Patch "rust: make `UnsafeCell` the outer type in `Opaque`" has been added to the 6.5-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    rust: make `UnsafeCell` the outer type in `Opaque`

to the 6.5-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     rust-make-unsafecell-the-outer-type-in-opaque.patch
and it can be found in the queue-6.5 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 8454e37da13e2e16b631683e9dbca6148aa5c5ee
Author: Alice Ryhl <aliceryhl@xxxxxxxxxx>
Date:   Wed Jun 14 11:53:28 2023 +0000

    rust: make `UnsafeCell` the outer type in `Opaque`
    
    [ Upstream commit 35cad617df2eeef8440a38e82bb2d81ae32ca50d ]
    
    When combining `UnsafeCell` with `MaybeUninit`, it is idiomatic to use
    `UnsafeCell` as the outer type. Intuitively, this is because a
    `MaybeUninit<T>` might not contain a `T`, but we always want the effect
    of the `UnsafeCell`, even if the inner value is uninitialized.
    
    Now, strictly speaking, this doesn't really make a difference. The
    compiler will always apply the `UnsafeCell` effect even if the inner
    value is uninitialized. But I think we should follow the convention
    here.
    
    Signed-off-by: Alice Ryhl <aliceryhl@xxxxxxxxxx>
    Reviewed-by: Benno Lossin <benno.lossin@xxxxxxxxx>
    Reviewed-by: Gary Guo <gary@xxxxxxxxxxx>
    Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@xxxxxxxxx>
    Link: https://lore.kernel.org/r/20230614115328.2825961-1-aliceryhl@xxxxxxxxxx
    Signed-off-by: Miguel Ojeda <ojeda@xxxxxxxxxx>
    Stable-dep-of: 0b4e3b6f6b79 ("rust: types: make `Opaque` be `!Unpin`")
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/rust/kernel/types.rs b/rust/kernel/types.rs
index d479f8da8f381..c0b8bb1a75393 100644
--- a/rust/kernel/types.rs
+++ b/rust/kernel/types.rs
@@ -206,17 +206,17 @@ fn drop(&mut self) {
 ///
 /// This is meant to be used with FFI objects that are never interpreted by Rust code.
 #[repr(transparent)]
-pub struct Opaque<T>(MaybeUninit<UnsafeCell<T>>);
+pub struct Opaque<T>(UnsafeCell<MaybeUninit<T>>);
 
 impl<T> Opaque<T> {
     /// Creates a new opaque value.
     pub const fn new(value: T) -> Self {
-        Self(MaybeUninit::new(UnsafeCell::new(value)))
+        Self(UnsafeCell::new(MaybeUninit::new(value)))
     }
 
     /// Creates an uninitialised value.
     pub const fn uninit() -> Self {
-        Self(MaybeUninit::uninit())
+        Self(UnsafeCell::new(MaybeUninit::uninit()))
     }
 
     /// Creates a pin-initializer from the given initializer closure.
@@ -240,7 +240,7 @@ pub fn ffi_init(init_func: impl FnOnce(*mut T)) -> impl PinInit<Self> {
 
     /// Returns a raw pointer to the opaque data.
     pub fn get(&self) -> *mut T {
-        UnsafeCell::raw_get(self.0.as_ptr())
+        UnsafeCell::get(&self.0).cast::<T>()
     }
 
     /// Gets the value behind `this`.
@@ -248,7 +248,7 @@ pub fn get(&self) -> *mut 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 {
-        UnsafeCell::raw_get(this.cast::<UnsafeCell<T>>())
+        UnsafeCell::raw_get(this.cast::<UnsafeCell<MaybeUninit<T>>>()).cast::<T>()
     }
 }