[PATCH v14 08/16] rust: sync: Add SpinLockIrq

[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()]

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>
Reviewed-by: Andreas Hindborg <a.hindborg@kernel.org>

---
V10:
* Also add support to GlobalLock
* Documentation fixes from Dirk
V11:
* Add unit test requested by Daniel Almeida
V14:
- Improve rustdoc for SpinLockIrqBackend

 rust/kernel/sync.rs               |   4 +-
 rust/kernel/sync/lock/global.rs   |   3 +
 rust/kernel/sync/lock/spinlock.rs | 229 ++++++++++++++++++++++++++++++
 3 files changed, 235 insertions(+), 1 deletion(-)

diff --git a/rust/kernel/sync.rs b/rust/kernel/sync.rs
index cf5b638a097d9..f293bbe13e855 100644
--- a/rust/kernel/sync.rs
+++ b/rust/kernel/sync.rs
@@ -26,7 +26,9 @@
 pub use condvar::{new_condvar, CondVar, CondVarTimeoutResult};
 pub use lock::global::{global_lock, GlobalGuard, GlobalLock, GlobalLockBackend, GlobalLockedBy};
 pub use lock::mutex::{new_mutex, Mutex, MutexGuard};
-pub use lock::spinlock::{new_spinlock, SpinLock, SpinLockGuard};
+pub use lock::spinlock::{
+    new_spinlock, new_spinlock_irq, SpinLock, SpinLockGuard, SpinLockIrq, SpinLockIrqGuard,
+};
 pub use locked_by::LockedBy;
 pub use refcount::Refcount;
 
diff --git a/rust/kernel/sync/lock/global.rs b/rust/kernel/sync/lock/global.rs
index 79d0ef7fda867..b8d78ca4c0cd3 100644
--- a/rust/kernel/sync/lock/global.rs
+++ b/rust/kernel/sync/lock/global.rs
@@ -299,4 +299,7 @@ macro_rules! global_lock_inner {
     (backend SpinLock) => {
         $crate::sync::lock::spinlock::SpinLockBackend
     };
+    (backend SpinLockIrq) => {
+        $crate::sync::lock::spinlock::SpinLockIrqBackend
+    };
 }
diff --git a/rust/kernel/sync/lock/spinlock.rs b/rust/kernel/sync/lock/spinlock.rs
index d7be38ccbdc7d..3fdfb0a8a0ab1 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::prelude::*;
 
