Re: [PATCH 6.6.y] rust: init: fix `Zeroable` implementation for `Option<NonNull<T>>` and `Option<Box<T>>`

[Sasha Levin <sashal@kernel.org>]

[ Sasha's backport helper bot ]

Hi,

✅ All tests passed successfully. No issues detected.
No action required from the submitter.

The upstream commit SHA1 provided is correct: df27cef153603b18a7d094b53cc3d5264ff32797

WARNING: Author mismatch between patch and upstream commit:
Backport author: Miguel Ojeda<ojeda@kernel.org>
Commit author: Benno Lossin<benno.lossin@proton.me>

Status in newer kernel trees:
6.13.y | Present (different SHA1: 1a1d0545f7a5)
6.12.y | Present (different SHA1: 0d876a8ae2cb)

Note: The patch differs from the upstream commit:
---
1:  df27cef153603 ! 1:  f87fa26b09a1f rust: init: fix `Zeroable` implementation for `Option<NonNull<T>>` and `Option<KBox<T>>`
    @@ Metadata
     Author: Benno Lossin <benno.lossin@proton.me>
     
      ## Commit message ##
    -    rust: init: fix `Zeroable` implementation for `Option<NonNull<T>>` and `Option<KBox<T>>`
    +    rust: init: fix `Zeroable` implementation for `Option<NonNull<T>>` and `Option<Box<T>>`
    +
    +    commit df27cef153603b18a7d094b53cc3d5264ff32797 upstream.
     
         According to [1], `NonNull<T>` and `#[repr(transparent)]` wrapper types
    -    such as our custom `KBox<T>` have the null pointer optimization only if
    -    `T: Sized`. Thus remove the `Zeroable` implementation for the unsized
    -    case.
    +    such as `Box<T>` have the null pointer optimization only if `T: Sized`.
    +    Thus remove the `Zeroable` implementation for the unsized case.
     
         Link: https://doc.rust-lang.org/stable/std/option/index.html#representation [1]
         Reported-by: Alice Ryhl <aliceryhl@google.com>
    @@ rust/kernel/init.rs: macro_rules! impl_zeroable {
     -    //
     -    // In this case we are allowed to use `T: ?Sized`, since all zeros is the `None` variant.
     -    {<T: ?Sized>} Option<NonNull<T>>,
    --    {<T: ?Sized>} Option<KBox<T>>,
    +-    {<T: ?Sized>} Option<Box<T>>,
     +    {<T>} Option<NonNull<T>>,
    -+    {<T>} Option<KBox<T>>,
    ++    {<T>} Option<Box<T>>,
      
          // SAFETY: `null` pointer is valid.
          //
---

Results of testing on various branches:

| Branch                    | Patch Apply | Build Test |
|---------------------------|-------------|------------|
| stable/linux-6.6.y        |  Success    |  Success   |