[POC 4/6] rust: sync: Add SpinLockIrq

[Boqun Feng <boqun.feng@gmail.com>]

From: Lyude Paul <lyude@redhat.com>

A variant of SpinLock that is expected to be used in noirq contexts, so
lock() will disable interrupts and unlock() (i.e. `Guard::drop()` will
undo the interrupt disable.

[Boqun: Port to use spin_lock_irq_disable() and
spin_unlock_irq_enable()]

Co-developed-by: Lyude Paul <lyude@redhat.com>
Signed-off-by: Lyude Paul <lyude@redhat.com>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
---
 rust/kernel/sync.rs               |  2 +-
 rust/kernel/sync/lock/spinlock.rs | 91 +++++++++++++++++++++++++++++++
 2 files changed, 92 insertions(+), 1 deletion(-)

diff --git a/rust/kernel/sync.rs b/rust/kernel/sync.rs
index 0ab20975a3b5..b028ee325f2a 100644
--- a/rust/kernel/sync.rs
+++ b/rust/kernel/sync.rs
@@ -15,7 +15,7 @@
 pub use arc::{Arc, ArcBorrow, UniqueArc};
 pub use condvar::{new_condvar, CondVar, CondVarTimeoutResult};
 pub use lock::mutex::{new_mutex, Mutex};
-pub use lock::spinlock::{new_spinlock, SpinLock};
+pub use lock::spinlock::{new_spinlock, new_spinlock_irq, SpinLock, SpinLockIrq};
 pub use locked_by::LockedBy;
 
 /// Represents a lockdep class. It's a wrapper around C's `lock_class_key`.
diff --git a/rust/kernel/sync/lock/spinlock.rs b/rust/kernel/sync/lock/spinlock.rs
index ea5c5bc1ce12..884d4d1cbf23 100644
--- a/rust/kernel/sync/lock/spinlock.rs
+++ b/rust/kernel/sync/lock/spinlock.rs
@@ -115,3 +115,94 @@ unsafe fn unlock(ptr: *mut Self::State, _guard_state: &Self::GuardState) {
         unsafe { bindings::spin_unlock(ptr) }
     }
 }
+
+/// Creates a [`SpinLockIrq`] 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_spinlock_irq {
+    ($inner:expr $(, $name:literal)? $(,)?) => {
+        $crate::sync::SpinLockIrq::new(
+            $inner, $crate::optional_name!($($name)?), $crate::static_lock_class!())
+    };
+}
+pub use new_spinlock_irq;
+
+/// A spinlock that may be acquired when interrupts are disabled.
+///
+/// A version of [`SpinLock`] that can only be used in contexts where interrupts for the local CPU
+/// are disabled. It requires that the user acquiring the lock provide proof that interrupts are
+/// disabled through [`IrqDisabled`].
+///
+/// For more info, see [`SpinLock`].
+///
+/// # Examples
+///
+/// The following example shows how to declare, allocate initialise and access a struct (`Example`)
+/// that contains an inner struct (`Inner`) that is protected by a spinlock.
+///
+/// ```
+/// use kernel::sync::{new_spinlock_irq, SpinLockIrq};
+///
+/// struct Inner {
+///     a: u32,
+///     b: u32,
+/// }
+///
+/// #[pin_data]
+/// struct Example {
+///     c: u32,
+///     #[pin]
+///     d: SpinLockIrq<Inner>,
+/// }
+///
+/// impl Example {
+///     fn new() -> impl PinInit<Self> {
+///         pin_init!(Self {
+///             c: 10,
+///             d <- new_spinlock_irq!(Inner { a: 20, b: 30 }),
+///         })
+///     }
+/// }
+///
+/// // Allocate a boxed `Example`
+/// let e = Box::pin_init(Example::new(), GFP_KERNEL)?;
+///
+/// // Accessing an `Example` from a context where IRQs may not be disabled already.
+/// let b = e.d.lock().b;
+///
+/// assert_eq!(b, 30);
+/// # Ok::<(), Error>(())
+/// ```
+pub type SpinLockIrq<T> = super::Lock<T, SpinLockIrqBackend>;
+
+/// A kernel `spinlock_t` lock backend that is acquired in interrupt disabled contexts.
+pub struct SpinLockIrqBackend;
+
+unsafe impl super::Backend for SpinLockIrqBackend {
+    type State = bindings::spinlock_t;
+    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::__spin_lock_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::spin_lock_irq_disable(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 spinlock.
+        unsafe { bindings::spin_unlock_irq_enable(ptr) }
+    }
+}
-- 
2.45.2