linux-kernel - Re: [PATCH v11 08/13] rust: hrtimer: implement `UnsafeHrTimerPointer` for `Pin<&mut T>`

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Message-ID: <87frjmldms.fsf@kernel.org>
Date: Sun, 09 Mar 2025 11:08:59 +0100
From: Andreas Hindborg <a.hindborg@...nel.org>
To: "Benno Lossin" <benno.lossin@...ton.me>
Cc: "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>,  "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 v11 08/13] rust: hrtimer: implement
 `UnsafeHrTimerPointer` for `Pin<&mut T>`

"Benno Lossin" <benno.lossin@...ton.me> writes:

> On Fri Mar 7, 2025 at 10:38 PM CET, Andreas Hindborg wrote:
>> +impl<'a, T> RawHrTimerCallback for Pin<&'a mut T>
>> +where
>> +    T: HasHrTimer<T>,
>> +    T: HrTimerCallback<Pointer<'a> = Self>,
>> +{
>> +    type CallbackTarget<'b> = Self;
>> +
>> +    unsafe extern "C" fn run(ptr: *mut bindings::hrtimer) -> bindings::hrtimer_restart {
>> +        // `HrTimer` is `repr(C)`
>> +        let timer_ptr = ptr as *mut HrTimer<T>;
>> +
>> +        // SAFETY: By the safety requirement of this function, `timer_ptr`
>> +        // points to a `HrTimer<T>` contained in an `T`.
>> +        let receiver_ptr = unsafe { T::timer_container_of(timer_ptr) };
>> +
>> +        // SAFETY:
>> +        //  - By the safety requirement of this function, `timer_ptr`
>> +        //    points to a `HrTimer<T>` contained in an `T`.
>> +        //  - As per he safety requirements of the trait `HrTimerHandle`, the
>> +        //    `PinMutHrTimerHandle` associated with this timer is guaranteed to
>> +        //    be alive until this method returns. As the handle borrows from
>> +        //    `T`, `T` is also guaranteed to be alive for the duration of this
>> +        //    function.
>
> Ah one more thing, I don't think that the second part is needed (i.e.
> that `T` is alive). How about:
>
>         //  - As per the safety requirements of the trait `HrTimerHandle`, the `PinMutHrTimerHandle`
>         //  associated with this timer is guaranteed to be alive until this method returns. That
>         //  handle borrows the `T` behind `receiver_ptr` mutably thus guaranteeing the validity of
>         //  the reference created below.

OK.

>
> Can you also adjust the other instances of this in the other patches?
> Thanks!

Yes!


Best regards,
Andreas Hindborg