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

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Message-ID: <CANiq72nQ6b1wO6i6zWW6ZWeQFN4SJVB28b216FDU70KmtCbaxA@mail.gmail.com>
Date: Tue, 5 Nov 2024 13:29:20 +0100
From: Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
To: Boqun Feng <boqun.feng@...il.com>
Cc: Tamir Duberstein <tamird@...il.com>, 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 11:42 PM Boqun Feng <boqun.feng@...il.com> wrote:
>
> 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].

Hmm... But they use `may_dangle` in their `Drop` and we don't (and we
have a `Drop` unlike something like `Unique`), no? Or am I confused?
i.e. if I understand correctly, that would have been needed in the
past, but not anymore.

In any case, a comment here clarifying would be good -- the standard
library does that in some of its types, which is a good idea. At the
very least, the name of the field should indicate why we have the
marker. I will add that to the guidelines patch I have to send...

Thanks!

Cheers,
Miguel