 /// Creates a [`SpinLock`] initialiser with the given name and a newly-created lock class.
 ///
@@ -139,3 +140,231 @@ unsafe fn assert_is_held(ptr: *mut Self::State) {
         unsafe { bindings::spin_assert_is_held(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 local processor interrupts are disabled.
+///
+/// This is a version of [`SpinLock`] that can only be used in contexts where interrupts for the
+/// local CPU are disabled. It can be acquired in two ways:
+///
+/// - Using [`lock()`] like any other type of lock, in which case the bindings will modify the
+///   interrupt state to ensure that local processor interrupts remain disabled for at least as long
+///   as the [`SpinLockIrqGuard`] exists.
+/// - Using [`lock_with()`] in contexts where a [`LocalInterruptDisabled`] token is present and
+///   local processor interrupts are already known to be disabled, in which case the local interrupt
+///   state will not be touched. This method should be preferred if a [`LocalInterruptDisabled`]
+///   token is present in the scope.
+///
+/// For more info on spinlocks, see [`SpinLock`]. For more information on interrupts,
+/// [see the interrupt module](kernel::interrupt).
+///
+/// # 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 that requires local
+/// processor interrupts to be disabled.
+///
+/// ```
+/// use kernel::sync::{new_spinlock_irq, SpinLockIrq};
+///
+/// struct Inner {
+///     a: u32,
+///     b: u32,
+/// }
+///
+/// #[pin_data]
+/// struct Example {
+///     #[pin]
+///     c: SpinLockIrq<Inner>,
+///     #[pin]
+///     d: SpinLockIrq<Inner>,
+/// }
+///
+/// impl Example {
+///     fn new() -> impl PinInit<Self> {
+///         pin_init!(Self {
+///             c <- new_spinlock_irq!(Inner { a: 0, b: 10 }),
+///             d <- new_spinlock_irq!(Inner { a: 20, b: 30 }),
+///         })
+///     }
+/// }
+///
+/// // Allocate a boxed `Example`
+/// let e = KBox::pin_init(Example::new(), GFP_KERNEL)?;
+///
+/// // Accessing an `Example` from a context where interrupts may not be disabled already.
+/// let c_guard = e.c.lock(); // interrupts are disabled now, +1 interrupt disable refcount
+/// let d_guard = e.d.lock(); // no interrupt state change, +1 interrupt disable refcount
+///
+/// assert_eq!(c_guard.a, 0);
+/// assert_eq!(c_guard.b, 10);
+/// assert_eq!(d_guard.a, 20);
+/// assert_eq!(d_guard.b, 30);
+///
+/// drop(c_guard); // Dropping c_guard will not re-enable interrupts just yet, since d_guard is
+///                // still in scope.
+/// drop(d_guard); // Last interrupt disable reference dropped here, so interrupts are re-enabled
+///                // now
+/// # Ok::<(), Error>(())
+/// ```
+///
+/// [`lock()`]: SpinLockIrq::lock
+/// [`lock_with()`]: SpinLockIrq::lock_with
+pub type SpinLockIrq<T> = super::Lock<T, SpinLockIrqBackend>;
+
+/// A kernel `spinlock_t` lock backend that can only be acquired in interrupt disabled contexts.
+pub struct SpinLockIrqBackend;
+
+/// A [`Guard`] acquired from locking a [`SpinLockIrq`] using [`lock()`].
+///
+/// This is simply a type alias for a [`Guard`] returned from locking a [`SpinLockIrq`] using
+/// [`lock_with()`]. It will unlock the [`SpinLockIrq`] and decrement the local processor's
+/// interrupt disablement refcount upon being dropped.
+///
+/// [`Guard`]: super::Guard
+/// [`lock()`]: SpinLockIrq::lock
+/// [`lock_with()`]: SpinLockIrq::lock_with
+pub type SpinLockIrqGuard<'a, T> = super::Guard<'a, T, SpinLockIrqBackend>;
+
+// SAFETY: The underlying kernel `spinlock_t` object ensures mutual exclusion. `relock` uses the
+// default implementation that always calls the same locking method.
+unsafe impl super::Backend for SpinLockIrqBackend {
+    type State = bindings::spinlock_t;
+    type GuardState = ();
+
+    unsafe fn init(
+        ptr: *mut Self::State,
+        name: *const crate::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) }
+    }
+
+    unsafe fn try_lock(ptr: *mut Self::State) -> Option<Self::GuardState> {
+        // SAFETY: The `ptr` pointer is guaranteed to be valid and initialized before use.
+        let result = unsafe { bindings::spin_trylock_irq_disable(ptr) };
+
+        if result != 0 {
+            Some(())
+        } else {
+            None
+        }
+    }
+
+    unsafe fn assert_is_held(ptr: *mut Self::State) {
+        // SAFETY: The `ptr` pointer is guaranteed to be valid and initialized before use.
+        unsafe { bindings::spin_assert_is_held(ptr) }
+    }
+}
+
+#[kunit_tests(rust_spinlock_irq_condvar)]
+mod tests {
+    use super::*;
+    use crate::{
+        sync::*,
+        workqueue::{self, impl_has_work, new_work, Work, WorkItem},
+    };
+
+    struct TestState {
+        value: u32,
+        waiter_ready: bool,
+    }
+
+    #[pin_data]
+    struct Test {
+        #[pin]
+        state: SpinLockIrq<TestState>,
+
+        #[pin]
+        state_changed: CondVar,
+
+        #[pin]
+        waiter_state_changed: CondVar,
+
+        #[pin]
+        wait_work: Work<Self>,
+    }
+
+    impl_has_work! {
+        impl HasWork<Self> for Test { self.wait_work }
+    }
+
+    impl Test {
+        pub(crate) fn new() -> Result<Arc<Self>> {
+            Arc::try_pin_init(
+                try_pin_init!(
+                    Self {
+                        state <- new_spinlock_irq!(TestState {
+                            value: 1,
+                            waiter_ready: false
+                        }),
+                        state_changed <- new_condvar!(),
+                        waiter_state_changed <- new_condvar!(),
+                        wait_work <- new_work!("IrqCondvarTest::wait_work")
+                    }
+                ),
+                GFP_KERNEL,
+            )
+        }
+    }
+
+    impl WorkItem for Test {
+        type Pointer = Arc<Self>;
+
+        fn run(this: Arc<Self>) {
+            // Wait for the test to be ready to wait for us
+            let mut state = this.state.lock();
+
+            while !state.waiter_ready {
+                this.waiter_state_changed.wait(&mut state);
+            }
+
+            // Deliver the exciting value update our test has been waiting for
+            state.value += 1;
+            this.state_changed.notify_sync();
+        }
+    }
+
+    #[test]
+    fn spinlock_irq_condvar() -> Result {
+        let testdata = Test::new()?;
+
+        let _ = workqueue::system().enqueue(testdata.clone());
+
+        // Let the updater know when we're ready to wait
+        let mut state = testdata.state.lock();
+        state.waiter_ready = true;
+        testdata.waiter_state_changed.notify_sync();
+
+        // Wait for the exciting value update
+        testdata.state_changed.wait(&mut state);
+        assert_eq!(state.value, 2);
+        Ok(())
+    }
+}
-- 
2.51.1