linux-kernel - [PATCH v9 7/9] rust: sync: Introduce lock::Backend::Context

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Message-ID: <20250227221924.265259-8-lyude@redhat.com>
Date: Thu, 27 Feb 2025 17:10:18 -0500
From: Lyude Paul <lyude@...hat.com>
To: rust-for-linux@...r.kernel.org,
	Thomas Gleixner <tglx@...utronix.de>
Cc: Boqun Feng <boqun.feng@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Will Deacon <will@...nel.org>,
	Waiman Long <longman@...hat.com>,
	Miguel Ojeda <ojeda@...nel.org>,
	Alex Gaynor <alex.gaynor@...il.com>,
	Gary Guo <gary@...yguo.net>,
	Björn Roy Baron <bjorn3_gh@...tonmail.com>,
	Benno Lossin <benno.lossin@...ton.me>,
	Andreas Hindborg <a.hindborg@...nel.org>,
	Alice Ryhl <aliceryhl@...gle.com>,
	Trevor Gross <tmgross@...ch.edu>,
	linux-kernel@...r.kernel.org (open list:LOCKING PRIMITIVES)
Subject: [PATCH v9 7/9] rust: sync: Introduce lock::Backend::Context

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` has the
same lifetime, interrupts cannot be enabled whiel the Guard exists.

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

[Boqun: Change the interface a lot, now `SpinLockIrq` can use the
`lock()` function, but it always disable the interrupts, reuse the
`lock_with()` method to provide a way for locking if interrupts are
already disabled. `lock_with()` implementation will be added later.]

Signed-off-by: Lyude Paul <lyude@...hat.com>
Co-Developed-by: Boqun Feng <boqun.feng@...il.com>
Signed-off-by: Boqun Feng <boqun.feng@...il.com>
---
 rust/kernel/sync/lock.rs          | 12 +++++++++++-
 rust/kernel/sync/lock/mutex.rs    |  1 +
 rust/kernel/sync/lock/spinlock.rs |  3 +++
 3 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/rust/kernel/sync/lock.rs b/rust/kernel/sync/lock.rs
index eb80048e0110d..e7c1fd028435e 100644
--- a/rust/kernel/sync/lock.rs
+++ b/rust/kernel/sync/lock.rs
@@ -46,6 +46,9 @@ 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
@@ -165,8 +168,15 @@ 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 70cadbc2e8e23..53c8e8b90b85c 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 ac66493f681ce..6b355887bd3ea 100644
--- a/rust/kernel/sync/lock/spinlock.rs
+++ b/rust/kernel/sync/lock/spinlock.rs
@@ -3,6 +3,7 @@
 //! A kernel spinlock.
 //!
 //! This module allows Rust code to use the kernel's `spinlock_t`.
+use crate::interrupt::LocalInterruptDisabled;
 
 /// Creates a [`SpinLock`] initialiser with the given name and a newly-created lock class.
 ///
@@ -100,6 +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,
@@ -241,6 +243,7 @@ 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,
-- 
2.48.1