Merge tag 'rust-6.3' of https://github.com/Rust-for-Linux/linux

Pull Rust updates from Miguel Ojeda:
 "More core additions, getting closer to a point where the first Rust
  modules can be upstreamed. The major ones being:

   - Sync: new types 'Arc', 'ArcBorrow' and 'UniqueArc'.

   - Types: new trait 'ForeignOwnable' and new type 'ScopeGuard'.

  There is also a substantial removal in terms of lines:

   - 'alloc' crate: remove the 'borrow' module (type 'Cow' and trait
     'ToOwned')"

* tag 'rust-6.3' of https://github.com/Rust-for-Linux/linux:
  rust: delete rust-project.json when running make clean
  rust: MAINTAINERS: Add the zulip link
  rust: types: implement `ForeignOwnable` for `Arc<T>`
  rust: types: implement `ForeignOwnable` for the unit type
  rust: types: implement `ForeignOwnable` for `Box<T>`
  rust: types: introduce `ForeignOwnable`
  rust: types: introduce `ScopeGuard`
  rust: prelude: prevent doc inline of external imports
  rust: sync: add support for dispatching on Arc and ArcBorrow.
  rust: sync: introduce `UniqueArc`
  rust: sync: allow type of `self` to be `ArcBorrow<T>`
  rust: sync: introduce `ArcBorrow`
  rust: sync: allow coercion from `Arc<T>` to `Arc<U>`
  rust: sync: allow type of `self` to be `Arc<T>` or variants
  rust: sync: add `Arc` for ref-counted allocations
  rust: compiler_builtins: make stubs non-global
  rust: alloc: remove the `borrow` module (`ToOwned`, `Cow`)

13 files changed, 806 insertions, 502 deletions

diff --git a/rust/Makefile b/rust/Makefile
index ff70c4c916f802..8a521f2b642201 100644
--- a/rust/Makefile
+++ b/rust/Makefile
@@ -50,6 +50,7 @@ core-cfgs = \
     --cfg no_fp_fmt_parse
 
 alloc-cfgs = \
+    --cfg no_borrow \
     --cfg no_fmt \
     --cfg no_global_oom_handling \
     --cfg no_macros \
@@ -359,8 +360,22 @@ rust-analyzer:
 	$(Q)$(srctree)/scripts/generate_rust_analyzer.py $(srctree) $(objtree) \
 		$(RUST_LIB_SRC) > $(objtree)/rust-project.json
 
