fix: prevent optimize of try_lock in park.rs leading to race conditions (#6355)

[leso-kn]

Motivation

This PR addresses the issue described in #6355, it fixes a segmentation fault in park_timeout() on riscv64.

Solution

Following the rust documentation on black_box in std::hint it's possible to instruct the compiler to prevent optimizing a specific call.

tokio/tokio/src/runtime/scheduler/multi_thread/park.rs

Line 74 in b32826b

if let Some(mut driver) = self.inner.shared.driver.try_lock() {

Wrapping try_lock() with black_box() in park.rs:74 causes the compiler to block optimizations for the call and prevents omission of the call.

Tested on Alpine Linux edge (riscv64)

See https://gitlab.alpinelinux.org/alpine/aports/-/merge_requests/50419 for details.

[leso-kn]

Note on the minrust CI job: The black_box() hint has been stabilized since rust version 1.66.0 (minrust uses 1.63.0)

[Darksonn]

Closing for the reasons outlined in #6355 (comment).