2 files changed, 30 insertions, 2 deletions
diff --git a/rust/kernel/sync/lock.rs b/rust/kernel/sync/lock.rs
index 46e3328b67a6..802465d1fa54 100644
--- a/rust/kernel/sync/lock.rs
+++ b/rust/kernel/sync/lock.rs
@@ -6,7 +6,7 @@
 //! spinlocks, raw spinlocks) to be provided with minimal effort.
 
 use super::LockClassKey;
-use crate::{bindings, init::PinInit, pin_init, str::CStr, types::Opaque};
+use crate::{bindings, init::PinInit, pin_init, str::CStr, types::Opaque, types::ScopeGuard};
 use core::{cell::UnsafeCell, marker::PhantomData, marker::PhantomPinned};
 use macros::pin_data;
 
@@ -22,6 +22,8 @@ pub mod spinlock;
 ///
 /// - Implementers must ensure that only one thread/CPU may access the protected data once the lock
 /// is owned, that is, between calls to `lock` and `unlock`.
+/// - Implementers must also ensure that `relock` uses the same locking method as the original
+/// lock operation.
 pub unsafe trait Backend {
     /// The state required by the lock.
     type State;
@@ -55,6 +57,17 @@ pub unsafe trait Backend {
     ///
     /// It must only be called by the current owner of the lock.
     unsafe fn unlock(ptr: *mut Self::State, guard_state: &Self::GuardState);
+
+    /// Reacquires the lock, making the caller its owner.
+    ///
+    /// # Safety
+    ///
+    /// Callers must ensure that `guard_state` comes from a previous call to [`Backend::lock`] (or
+    /// variant) that has been unlocked with [`Backend::unlock`] and will be relocked now.
+    unsafe fn relock(ptr: *mut Self::State, guard_state: &mut Self::GuardState) {
+        // SAFETY: The safety requirements ensure that the lock is initialised.
+        *guard_state = unsafe { Self::lock(ptr) };
+    }
 }
 
 /// A mutual exclusion primitive.
@@ -126,6 +139,20 @@ pub struct Guard<'a, T: ?Sized, B: Backend> {
 // SAFETY: `Guard` is sync when the data protected by the lock is also sync.
 unsafe impl<T: Sync + ?Sized, B: Backend> Sync for Guard<'_, T, B> {}
 
+impl<T: ?Sized, B: Backend> Guard<'_, T, B> {
+    #[allow(dead_code)]
+    pub(crate) fn do_unlocked(&mut self, cb: impl FnOnce()) {
+        // SAFETY: The caller owns the lock, so it is safe to unlock it.
+        unsafe { B::unlock(self.lock.state.get(), &self.state) };
+
+        // SAFETY: The lock was just unlocked above and is being relocked now.
+        let _relock =
+            ScopeGuard::new(|| unsafe { B::relock(self.lock.state.get(), &mut self.state) });
+
+        cb();
+    }
+}
+
 impl<T: ?Sized, B: Backend> core::ops::Deref for Guard<'_, T, B> {
     type Target = T;
 
diff --git a/rust/kernel/sync/lock/spinlock.rs b/rust/kernel/sync/lock/spinlock.rs
index a52d20fc9755..979b56464a4e 100644
--- a/rust/kernel/sync/lock/spinlock.rs
+++ b/rust/kernel/sync/lock/spinlock.rs
@@ -87,7 +87,8 @@ pub type SpinLock<T> = super::Lock<T, SpinLockBackend>;
 /// A kernel `spinlock_t` lock backend.
 pub struct SpinLockBackend;
 
-// SAFETY: The underlying kernel `spinlock_t` object ensures mutual exclusion.
+// 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 SpinLockBackend {
     type State = bindings::spinlock_t;
     type GuardState = ();