+redirect-intrinsics = \
+	__eqsf2 __gesf2 __lesf2 __nesf2 __unordsf2 \
+	__unorddf2 \
+	__muloti4 __multi3 \
+	__udivmodti4 __udivti3 __umodti3
+
+ifneq ($(or $(CONFIG_ARM64),$(and $(CONFIG_RISCV),$(CONFIG_64BIT))),)
+	# These intrinsics are defined for ARM64 and RISCV64
+	redirect-intrinsics += \
+		__ashrti3 \
+		__ashlti3 __lshrti3
+endif
+
 $(obj)/core.o: private skip_clippy = 1
 $(obj)/core.o: private skip_flags = -Dunreachable_pub
+$(obj)/core.o: private rustc_objcopy = $(foreach sym,$(redirect-intrinsics),--redefine-sym $(sym)=__rust$(sym))
 $(obj)/core.o: private rustc_target_flags = $(core-cfgs)
 $(obj)/core.o: $(RUST_LIB_SRC)/core/src/lib.rs $(obj)/target.json FORCE
 	$(call if_changed_dep,rustc_library)
diff --git a/rust/alloc/borrow.rs b/rust/alloc/borrow.rs
deleted file mode 100644
index dde4957200d406..00000000000000
--- a/rust/alloc/borrow.rs
+++ /dev/null
@@ -1,498 +0,0 @@
-// SPDX-License-Identifier: Apache-2.0 OR MIT
-
-//! A module for working with borrowed data.
-
-#![stable(feature = "rust1", since = "1.0.0")]
-
-use core::cmp::Ordering;
-use core::hash::{Hash, Hasher};
-use core::ops::Deref;
-#[cfg(not(no_global_oom_handling))]
-use core::ops::{Add, AddAssign};
-
-#[stable(feature = "rust1", since = "1.0.0")]
-pub use core::borrow::{Borrow, BorrowMut};
-
-use core::fmt;
-#[cfg(not(no_global_oom_handling))]
-use crate::string::String;
-
-use Cow::*;
-
-#[stable(feature = "rust1", since = "1.0.0")]
-impl<'a, B: ?Sized> Borrow<B> for Cow<'a, B>
-where
-    B: ToOwned,
-    <B as ToOwned>::Owned: 'a,
-{
-    fn borrow(&self) -> &B {
-        &**self
-    }
-}
-
-/// A generalization of `Clone` to borrowed data.
-///
-/// Some types make it possible to go from borrowed to owned, usually by
-/// implementing the `Clone` trait. But `Clone` works only for going from `&T`
-/// to `T`. The `ToOwned` trait generalizes `Clone` to construct owned data
-/// from any borrow of a given type.
-#[cfg_attr(not(test), rustc_diagnostic_item = "ToOwned")]
-#[stable(feature = "rust1", since = "1.0.0")]
-pub trait ToOwned {
-    /// The resulting type after obtaining ownership.
-    #[stable(feature = "rust1", since = "1.0.0")]
-    type Owned: Borrow<Self>;
-
-    /// Creates owned data from borrowed data, usually by cloning.
-    ///
-    /// # Examples
-    ///
-    /// Basic usage:
-    ///
-    /// ```
-    /// let s: &str = "a";
-    /// let ss: String = s.to_owned();
-    ///
-    /// let v: &[i32] = &[1, 2];
-    /// let vv: Vec<i32> = v.to_owned();
-    /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
-    #[must_use = "cloning is often expensive and is not expected to have side effects"]
-    fn to_owned(&self) -> Self::Owned;
-
-    /// Uses borrowed data to replace owned data, usually by cloning.
-    ///
-    /// This is borrow-generalized version of `Clone::clone_from`.
-    ///
-    /// # Examples
-    ///
-    /// Basic usage:
-    ///
-    /// ```
-    /// # #![feature(toowned_clone_into)]
-    /// let mut s: String = String::new();
-    /// "hello".clone_into(&mut s);
-    ///
-    /// let mut v: Vec<i32> = Vec::new();
-    /// [1, 2][..].clone_into(&mut v);
-    /// ```
-    #[unstable(feature = "toowned_clone_into", reason = "recently added", issue = "41263")]
-    fn clone_into(&self, target: &mut Self::Owned) {
-        *target = self.to_owned();
-    }
-}
-
-#[stable(feature = "rust1", since = "1.0.0")]
-impl<T> ToOwned for T
-where
-    T: Clone,
-{
-    type Owned = T;
-    fn to_owned(&self) -> T {
-        self.clone()
-    }
-
-    fn clone_into(&self, target: &mut T) {
-        target.clone_from(self);
-    }
-}
-
-/// A clone-on-write smart pointer.
-///
-/// The type `Cow` is a smart pointer providing clone-on-write functionality: it
-/// can enclose and provide immutable access to borrowed data, and clone the
-/// data lazily when mutation or ownership is required. The type is designed to
-/// work with general borrowed data via the `Borrow` trait.
-///
-/// `Cow` implements `Deref`, which means that you can call
-/// non-mutating methods directly on the data it encloses. If mutation
-/// is desired, `to_mut` will obtain a mutable reference to an owned
-/// value, cloning if necessary.
-///
-/// If you need reference-counting pointers, note that
-/// [`Rc::make_mut`][crate::rc::Rc::make_mut] and
-/// [`Arc::make_mut`][crate::sync::Arc::make_mut] can provide clone-on-write
-/// functionality as well.
-///
-/// # Examples
-///
-/// ```
-/// use std::borrow::Cow;
-///
-/// fn abs_all(input: &mut Cow<[i32]>) {
-///     for i in 0..input.len() {
-///         let v = input[i];
-///         if v < 0 {
-///             // Clones into a vector if not already owned.
-///             input.to_mut()[i] = -v;
-///         }
-///     }
-/// }
-///
-/// // No clone occurs because `input` doesn't need to be mutated.
-/// let slice = [0, 1, 2];
-/// let mut input = Cow::from(&slice[..]);
-/// abs_all(&mut input);
-///
-/// // Clone occurs because `input` needs to be mutated.
-/// let slice = [-1, 0, 1];
-/// let mut input = Cow::from(&slice[..]);
-/// abs_all(&mut input);
-///
-/// // No clone occurs because `input` is already owned.
-/// let mut input = Cow::from(vec![-1, 0, 1]);
-/// abs_all(&mut input);
-/// ```
-///
-/// Another example showing how to keep `Cow` in a struct:
-///
-/// ```
-/// use std::borrow::Cow;
-///
-/// struct Items<'a, X: 'a> where [X]: ToOwned<Owned = Vec<X>> {
-///     values: Cow<'a, [X]>,
-/// }
-///
-/// impl<'a, X: Clone + 'a> Items<'a, X> where [X]: ToOwned<Owned = Vec<X>> {
-///     fn new(v: Cow<'a, [X]>) -> Self {
-///         Items { values: v }
-///     }
-/// }
-///
-/// // Creates a container from borrowed values of a slice
-/// let readonly = [1, 2];
-/// let borrowed = Items::new((&readonly[..]).into());
-/// match borrowed {
-///     Items { values: Cow::Borrowed(b) } => println!("borrowed {b:?}"),
-///     _ => panic!("expect borrowed value"),
-/// }
-///
-/// let mut clone_on_write = borrowed;
-/// // Mutates the data from slice into owned vec and pushes a new value on top
-/// clone_on_write.values.to_mut().push(3);
-/// println!("clone_on_write = {:?}", clone_on_write.values);
-///
-/// // The data was mutated. Let's check it out.
-/// match clone_on_write {
-///     Items { values: Cow::Owned(_) } => println!("clone_on_write contains owned data"),
-///     _ => panic!("expect owned data"),
-/// }
-/// ```
-#[stable(feature = "rust1", since = "1.0.0")]
-#[cfg_attr(not(test), rustc_diagnostic_item = "Cow")]
-pub enum Cow<'a, B: ?Sized + 'a>
-where
-    B: ToOwned,
-{
-    /// Borrowed data.
-    #[stable(feature = "rust1", since = "1.0.0")]
-    Borrowed(#[stable(feature = "rust1", since = "1.0.0")] &'a B),
-
-    /// Owned data.
-    #[stable(feature = "rust1", since = "1.0.0")]
-    Owned(#[stable(feature = "rust1", since = "1.0.0")] <B as ToOwned>::Owned),
-}
-
-#[stable(feature = "rust1", since = "1.0.0")]
-impl<B: ?Sized + ToOwned> Clone for Cow<'_, B> {
-    fn clone(&self) -> Self {
-        match *self {
-            Borrowed(b) => Borrowed(b),
-            Owned(ref o) => {
-                let b: &B = o.borrow();
-                Owned(b.to_owned())
-            }
-        }
-    }
-
-    fn clone_from(&mut self, source: &Self) {
-        match (self, source) {
-            (&mut Owned(ref mut dest), &Owned(ref o)) => o.borrow().clone_into(dest),
-            (t, s) => *t = s.clone(),
-        }
-    }
-}
-
-impl<B: ?Sized + ToOwned> Cow<'_, B> {
-    /// Returns true if the data is borrowed, i.e. if `to_mut` would require additional work.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// #![feature(cow_is_borrowed)]
-    /// use std::borrow::Cow;
-    ///
-    /// let cow = Cow::Borrowed("moo");
-    /// assert!(cow.is_borrowed());
-    ///
-    /// let bull: Cow<'_, str> = Cow::Owned("...moo?".to_string());
-    /// assert!(!bull.is_borrowed());
-    /// ```
-    #[unstable(feature = "cow_is_borrowed", issue = "65143")]
-    #[rustc_const_unstable(feature = "const_cow_is_borrowed", issue = "65143")]
-    pub const fn is_borrowed(&self) -> bool {
-        match *self {
