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Message-ID: <83f2822e-f36c-0dbf-8226-cef3dc2ba072@gmail.com>
Date:   Tue, 23 May 2023 13:41:35 -0300
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Subject: Re: [PATCH v2 4/4] rust: task: add `Send` marker to `Task`
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To:     Alice Ryhl <aliceryhl@google.com>, Miguel Ojeda <ojeda@kernel.org>,
        Wedson Almeida Filho <wedsonaf@gmail.com>,
        Alex Gaynor <alex.gaynor@gmail.com>
Cc:     Boqun Feng <boqun.feng@gmail.com>, Gary Guo <gary@garyguo.net>,
        =?UTF-8?Q?Bj=c3=b6rn_Roy_Baron?= <bjorn3_gh@protonmail.com>,
        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>
References: <20230523144418.1250547-1-aliceryhl@google.com>
 <20230523144418.1250547-5-aliceryhl@google.com>
From:   Martin Rodriguez Reboredo <yakoyoku@gmail.com>
In-Reply-To: <20230523144418.1250547-5-aliceryhl@google.com>
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On 5/23/23 11:44, Alice Ryhl wrote:
> When a type also implements `Sync`, the meaning of `Send` is just "this
> type may be accessed mutably from threads other than the one it is
> created on". That's ok for this type.
> 
> Signed-off-by: Alice Ryhl <aliceryhl@google.com>
> Reviewed-by: Andreas Hindborg <a.hindborg@samsung.com>
> ---
> [...]
>   
> -// SAFETY: It's OK to access `Task` through references from other threads because we're either
> -// accessing properties that don't change (e.g., `pid`, `group_leader`) or that are properly
> +// SAFETY: By design, the only way to access a `Task` is via the `current` function or via an
> +// `ARef<Task>` obtained through the `AlwaysRefCounted` impl. This means that the only situation in
> +// which a `Task` can be accessed mutably is when the refcount drops to zero and the destructor
> +// runs. It is safe for that to happen on any thread, so it is ok for this type to be `Send`.
> +unsafe impl Send for Task {}
> +
> +// SAFETY: It's OK to access `Task` through shared references from other threads because we're
> +// either accessing properties that don't change (e.g., `pid`, `group_leader`) or that are properly
>   // synchronised by C code (e.g., `signal_pending`).
>   unsafe impl Sync for Task {}
>   

Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com>