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 ff70c4c916f8..8a521f2b6422 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 dde4957200d4..000000000000
--- 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 233bcd5e4654..3aebf83c9967 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 8ac6c1e3b2a8..f77c7368d534 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 c48bc284214a..75d85bd6c592 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 6c50ee62c56b..7b246454e009 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 f8f39a3e6855..43378357ece9 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 b4f15eee2ffd..09a4d93f9d62 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 53040fa9e897..223564f9f0cc 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 7a90249ee9b9..0bc1c97e5604 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 000000000000..33da23e3076d
--- /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 000000000000..f2f1c83d72ba
--- /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)