-            Borrowed(_) => true,
-            Owned(_) => false,
-        }
-    }
-
-    /// Returns true if the data is owned, i.e. if `to_mut` would be a no-op.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// #![feature(cow_is_borrowed)]
-    /// use std::borrow::Cow;
-    ///
-    /// let cow: Cow<'_, str> = Cow::Owned("moo".to_string());
-    /// assert!(cow.is_owned());
-    ///
-    /// let bull = Cow::Borrowed("...moo?");
-    /// assert!(!bull.is_owned());
-    /// ```
-    #[unstable(feature = "cow_is_borrowed", issue = "65143")]
-    #[rustc_const_unstable(feature = "const_cow_is_borrowed", issue = "65143")]
-    pub const fn is_owned(&self) -> bool {
-        !self.is_borrowed()
-    }
-
-    /// Acquires a mutable reference to the owned form of the data.
-    ///
-    /// Clones the data if it is not already owned.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// use std::borrow::Cow;
-    ///
-    /// let mut cow = Cow::Borrowed("foo");
-    /// cow.to_mut().make_ascii_uppercase();
-    ///
-    /// assert_eq!(
-    ///   cow,
-    ///   Cow::Owned(String::from("FOO")) as Cow<str>
-    /// );
-    /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
-    pub fn to_mut(&mut self) -> &mut <B as ToOwned>::Owned {
-        match *self {
-            Borrowed(borrowed) => {
-                *self = Owned(borrowed.to_owned());
-                match *self {
-                    Borrowed(..) => unreachable!(),
-                    Owned(ref mut owned) => owned,
-                }
-            }
-            Owned(ref mut owned) => owned,
-        }
-    }
-
-    /// Extracts the owned data.
-    ///
-    /// Clones the data if it is not already owned.
-    ///
-    /// # Examples
-    ///
-    /// Calling `into_owned` on a `Cow::Borrowed` returns a clone of the borrowed data:
-    ///
-    /// ```
-    /// use std::borrow::Cow;
-    ///
-    /// let s = "Hello world!";
-    /// let cow = Cow::Borrowed(s);
-    ///
-    /// assert_eq!(
-    ///   cow.into_owned(),
-    ///   String::from(s)
-    /// );
-    /// ```
-    ///
-    /// Calling `into_owned` on a `Cow::Owned` returns the owned data. The data is moved out of the
-    /// `Cow` without being cloned.
-    ///
-    /// ```
-    /// use std::borrow::Cow;
-    ///
-    /// let s = "Hello world!";
-    /// let cow: Cow<str> = Cow::Owned(String::from(s));
-    ///
-    /// assert_eq!(
-    ///   cow.into_owned(),
-    ///   String::from(s)
-    /// );
-    /// ```
-    #[stable(feature = "rust1", since = "1.0.0")]
-    pub fn into_owned(self) -> <B as ToOwned>::Owned {
-        match self {
-            Borrowed(borrowed) => borrowed.to_owned(),
-            Owned(owned) => owned,
-        }
-    }
-}
-
-#[stable(feature = "rust1", since = "1.0.0")]
-#[rustc_const_unstable(feature = "const_deref", issue = "88955")]
-impl<B: ?Sized + ToOwned> const Deref for Cow<'_, B>
-where
-    B::Owned: ~const Borrow<B>,
-{
-    type Target = B;
-
-    fn deref(&self) -> &B {
-        match *self {
-            Borrowed(borrowed) => borrowed,
-            Owned(ref owned) => owned.borrow(),
-        }
-    }
-}
-
-#[stable(feature = "rust1", since = "1.0.0")]
-impl<B: ?Sized> Eq for Cow<'_, B> where B: Eq + ToOwned {}
-
-#[stable(feature = "rust1", since = "1.0.0")]
-impl<B: ?Sized> Ord for Cow<'_, B>
-where
-    B: Ord + ToOwned,
-{
-    #[inline]
-    fn cmp(&self, other: &Self) -> Ordering {
-        Ord::cmp(&**self, &**other)
-    }
-}
-
-#[stable(feature = "rust1", since = "1.0.0")]
-impl<'a, 'b, B: ?Sized, C: ?Sized> PartialEq<Cow<'b, C>> for Cow<'a, B>
-where
-    B: PartialEq<C> + ToOwned,
-    C: ToOwned,
-{
-    #[inline]
-    fn eq(&self, other: &Cow<'b, C>) -> bool {
-        PartialEq::eq(&**self, &**other)
-    }
-}
-
-#[stable(feature = "rust1", since = "1.0.0")]
-impl<'a, B: ?Sized> PartialOrd for Cow<'a, B>
-where
-    B: PartialOrd + ToOwned,
-{
-    #[inline]
-    fn partial_cmp(&self, other: &Cow<'a, B>) -> Option<Ordering> {
-        PartialOrd::partial_cmp(&**self, &**other)
-    }
-}
-
-#[stable(feature = "rust1", since = "1.0.0")]
-impl<B: ?Sized> fmt::Debug for Cow<'_, B>
-where
-    B: fmt::Debug + ToOwned<Owned: fmt::Debug>,
-{
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        match *self {
-            Borrowed(ref b) => fmt::Debug::fmt(b, f),
-            Owned(ref o) => fmt::Debug::fmt(o, f),
-        }
-    }
-}
-
-#[stable(feature = "rust1", since = "1.0.0")]
-impl<B: ?Sized> fmt::Display for Cow<'_, B>
-where
-    B: fmt::Display + ToOwned<Owned: fmt::Display>,
-{
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        match *self {
-            Borrowed(ref b) => fmt::Display::fmt(b, f),
-            Owned(ref o) => fmt::Display::fmt(o, f),
-        }
-    }
-}
-
-#[stable(feature = "default", since = "1.11.0")]
-impl<B: ?Sized> Default for Cow<'_, B>
-where
-    B: ToOwned<Owned: Default>,
-{
-    /// Creates an owned Cow<'a, B> with the default value for the contained owned value.
-    fn default() -> Self {
-        Owned(<B as ToOwned>::Owned::default())
-    }
-}
-
-#[stable(feature = "rust1", since = "1.0.0")]
-impl<B: ?Sized> Hash for Cow<'_, B>
-where
-    B: Hash + ToOwned,
-{
-    #[inline]
-    fn hash<H: Hasher>(&self, state: &mut H) {
-        Hash::hash(&**self, state)
-    }
-}
-
-#[stable(feature = "rust1", since = "1.0.0")]
-impl<T: ?Sized + ToOwned> AsRef<T> for Cow<'_, T> {
-    fn as_ref(&self) -> &T {
-        self
-    }
-}
-
-#[cfg(not(no_global_oom_handling))]
-#[stable(feature = "cow_add", since = "1.14.0")]
-impl<'a> Add<&'a str> for Cow<'a, str> {
-    type Output = Cow<'a, str>;
-
-    #[inline]
-    fn add(mut self, rhs: &'a str) -> Self::Output {
-        self += rhs;
-        self
-    }
-}
-
-#[cfg(not(no_global_oom_handling))]
-#[stable(feature = "cow_add", since = "1.14.0")]
-impl<'a> Add<Cow<'a, str>> for Cow<'a, str> {
-    type Output = Cow<'a, str>;
-
-    #[inline]
-    fn add(mut self, rhs: Cow<'a, str>) -> Self::Output {
-        self += rhs;
-        self
-    }
-}
-
-#[cfg(not(no_global_oom_handling))]
-#[stable(feature = "cow_add", since = "1.14.0")]
-impl<'a> AddAssign<&'a str> for Cow<'a, str> {
-    fn add_assign(&mut self, rhs: &'a str) {
-        if self.is_empty() {
-            *self = Cow::Borrowed(rhs)
-        } else if !rhs.is_empty() {
-            if let Cow::Borrowed(lhs) = *self {
-                let mut s = String::with_capacity(lhs.len() + rhs.len());
-                s.push_str(lhs);
-                *self = Cow::Owned(s);
-            }
-            self.to_mut().push_str(rhs);
-        }
-    }
-}
-
-#[cfg(not(no_global_oom_handling))]
-#[stable(feature = "cow_add", since = "1.14.0")]
-impl<'a> AddAssign<Cow<'a, str>> for Cow<'a, str> {
-    fn add_assign(&mut self, rhs: Cow<'a, str>) {
-        if self.is_empty() {
-            *self = rhs
-        } else if !rhs.is_empty() {
-            if let Cow::Borrowed(lhs) = *self {
-                let mut s = String::with_capacity(lhs.len() + rhs.len());
-                s.push_str(lhs);
-                *self = Cow::Owned(s);
-            }
-            self.to_mut().push_str(&rhs);
-        }
-    }
-}
diff --git a/rust/alloc/lib.rs b/rust/alloc/lib.rs
index 233bcd5e46544c..3aebf83c9967ea 100644
--- a/rust/alloc/lib.rs
+++ b/rust/alloc/lib.rs
@@ -100,7 +100,7 @@
 #![cfg_attr(not(no_global_oom_handling), feature(const_alloc_error))]
 #![feature(const_box)]
 #![cfg_attr(not(no_global_oom_handling), feature(const_btree_new))]
-#![feature(const_cow_is_borrowed)]
+#![cfg_attr(not(no_borrow), feature(const_cow_is_borrowed))]
 #![feature(const_convert)]
 #![feature(const_size_of_val)]
 #![feature(const_align_of_val)]
@@ -215,6 +215,7 @@ pub mod boxed;
 mod boxed {
     pub use std::boxed::Box;
 }
+#[cfg(not(no_borrow))]
 pub mod borrow;
 pub mod collections;
 #[cfg(not(no_global_oom_handling))]
diff --git a/rust/alloc/vec/mod.rs b/rust/alloc/vec/mod.rs
index 8ac6c1e3b2a81b..f77c7368d53478 100644
--- a/rust/alloc/vec/mod.rs
+++ b/rust/alloc/vec/mod.rs
@@ -72,6 +72,7 @@ use core::ptr::{self, NonNull};
 use core::slice::{self, SliceIndex};
 
