linux-kernel - Re: [PATCH v10 08/13] rust: hrtimer: implement `UnsafeHrTimerPointer` for `Pin<&mut T>`

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Message-ID: <D8A2YP4GF2XL.2MN17TTXW6GM1@proton.me>
Date: Fri, 07 Mar 2025 13:49:43 +0000
From: Benno Lossin <benno.lossin@...ton.me>
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>, Danilo Krummrich <dakr@...nel.org>
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>, Alice Ryhl <aliceryhl@...gle.com>, Trevor Gross <tmgross@...ch.edu>, Lyude Paul <lyude@...hat.com>, Guangbo Cui <2407018371@...com>, Dirk Behme <dirk.behme@...il.com>, Daniel Almeida <daniel.almeida@...labora.com>, Tamir Duberstein <tamird@...il.com>, Markus Elfring <Markus.Elfring@....de>, rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v10 08/13] rust: hrtimer: implement `UnsafeHrTimerPointer` for `Pin<&mut T>`

On Fri Mar 7, 2025 at 11:11 AM CET, Andreas Hindborg wrote:
> Allow pinned mutable references to structs that contain a `HrTimer` node to
> be scheduled with the `hrtimer` subsystem.
>
> Acked-by: Frederic Weisbecker <frederic@...nel.org>
> Reviewed-by: Lyude Paul <lyude@...hat.com>
> Signed-off-by: Andreas Hindborg <a.hindborg@...nel.org>
> ---
>  rust/kernel/time/hrtimer.rs         |   2 +
>  rust/kernel/time/hrtimer/pin_mut.rs | 101 ++++++++++++++++++++++++++++++++++++
>  2 files changed, 103 insertions(+)
>
> diff --git a/rust/kernel/time/hrtimer.rs b/rust/kernel/time/hrtimer.rs
> index 2ca56397eade..d2791fd624b7 100644
> --- a/rust/kernel/time/hrtimer.rs
> +++ b/rust/kernel/time/hrtimer.rs
> @@ -441,3 +441,5 @@ unsafe fn timer_container_of(ptr: *mut $crate::time::hrtimer::HrTimer<$timer_typ
>  pub use arc::ArcHrTimerHandle;
>  mod pin;
>  pub use pin::PinHrTimerHandle;
> +mod pin_mut;
> +pub use pin_mut::PinMutHrTimerHandle;
> diff --git a/rust/kernel/time/hrtimer/pin_mut.rs b/rust/kernel/time/hrtimer/pin_mut.rs
> new file mode 100644
> index 000000000000..4f4a9e9602d8
> --- /dev/null
> +++ b/rust/kernel/time/hrtimer/pin_mut.rs
> @@ -0,0 +1,101 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +use super::HasHrTimer;
> +use super::HrTimer;
> +use super::HrTimerCallback;
> +use super::HrTimerHandle;
> +use super::RawHrTimerCallback;
> +use super::UnsafeHrTimerPointer;
> +use crate::time::Ktime;
> +use core::pin::Pin;
> +
> +/// A handle for a `Pin<&mut HasHrTimer>`. When the handle exists, the timer might
> +/// be running.
> +pub struct PinMutHrTimerHandle<'a, T>
> +where
> +    T: HasHrTimer<T>,
> +{
> +    pub(crate) inner: Pin<&'a mut T>,

I just noticed, if `T: Unpin`, this is unsound in combination with you
creating another `Pin<&mut T>` reference below for the callback, since
then we have two `&mut T` pointing to the same value. So you should
store a raw pointer instead.

---
Cheers,
Benno