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From: Andreas Hindborg <a.hindborg@kernel.org>
To: "Benno Lossin" <benno.lossin@proton.me>
Cc: "Miguel Ojeda" <ojeda@kernel.org>,  "Anna-Maria Behnsen"
 <anna-maria@linutronix.de>,  "Frederic Weisbecker" <frederic@kernel.org>,
  "Thomas Gleixner" <tglx@linutronix.de>,  "Danilo Krummrich"
 <dakr@kernel.org>,  "Alex Gaynor" <alex.gaynor@gmail.com>,  "Boqun Feng"
 <boqun.feng@gmail.com>,  "Gary Guo" <gary@garyguo.net>,  =?utf-8?Q?Bj?=
 =?utf-8?Q?=C3=B6rn?= Roy Baron
 <bjorn3_gh@protonmail.com>,  "Alice Ryhl" <aliceryhl@google.com>,  "Trevor
 Gross" <tmgross@umich.edu>,  "Lyude Paul" <lyude@redhat.com>,  "Guangbo
 Cui" <2407018371@qq.com>,  "Dirk Behme" <dirk.behme@gmail.com>,  "Daniel
 Almeida" <daniel.almeida@collabora.com>,  "Tamir Duberstein"
 <tamird@gmail.com>,  "Markus Elfring" <Markus.Elfring@web.de>,
  <rust-for-linux@vger.kernel.org>,  <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v11 08/13] rust: hrtimer: implement
 `UnsafeHrTimerPointer` for `Pin<&mut T>`
In-Reply-To: <D8BNFIK9U108.273II0I7NZUG1@proton.me> (Benno Lossin's message of
	"Sun, 09 Mar 2025 10:04:42 +0000")
References: <20250307-hrtimer-v3-v6-12-rc2-v11-0-7934aefd6993@kernel.org>
	<20250307-hrtimer-v3-v6-12-rc2-v11-8-7934aefd6993@kernel.org>
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	<D8BNFIK9U108.273II0I7NZUG1@proton.me>
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Date: Sun, 09 Mar 2025 11:08:59 +0100
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"Benno Lossin" <benno.lossin@proton.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