linux-kernel - [PATCH v4 2/3] rust: sync: Introduce lock::Backend::Context

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Message-ID: <20240912005539.175428-3-lyude@redhat.com>
Date: Wed, 11 Sep 2024 20:55:33 -0400
From: Lyude Paul <lyude@...hat.com>
To: rust-for-linux@...r.kernel.org
Cc: Danilo Krummrich <dakr@...hat.com>,
	airlied@...hat.com,
	Ingo Molnar <mingo@...hat.com>,
	Will Deacon <will@...nel.org>,
	Waiman Long <longman@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org,
	Miguel Ojeda <ojeda@...nel.org>,
	Alex Gaynor <alex.gaynor@...il.com>,
	Wedson Almeida Filho <wedsonaf@...il.com>,
	Boqun Feng <boqun.feng@...il.com>,
	Gary Guo <gary@...yguo.net>,
	Björn Roy Baron <bjorn3_gh@...tonmail.com>,
	Benno Lossin <benno.lossin@...ton.me>,
	Andreas Hindborg <a.hindborg@...sung.com>,
	Alice Ryhl <aliceryhl@...gle.com>,
	Martin Rodriguez Reboredo <yakoyoku@...il.com>,
	Valentin Obst <kernel@...entinobst.de>,
	Trevor Gross <tmgross@...ch.edu>
Subject: [PATCH v4 2/3] rust: sync: Introduce lock::Backend::Context

Now that we've introduced an `IrqDisabled` token for marking contexts in
which IRQs are disabled, we need a way to be able to pass it to locks that
require that IRQs are disabled. In order to continue using the
`lock::Backend` type instead of inventing our own thing, we accomplish this
by adding the associated Context type, along with a `lock_with()` function
that can accept a Context when acquiring a lock. To allow current users of
context-less locks to keep using the normal `lock()` method, we take an
example from Wedson Almeida Filho's work and add a `where T<'a>: Default`
bound to `lock()` so that it can only be called on lock types where the
context is simply a placeholder value, then re-implement it through the new
`lock_with()` function.

Signed-off-by: Lyude Paul <lyude@...hat.com>

---

V3:
* Use explicit lifetimes in lock_with() to ensure self and _context have
  the same lifetime (Benno)
* Use () for locks that don't need a Context instead of PhantomData (Benno)
V4:
* Fix typo (Dirk)

Signed-off-by: Lyude Paul <lyude@...hat.com>
---
 rust/kernel/sync/lock.rs          | 17 +++++++++++++++--
 rust/kernel/sync/lock/mutex.rs    |  1 +
 rust/kernel/sync/lock/spinlock.rs |  1 +
 3 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/rust/kernel/sync/lock.rs b/rust/kernel/sync/lock.rs
index f6c34ca4d819f..7429bda852173 100644
--- a/rust/kernel/sync/lock.rs
+++ b/rust/kernel/sync/lock.rs
@@ -38,6 +38,9 @@ pub unsafe trait Backend {
     /// [`unlock`]: Backend::unlock
     type GuardState;
 
+    /// The context which must be provided to acquire the lock.
+    type Context<'a>;
+
     /// Initialises the lock.
     ///
     /// # Safety
@@ -120,14 +123,24 @@ pub fn new(t: T, name: &'static CStr, key: &'static LockClassKey) -> impl PinIni
 }
 
 impl<T: ?Sized, B: Backend> Lock<T, B> {
-    /// Acquires the lock and gives the caller access to the data protected by it.
-    pub fn lock(&self) -> Guard<'_, 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> {
         // 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()) };
         // SAFETY: The lock was just acquired.
         unsafe { Guard::new(self, state) }
     }
+
+    /// Acquires the lock and gives the caller access to the data protected by it.
+    #[inline]
+    pub fn lock<'a>(&'a self) -> Guard<'a, T, B>
+    where
+        B::Context<'a>: Default,
+    {
+        self.lock_with(B::Context::default())
+    }
 }
 
 /// A lock guard.
diff --git a/rust/kernel/sync/lock/mutex.rs b/rust/kernel/sync/lock/mutex.rs
index 30632070ee670..7c2c239944931 100644
--- a/rust/kernel/sync/lock/mutex.rs
+++ b/rust/kernel/sync/lock/mutex.rs
@@ -93,6 +93,7 @@ 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 ea5c5bc1ce12e..97d85a5576615 100644
--- a/rust/kernel/sync/lock/spinlock.rs
+++ b/rust/kernel/sync/lock/spinlock.rs
@@ -92,6 +92,7 @@ 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,
-- 
2.46.0