linux-kernel - Re: [PATCH 2/2] rust: sync: require `Sync` for `Backend::GuardState`

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Message-ID: <CAH5fLgjicT5O77UviXUPxc0-O7nQO4J+M3Nfo+6Mm-DVGQBhMg@mail.gmail.com>
Date: Tue, 3 Sep 2024 11:32:48 +0200
From: Alice Ryhl <aliceryhl@...gle.com>
To: Benno Lossin <benno.lossin@...ton.me>
Cc: Miguel Ojeda <ojeda@...nel.org>, Alex Gaynor <alex.gaynor@...il.com>, 
	Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>, 
	Björn Roy Baron <bjorn3_gh@...tonmail.com>, 
	Andreas Hindborg <a.hindborg@...sung.com>, rust-for-linux@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] rust: sync: require `Sync` for `Backend::GuardState`

On Tue, Sep 3, 2024 at 11:17 AM Benno Lossin <benno.lossin@...ton.me> wrote:
>
> `Guard<T, B>` implements `Sync` when `T` is `Sync`. Since this does not
> depend on `B`, creating a `Guard` that is `Sync`, but with `!Sync` state
> is possible. This is a soundness issue, thus add the bounds to the
> respective impls.
>
> Signed-off-by: Benno Lossin <benno.lossin@...ton.me>

Right now, a `&Guard<T, B>` has exactly the same powers as &T, as the
only thing you can do on the guard with only a shared reference is
deref to a &T. So the bounds are correct as they are, unless new APIs
are added (which seems unlikely?). But the safety comment could
certainly be improved.

Alice