[PATCH v2 03/13] rust: lock: introduce `Mutex`

Wedson Almeida Filho
2023-04-05T17:52:04Z

From: Wedson Almeida Filho <walmeida@microsoft.com>

This is the `struct mutex` lock backend and allows Rust code to use the
kernel mutex idiomatically.

Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Will Deacon <will@kernel.org>
Cc: Waiman Long <longman@redhat.com>
Signed-off-by: Wedson Almeida Filho <walmeida@microsoft.com>
---
v1 -> v2: No changes

rust/helpers.c | 7 ++
rust/kernel/sync.rs | 1 +
rust/kernel/sync/lock.rs | 2 +
rust/kernel/sync/lock/mutex.rs | 118 +++++++++++++++++++++++++++++++++
4 files changed, 128 insertions(+)
create mode 100644 rust/kernel/sync/lock/mutex.rs

diff --git a/rust/helpers.c b/rust/helpers.c
index 09a4d93f9d62..3010a2ec26e2 100644
--- a/rust/helpers.c
+++ b/rust/helpers.c
@@ -21,6 +21,7 @@
#include <linux/bug.h>
#include <linux/build_bug.h>
#include <linux/refcount.h>
+#include <linux/mutex.h>

__noreturn void rust_helper_BUG(void)
{
@@ -28,6 +29,12 @@ __noreturn void rust_helper_BUG(void)
}
EXPORT_SYMBOL_GPL(rust_helper_BUG);

+void rust_helper_mutex_lock(struct mutex *lock)
+{
+ mutex_lock(lock);
+}
+EXPORT_SYMBOL_GPL(rust_helper_mutex_lock);
+
refcount_t rust_helper_REFCOUNT_INIT(int n)
{
return (refcount_t)REFCOUNT_INIT(n);
diff --git a/rust/kernel/sync.rs b/rust/kernel/sync.rs
index bf088b324af4..9ff116b2eebe 100644
--- a/rust/kernel/sync.rs
+++ b/rust/kernel/sync.rs
@@ -11,6 +11,7 @@ mod arc;
pub mod lock;

pub use arc::{Arc, ArcBorrow, UniqueArc};
+pub use lock::mutex::Mutex;

/// Represents a lockdep class. It's a wrapper around C's `lock_class_key`.
#[repr(transparent)]
diff --git a/rust/kernel/sync/lock.rs b/rust/kernel/sync/lock.rs
index f5614bed2a78..cec1d68bab86 100644
--- a/rust/kernel/sync/lock.rs
+++ b/rust/kernel/sync/lock.rs
@@ -10,6 +10,8 @@ use crate::{bindings, init::PinInit, pin_init, str::CStr, types::Opaque};
use core::{cell::UnsafeCell, marker::PhantomData, marker::PhantomPinned};
use macros::pin_data;

+pub mod mutex;
+
/// The "backend" of a lock.
///
/// It is the actual implementation of the lock, without the need to repeat patterns used in all
diff --git a/rust/kernel/sync/lock/mutex.rs b/rust/kernel/sync/lock/mutex.rs
new file mode 100644
index 000000000000..923472f04af4
--- /dev/null
+++ b/rust/kernel/sync/lock/mutex.rs
@@ -0,0 +1,118 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! A kernel mutex.
+//!
+//! This module allows Rust code to use the kernel's `struct mutex`.
+
+use crate::bindings;
+
+/// Creates a [`Mutex`] initialiser with the given name and a newly-created lock class.
+///
+/// It uses the name if one is given, otherwise it generates one based on the file name and line
+/// number.
+#[macro_export]
+macro_rules! new_mutex {
+ ($inner:expr $(, $name:literal)? $(,)?) => {
+ $crate::sync::Mutex::new(
+ $inner, $crate::optional_name!($($name)?), $crate::static_lock_class!())
+ };
+}
+
+/// A mutual exclusion primitive.
+///
+/// Exposes the kernel's [`struct mutex`]. When multiple threads attempt to lock the same mutex,
+/// only one at a time is allowed to progress, the others will block (sleep) until the mutex is
+/// unlocked, at which point another thread will be allowed to wake up and make progress.
+///
+/// Since it may block, [`Mutex`] needs to be used with care in atomic contexts.
+///
+/// Instances of [`Mutex`] need a lock class and to be pinned. The recommended way to create such
+/// instances is with the [`pin_init`](crate::pin_init) and [`new_mutex`] macros.
+///
+/// # Examples
+///
+/// The following example shows how to declare, allocate and initialise a struct (`Example`) that
+/// contains an inner struct (`Inner`) that is protected by a mutex.
+///
+/// ```
+/// use kernel::{init::InPlaceInit, init::PinInit, new_mutex, pin_init, sync::Mutex};
+///
+/// struct Inner {
+/// a: u32,
+/// b: u32,
+/// }
+///
+/// #[pin_data]
+/// struct Example {
+/// c: u32,
+/// #[pin]
+/// d: Mutex<Inner>,
+/// }
+///
+/// impl Example {
+/// fn new() -> impl PinInit<Self> {
+/// pin_init!(Self {
+/// c: 10,
+/// d <- new_mutex!(Inner { a: 20, b: 30 }),
+/// })
+/// }
+/// }
+///
+/// // Allocate a boxed `Example`.
+/// let e = Box::pin_init(Example::new())?;
+/// assert_eq!(e.c, 10);
+/// assert_eq!(e.d.lock().a, 20);
+/// assert_eq!(e.d.lock().b, 30);
+/// ```
+///
+/// The following example shows how to use interior mutability to modify the contents of a struct
+/// protected by a mutex despite only having a shared reference:
+///
+/// ```
+/// use kernel::sync::Mutex;
+///
+/// struct Example {
+/// a: u32,
+/// b: u32,
+/// }
+///
+/// fn example(m: &Mutex<Example>) {
+/// let mut guard = m.lock();
+/// guard.a += 10;
+/// guard.b += 20;
+/// }
+/// ```
+///
+/// [`struct mutex`]: ../../../../include/linux/mutex.h
+pub type Mutex<T> = super::Lock<T, MutexBackend>;
+
+/// A kernel `struct mutex` lock backend.
+pub struct MutexBackend;
+
+// SAFETY: The underlying kernel `struct mutex` object ensures mutual exclusion.
+unsafe impl super::Backend for MutexBackend {
+ type State = bindings::mutex;
+ type GuardState = ();
+
+ unsafe fn init(
+ ptr: *mut Self::State,
+ name: *const core::ffi::c_char,
+ key: *mut bindings::lock_class_key,
+ ) {
+ // SAFETY: The safety requirements ensure that `ptr` is valid for writes, and `name` and
+ // `key` are valid for read indefinitely.
+ unsafe { bindings::__mutex_init(ptr, name, key) }
+ }
+
+ unsafe fn lock(ptr: *mut Self::State) -> Self::GuardState {
+ // SAFETY: The safety requirements of this function ensure that `ptr` points to valid
+ // memory, and that it has been initialised before.
+ unsafe { bindings::mutex_lock(ptr) };
+ }
+
+ unsafe fn unlock(ptr: *mut Self::State, _guard_state: &Self::GuardState) {
+ // SAFETY: The safety requirements of this function ensure that `ptr` is valid and that the
+ // caller is the owner of the mutex.
+ unsafe { bindings::mutex_unlock(ptr) };
+ }
+}
--
2.34.1