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143 lines
3.8 KiB
143 lines
3.8 KiB
/* 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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* (C) Copyright 2013-2014 Hewlett-Packard Development Company, L.P. |
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* |
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* Authors: Waiman Long <[email protected]> |
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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 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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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 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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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 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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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 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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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 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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* queued_rwlock_is_contended - check if the lock is contended |
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* @lock : Pointer to queue 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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* 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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#define arch_rwlock_is_contended(l) queued_rwlock_is_contended(l) |
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#endif /* __ASM_GENERIC_QRWLOCK_H */
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