linux-kernel - Re: [PATCH v3 06/13] rust: hrtimer: add `UnsafeTimerPointer`

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Message-ID: <3a94c12f91964c5c89476bb2376a7489ccc0d154.camel@redhat.com>
Date: Wed, 13 Nov 2024 18:27:32 -0500
From: Lyude Paul <lyude@...hat.com>
To: Andreas Hindborg <a.hindborg@...nel.org>, Miguel Ojeda
 <ojeda@...nel.org>,  Anna-Maria Behnsen <anna-maria@...utronix.de>,
 Frederic Weisbecker <frederic@...nel.org>, Thomas Gleixner
 <tglx@...utronix.de>
Cc: Alex Gaynor <alex.gaynor@...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>, Alice
 Ryhl <aliceryhl@...gle.com>, Trevor Gross <tmgross@...ch.edu>, 
 rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 06/13] rust: hrtimer: add `UnsafeTimerPointer`

On Thu, 2024-10-17 at 15:04 +0200, Andreas Hindborg wrote:
> Add a trait to allow unsafely queuing stack allocated timers.
> 
> Signed-off-by: Andreas Hindborg <a.hindborg@...nel.org>
> ---
>  rust/kernel/hrtimer.rs | 33 +++++++++++++++++++++++++++++++++
>  1 file changed, 33 insertions(+)
> 
> diff --git a/rust/kernel/hrtimer.rs b/rust/kernel/hrtimer.rs
> index eeed2afd501b64b94d57cc658616659e28785078..e97d7b8ec63ce6c9ac3fe9522192a28fba78b8ba 100644
> --- a/rust/kernel/hrtimer.rs
> +++ b/rust/kernel/hrtimer.rs
> @@ -151,6 +151,39 @@ pub trait TimerPointer: Sync + Sized {
>      fn start(self, expires: Ktime) -> Self::TimerHandle;
>  }
>  
> +/// Unsafe version of [`TimerPointer`] for situations where leaking the
> +/// `TimerHandle` returned by `start` would be unsound. This is the case for
> +/// stack allocated timers.
> +///
> +/// Typical implementers are pinned references such as [`Pin<&T>].

Missing a `

> +///
> +/// # Safety
> +///
> +/// Implementers of this trait must ensure that instances of types implementing
> +/// [`UnsafeTimerPointer`] outlives any associated [`TimerPointer::TimerHandle`]
> +/// instances.
> +///
> +/// [`Pin<&T>`]: Box
> +pub unsafe trait UnsafeTimerPointer: Sync + Sized {
> +    /// A handle representing a running timer.
> +    ///
> +    /// # Safety
> +    ///
> +    /// If the timer is running, or if the timer callback is executing when the
> +    /// handle is dropped, the drop method of `TimerHandle` must not return
> +    /// until the timer is stopped and the callback has completed.
> +    type TimerHandle: TimerHandle;
> +
> +    /// Start the timer after `expires` time units. If the timer was already
> +    /// running, it is restarted at the new expiry time.
> +    ///
> +    /// # Safety
> +    ///
> +    /// Caller promises keep the timer structure alive until the timer is dead.
> +    /// Caller can ensure this by not leaking the returned `Self::TimerHandle`.
> +    unsafe fn start(self, expires: Ktime) -> Self::TimerHandle;
> +}
> +
>  /// Implemented by [`TimerPointer`] implementers to give the C timer callback a
>  /// function to call.
>  // This is split from `TimerPointer` to make it easier to specify trait bounds.
> 

-- 
Cheers,
 Lyude Paul (she/her)
 Software Engineer at Red Hat

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