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