Re: [PATCH v5 0/2] rust: revocable: documentation and refactorings

[Marcelo Moreira <marcelomoreira1905@gmail.com>]

Em qui., 3 de jul. de 2025 às 05:24, Benno Lossin <lossin@kernel.org> escreveu:
>
> On Thu Jun 26, 2025 at 6:59 PM CEST, Marcelo Moreira wrote:
> > This patch series brings documentation and refactorings to the `Revocable` type.
> >
> > Changes include:
> > - Clarifying the write invariant and updating associated safety comments for `Revocable<T>`.
> > - Splitting the internal `revoke_internal` function into two distinct, explicit functions: `revoke()` (safe, synchronizing with RCU) and `revoke_nosync()` (unsafe, without RCU synchronization), now returning `bool` to indicate revocation status.
>
> Could you wrap your text to a more readable column? Thanks!

Sure! Thanks!

>
> >
> > Marcelo Moreira (2):
> >   rust: revocable: Refactor revocation mechanism to remove generic
> >     revoke_internal
> >   rust: revocable: Clarify write invariant and update safety comments
> >
> > Changelog
> > ---------
> >
> > Changes since v4:
> > - Rebased the series onto the latest `rfl/rust-next` to integrate recent changes, specifically the `bool` return for `revoke()` and `revoke_nosync()`.
> > - Dropped the "rust: revocable: simplify RevocableGuard for internal safety" patch, as the approach of using a direct reference (`&'a T`) for `RevocableGuard` was found to be unsound due to Rust's aliasing rules and LLVM's `dereferencable` attribute guarantees, which require references to remain valid for the entire function call duration, even if the internal RCU guard is dropped earlier.
> > - Refined the `PinnedDrop::drop` `SAFETY` comment based on Benno Lossin's and Miguel Ojeda's feedback, adopting a more concise and standard Kernel-style bullet point format.
> > - Corrected a duplicated line in the commit message of the second patch.
>
> Now since we had to drop the `RevocableGuard` change, its safety
> invariant & comment in `deref` is insufficient. It shouldn't have the
> invariant that the rcu lock is held (since it owns an `rcu::Guard`, that
> already is guaranteed), but instead it should require that the
> `data_ref` pointer is valid. That invariant is then used by the safety
> comment in `deref` to justify dereferencing the pointer.
>
> Also, I think it's better to reorder the patches again (since the
> current first one relies on changes from the second one), the first one
> should be the change to the invariants section of `Revocable` (so
> currently the second patch). Then the second and third patches can be
> the removal of `revoke_internal` and the `RevocableGuard` safety
> documentation fix.

All right Benno, I'll prepare the comment for `RevocableGuard` and send v6.

The order now is:
1- Documentation for invariant and updates associated `SAFETY` comments
2- Remove `revoke_internal` (Refactoring)
3- `RevocableGuard` safety documentation fix.

Thanks! :)

--
Cheers,
Marcelo Moreira