[PATCH v2 07/13] rust: lock: implement `IrqSaveBackend` for `SpinLock`

[Wedson Almeida Filho <wedsonaf@gmail.com>]

From: Wedson Almeida Filho <walmeida@microsoft.com>

This allows Rust code to use the `lock_irqsave` variant of spinlocks.

Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Will Deacon <will@kernel.org>
Cc: Waiman Long <longman@redhat.com>
Signed-off-by: Wedson Almeida Filho <walmeida@microsoft.com>
---
v1 -> v2: No changes

 rust/helpers.c                    | 16 +++++++++++++
 rust/kernel/sync/lock/spinlock.rs | 38 ++++++++++++++++++++++++++-----
 2 files changed, 48 insertions(+), 6 deletions(-)

diff --git a/rust/helpers.c b/rust/helpers.c
index 05694e3f8f70..e42f5b446f92 100644
--- a/rust/helpers.c
+++ b/rust/helpers.c
@@ -59,6 +59,22 @@ void rust_helper_spin_unlock(spinlock_t *lock)
 }
 EXPORT_SYMBOL_GPL(rust_helper_spin_unlock);
 
+unsigned long rust_helper_spin_lock_irqsave(spinlock_t *lock)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(lock, flags);
+
+	return flags;
+}
+EXPORT_SYMBOL_GPL(rust_helper_spin_lock_irqsave);
+
+void rust_helper_spin_unlock_irqrestore(spinlock_t *lock, unsigned long flags)
+{
+	spin_unlock_irqrestore(lock, flags);
+}
+EXPORT_SYMBOL_GPL(rust_helper_spin_unlock_irqrestore);
+
 refcount_t rust_helper_REFCOUNT_INIT(int n)
 {
 	return (refcount_t)REFCOUNT_INIT(n);
diff --git a/rust/kernel/sync/lock/spinlock.rs b/rust/kernel/sync/lock/spinlock.rs
index a52d20fc9755..34dec09a97c0 100644
--- a/rust/kernel/sync/lock/spinlock.rs
+++ b/rust/kernel/sync/lock/spinlock.rs
@@ -61,6 +61,8 @@ macro_rules! new_spinlock {
 /// assert_eq!(e.c, 10);
 /// assert_eq!(e.d.lock().a, 20);
 /// assert_eq!(e.d.lock().b, 30);
+/// assert_eq!(e.d.lock_irqsave().a, 20);
+/// assert_eq!(e.d.lock_irqsave().b, 30);
 /// ```
 ///
 /// The following example shows how to use interior mutability to modify the contents of a struct
@@ -79,6 +81,12 @@ macro_rules! new_spinlock {
 ///     guard.a += 10;
 ///     guard.b += 20;
 /// }
+///
+/// fn example2(m: &SpinLock<Example>) {
+///     let mut guard = m.lock_irqsave();
+///     guard.a += 10;
+///     guard.b += 20;
+/// }
 /// ```
 ///
 /// [`spinlock_t`]: ../../../../include/linux/spinlock.h
@@ -90,7 +98,7 @@ pub struct SpinLockBackend;
 // SAFETY: The underlying kernel `spinlock_t` object ensures mutual exclusion.
 unsafe impl super::Backend for SpinLockBackend {
     type State = bindings::spinlock_t;
-    type GuardState = ();
+    type GuardState = Option<core::ffi::c_ulong>;
 
     unsafe fn init(
         ptr: *mut Self::State,
@@ -105,12 +113,30 @@ unsafe impl super::Backend for SpinLockBackend {
     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(ptr) }
+        unsafe { bindings::spin_lock(ptr) };
+        None
     }
 
-    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 mutex.
-        unsafe { bindings::spin_unlock(ptr) }
+    unsafe fn unlock(ptr: *mut Self::State, guard_state: &Self::GuardState) {
+        match guard_state {
+            // SAFETY: The safety requirements of this function ensure that `ptr` is valid and that
+            // the caller is the owner of the mutex.
+            Some(flags) => unsafe { bindings::spin_unlock_irqrestore(ptr, *flags) },
+            // SAFETY: The safety requirements of this function ensure that `ptr` is valid and that
+            // the caller is the owner of the mutex.
+            None => unsafe { bindings::spin_unlock(ptr) },
+        }
+    }
+}
+
+// SAFETY: The underlying kernel `spinlock_t` object ensures mutual exclusion. We use the `irqsave`
+// variant of the C lock acquisition functions to disable interrupts and retrieve the original
+// interrupt state, and the `irqrestore` variant of the lock release functions to restore the state
+// in `unlock` -- we use the guard context to determine which method was used to acquire the lock.
+unsafe impl super::IrqSaveBackend for SpinLockBackend {
+    unsafe fn lock_irqsave(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.
+        Some(unsafe { bindings::spin_lock_irqsave(ptr) })
     }
 }
-- 
2.34.1