 use crate::alloc::{Allocator, Global};
+#[cfg(not(no_borrow))]
 use crate::borrow::{Cow, ToOwned};
 use crate::boxed::Box;
 use crate::collections::TryReserveError;
@@ -94,6 +95,7 @@ pub use self::drain::Drain;
 
 mod drain;
 
+#[cfg(not(no_borrow))]
 #[cfg(not(no_global_oom_handling))]
 mod cow;
 
@@ -3103,6 +3105,7 @@ impl<T, const N: usize> From<[T; N]> for Vec<T> {
     }
 }
 
+#[cfg(not(no_borrow))]
 #[stable(feature = "vec_from_cow_slice", since = "1.14.0")]
 impl<'a, T> From<Cow<'a, [T]>> for Vec<T>
 where
diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h
index c48bc284214ab1..75d85bd6c59211 100644
--- a/rust/bindings/bindings_helper.h
+++ b/rust/bindings/bindings_helper.h
@@ -7,6 +7,7 @@
  */
 
 #include <linux/slab.h>
+#include <linux/refcount.h>
 
 /* `bindgen` gets confused at certain things. */
 const gfp_t BINDINGS_GFP_KERNEL = GFP_KERNEL;
diff --git a/rust/bindings/lib.rs b/rust/bindings/lib.rs
index 6c50ee62c56b6e..7b246454e00918 100644
--- a/rust/bindings/lib.rs
+++ b/rust/bindings/lib.rs
@@ -41,6 +41,7 @@ mod bindings_raw {
 #[allow(dead_code)]
 mod bindings_helper {
     // Import the generated bindings for types.
+    use super::bindings_raw::*;
     include!(concat!(
         env!("OBJTREE"),
         "/rust/bindings/bindings_helpers_generated.rs"
diff --git a/rust/compiler_builtins.rs b/rust/compiler_builtins.rs
index f8f39a3e685514..43378357ece99b 100644
--- a/rust/compiler_builtins.rs
+++ b/rust/compiler_builtins.rs
@@ -28,7 +28,7 @@ macro_rules! define_panicking_intrinsics(
     ($reason: tt, { $($ident: ident, )* }) => {
         $(
             #[doc(hidden)]
-            #[no_mangle]
+            #[export_name = concat!("__rust", stringify!($ident))]
             pub extern "C" fn $ident() {
                 panic!($reason);
             }
@@ -61,3 +61,6 @@ define_panicking_intrinsics!("`u128` should not be used", {
     __udivti3,
     __umodti3,
 });
+
+// NOTE: if you are adding a new intrinsic here, you should also add it to
+// `redirect-intrinsics` in `rust/Makefile`.
diff --git a/rust/helpers.c b/rust/helpers.c
index b4f15eee2ffdbb..09a4d93f9d62cc 100644
--- a/rust/helpers.c
+++ b/rust/helpers.c
@@ -20,6 +20,7 @@
 
 #include <linux/bug.h>
 #include <linux/build_bug.h>
+#include <linux/refcount.h>
 
 __noreturn void rust_helper_BUG(void)
 {
@@ -27,6 +28,24 @@ __noreturn void rust_helper_BUG(void)
 }
 EXPORT_SYMBOL_GPL(rust_helper_BUG);
 
+refcount_t rust_helper_REFCOUNT_INIT(int n)
+{
+	return (refcount_t)REFCOUNT_INIT(n);
+}
+EXPORT_SYMBOL_GPL(rust_helper_REFCOUNT_INIT);
+
+void rust_helper_refcount_inc(refcount_t *r)
+{
+	refcount_inc(r);
+}
+EXPORT_SYMBOL_GPL(rust_helper_refcount_inc);
+
+bool rust_helper_refcount_dec_and_test(refcount_t *r)
+{
+	return refcount_dec_and_test(r);
+}
+EXPORT_SYMBOL_GPL(rust_helper_refcount_dec_and_test);
+
 /*
  * We use `bindgen`'s `--size_t-is-usize` option to bind the C `size_t` type
  * as the Rust `usize` type, so we can use it in contexts where Rust
diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
index 53040fa9e89740..223564f9f0cc38 100644
--- a/rust/kernel/lib.rs
+++ b/rust/kernel/lib.rs
@@ -13,7 +13,12 @@
 
 #![no_std]
 #![feature(allocator_api)]
+#![feature(coerce_unsized)]
 #![feature(core_ffi_c)]
+#![feature(dispatch_from_dyn)]
+#![feature(generic_associated_types)]
+#![feature(receiver_trait)]
+#![feature(unsize)]
 
 // Ensure conditional compilation based on the kernel configuration works;
 // otherwise we may silently break things like initcall handling.
@@ -31,6 +36,7 @@ mod static_assert;
 #[doc(hidden)]
 pub mod std_vendor;
 pub mod str;
+pub mod sync;
 pub mod types;
 
 #[doc(hidden)]
diff --git a/rust/kernel/prelude.rs b/rust/kernel/prelude.rs
index 7a90249ee9b9e7..0bc1c97e5604c6 100644
--- a/rust/kernel/prelude.rs
+++ b/rust/kernel/prelude.rs
@@ -11,15 +11,21 @@
 //! use kernel::prelude::*;
 //! ```
 
+#[doc(no_inline)]
 pub use core::pin::Pin;
 
+#[doc(no_inline)]
 pub use alloc::{boxed::Box, vec::Vec};
 
+#[doc(no_inline)]
 pub use macros::{module, vtable};
 
 pub use super::build_assert;
 
-pub use super::{dbg, pr_alert, pr_crit, pr_debug, pr_emerg, pr_err, pr_info, pr_notice, pr_warn};
+// `super::std_vendor` is hidden, which makes the macro inline for some reason.
+#[doc(no_inline)]
+pub use super::dbg;
+pub use super::{pr_alert, pr_crit, pr_debug, pr_emerg, pr_err, pr_info, pr_notice, pr_warn};
 
 pub use super::static_assert;
 
