mirror of https://github.com/torvalds/linux.git
49 lines
1.4 KiB
C
49 lines
1.4 KiB
C
/* SPDX-License-Identifier: GPL-2.0-or-later */
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/*
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* Resilient Queued Spin Lock defines
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*
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* (C) Copyright 2024-2025 Meta Platforms, Inc. and affiliates.
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*
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* Authors: Kumar Kartikeya Dwivedi <memxor@gmail.com>
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*/
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#ifndef __LINUX_RQSPINLOCK_H
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#define __LINUX_RQSPINLOCK_H
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#include "../locking/qspinlock.h"
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/*
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* try_cmpxchg_tail - Return result of cmpxchg of tail word with a new value
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* @lock: Pointer to queued spinlock structure
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* @tail: The tail to compare against
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* @new_tail: The new queue tail code word
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* Return: Bool to indicate whether the cmpxchg operation succeeded
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*
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* This is used by the head of the wait queue to clean up the queue.
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* Provides relaxed ordering, since observers only rely on initialized
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* state of the node which was made visible through the xchg_tail operation,
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* i.e. through the smp_wmb preceding xchg_tail.
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*
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* We avoid using 16-bit cmpxchg, which is not available on all architectures.
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*/
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static __always_inline bool try_cmpxchg_tail(struct qspinlock *lock, u32 tail, u32 new_tail)
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{
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u32 old, new;
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old = atomic_read(&lock->val);
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do {
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/*
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* Is the tail part we compare to already stale? Fail.
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*/
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if ((old & _Q_TAIL_MASK) != tail)
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return false;
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/*
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* Encode latest locked/pending state for new tail.
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*/
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new = (old & _Q_LOCKED_PENDING_MASK) | new_tail;
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} while (!atomic_try_cmpxchg_relaxed(&lock->val, &old, new));
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return true;
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}
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#endif /* __LINUX_RQSPINLOCK_H */
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