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

[Benno Lossin]

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@xxxxxxxxxx>
> Reviewed-by: Lyude Paul <lyude@xxxxxxxxxx>
> Signed-off-by: Andreas Hindborg <a.hindborg@xxxxxxxxxx>
> ---
>  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