diff --git a/rust/kernel/sync.rs b/rust/kernel/sync.rs
new file mode 100644
index 00000000000000..33da23e3076d2f
--- /dev/null
+++ b/rust/kernel/sync.rs
@@ -0,0 +1,10 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Synchronisation primitives.
+//!
+//! This module contains the kernel APIs related to synchronisation that have been ported or
+//! wrapped for usage by Rust code in the kernel.
+
+mod arc;
+
+pub use arc::{Arc, ArcBorrow, UniqueArc};
diff --git a/rust/kernel/sync/arc.rs b/rust/kernel/sync/arc.rs
new file mode 100644
index 00000000000000..f2f1c83d72ba21
--- /dev/null
+++ b/rust/kernel/sync/arc.rs
@@ -0,0 +1,524 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! A reference-counted pointer.
+//!
+//! This module implements a way for users to create reference-counted objects and pointers to
+//! them. Such a pointer automatically increments and decrements the count, and drops the
+//! underlying object when it reaches zero. It is also safe to use concurrently from multiple
+//! threads.
+//!
+//! It is different from the standard library's [`Arc`] in a few ways:
+//! 1. It is backed by the kernel's `refcount_t` type.
+//! 2. It does not support weak references, which allows it to be half the size.
+//! 3. It saturates the reference count instead of aborting when it goes over a threshold.
+//! 4. It does not provide a `get_mut` method, so the ref counted object is pinned.
+//!
+//! [`Arc`]: https://doc.rust-lang.org/std/sync/struct.Arc.html
+
+use crate::{
+    bindings,
+    error::Result,
+    types::{ForeignOwnable, Opaque},
+};
+use alloc::boxed::Box;
+use core::{
+    marker::{PhantomData, Unsize},
+    mem::{ManuallyDrop, MaybeUninit},
+    ops::{Deref, DerefMut},
+    pin::Pin,
+    ptr::NonNull,
+};
+
+/// A reference-counted pointer to an instance of `T`.
+///
+/// The reference count is incremented when new instances of [`Arc`] are created, and decremented
+/// when they are dropped. When the count reaches zero, the underlying `T` is also dropped.
+///
+/// # Invariants
+///
+/// The reference count on an instance of [`Arc`] is always non-zero.
+/// The object pointed to by [`Arc`] is always pinned.
+///
+/// # Examples
+///
+/// ```
+/// use kernel::sync::Arc;
+///
+/// struct Example {
+///     a: u32,
+///     b: u32,
+/// }
+///
+/// // Create a ref-counted instance of `Example`.
+/// let obj = Arc::try_new(Example { a: 10, b: 20 })?;
+///
+/// // Get a new pointer to `obj` and increment the refcount.
+/// let cloned = obj.clone();
+///
+/// // Assert that both `obj` and `cloned` point to the same underlying object.
+/// assert!(core::ptr::eq(&*obj, &*cloned));
+///
+/// // Destroy `obj` and decrement its refcount.
+/// drop(obj);
+///
+/// // Check that the values are still accessible through `cloned`.
+/// assert_eq!(cloned.a, 10);
+/// assert_eq!(cloned.b, 20);
+///
+/// // The refcount drops to zero when `cloned` goes out of scope, and the memory is freed.
+/// ```
+///
+/// Using `Arc<T>` as the type of `self`:
+///
+/// ```
+/// use kernel::sync::Arc;
+///
+/// struct Example {
+///     a: u32,
+///     b: u32,
+/// }
+///
+/// impl Example {
+///     fn take_over(self: Arc<Self>) {
+///         // ...
+///     }
+///
+///     fn use_reference(self: &Arc<Self>) {
+///         // ...
+///     }
+/// }
+///
+/// let obj = Arc::try_new(Example { a: 10, b: 20 })?;
+/// obj.use_reference();
+/// obj.take_over();
+/// ```
+///
+/// Coercion from `Arc<Example>` to `Arc<dyn MyTrait>`:
+///
+/// ```
+/// use kernel::sync::{Arc, ArcBorrow};
+///
+/// trait MyTrait {
+///     // Trait has a function whose `self` type is `Arc<Self>`.
+///     fn example1(self: Arc<Self>) {}
+///
+///     // Trait has a function whose `self` type is `ArcBorrow<'_, Self>`.
+///     fn example2(self: ArcBorrow<'_, Self>) {}
+/// }
+///
+/// struct Example;
+/// impl MyTrait for Example {}
+///
+/// // `obj` has type `Arc<Example>`.
+/// let obj: Arc<Example> = Arc::try_new(Example)?;
+///
+/// // `coerced` has type `Arc<dyn MyTrait>`.
+/// let coerced: Arc<dyn MyTrait> = obj;
+/// ```
+pub struct Arc<T: ?Sized> {
+    ptr: NonNull<ArcInner<T>>,
+    _p: PhantomData<ArcInner<T>>,
+}
+
+#[repr(C)]
+struct ArcInner<T: ?Sized> {
+    refcount: Opaque<bindings::refcount_t>,
+    data: T,
+}
+
+// This is to allow [`Arc`] (and variants) to be used as the type of `self`.
+impl<T: ?Sized> core::ops::Receiver for Arc<T> {}
+
+// This is to allow coercion from `Arc<T>` to `Arc<U>` if `T` can be converted to the
+// dynamically-sized type (DST) `U`.
+impl<T: ?Sized + Unsize<U>, U: ?Sized> core::ops::CoerceUnsized<Arc<U>> for Arc<T> {}
+
+// This is to allow `Arc<U>` to be dispatched on when `Arc<T>` can be coerced into `Arc<U>`.
+impl<T: ?Sized + Unsize<U>, U: ?Sized> core::ops::DispatchFromDyn<Arc<U>> for Arc<T> {}
+
+// SAFETY: It is safe to send `Arc<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 `Arc<T>` may ultimately access `T` directly, for
+// example, when the reference count reaches zero and `T` is dropped.
+unsafe impl<T: ?Sized + Sync + Send> Send for Arc<T> {}
+
+// SAFETY: It is safe to send `&Arc<T>` to another thread when the underlying `T` is `Sync` for the
+// same reason as above. `T` needs to be `Send` as well because a thread can clone an `&Arc<T>`
+// into an `Arc<T>`, which may lead to `T` being accessed by the same reasoning as above.
+unsafe impl<T: ?Sized + Sync + Send> Sync for Arc<T> {}
+
+impl<T> Arc<T> {
+    /// Constructs a new reference counted instance of `T`.
+    pub fn try_new(contents: T) -> Result<Self> {
+        // INVARIANT: The refcount is initialised to a non-zero value.
+        let value = ArcInner {
+            // SAFETY: There are no safety requirements for this FFI call.
+            refcount: Opaque::new(unsafe { bindings::REFCOUNT_INIT(1) }),
+            data: contents,
+        };
+
+        let inner = Box::try_new(value)?;
+
+        // SAFETY: We just created `inner` with a reference count of 1, which is owned by the new
+        // `Arc` object.
+        Ok(unsafe { Self::from_inner(Box::leak(inner).into()) })
+    }
+}
+
+impl<T: ?Sized> Arc<T> {
+    /// Constructs a new [`Arc`] from an existing [`ArcInner`].
+    ///
+    /// # Safety
+    ///
+    /// The caller must ensure that `inner` points to a valid location and has a non-zero reference
