Re: [PATCH v3 2/2] rust: lockdep: Use Pin for all LockClassKey usages

[Benno Lossin]

On 05.02.25 20:59, Mitchell Levy wrote:
> diff --git a/rust/kernel/sync/lock.rs b/rust/kernel/sync/lock.rs
> index 41dcddac69e2..119e5f569bdb 100644
> --- a/rust/kernel/sync/lock.rs
> +++ b/rust/kernel/sync/lock.rs
> @@ -7,12 +7,9 @@
> 
>  use super::LockClassKey;
>  use crate::{
> -    init::PinInit,
> -    pin_init,
> -    str::CStr,
> -    types::{NotThreadSafe, Opaque, ScopeGuard},
> +    init::PinInit, pin_init, str::CStr, types::NotThreadSafe, types::Opaque, types::ScopeGuard,
>  };
> -use core::{cell::UnsafeCell, marker::PhantomPinned};
> +use core::{cell::UnsafeCell, marker::PhantomPinned, pin::Pin};
>  use macros::pin_data;
> 
>  pub mod mutex;
> @@ -121,7 +118,7 @@ unsafe impl<T: ?Sized + Send, B: Backend> Sync for Lock<T, B> {}
> 
>  impl<T, B: Backend> Lock<T, B> {
>      /// Constructs a new lock initialiser.
> -    pub fn new(t: T, name: &'static CStr, key: &'static LockClassKey) -> impl PinInit<Self> {
> +    pub fn new(t: T, name: &'static CStr, key: Pin<&'static LockClassKey>) -> impl PinInit<Self> {

Static references do not need `Pin`, since `Pin::static_ref` [1] exists,
so you can just as well not add the `Pin` here and the other places
where you have `Pin<&'static T>`.

The reasoning is that since the data lives for `'static` at that
location, it will never move (since it is borrowed for `'static` after
all).

[1]: https://doc.rust-lang.org/std/pin/struct.Pin.html#method.static_ref

---
Cheers,
Benno

>          pin_init!(Self {
>              data: UnsafeCell::new(t),
>              _pin: PhantomPinned,
> diff --git a/rust/kernel/sync/lock/global.rs b/rust/kernel/sync/lock/global.rs
> index 480ee724e3cc..d65f94b5caf2 100644
> --- a/rust/kernel/sync/lock/global.rs
> +++ b/rust/kernel/sync/lock/global.rs
> @@ -13,6 +13,7 @@
>  use core::{
>      cell::UnsafeCell,
>      marker::{PhantomData, PhantomPinned},
> +    pin::Pin,
>  };
> 
>  /// Trait implemented for marker types for global locks.