - acquire read lock of a queue rwlock
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* @lock: Pointer to queue rwlock structure
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*/
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static inline void queued_read_lock(struct qrwlock *lock)
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{
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u32 cnts;
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cnts = atomic_add_return_acquire(_QR_BIAS, &lock->cnts);
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if (likely(!(cnts & _QW_WMASK)))
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return;
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/* The slowpath will decrement the reader count, if necessary. */
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queued_read_lock_slowpath(lock);
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}
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/**
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* queued_write_lock - acquire write lock of a queue rwlock
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* @lock : Pointer to queue rwlock structure
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*/
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static inline void queued_write_lock(struct qrwlock *lock)
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{
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/* Optimize for the unfair lock case where the fair flag is 0. */
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if (atomic_cmpxchg_acquire(&lock->cnts, 0, _QW_LOCKED) == 0)
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return;
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queued_write_lock_slowpath(lock);
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}
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/**
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* queued_read_unlock - release read lock of a queue rwlock
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* @lock : Pointer to queue rwlock structure
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*/
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static inline void queued_read_unlock(struct qrwlock *lock)
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{
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/*
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* Atomically decrement the reader count
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*/
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(void)atomic_sub_return_release(_QR_BIAS, &lock->cnts);
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}
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/**
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* queued_write_unlock - release write lock of a queue rwlock
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* @lock : Pointer to queue rwlock structure
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*/
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static inline void queued_write_unlock(struct qrwlock *lock)
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{
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smp_store_release(&lock->wlocked, 0);
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}
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/*
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* Remapping rwlock architecture specific functions to the corresponding
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* queue rwlock functions.
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*/
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#define arch_read_lock(l) queued_read_lock(l)
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#define arch_write_lock(l) queued_write_lock(l)
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#define arch_read_trylock(l) queued_read_trylock(l)
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#define arch_write_trylock(l) queued_write_trylock(l)
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#define arch_read_unlock(l) queued_read_unlock(l)
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#define arch_write_unlock(l) queued_write_unlock(l)
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#endif /* __ASM_GENERIC_QRWLOCK_H */
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