+    /// count, one of which will be owned by the new [`Arc`] instance.
+    unsafe fn from_inner(inner: NonNull<ArcInner<T>>) -> Self {
+        // INVARIANT: By the safety requirements, the invariants hold.
+        Arc {
+            ptr: inner,
+            _p: PhantomData,
+        }
+    }
+
+    /// Returns an [`ArcBorrow`] from the given [`Arc`].
+    ///
+    /// This is useful when the argument of a function call is an [`ArcBorrow`] (e.g., in a method
+    /// receiver), but we have an [`Arc`] instead. Getting an [`ArcBorrow`] is free when optimised.
+    #[inline]
+    pub fn as_arc_borrow(&self) -> ArcBorrow<'_, T> {
+        // SAFETY: The constraint that the lifetime of the shared reference must outlive that of
+        // the returned `ArcBorrow` ensures that the object remains alive and that no mutable
+        // reference can be created.
+        unsafe { ArcBorrow::new(self.ptr) }
+    }
+}
+
+impl<T: 'static> ForeignOwnable for Arc<T> {
+    type Borrowed<'a> = ArcBorrow<'a, T>;
+
+    fn into_foreign(self) -> *const core::ffi::c_void {
+        ManuallyDrop::new(self).ptr.as_ptr() as _
+    }
+
+    unsafe fn borrow<'a>(ptr: *const core::ffi::c_void) -> ArcBorrow<'a, T> {
+        // SAFETY: By the safety requirement of this function, we know that `ptr` came from
+        // a previous call to `Arc::into_foreign`.
+        let inner = NonNull::new(ptr as *mut ArcInner<T>).unwrap();
+
+        // SAFETY: The safety requirements of `from_foreign` ensure that the object remains alive
+        // for the lifetime of the returned value. Additionally, the safety requirements of
+        // `ForeignOwnable::borrow_mut` ensure that no new mutable references are created.
+        unsafe { ArcBorrow::new(inner) }
+    }
+
+    unsafe fn from_foreign(ptr: *const core::ffi::c_void) -> Self {
+        // SAFETY: By the safety requirement of this function, we know that `ptr` came from
+        // a previous call to `Arc::into_foreign`, which guarantees that `ptr` is valid and
+        // holds a reference count increment that is transferrable to us.
+        unsafe { Self::from_inner(NonNull::new(ptr as _).unwrap()) }
+    }
+}
+
+impl<T: ?Sized> Deref for Arc<T> {
+    type Target = T;
+
+    fn deref(&self) -> &Self::Target {
+        // SAFETY: By the type invariant, there is necessarily a reference to the object, so it is
+        // safe to dereference it.
+        unsafe { &self.ptr.as_ref().data }
+    }
+}
+
+impl<T: ?Sized> Clone for Arc<T> {
+    fn clone(&self) -> Self {
+        // INVARIANT: C `refcount_inc` saturates the refcount, so it cannot overflow to zero.
+        // SAFETY: By the type invariant, there is necessarily a reference to the object, so it is
+        // safe to increment the refcount.
+        unsafe { bindings::refcount_inc(self.ptr.as_ref().refcount.get()) };
+
+        // SAFETY: We just incremented the refcount. This increment is now owned by the new `Arc`.
+        unsafe { Self::from_inner(self.ptr) }
+    }
+}
+
+impl<T: ?Sized> Drop for Arc<T> {
+    fn drop(&mut self) {
+        // SAFETY: By the type invariant, there is necessarily a reference to the object. We cannot
+        // touch `refcount` after it's decremented to a non-zero value because another thread/CPU
+        // may concurrently decrement it to zero and free it. It is ok to have a raw pointer to
+        // freed/invalid memory as long as it is never dereferenced.
+        let refcount = unsafe { self.ptr.as_ref() }.refcount.get();
+
+        // INVARIANT: If the refcount reaches zero, there are no other instances of `Arc`, and
+        // this instance is being dropped, so the broken invariant is not observable.
+        // SAFETY: Also by the type invariant, we are allowed to decrement the refcount.
+        let is_zero = unsafe { bindings::refcount_dec_and_test(refcount) };
+        if is_zero {
+            // The count reached zero, we must free the memory.
+            //
+            // SAFETY: The pointer was initialised from the result of `Box::leak`.
+            unsafe { Box::from_raw(self.ptr.as_ptr()) };
+        }
+    }
+}
+
+impl<T: ?Sized> From<UniqueArc<T>> for Arc<T> {
+    fn from(item: UniqueArc<T>) -> Self {
+        item.inner
+    }
+}
+
+impl<T: ?Sized> From<Pin<UniqueArc<T>>> for Arc<T> {
+    fn from(item: Pin<UniqueArc<T>>) -> Self {
+        // SAFETY: The type invariants of `Arc` guarantee that the data is pinned.
+        unsafe { Pin::into_inner_unchecked(item).inner }
+    }
+}
+
+/// A borrowed reference to an [`Arc`] instance.
+///
+/// For cases when one doesn't ever need to increment the refcount on the allocation, it is simpler
+/// to use just `&T`, which we can trivially get from an `Arc<T>` instance.
+///
+/// However, when one may need to increment the refcount, it is preferable to use an `ArcBorrow<T>`
+/// over `&Arc<T>` because the latter results in a double-indirection: a pointer (shared reference)
+/// to a pointer (`Arc<T>`) to the object (`T`). An [`ArcBorrow`] eliminates this double
+/// indirection while still allowing one to increment the refcount and getting an `Arc<T>` when/if
+/// needed.
+///
+/// # Invariants
+///
+/// There are no mutable references to the underlying [`Arc`], and it remains valid for the
+/// lifetime of the [`ArcBorrow`] instance.
+///
+/// # Example
+///
+/// ```
+/// use crate::sync::{Arc, ArcBorrow};
+///
+/// struct Example;
+///
+/// fn do_something(e: ArcBorrow<'_, Example>) -> Arc<Example> {
+///     e.into()
+/// }
+///
+/// let obj = Arc::try_new(Example)?;
+/// let cloned = do_something(obj.as_arc_borrow());
+///
+/// // Assert that both `obj` and `cloned` point to the same underlying object.
+/// assert!(core::ptr::eq(&*obj, &*cloned));
+/// ```
+///
+/// Using `ArcBorrow<T>` as the type of `self`:
+///
+/// ```
+/// use crate::sync::{Arc, ArcBorrow};
+///
+/// struct Example {
+///     a: u32,
+///     b: u32,
+/// }
+///
+/// impl Example {
+///     fn use_reference(self: ArcBorrow<'_, Self>) {
+///         // ...
+///     }
+/// }
+///
+/// let obj = Arc::try_new(Example { a: 10, b: 20 })?;
+/// obj.as_arc_borrow().use_reference();
+/// ```
+pub struct ArcBorrow<'a, T: ?Sized + 'a> {
+    inner: NonNull<ArcInner<T>>,
+    _p: PhantomData<&'a ()>,
+}
+
+// This is to allow [`ArcBorrow`] (and variants) to be used as the type of `self`.
