linux-kernel - Re: [PATCH 2/2] rust: workqueue: remove HasWork::OFFSET

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <CAJ-ks9m2ZHguB9N9-WM0EsO5MjaZ9yRamo_9NytAdzaDdb9aWQ@mail.gmail.com>
Date: Fri, 14 Mar 2025 16:44:08 -0400
From: Tamir Duberstein <tamird@...il.com>
To: Benno Lossin <benno.lossin@...ton.me>
Cc: Miguel Ojeda <ojeda@...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>, 
	Andreas Hindborg <a.hindborg@...nel.org>, Alice Ryhl <aliceryhl@...gle.com>, 
	Trevor Gross <tmgross@...ch.edu>, Bjorn Helgaas <bhelgaas@...gle.com>, 
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>, "Rafael J. Wysocki" <rafael@...nel.org>, 
	Danilo Krummrich <dakr@...nel.org>, rust-for-linux@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org
Subject: Re: [PATCH 2/2] rust: workqueue: remove HasWork::OFFSET

On Fri, Mar 14, 2025 at 3:20 PM Benno Lossin <benno.lossin@...ton.me> wrote:
>
> On Fri Mar 7, 2025 at 10:58 PM CET, Tamir Duberstein wrote:
> > Implement `HasWork::work_container_of` in `impl_has_work!`, narrowing
> > the interface of `HasWork` and replacing pointer arithmetic with
> > `container_of!`. Remove the provided implementation of
> > `HasWork::get_work_offset` without replacement; an implementation is
> > already generated in `impl_has_work!`. Remove the `Self: Sized` bound on
> > `HasWork::work_container_of` which was apparently necessary to access
> > `OFFSET` as `OFFSET` no longer exists.
> >
> > A similar API change was discussed on the hrtimer series[1].
> >
> > Link: https://lore.kernel.org/all/20250224-hrtimer-v3-v6-12-rc2-v9-1-5bd3bf0ce6cc@kernel.org/ [1]
> > Signed-off-by: Tamir Duberstein <tamird@...il.com>
> > ---
> >  rust/kernel/workqueue.rs | 45 ++++++++++++---------------------------------
> >  1 file changed, 12 insertions(+), 33 deletions(-)
>
> What is the motivation of this change? I didn't follow the discussion,
> so if you explained it there, it would be nice if you could also add it
> to this commit message.

The motivation is right at the top: it narrows the interface and
replaces pointer arithmetic with an existing macro, and then deletes
unnecessary code.

> > diff --git a/rust/kernel/workqueue.rs b/rust/kernel/workqueue.rs
> > index 0cd100d2aefb..0e2e0ecc58a6 100644
> > --- a/rust/kernel/workqueue.rs
> > +++ b/rust/kernel/workqueue.rs
> > @@ -429,51 +429,23 @@ pub unsafe fn raw_get(ptr: *const Self) -> *mut bindings::work_struct {
> >  ///
> >  /// # Safety
> >  ///
> > -/// The [`OFFSET`] constant must be the offset of a field in `Self` of type [`Work<T, ID>`]. The
> > -/// methods on this trait must have exactly the behavior that the definitions given below have.
> > +/// The methods on this trait must have exactly the behavior that the definitions given below have.
> >  ///
> >  /// [`impl_has_work!`]: crate::impl_has_work
> > -/// [`OFFSET`]: HasWork::OFFSET
> >  pub unsafe trait HasWork<T, const ID: u64 = 0> {
> > -    /// The offset of the [`Work<T, ID>`] field.
> > -    const OFFSET: usize;
> > -
> > -    /// Returns the offset of the [`Work<T, ID>`] field.
> > -    ///
> > -    /// This method exists because the [`OFFSET`] constant cannot be accessed if the type is not
> > -    /// [`Sized`].
> > -    ///
> > -    /// [`OFFSET`]: HasWork::OFFSET
> > -    #[inline]
> > -    fn get_work_offset(&self) -> usize {
> > -        Self::OFFSET
> > -    }
> > -
> >      /// Returns a pointer to the [`Work<T, ID>`] field.
> >      ///
> >      /// # Safety
> >      ///
> >      /// The provided pointer must point at a valid struct of type `Self`.
> > -    #[inline]
> > -    unsafe fn raw_get_work(ptr: *mut Self) -> *mut Work<T, ID> {
> > -        // SAFETY: The caller promises that the pointer is valid.
> > -        unsafe { (ptr as *mut u8).add(Self::OFFSET) as *mut Work<T, ID> }
> > -    }
> > +    unsafe fn raw_get_work(ptr: *mut Self) -> *mut Work<T, ID>;
> >
> >      /// Returns a pointer to the struct containing the [`Work<T, ID>`] field.
> >      ///
> >      /// # Safety
> >      ///
> >      /// The pointer must point at a [`Work<T, ID>`] field in a struct of type `Self`.
> > -    #[inline]
> > -    unsafe fn work_container_of(ptr: *mut Work<T, ID>) -> *mut Self
> > -    where
> > -        Self: Sized,
>
> This bound is required in order to allow the usage of `dyn HasWork` (ie
> object safety), so it should stay.
>
> Maybe add a comment explaining why it's there.

I guess a doctest would be better, but I still don't understand why
the bound is needed. Sorry, can you cite something or explain in more
detail please?