linux-kernel - Re: [PATCH v2 2/8] rust: hrtimer: Add HrTimer::raw

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Message-ID: <87frhzm5y5.fsf@kernel.org>
Date: Wed, 23 Apr 2025 14:13:22 +0200
From: Andreas Hindborg <a.hindborg@...nel.org>
To: Lyude Paul <lyude@...hat.com>
Cc: rust-for-linux@...r.kernel.org,  linux-kernel@...r.kernel.org,  Boqun
 Feng <boqun.feng@...il.com>,  FUJITA Tomonori <fujita.tomonori@...il.com>,
  Frederic Weisbecker <frederic@...nel.org>,  Thomas Gleixner
 <tglx@...utronix.de>,  Anna-Maria Behnsen <anna-maria@...utronix.de>,
  John Stultz <jstultz@...gle.com>,  Stephen Boyd <sboyd@...nel.org>,
  Miguel Ojeda <ojeda@...nel.org>,  Alex Gaynor <alex.gaynor@...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>,  Danilo
 Krummrich <dakr@...nel.org>
Subject: Re: [PATCH v2 2/8] rust: hrtimer: Add HrTimer::raw_forward() and
 forward()

Lyude Paul <lyude@...hat.com> writes:

> Within the hrtimer API there are quite a number of functions that can only
> be safely called from one of two contexts:
>
> * When we have exclusive access to the hrtimer and the timer is not active.
> * When we're within the hrtimer's callback context as it is being executed.
>
> This commit adds bindings for hrtimer_forward() for the first such context,
> along with HrTimer::raw_forward() for later use in implementing the
> hrtimer_forward() in the latter context.
>
> Since we can only retrieve a &mut reference to an HrTimer<T> in contexts
> where it is not possible for the timer to be accessed by others or
> currently executing (e.g. a UniqueArc), a &mut is actually enough of a
> guarantee to safely fulfill the C API requirements here.
>
> Signed-off-by: Lyude Paul <lyude@...hat.com>
> ---
>  rust/kernel/time/hrtimer.rs | 36 +++++++++++++++++++++++++++++++++++-
>  1 file changed, 35 insertions(+), 1 deletion(-)
>
> diff --git a/rust/kernel/time/hrtimer.rs b/rust/kernel/time/hrtimer.rs
> index bfe0e25f5abd0..aadae8666f7ea 100644
> --- a/rust/kernel/time/hrtimer.rs
> +++ b/rust/kernel/time/hrtimer.rs
> @@ -68,7 +68,11 @@
>  //! `start` operation.
>  
>  use super::ClockId;
> -use crate::{prelude::*, time::Instant, types::Opaque};
> +use crate::{
> +    prelude::*,
> +    time::{Delta, Instant},
> +    types::Opaque,
> +};
>  use core::marker::PhantomData;
>  use pin_init::PinInit;
>  
> @@ -164,6 +168,36 @@ pub(crate) unsafe fn raw_cancel(this: *const Self) -> bool {
>          // handled on the C side.
>          unsafe { bindings::hrtimer_cancel(c_timer_ptr) != 0 }
>      }
> +
> +    /// Forward the timer expiry for a given timer pointer.
> +    ///
> +    /// # Safety
> +    ///
> +    /// `self_ptr` must point to a valid `Self`.

I don't think safety requirements are tight enough. We must also have
exclusive ownership of the pointee of `self_ptr`.


Best regards,
Andreas Hindborg