+impl<T: ?Sized> core::ops::Receiver for ArcBorrow<'_, T> {}
+
+// This is to allow `ArcBorrow<U>` to be dispatched on when `ArcBorrow<T>` can be coerced into
+// `ArcBorrow<U>`.
+impl<T: ?Sized + Unsize<U>, U: ?Sized> core::ops::DispatchFromDyn<ArcBorrow<'_, U>>
+    for ArcBorrow<'_, T>
+{
+}
+
+impl<T: ?Sized> Clone for ArcBorrow<'_, T> {
+    fn clone(&self) -> Self {
+        *self
+    }
+}
+
+impl<T: ?Sized> Copy for ArcBorrow<'_, T> {}
+
+impl<T: ?Sized> ArcBorrow<'_, T> {
+    /// Creates a new [`ArcBorrow`] instance.
+    ///
+    /// # Safety
+    ///
+    /// Callers must ensure the following for the lifetime of the returned [`ArcBorrow`] instance:
+    /// 1. That `inner` remains valid;
+    /// 2. That no mutable references to `inner` are created.
+    unsafe fn new(inner: NonNull<ArcInner<T>>) -> Self {
+        // INVARIANT: The safety requirements guarantee the invariants.
+        Self {
+            inner,
+            _p: PhantomData,
+        }
+    }
+}
+
+impl<T: ?Sized> From<ArcBorrow<'_, T>> for Arc<T> {
+    fn from(b: ArcBorrow<'_, T>) -> Self {
+        // SAFETY: The existence of `b` guarantees that the refcount is non-zero. `ManuallyDrop`
+        // guarantees that `drop` isn't called, so it's ok that the temporary `Arc` doesn't own the
+        // increment.
+        ManuallyDrop::new(unsafe { Arc::from_inner(b.inner) })
+            .deref()
+            .clone()
+    }
+}
+
+impl<T: ?Sized> Deref for ArcBorrow<'_, T> {
+    type Target = T;
+
+    fn deref(&self) -> &Self::Target {
+        // SAFETY: By the type invariant, the underlying object is still alive with no mutable
+        // references to it, so it is safe to create a shared reference.
+        unsafe { &self.inner.as_ref().data }
+    }
+}
+
+/// A refcounted object that is known to have a refcount of 1.
+///
+/// It is mutable and can be converted to an [`Arc`] so that it can be shared.
+///
+/// # Invariants
+///
+/// `inner` always has a reference count of 1.
+///
+/// # Examples
+///
+/// In the following example, we make changes to the inner object before turning it into an
+/// `Arc<Test>` object (after which point, it cannot be mutated directly). Note that `x.into()`
+/// cannot fail.
+///
+/// ```
+/// use kernel::sync::{Arc, UniqueArc};
+///
+/// struct Example {
+///     a: u32,
+///     b: u32,
+/// }
+///
+/// fn test() -> Result<Arc<Example>> {
+///     let mut x = UniqueArc::try_new(Example { a: 10, b: 20 })?;
+///     x.a += 1;
+///     x.b += 1;
+///     Ok(x.into())
+/// }
+///
+/// # test().unwrap();
+/// ```
+///
+/// In the following example we first allocate memory for a ref-counted `Example` but we don't
+/// initialise it on allocation. We do initialise it later with a call to [`UniqueArc::write`],
+/// followed by a conversion to `Arc<Example>`. This is particularly useful when allocation happens
+/// in one context (e.g., sleepable) and initialisation in another (e.g., atomic):
+///
+/// ```
+/// use kernel::sync::{Arc, UniqueArc};
+///
+/// struct Example {
+///     a: u32,
+///     b: u32,
+/// }
+///
+/// fn test() -> Result<Arc<Example>> {
+///     let x = UniqueArc::try_new_uninit()?;
+///     Ok(x.write(Example { a: 10, b: 20 }).into())
+/// }
+///
+/// # test().unwrap();
+/// ```
+///
+/// In the last example below, the caller gets a pinned instance of `Example` while converting to
+/// `Arc<Example>`; this is useful in scenarios where one needs a pinned reference during
+/// initialisation, for example, when initialising fields that are wrapped in locks.
+///
+/// ```
+/// use kernel::sync::{Arc, UniqueArc};
+///
+/// struct Example {
+///     a: u32,
+///     b: u32,
+/// }
+///
+/// fn test() -> Result<Arc<Example>> {
+///     let mut pinned = Pin::from(UniqueArc::try_new(Example { a: 10, b: 20 })?);
+///     // We can modify `pinned` because it is `Unpin`.
+///     pinned.as_mut().a += 1;
+///     Ok(pinned.into())
+/// }
+///
+/// # test().unwrap();
+/// ```
+pub struct UniqueArc<T: ?Sized> {
+    inner: Arc<T>,
+}
+
+impl<T> UniqueArc<T> {
+    /// Tries to allocate a new [`UniqueArc`] instance.
+    pub fn try_new(value: T) -> Result<Self> {
+        Ok(Self {
+            // INVARIANT: The newly-created object has a ref-count of 1.
+            inner: Arc::try_new(value)?,
+        })
+    }
+
+    /// Tries to allocate a new [`UniqueArc`] instance whose contents are not initialised yet.
+    pub fn try_new_uninit() -> Result<UniqueArc<MaybeUninit<T>>> {
+        Ok(UniqueArc::<MaybeUninit<T>> {
+            // INVARIANT: The newly-created object has a ref-count of 1.
+            inner: Arc::try_new(MaybeUninit::uninit())?,
+        })
+    }
+}
+
+impl<T> UniqueArc<MaybeUninit<T>> {
+    /// Converts a `UniqueArc<MaybeUninit<T>>` into a `UniqueArc<T>` by writing a value into it.
+    pub fn write(mut self, value: T) -> UniqueArc<T> {
+        self.deref_mut().write(value);
+        let inner = ManuallyDrop::new(self).inner.ptr;
+        UniqueArc {
+            // SAFETY: The new `Arc` is taking over `ptr` from `self.inner` (which won't be
+            // dropped). The types are compatible because `MaybeUninit<T>` is compatible with `T`.
+            inner: unsafe { Arc::from_inner(inner.cast()) },
+        }
+    }
+}
+
+impl<T: ?Sized> From<UniqueArc<T>> for Pin<UniqueArc<T>> {
+    fn from(obj: UniqueArc<T>) -> Self {
+        // SAFETY: It is not possible to move/replace `T` inside a `Pin<UniqueArc<T>>` (unless `T`
+        // is `Unpin`), so it is ok to convert it to `Pin<UniqueArc<T>>`.
+        unsafe { Pin::new_unchecked(obj) }
+    }
+}
+
+impl<T: ?Sized> Deref for UniqueArc<T> {
+    type Target = T;
+
+    fn deref(&self) -> &Self::Target {
+        self.inner.deref()
+    }
+}
+
+impl<T: ?Sized> DerefMut for UniqueArc<T> {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        // SAFETY: By the `Arc` type invariant, there is necessarily a reference to the object, so
+        // it is safe to dereference it. Additionally, we know there is only one reference when
+        // it's inside a `UniqueArc`, so it is safe to get a mutable reference.
+        unsafe { &mut self.inner.ptr.as_mut().data }
+    }
+}
diff --git a/rust/kernel/types.rs b/rust/kernel/types.rs
index e84e51ec97167d..9d0fdbc558433e 100644
--- a/rust/kernel/types.rs
+++ b/rust/kernel/types.rs
@@ -2,7 +2,220 @@
 
