[BUG] nxmutex_trylock 在ARM平台上的语意错误

[qingquanzhang151]

Description / Steps to reproduce the issue

您好，
在使用小米 Vela OS 的 nxmutex_trylock 接口时，发现 ARM 平台下存在语义不符合预期的情况：由于该接口底层依赖atomic_compare_exchange_weak_explicit实现，而 ARM 架构的 LL/SC 指令特性会导致atomic_compare_exchange_weak出现 “虚假失败”（即使锁未被占用也可能返回失败），最终造成nxmutex_trylock在无真实竞争时误判失败，违背了nxmutex_trylock接口 “仅当锁被实际占用时返回失败” 的语义约定，且该问题具有明显的平台相关性。
nxmutex_trylock作为通用同步接口，应保证跨平台的语义一致性，而当前实现未屏蔽原子操作的底层平台特性，可能给上层应用带来兼容性问题。建议可通过以下方式优化：

1. 替换为atomic_compare_exchange_strong_explicit，消除虚假失败；
2. 若保留weak版本以追求性能，可增加循环逻辑过滤虚假失败。

希望该问题能得到关注，感谢 Vela 团队的开源贡献！

Hello,
When using the nxmutex_trylock interface of Xiaomi Vela OS, we encountered a semantic inconsistency issue on ARM platforms. The root cause is that this interface is implemented based on atomic_compare_exchange_weak_explicit under the hood. Due to the LL/SC (Load-Linked/Store-Conditional) instruction characteristics of the ARM architecture, atomic_compare_exchange_weak may produce "spurious failures" — it might return failure even when the mutex is not occupied. This ultimately leads to nxmutex_trylock incorrectly reporting failure in the absence of real contention, which violates the core semantic contract of a trylock interface: failure should only occur when the mutex is actually held by another thread. Additionally, this issue is explicitly platform-dependent.
As a general-purpose synchronization interface, nxmutex_trylock should guarantee cross-platform semantic consistency. The current implementation fails to abstract underlying platform-specific behaviors of atomic operations, potentially introducing compatibility issues for upper-layer applications. We propose the following optimization approaches:

1. Replace atomic_compare_exchange_weak_explicit with atomic_compare_exchange_strong_explicit to eliminate spurious failures entirely;
2. If retaining the weak variant for performance optimization (e.g., reducing bus traffic under high contention), add a loop to filter out spurious failures.

We hope this issue receives your attention. Thank you for the excellent open-source work of the Vela team!

Issue Architecture

[Arch: arm]

[xiaoxiang781216]

这个问题@jasonbu已经修复，会很快更新到openvelashang。