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Date:   Thu, 25 May 2023 13:35:08 +0000
To:     Alice Ryhl <aliceryhl@google.com>
From:   Benno Lossin <benno.lossin@proton.me>
Cc:     Miguel Ojeda <ojeda@kernel.org>,
        Wedson Almeida Filho <wedsonaf@gmail.com>,
        Alex Gaynor <alex.gaynor@gmail.com>,
        Boqun Feng <boqun.feng@gmail.com>, Gary Guo <gary@garyguo.net>,
        =?utf-8?Q?Bj=C3=B6rn_Roy_Baron?= <bjorn3_gh@protonmail.com>,
        Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Will Deacon <will@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        rust-for-linux@vger.kernel.org, linux-kernel@vger.kernel.org,
        patches@lists.linux.dev, Andreas Hindborg <a.hindborg@samsung.com>
Subject: Re: [PATCH v2 1/4] rust: sync: reword the `Arc` safety comment for `Send`
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On 5/23/23 16:44, Alice Ryhl wrote:
> The safety comment on `impl Send for Arc` talks about "directly"
> accessing the value, when it really means "accessing the value with a
> mutable reference". This commit clarifies that.
>=20
> Suggested-by: Boqun Feng <boqun.feng@gmail.com>
> Signed-off-by: Alice Ryhl <aliceryhl@google.com>
> Reviewed-by: Andreas Hindborg <a.hindborg@samsung.com>
> Reviewed-by: Boqun Feng <boqun.feng@gmail.com>

Reviewed-by: Benno Lossin <benno.lossin@proton.me>

> ---
>   rust/kernel/sync/arc.rs | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
>=20
> diff --git a/rust/kernel/sync/arc.rs b/rust/kernel/sync/arc.rs
> index e6d206242465..87a4c9ed712b 100644
> --- a/rust/kernel/sync/arc.rs
> +++ b/rust/kernel/sync/arc.rs
> @@ -146,8 +146,8 @@ impl<T: ?Sized + Unsize<U>, U: ?Sized> core::ops::Dis=
patchFromDyn<Arc<U>> for Ar
>=20
>   // SAFETY: It is safe to send `Arc<T>` to another thread when the under=
lying `T` is `Sync` because
>   // it effectively means sharing `&T` (which is safe because `T` is `Syn=
c`); additionally, it needs
> -// `T` to be `Send` because any thread that has an `Arc<T>` may ultimate=
ly access `T` directly, for
> -// example, when the reference count reaches zero and `T` is dropped.
> +// `T` to be `Send` because any thread that has an `Arc<T>` may ultimate=
ly access `T` using a
> +// mutable reference, for example, when the reference count reaches zero=
 and `T` is dropped.
>   unsafe impl<T: ?Sized + Sync + Send> Send for Arc<T> {}
>=20
>   // SAFETY: It is safe to send `&Arc<T>` to another thread when the unde=
rlying `T` is `Sync` for the
> --
> 2.40.1.698.g37aff9b760-goog
>=20

--=20
Cheers,
Benno