 //! Kernel types.
 
-use core::{cell::UnsafeCell, mem::MaybeUninit};
+use alloc::boxed::Box;
+use core::{
+    cell::UnsafeCell,
+    mem::MaybeUninit,
+    ops::{Deref, DerefMut},
+};
+
+/// 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
+/// later may be transferred back to Rust by calling [`Self::from_foreign`].
+///
+/// This trait is meant to be used in cases when Rust objects are stored in C objects and
+/// eventually "freed" back to Rust.
+pub trait ForeignOwnable: Sized {
+    /// Type of values borrowed between calls to [`ForeignOwnable::into_foreign`] and
+    /// [`ForeignOwnable::from_foreign`].
+    type Borrowed<'a>;
+
+    /// Converts a Rust-owned object to a foreign-owned one.
+    ///
+    /// The foreign representation is a pointer to void.
+    fn into_foreign(self) -> *const core::ffi::c_void;
+
+    /// Borrows a foreign-owned object.
+    ///
+    /// # Safety
+    ///
+    /// `ptr` must have been returned by a previous call to [`ForeignOwnable::into_foreign`] for
+    /// which a previous matching [`ForeignOwnable::from_foreign`] hasn't been called yet.
+    /// Additionally, all instances (if any) of values returned by [`ForeignOwnable::borrow_mut`]
+    /// for this object must have been dropped.
+    unsafe fn borrow<'a>(ptr: *const core::ffi::c_void) -> Self::Borrowed<'a>;
+
+    /// Mutably borrows a foreign-owned object.
+    ///
+    /// # Safety
+    ///
+    /// `ptr` must have been returned by a previous call to [`ForeignOwnable::into_foreign`] for
+    /// which a previous matching [`ForeignOwnable::from_foreign`] hasn't been called yet.
+    /// Additionally, all instances (if any) of values returned by [`ForeignOwnable::borrow`] and
+    /// [`ForeignOwnable::borrow_mut`] for this object must have been dropped.
+    unsafe fn borrow_mut(ptr: *const core::ffi::c_void) -> ScopeGuard<Self, fn(Self)> {
+        // SAFETY: The safety requirements ensure that `ptr` came from a previous call to
+        // `into_foreign`.
+        ScopeGuard::new_with_data(unsafe { Self::from_foreign(ptr) }, |d| {
+            d.into_foreign();
+        })
+    }
+
+    /// Converts a foreign-owned object back to a Rust-owned one.
+    ///
+    /// # Safety
+    ///
+    /// `ptr` must have been returned by a previous call to [`ForeignOwnable::into_foreign`] for
+    /// which a previous matching [`ForeignOwnable::from_foreign`] hasn't been called yet.
+    /// Additionally, all instances (if any) of values returned by [`ForeignOwnable::borrow`] and
+    /// [`ForeignOwnable::borrow_mut`] for this object must have been dropped.
+    unsafe fn from_foreign(ptr: *const core::ffi::c_void) -> Self;
+}
+
+impl<T: 'static> ForeignOwnable for Box<T> {
+    type Borrowed<'a> = &'a T;
+
+    fn into_foreign(self) -> *const core::ffi::c_void {
+        Box::into_raw(self) as _
+    }
+
+    unsafe fn borrow<'a>(ptr: *const core::ffi::c_void) -> &'a T {
+        // SAFETY: The safety requirements for this function ensure that the object is still alive,
+        // so it is safe to dereference the raw pointer.
+        // The safety requirements of `from_foreign` also ensure that the object remains alive for
+        // the lifetime of the returned value.
+        unsafe { &*ptr.cast() }
+    }
+
+    unsafe fn from_foreign(ptr: *const core::ffi::c_void) -> Self {
+        // SAFETY: The safety requirements of this function ensure that `ptr` comes from a previous
+        // call to `Self::into_foreign`.
+        unsafe { Box::from_raw(ptr as _) }
+    }
+}
+
+impl ForeignOwnable for () {
+    type Borrowed<'a> = ();
+
+    fn into_foreign(self) -> *const core::ffi::c_void {
+        core::ptr::NonNull::dangling().as_ptr()
+    }
+
+    unsafe fn borrow<'a>(_: *const core::ffi::c_void) -> Self::Borrowed<'a> {}
+
+    unsafe fn from_foreign(_: *const core::ffi::c_void) -> Self {}
+}
+
+/// Runs a cleanup function/closure when dropped.
+///
+/// The [`ScopeGuard::dismiss`] function prevents the cleanup function from running.
+///
+/// # Examples
+///
+/// In the example below, we have multiple exit paths and we want to log regardless of which one is
+/// taken:
+/// ```
+/// # use kernel::ScopeGuard;
+/// fn example1(arg: bool) {
+///     let _log = ScopeGuard::new(|| pr_info!("example1 completed\n"));
+///
+///     if arg {
+///         return;
+///     }
+///
+///     pr_info!("Do something...\n");
+/// }
+///
+/// # example1(false);
+/// # example1(true);
+/// ```
+///
+/// In the example below, we want to log the same message on all early exits but a different one on
+/// the main exit path:
+/// ```
+/// # use kernel::ScopeGuard;
+/// fn example2(arg: bool) {
+///     let log = ScopeGuard::new(|| pr_info!("example2 returned early\n"));
+///
+///     if arg {
+///         return;
+///     }
+///
+///     // (Other early returns...)
+///
+///     log.dismiss();
+///     pr_info!("example2 no early return\n");
+/// }
+///
+/// # example2(false);
+/// # example2(true);
+/// ```
+///
+/// In the example below, we need a mutable object (the vector) to be accessible within the log
+/// function, so we wrap it in the [`ScopeGuard`]:
+/// ```
+/// # use kernel::ScopeGuard;
+/// fn example3(arg: bool) -> Result {
+///     let mut vec =
+///         ScopeGuard::new_with_data(Vec::new(), |v| pr_info!("vec had {} elements\n", v.len()));
+///
+///     vec.try_push(10u8)?;
+///     if arg {
+///         return Ok(());
+///     }
+///     vec.try_push(20u8)?;
+///     Ok(())
+/// }
+///
+/// # assert_eq!(example3(false), Ok(()));
+/// # assert_eq!(example3(true), Ok(()));
+/// ```
+///
+/// # Invariants
+///
+/// The value stored in the struct is nearly always `Some(_)`, except between
+/// [`ScopeGuard::dismiss`] and [`ScopeGuard::drop`]: in this case, it will be `None` as the value
+/// will have been returned to the caller. Since  [`ScopeGuard::dismiss`] consumes the guard,
+/// callers won't be able to use it anymore.
+pub struct ScopeGuard<T, F: FnOnce(T)>(Option<(T, F)>);
+
+impl<T, F: FnOnce(T)> ScopeGuard<T, F> {
+    /// Creates a new guarded object wrapping the given data and with the given cleanup function.
+    pub fn new_with_data(data: T, cleanup_func: F) -> Self {
+        // INVARIANT: The struct is being initialised with `Some(_)`.
+        Self(Some((data, cleanup_func)))
+    }
+
+    /// Prevents the cleanup function from running and returns the guarded data.
+    pub fn dismiss(mut self) -> T {
+        // INVARIANT: This is the exception case in the invariant; it is not visible to callers
+        // because this function consumes `self`.
+        self.0.take().unwrap().0
+    }
+}
+
+impl ScopeGuard<(), fn(())> {
+    /// Creates a new guarded object with the given cleanup function.
+    pub fn new(cleanup: impl FnOnce()) -> ScopeGuard<(), impl FnOnce(())> {
+        ScopeGuard::new_with_data((), move |_| cleanup())
+    }
+}
+
+impl<T, F: FnOnce(T)> Deref for ScopeGuard<T, F> {
+    type Target = T;
+
+    fn deref(&self) -> &T {
+        // The type invariants guarantee that `unwrap` will succeed.
+        &self.0.as_ref().unwrap().0
+    }
+}
+
+impl<T, F: FnOnce(T)> DerefMut for ScopeGuard<T, F> {
+    fn deref_mut(&mut self) -> &mut T {
+        // The type invariants guarantee that `unwrap` will succeed.
+        &mut self.0.as_mut().unwrap().0
+    }
+}
+
+impl<T, F: FnOnce(T)> Drop for ScopeGuard<T, F> {
+    fn drop(&mut self) {
+        // Run the cleanup function if one is still present.
+        if let Some((data, cleanup)) = self.0.take() {
+            cleanup(data)
+        }
+    }
+}
 
 /// Stores an opaque value.
 ///