[PATCH v13 10/17] rust: sync: Introduce lock::Backend::Context

Lyude Paul
2025-10-13T15:54:40Z

Now that we've introduced an `InterruptDisabled` token for marking
contexts in which IRQs are disabled, we can have a way to avoid
`SpinLockIrq` disabling interrupts if the interrupts have already been
disabled. Basically, a `SpinLockIrq` should work like a `SpinLock` if
interrupts are disabled. So a function:

(&'a SpinLockIrq, &'a InterruptDisabled) -> Guard<'a, .., SpinLockBackend>

makes senses. Note that due to `Guard` and `InterruptDisabled` having the
same lifetime, interrupts cannot be enabled while the Guard exists.

Add a `lock_with()` interface for `Lock`, and an associate type of
`Backend` to describe the context.

Signed-off-by: Lyude Paul <lyude@redhat.com>
Co-developed-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>

---
V10:
- Fix typos - Dirk

rust/kernel/sync/lock.rs | 12 +++++++++++-
rust/kernel/sync/lock/mutex.rs | 1 +
rust/kernel/sync/lock/spinlock.rs | 4 +++-
3 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/rust/kernel/sync/lock.rs b/rust/kernel/sync/lock.rs
index 27202beef90c8..ae42458bff1c0 100644
--- a/rust/kernel/sync/lock.rs
+++ b/rust/kernel/sync/lock.rs
@@ -44,6 +44,9 @@ pub unsafe trait Backend {
/// [`unlock`]: Backend::unlock
type GuardState;

+ /// The context which can be provided to acquire the lock with a different backend.
+ type Context<'a>;
+
/// Initialises the lock.
///
/// # Safety
@@ -163,8 +166,15 @@ pub unsafe fn from_raw<'a>(ptr: *mut B::State) -> &'a Self {
}

impl<T: ?Sized, B: Backend> Lock<T, B> {
+ /// Acquires the lock with the given context and gives the caller access to the data protected
+ /// by it.
+ pub fn lock_with<'a>(&'a self, _context: B::Context<'a>) -> Guard<'a, T, B> {
+ todo!()
+ }
+
/// Acquires the lock and gives the caller access to the data protected by it.
- pub fn lock(&self) -> Guard<'_, T, B> {
+ #[inline]
+ pub fn lock<'a>(&'a self) -> Guard<'a, T, B> {
// SAFETY: The constructor of the type calls `init`, so the existence of the object proves
// that `init` was called.
let state = unsafe { B::lock(self.state.get()) };
diff --git a/rust/kernel/sync/lock/mutex.rs b/rust/kernel/sync/lock/mutex.rs
index 581cee7ab842a..be1e2e18cf42d 100644
--- a/rust/kernel/sync/lock/mutex.rs
+++ b/rust/kernel/sync/lock/mutex.rs
@@ -101,6 +101,7 @@ macro_rules! new_mutex {
unsafe impl super::Backend for MutexBackend {
type State = bindings::mutex;
type GuardState = ();
+ type Context<'a> = ();

unsafe fn init(
ptr: *mut Self::State,
diff --git a/rust/kernel/sync/lock/spinlock.rs b/rust/kernel/sync/lock/spinlock.rs
index 6e6d571acd90c..73a7ec554baac 100644
--- a/rust/kernel/sync/lock/spinlock.rs
+++ b/rust/kernel/sync/lock/spinlock.rs
@@ -3,7 +3,7 @@
//! A kernel spinlock.
//!
//! This module allows Rust code to use the kernel's `spinlock_t`.
-use crate::prelude::*;
+use crate::{interrupt::LocalInterruptDisabled, prelude::*};

/// Creates a [`SpinLock`] initialiser with the given name and a newly-created lock class.
///
@@ -101,6 +101,7 @@ macro_rules! new_spinlock {
unsafe impl super::Backend for SpinLockBackend {
type State = bindings::spinlock_t;
type GuardState = ();
+ type Context<'a> = ();

unsafe fn init(
ptr: *mut Self::State,
@@ -243,6 +244,7 @@ macro_rules! new_spinlock_irq {
unsafe impl super::Backend for SpinLockIrqBackend {
type State = bindings::spinlock_t;
type GuardState = ();
+ type Context<'a> = &'a LocalInterruptDisabled;

unsafe fn init(
ptr: *mut Self::State,
--
2.51.0