linux-kernel - Re: [PATCH 2/2] rust: sync: add `CondVar::wait

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Date:   Fri, 08 Dec 2023 19:04:06 +0000
From:   Benno Lossin <benno.lossin@...ton.me>
To:     Alice Ryhl <aliceryhl@...gle.com>
Cc:     Miguel Ojeda <ojeda@...nel.org>,
        Alex Gaynor <alex.gaynor@...il.com>,
        Wedson Almeida Filho <wedsonaf@...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>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
        Waiman Long <longman@...hat.com>,
        rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] rust: sync: add `CondVar::wait_timeout`

On 12/6/23 11:09, Alice Ryhl wrote:
> +    /// Atomically releases the given lock (whose ownership is proven by the guard) and puts the
> +    /// thread to sleep. It wakes up when notified by [`CondVar::notify_one`] or
> +    /// [`CondVar::notify_all`], or when the thread receives a signal.
> +    ///
> +    /// Returns whether there is a signal pending.
> +    fn wait_internal_timeout<T, B>(
> +        &self,
> +        wait_state: u32,
> +        guard: &mut Guard<'_, T, B>,
> +        timeout: u64,
> +    ) -> u64
> +    where
> +        T: ?Sized,
> +        B: Backend,
> +    {
> +        let wait = Opaque::<bindings::wait_queue_entry>::uninit();
> +
> +        // SAFETY: `wait` points to valid memory.
> +        unsafe { bindings::init_wait(wait.get()) };
> +
> +        // SAFETY: Both `wait` and `wait_list` point to valid memory.
> +        unsafe {
> +            bindings::prepare_to_wait_exclusive(self.wait_list.get(), wait.get(), wait_state as _)

Does `.into()` work here? If for some reason the type here changes, we
probably want to know about it.

> +        };
> +
> +        // SAFETY: Switches to another thread.
> +        let timeout =
> +            guard.do_unlocked(|| unsafe { bindings::schedule_timeout(timeout as _) as _ });

Ditto.

-- 
Cheers,
Benno

> +
> +        // SAFETY: Both `wait` and `wait_list` point to valid memory.
> +        unsafe { bindings::finish_wait(self.wait_list.get(), wait.get()) };
> +
> +        timeout
> +    }