Message-ID: <20250723112605.74f1c077@canb.auug.org.au>
Date: Wed, 23 Jul 2025 11:26:05 +1000
From: Stephen Rothwell <sfr@...b.auug.org.au>
To: Miguel Ojeda <ojeda@...nel.org>, Greg KH <greg@...ah.com>, Danilo
 Krummrich <dakr@...nel.org>, "Rafael J. Wysocki" <rafael@...nel.org>
Cc: Alice Ryhl <aliceryhl@...gle.com>, Christian Schrefl
 <chrisi.schrefl@...il.com>, Linux Kernel Mailing List
 <linux-kernel@...r.kernel.org>, Linux Next Mailing List
 <linux-next@...r.kernel.org>, Shankari Anand <shankari.ak0208@...il.com>
Subject: linux-next: manual merge of the rust tree with the driver-core tree

Hi all,

Today's linux-next merge of the rust tree got a conflict in:

  rust/kernel/types.rs

between commit:

  64888dfdfac7 ("rust: implement `Wrapper<T>` for `Opaque<T>`")

from the driver-core tree and commits:

  8802e1684378 ("rust: types: add Opaque::cast_from")
  07dad44aa9a9 ("rust: kernel: move ARef and AlwaysRefCounted to sync::aref")

from the rust tree.

I fixed it up (see below) and can carry the fix as necessary. This
is now fixed as far as linux-next is concerned, but any non trivial
conflicts should be mentioned to your upstream maintainer when your tree
is submitted for merging.  You may also want to consider cooperating
with the maintainer of the conflicting tree to minimise any particularly
complex conflicts.

-- 
Cheers,
Stephen Rothwell

diff --cc rust/kernel/types.rs
index 3958a5f44d56,ec82a163cb0e..000000000000
--- a/rust/kernel/types.rs
+++ b/rust/kernel/types.rs
@@@ -5,12 -6,13 +6,13 @@@ use crate::ffi::c_void
  use core::{
      cell::UnsafeCell,
      marker::{PhantomData, PhantomPinned},
-     mem::{ManuallyDrop, MaybeUninit},
+     mem::MaybeUninit,
      ops::{Deref, DerefMut},
-     ptr::NonNull,
  };
 -use pin_init::{PinInit, Zeroable};
 +use pin_init::{PinInit, Wrapper, Zeroable};
  
+ pub use crate::sync::aref::{ARef, AlwaysRefCounted};
+ 
  /// Used to transfer ownership to and from foreign (non-Rust) languages.
  ///
  /// Ownership is transferred from Rust to a foreign language by calling [`Self::into_foreign`] and
@@@ -399,191 -411,16 +400,29 @@@ impl<T> Opaque<T> 
      ///
      /// This function is useful to get access to the value without creating intermediate
      /// references.
-     pub const fn raw_get(this: *const Self) -> *mut T {
+     pub const fn cast_into(this: *const Self) -> *mut T {
          UnsafeCell::raw_get(this.cast::<UnsafeCell<MaybeUninit<T>>>()).cast::<T>()
      }
+ 
+     /// The opposite operation of [`Opaque::cast_into`].
+     pub const fn cast_from(this: *const T) -> *const Self {
+         this.cast()
+     }
  }
  
