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

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Date:   Wed, 6 Dec 2023 12:53:17 -0300
From:   Martin Rodriguez Reboredo <yakoyoku@...il.com>
To:     Alice Ryhl <aliceryhl@...gle.com>, 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>,
        Benno Lossin <benno.lossin@...ton.me>,
        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>
Cc:     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 07:09, Alice Ryhl wrote:
> Sleep on a condition variable with a timeout.
> 
> This is used by Rust Binder for process freezing. There, we want to
> sleep until the freeze operation completes, but we want to be able to
> abort the process freezing if it doesn't complete within some timeout.
> 
> Signed-off-by: Alice Ryhl <aliceryhl@...gle.com>
> ---
> [...]
>   
> +    /// 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.

Remaining jiffies or zero on timeout?

> +    fn wait_internal_timeout<T, B>(
> +        &self,
> +        wait_state: u32,
> +        guard: &mut Guard<'_, T, B>,
> +        timeout: u64,
> +    ) -> u64
> [...]
> +
> +    /// Releases the lock and waits for a notification in interruptible mode.
> +    ///
> +    /// 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 a timeout occurs, or when the thread receives a signal.
> +    ///
> +    /// Returns whether there is a signal pending.

This one is correct.

> +    #[must_use = "wait_timeout returns if a signal is pending, so the caller must check the return value"]
> +    pub fn wait_timeout<T: ?Sized, B: Backend>(
> +        &self,
> +        guard: &mut Guard<'_, T, B>,
> +        jiffies: u64,
> +    ) -> CondVarTimeoutResult {
> [...]