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

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Message-ID: <f7d854d557423be6411ccb7c641aa2ab4c579345.camel@redhat.com>
Date: Fri, 25 Apr 2025 16:15:14 -0400
From: Lyude Paul <lyude@...hat.com>
To: Andreas Hindborg <a.hindborg@...nel.org>
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()

On Wed, 2025-04-23 at 14:13 +0200, Andreas Hindborg wrote:
> Lyude Paul <lyude@...hat.com> writes:
> > 
> > +};
> >  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`.

Are we sure "exclusive ownership" is the right term here? We /technically/ can
be considered to have unique access over the time expiry since we allow racy
reads of it, and we only allow writes in situations where the timer access is
exclusive and the timer isn't started - or from the timer callback itself when
the timer is started. But we don't have the guarantee of unique access to
`Self`, and both context and context-less forward() make use of raw_forward()
since otherwise I wouldn't have really added a raw_ variant in the first
place.

> 
> 
> Best regards,
> Andreas Hindborg
> 
> 
> 

-- 
Cheers,
 Lyude Paul (she/her)
 Software Engineer at Red Hat

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