linux-kernel - Re: [PATCH] rust: init: remove impl Zeroable for Infallible

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Date: Mon, 18 Mar 2024 10:25:33 -0700
From: Boqun Feng <boqun.feng@...il.com>
To: Benno Lossin <benno.lossin@...ton.me>
Cc: Miguel Ojeda <ojeda@...nel.org>, Alex Gaynor <alex.gaynor@...il.com>,
	Wedson Almeida Filho <wedsonaf@...il.com>,
	Gary Guo <gary@...yguo.net>,
	Björn Roy Baron <bjorn3_gh@...tonmail.com>,
	Andreas Hindborg <a.hindborg@...sung.com>,
	Alice Ryhl <aliceryhl@...gle.com>,
	Martin Rodriguez Reboredo <yakoyoku@...il.com>,
	Laine Taffin Altman <alexanderaltman@...com>,
	stable@...r.kernel.org, rust-for-linux@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] rust: init: remove impl Zeroable for Infallible

On Wed, Mar 13, 2024 at 11:09:37PM +0000, Benno Lossin wrote:
> From: Laine Taffin Altman <alexanderaltman@...com>
> 
> It is not enough for a type to be a ZST to guarantee that zeroed memory
> is a valid value for it; it must also be inhabited. Creating a value of
> an uninhabited type, ZST or no, is immediate UB.
> Thus remove the implementation of `Zeroable` for `Infallible`, since
> that type is not inhabited.
> 
> Cc: stable@...r.kernel.org
> Fixes: 38cde0bd7b67 ("rust: init: add `Zeroable` trait and `init::zeroed` function")
> Closes: https://github.com/Rust-for-Linux/pinned-init/pull/13
> Signed-off-by: Laine Taffin Altman <alexanderaltman@...com>
> Signed-off-by: Benno Lossin <benno.lossin@...ton.me>

I think either in the commit log or in the code comment, there better be
a link or explanation on "(un)inhabited type". The rest looks good to
me.

Reviewed-by: Boqun Feng <boqun.feng@...il.com>

Regards,
Boqun

> ---
>  rust/kernel/init.rs | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/rust/kernel/init.rs b/rust/kernel/init.rs
> index 424257284d16..538e03cfc84a 100644
> --- a/rust/kernel/init.rs
> +++ b/rust/kernel/init.rs
> @@ -1292,8 +1292,8 @@ macro_rules! impl_zeroable {
>      i8, i16, i32, i64, i128, isize,
>      f32, f64,
>  
> -    // SAFETY: These are ZSTs, there is nothing to zero.
> -    {<T: ?Sized>} PhantomData<T>, core::marker::PhantomPinned, Infallible, (),
> +    // SAFETY: These are inhabited ZSTs, there is nothing to zero and a valid value exists.
> +    {<T: ?Sized>} PhantomData<T>, core::marker::PhantomPinned, (),
>  
>      // SAFETY: Type is allowed to take any value, including all zeros.
>      {<T>} MaybeUninit<T>,
> 
> base-commit: 768409cff6cc89fe1194da880537a09857b6e4db
> -- 
> 2.42.0
> 
> 
>