Re: FAILED: patch "[PATCH] rust: lockdep: Remove support for dynamically allocated" failed to apply to 6.6-stable tree

[Boqun Feng <boqun.feng@gmail.com>]

Hi Greg,

On Sun, Mar 16, 2025 at 08:15:32AM +0100, gregkh@linuxfoundation.org wrote:
> 
> The patch below does not apply to the 6.6-stable tree.
> If someone wants it applied there, or to any other stable or longterm
> tree, then please email the backport, including the original git commit
> id to <stable@vger.kernel.org>.
> 
> To reproduce the conflict and resubmit, you may use the following commands:
> 
> git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.6.y
> git checkout FETCH_HEAD
> git cherry-pick -x 966944f3711665db13e214fef6d02982c49bb972

It's weird because `cherry-pick` works for me:

$ git cherry-pick -x 966944f3711665db13e214fef6d02982c49bb972
Auto-merging rust/kernel/sync.rs
[stable-6.6 f5771e91eac3] rust: lockdep: Remove support for dynamically allocated LockClassKeys
 Author: Mitchell Levy <levymitchell0@gmail.com>
 Date: Fri Mar 7 15:27:00 2025 -0800
 1 file changed, 4 insertions(+), 6 deletions(-)

my base is 594a1dd5138a ("Linux 6.6.83").

I checked the original commit in Linus' tree, it removes the `impl
Default` which doesn't exist in 6.6, however it seems my `cherry-pick`
can realise and fix this! Anyway I will send the fixed patch soon.

Regards,
Boqun

> # <resolve conflicts, build, test, etc.>
> git commit -s
> git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2025031632-divorcee-duly-868e@gregkh' --subject-prefix 'PATCH 6.6.y' HEAD^..
> 
> Possible dependencies:
> 
> 
> 
> thanks,
> 
> greg k-h
> 
> ------------------ original commit in Linus's tree ------------------
> 
> From 966944f3711665db13e214fef6d02982c49bb972 Mon Sep 17 00:00:00 2001
> From: Mitchell Levy <levymitchell0@gmail.com>
> Date: Fri, 7 Mar 2025 15:27:00 -0800
> Subject: [PATCH] rust: lockdep: Remove support for dynamically allocated
>  LockClassKeys
> 
> Currently, dynamically allocated LockCLassKeys can be used from the Rust
> side without having them registered. This is a soundness issue, so
> remove them.
> 
> Fixes: 6ea5aa08857a ("rust: sync: introduce `LockClassKey`")
> Suggested-by: Alice Ryhl <aliceryhl@google.com>
> Signed-off-by: Mitchell Levy <levymitchell0@gmail.com>
> Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
> Signed-off-by: Ingo Molnar <mingo@kernel.org>
> Reviewed-by: Benno Lossin <benno.lossin@proton.me>
> Cc: stable@vger.kernel.org
> Link: https://lore.kernel.org/r/20250307232717.1759087-11-boqun.feng@gmail.com
> 
> diff --git a/rust/kernel/sync.rs b/rust/kernel/sync.rs
> index 3498fb344dc9..16eab9138b2b 100644
> --- a/rust/kernel/sync.rs
> +++ b/rust/kernel/sync.rs
> @@ -30,28 +30,20 @@
>  unsafe impl Sync for LockClassKey {}
>  
>  impl LockClassKey {
> -    /// Creates a new lock class key.
> -    pub const fn new() -> Self {
> -        Self(Opaque::uninit())
> -    }
> -
>      pub(crate) fn as_ptr(&self) -> *mut bindings::lock_class_key {
>          self.0.get()
>      }
>  }
>  
> -impl Default for LockClassKey {
> -    fn default() -> Self {
> -        Self::new()
> -    }
> -}
> -
>  /// Defines a new static lock class and returns a pointer to it.
>  #[doc(hidden)]
>  #[macro_export]
>  macro_rules! static_lock_class {
>      () => {{
> -        static CLASS: $crate::sync::LockClassKey = $crate::sync::LockClassKey::new();
> +        static CLASS: $crate::sync::LockClassKey =
> +            // SAFETY: lockdep expects uninitialized memory when it's handed a statically allocated
> +            // lock_class_key
> +            unsafe { ::core::mem::MaybeUninit::uninit().assume_init() };
>          &CLASS
>      }};
>  }
>