EDIT: Hacker News has limited my ability to respond. Please keep in mind that Rust has a large number of active fans, who may have biases for whatever reasons.

The absence of UB, undefined behavior, everything-bad-can-happen, in an Rust-unsafe block can depend on Rust-not-unsafe code in the surrounding module. Thus, even a single block of unsafe can in theory require going through the whole module to figure out where it went wrong or to ensure correctness. And if access control was not properly used, possibly more than the module.

If you look at the mentioned patches, the fixes are to code outside the described unsafe block, in Rust-not-unsafe code. It is perfectly possible to introduce UB through changes to "safe" Rust, if those changes end up violating some assumptions in some Rust-unsafe block somewhere.

https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux...

Another way to introduce UB in Rust-not-unsafe, is if no_std is used. In that case, a simple stack overflow can cause UB, no Rust-unsafe required.

Surprisingly many Rust developers do not understand these points. It may take some of the shine off of Rust, so some Rust fans refrain from explaining it properly. Which is not good.