/* 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 */