 +impl<T> Wrapper<T> for Opaque<T> {
 +    /// Create an opaque pin-initializer from the given pin-initializer.
 +    fn pin_init<E>(slot: impl PinInit<T, E>) -> impl PinInit<Self, E> {
 +        Self::try_ffi_init(|ptr: *mut T| {
 +            // SAFETY:
 +            //   - `ptr` is a valid pointer to uninitialized memory,
 +            //   - `slot` is not accessed on error,
 +            //   - `slot` is pinned in memory.
 +            unsafe { PinInit::<T, E>::__pinned_init(slot, ptr) }
 +        })
 +    }
 +}
 +
- /// Types that are _always_ reference counted.
- ///
- /// It allows such types to define their own custom ref increment and decrement functions.
- /// Additionally, it allows users to convert from a shared reference `&T` to an owned reference
- /// [`ARef<T>`].
- ///
- /// This is usually implemented by wrappers to existing structures on the C side of the code. For
- /// Rust code, the recommendation is to use [`Arc`](crate::sync::Arc) to create reference-counted
- /// instances of a type.
- ///
- /// # Safety
- ///
- /// Implementers must ensure that increments to the reference count keep the object alive in memory
- /// at least until matching decrements are performed.
- ///
- /// Implementers must also ensure that all instances are reference-counted. (Otherwise they
- /// won't be able to honour the requirement that [`AlwaysRefCounted::inc_ref`] keep the object
- /// alive.)
- pub unsafe trait AlwaysRefCounted {
-     /// Increments the reference count on the object.
-     fn inc_ref(&self);
- 
-     /// Decrements the reference count on the object.
-     ///
-     /// Frees the object when the count reaches zero.
-     ///
-     /// # Safety
-     ///
-     /// Callers must ensure that there was a previous matching increment to the reference count,
-     /// and that the object is no longer used after its reference count is decremented (as it may
-     /// result in the object being freed), unless the caller owns another increment on the refcount
-     /// (e.g., it calls [`AlwaysRefCounted::inc_ref`] twice, then calls
-     /// [`AlwaysRefCounted::dec_ref`] once).
-     unsafe fn dec_ref(obj: NonNull<Self>);
- }
- 
- /// An owned reference to an always-reference-counted object.
- ///
- /// The object's reference count is automatically decremented when an instance of [`ARef`] is
- /// dropped. It is also automatically incremented when a new instance is created via
- /// [`ARef::clone`].
- ///
- /// # Invariants
- ///
- /// The pointer stored in `ptr` is non-null and valid for the lifetime of the [`ARef`] instance. In
- /// particular, the [`ARef`] instance owns an increment on the underlying object's reference count.
- pub struct ARef<T: AlwaysRefCounted> {
-     ptr: NonNull<T>,
-     _p: PhantomData<T>,
- }
- 
- // SAFETY: It is safe to send `ARef<T>` to another thread when the underlying `T` is `Sync` because
- // it effectively means sharing `&T` (which is safe because `T` is `Sync`); additionally, it needs
- // `T` to be `Send` because any thread that has an `ARef<T>` may ultimately access `T` using a
- // mutable reference, for example, when the reference count reaches zero and `T` is dropped.
- unsafe impl<T: AlwaysRefCounted + Sync + Send> Send for ARef<T> {}
- 
- // SAFETY: It is safe to send `&ARef<T>` to another thread when the underlying `T` is `Sync`
- // because it effectively means sharing `&T` (which is safe because `T` is `Sync`); additionally,
- // it needs `T` to be `Send` because any thread that has a `&ARef<T>` may clone it and get an
- // `ARef<T>` on that thread, so the thread may ultimately access `T` using a mutable reference, for
- // example, when the reference count reaches zero and `T` is dropped.
- unsafe impl<T: AlwaysRefCounted + Sync + Send> Sync for ARef<T> {}
- 
- impl<T: AlwaysRefCounted> ARef<T> {
-     /// Creates a new instance of [`ARef`].
-     ///
-     /// It takes over an increment of the reference count on the underlying object.
-     ///
-     /// # Safety
-     ///
-     /// Callers must ensure that the reference count was incremented at least once, and that they
-     /// are properly relinquishing one increment. That is, if there is only one increment, callers
-     /// must not use the underlying object anymore -- it is only safe to do so via the newly
-     /// created [`ARef`].
-     pub unsafe fn from_raw(ptr: NonNull<T>) -> Self {
-         // INVARIANT: The safety requirements guarantee that the new instance now owns the
-         // increment on the refcount.
-         Self {
-             ptr,
-             _p: PhantomData,
-         }
-     }
- 
-     /// Consumes the `ARef`, returning a raw pointer.
-     ///
-     /// This function does not change the refcount. After calling this function, the caller is
-     /// responsible for the refcount previously managed by the `ARef`.
-     ///
-     /// # Examples
-     ///
-     /// ```
-     /// use core::ptr::NonNull;
-     /// use kernel::types::{ARef, AlwaysRefCounted};
-     ///
-     /// struct Empty {}
-     ///
-     /// # // SAFETY: TODO.
-     /// unsafe impl AlwaysRefCounted for Empty {
-     ///     fn inc_ref(&self) {}
-     ///     unsafe fn dec_ref(_obj: NonNull<Self>) {}
-     /// }
-     ///
-     /// let mut data = Empty {};
-     /// let ptr = NonNull::<Empty>::new(&mut data).unwrap();
-     /// # // SAFETY: TODO.
-     /// let data_ref: ARef<Empty> = unsafe { ARef::from_raw(ptr) };
-     /// let raw_ptr: NonNull<Empty> = ARef::into_raw(data_ref);
-     ///
-     /// assert_eq!(ptr, raw_ptr);
-     /// ```
-     pub fn into_raw(me: Self) -> NonNull<T> {
-         ManuallyDrop::new(me).ptr
-     }
- }
- 
- impl<T: AlwaysRefCounted> Clone for ARef<T> {
-     fn clone(&self) -> Self {
-         self.inc_ref();
-         // SAFETY: We just incremented the refcount above.
-         unsafe { Self::from_raw(self.ptr) }
-     }
- }
- 
- impl<T: AlwaysRefCounted> Deref for ARef<T> {
-     type Target = T;
- 
-     fn deref(&self) -> &Self::Target {
-         // SAFETY: The type invariants guarantee that the object is valid.
-         unsafe { self.ptr.as_ref() }
-     }
- }
- 
- impl<T: AlwaysRefCounted> From<&T> for ARef<T> {
-     fn from(b: &T) -> Self {
-         b.inc_ref();
-         // SAFETY: We just incremented the refcount above.
-         unsafe { Self::from_raw(NonNull::from(b)) }
-     }
- }
- 
- impl<T: AlwaysRefCounted> Drop for ARef<T> {
-     fn drop(&mut self) {
-         // SAFETY: The type invariants guarantee that the `ARef` owns the reference we're about to
-         // decrement.
-         unsafe { T::dec_ref(self.ptr) };
-     }
- }
- 
- /// A sum type that always holds either a value of type `L` or `R`.
- ///
- /// # Examples
- ///
- /// ```
- /// use kernel::types::Either;
- ///
- /// let left_value: Either<i32, &str> = Either::Left(7);
- /// let right_value: Either<i32, &str> = Either::Right("right value");
- /// ```
- pub enum Either<L, R> {
-     /// Constructs an instance of [`Either`] containing a value of type `L`.
-     Left(L),
- 
-     /// Constructs an instance of [`Either`] containing a value of type `R`.
-     Right(R),
- }
- 
  /// Zero-sized type to mark types not [`Send`].
  ///
  /// Add this type as a field to your struct if your type should not be sent to a different task.

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