alt Hacker NewsThe SAFETY comment is just a brief description of the important points the author considered when writing the block, and perhaps points you need to consider if you modify it. Do people just blindly assume that comments in an algorithm are correct and not misleading? In other languages they don't, I don't see why rust'd be any different.
A SAFETY comment is supposed to justify why the unsafe code is sound. Here it justified the wrong thing. Ownership was not the problem, concurrent mutation was. That is exactly the kind of gap a SAFETY comment can hide by giving a false sense that the hard parts were already considered.
The fact that this survived review is the worrying part. Unsafe blocks are intentionally small and localized in Rust precisely so the safety argument can be checked. If the stated safety argument is incomplete and still passes review, that suggests reviewers are relying on the comment as the proof, rather than rederiving the invariants themselves. Unless of course the wrong people are reviewing these changes. Why rewrite in Rust if we don't apply extreme scrutiny to the tiny subset (presumably) that should be scrutinized.
To be clear, I think this is a failure of process, not Rust of course.