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Date:   Tue, 23 May 2023 16:49:01 +0100
From:   Gary Guo <gary@garyguo.net>
To:     Alice Ryhl <aliceryhl@google.com>
Cc:     Miguel Ojeda <ojeda@kernel.org>,
        Wedson Almeida Filho <wedsonaf@gmail.com>,
        Alex Gaynor <alex.gaynor@gmail.com>,
        Boqun Feng <boqun.feng@gmail.com>,
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        Benno Lossin <benno.lossin@proton.me>,
        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`
Message-ID: <20230523164901.2fe8621e.gary@garyguo.net>
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On Tue, 23 May 2023 14:44:15 +0000
Alice Ryhl <aliceryhl@google.com> 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.
> 
> 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: Gary Guo <gary@garyguo.net>

> ---
>  rust/kernel/sync/arc.rs | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> 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::DispatchFromDyn<Arc<U>> for Ar
>  
>  // SAFETY: It is safe to send `Arc<T>` to another thread when the underlying `T` is `Sync` because
>  // it effectively means sharing `&T` (which is safe because `T` is `Sync`); additionally, it needs
> -// `T` to be `Send` because any thread that has an `Arc<T>` may ultimately 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 ultimately 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> {}
>  
>  // SAFETY: It is safe to send `&Arc<T>` to another thread when the underlying `T` is `Sync` for the