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`)

MAINTAINERS

@@ -18234,6 +18234,7 @@ L:	rust-for-linux@vger.kernel.org
 S:	Supported
 W:	https://github.com/Rust-for-Linux/linux
 B:	https://github.com/Rust-for-Linux/linux/issues
+C:	zulip://rust-for-linux.zulipchat.com
 T:	git https://github.com/Rust-for-Linux/linux.git rust-next
 F:	Documentation/rust/
 F:	rust/

Makefile

@@ -1602,7 +1602,7 @@ endif # CONFIG_MODULES
 CLEAN_FILES += include/ksym vmlinux.symvers modules-only.symvers \
 	       modules.builtin modules.builtin.modinfo modules.nsdeps \
 	       compile_commands.json .thinlto-cache rust/test rust/doc \
-	       .vmlinux.objs .vmlinux.export.c
+	       rust-project.json .vmlinux.objs .vmlinux.export.c
 
 # Directories & files removed with 'make mrproper'
 MRPROPER_FILES += include/config include/generated          \

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)

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 @@
 mod boxed {
     pub use std::boxed::Box;
 }
+#[cfg(not(no_borrow))]
 pub mod borrow;
 pub mod collections;
 #[cfg(not(no_global_oom_handling))]

rust/alloc/vec/mod.rs

@@ -72,6 +72,7 @@
 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 @@
 
 mod drain;
 
+#[cfg(not(no_borrow))]
 #[cfg(not(no_global_oom_handling))]
 mod cow;
 
@@ -3103,6 +3105,7 @@ fn from(s: &mut [T]) -> 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

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;

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"

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 @@ pub extern "C" fn $ident() {
     __udivti3,
     __umodti3,
 });
+
+// NOTE: if you are adding a new intrinsic here, you should also add it to
+// `redirect-intrinsics` in `rust/Makefile`.

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

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 @@
 #[doc(hidden)]
 pub mod std_vendor;
 pub mod str;
+pub mod sync;
 pub mod types;
 
 #[doc(hidden)]

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;
 

rust/kernel/sync.rs

+// 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};

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.
 ///