linux-kernel - Re: [PATCH] rust: arc: remove unused PhantomData

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Message-ID: <CAJ-ks9=vUn1LKC12R05LZWwtoKC6QzvXCUyyaB4VKqAHEsGczw@mail.gmail.com>
Date: Tue, 5 Nov 2024 07:24:30 -0400
From: Tamir Duberstein <tamird@...il.com>
To: Boqun Feng <boqun.feng@...il.com>
Cc: 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>, Andreas Hindborg <a.hindborg@...nel.org>, 
	Alice Ryhl <aliceryhl@...gle.com>, Trevor Gross <tmgross@...ch.edu>, rust-for-linux@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] rust: arc: remove unused PhantomData

On Mon, Nov 4, 2024 at 6:42 PM Boqun Feng <boqun.feng@...il.com> wrote:
>
> Hi Tamir,
>
> On Mon, Nov 04, 2024 at 05:23:44PM -0400, Tamir Duberstein wrote:
> > There's no need for this. The type had the same form when it was first
>
> I believe we need this `PhantomData` to inform drop chec [1] that the
> drop of `Arc` may result into the drop of an `ArcInner<T>`. Rust std
> `Arc` has the similar definition [2], you can find more information
> about PhantomData usage on drop checking at [3].
>
> [1]: https://doc.rust-lang.org/nightly/std/ops/trait.Drop.html#drop-check
> [2]: https://doc.rust-lang.org/src/alloc/sync.rs.html#245
> [3]: https://doc.rust-lang.org/nightly/std/marker/struct.PhantomData.html#ownership-and-the-drop-check
>
> Regards,
> Boqun

Thanks for explaining! Withdrawn.

> > introduced, so it seems this was never necessary.
> >
> > Fixed: 9dc043655003 ("rust: sync: add `Arc` for ref-counted allocations")
> > Signed-off-by: Tamir Duberstein <tamird@...il.com>
> > ---
> >  rust/kernel/sync/arc.rs | 2 --
> >  1 file changed, 2 deletions(-)
> >
> > diff --git a/rust/kernel/sync/arc.rs b/rust/kernel/sync/arc.rs
> > index db9da352d588f65348aa7a5204abbb165b70197f..7e54d31538273d410f80fd65b2070e75e4f69428 100644
> > --- a/rust/kernel/sync/arc.rs
> > +++ b/rust/kernel/sync/arc.rs
> > @@ -127,7 +127,6 @@
> >  /// ```
> >  pub struct Arc<T: ?Sized> {
> >      ptr: NonNull<ArcInner<T>>,
> > -    _p: PhantomData<ArcInner<T>>,
> >  }
> >
> >  #[pin_data]
> > @@ -219,7 +218,6 @@ unsafe fn from_inner(inner: NonNull<ArcInner<T>>) -> Self {
> >          // INVARIANT: By the safety requirements, the invariants hold.
> >          Arc {
> >              ptr: inner,
> > -            _p: PhantomData,
> >          }
> >      }
> >
> >
> > ---
> > base-commit: ae7851c29747fa3765ecb722fe722117a346f988
> > change-id: 20241104-simplify-arc-70c3574b5fac
> >
> > Best regards,
> > --
> > Tamir Duberstein <tamird@...il.com>
> >