148 lines
4.0 KiB
C
148 lines
4.0 KiB
C
/* SPDX-License-Identifier: GPL-2.0-or-later */
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/*
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* Queue read/write lock
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*
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* These use generic atomic and locking routines, but depend on a fair spinlock
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* implementation in order to be fair themselves. The implementation in
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* asm-generic/spinlock.h meets these requirements.
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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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/* Must be included from asm/spinlock.h after defining arch_spin_is_locked. */
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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 queued rwlock
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* @lock : Pointer to queued 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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int 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 queued rwlock
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* @lock : Pointer to queued 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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int 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_try_cmpxchg_acquire(&lock->cnts, &cnts,
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_QW_LOCKED));
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}
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/**
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* queued_read_lock - acquire read lock of a queued rwlock
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* @lock: Pointer to queued 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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int 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 queued rwlock
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* @lock : Pointer to queued 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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int cnts = 0;
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/* Optimize for the unfair lock case where the fair flag is 0. */
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if (likely(atomic_try_cmpxchg_acquire(&lock->cnts, &cnts, _QW_LOCKED)))
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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 queued rwlock
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* @lock : Pointer to queued 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 queued rwlock
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* @lock : Pointer to queued 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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* queued_rwlock_is_contended - check if the lock is contended
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* @lock : Pointer to queued rwlock structure
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* Return: 1 if lock contended, 0 otherwise
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*/
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static inline int queued_rwlock_is_contended(struct qrwlock *lock)
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{
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return arch_spin_is_locked(&lock->wait_lock);
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}
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/*
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* Remapping rwlock architecture specific functions to the corresponding
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* queued 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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#define arch_rwlock_is_contended(l) queued_rwlock_is_contended(l)
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#endif /* __ASM_GENERIC_QRWLOCK_H */
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