linux-kernel - Re: [PATCH v2] rust: sync: require `T: Sync` for `LockedBy::access`

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Message-ID: <CAH5fLgigL5muhhWNvYHbGUf+7eZnvfoZkXpUMXQqNeP4sn-6fw@mail.gmail.com>
Date: Mon, 23 Sep 2024 11:14:52 +0200
From: Alice Ryhl <aliceryhl@...gle.com>
To: Gary Guo <gary@...yguo.net>
Cc: Miguel Ojeda <ojeda@...nel.org>, Boqun Feng <boqun.feng@...il.com>, 
	Björn Roy Baron <bjorn3_gh@...tonmail.com>, 
	Benno Lossin <benno.lossin@...ton.me>, Andreas Hindborg <a.hindborg@...sung.com>, 
	Trevor Gross <tmgross@...ch.edu>, Martin Rodriguez Reboredo <yakoyoku@...il.com>, rust-for-linux@...r.kernel.org, 
	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH v2] rust: sync: require `T: Sync` for `LockedBy::access`

On Sun, Sep 15, 2024 at 5:36 PM Gary Guo <gary@...yguo.net> wrote:
>
> On Sun, 15 Sep 2024 14:41:28 +0000
> Alice Ryhl <aliceryhl@...gle.com> wrote:
>
> > The `LockedBy::access` method only requires a shared reference to the
> > owner, so if we have shared access to the `LockedBy` from several
> > threads at once, then two threads could call `access` in parallel and
> > both obtain a shared reference to the inner value. Thus, require that
> > `T: Sync` when calling the `access` method.
> >
> > An alternative is to require `T: Sync` in the `impl Sync for LockedBy`.
> > This patch does not choose that approach as it gives up the ability to
> > use `LockedBy` with `!Sync` types, which is okay as long as you only use
> > `access_mut`.
> >
> > Cc: stable@...r.kernel.org
> > Fixes: 7b1f55e3a984 ("rust: sync: introduce `LockedBy`")
> > Signed-off-by: Alice Ryhl <aliceryhl@...gle.com>
>
> Reviewed-by: Gary Guo <gary@...yguo.net>
>
> You probably also want to have a Suggested-by to credit Boqun for
> suggesting the current implementation.

That's fine. Miguel can add that when he picks this.

Alice