[PATCH v3] rust: sync: export lock::do_unlocked

[Andreas Hindborg <a.hindborg@kernel.org>]

Export lock::do_unlocked publicly. Add documentation for the method.

Reviewed-by: Benno Lossin <lossin@kernel.org>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
---
Changes in v3:
- Rebase on v7.3-rc5.
- Do not import prelude in example (Alice).
- Link to v2: https://msgid.link/20260605-export-do-unlocked-v2-1-e23001390231@kernel.org

Changes in v2:
- Drop spurious space before `guard.do_unlocked` in the doc example (Benno).
- Un-hide the imports in the doc example so the rendered docs no longer have a spurious blank line after them (Alice).
- Link to v1: https://msgid.link/20260215-export-do-unlocked-v1-1-f5cd2203b20f@kernel.org
---
 rust/kernel/sync/lock.rs | 26 +++++++++++++++++++++++++-
 1 file changed, 25 insertions(+), 1 deletion(-)

diff --git a/rust/kernel/sync/lock.rs b/rust/kernel/sync/lock.rs
index 10b6b5e9b024..edfff9e10199 100644
--- a/rust/kernel/sync/lock.rs
+++ b/rust/kernel/sync/lock.rs
@@ -238,7 +238,31 @@ pub fn lock_ref(&self) -> &'a Lock<T, B> {
         self.lock
     }
 
-    pub(crate) fn do_unlocked<U>(&mut self, cb: impl FnOnce() -> U) -> U {
+    /// Temporarily unlock the lock to execute the given closure.
+    ///
+    /// This method unlocks the lock before calling the closure `cb`, and re-locks it afterwards.
+    /// This is useful when you need to perform operations that are not allowed while holding
+    /// certain locks, such as allocating memory (which is prohibited while holding a spinlock).
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use kernel::new_spinlock;
+    /// use pin_init::stack_pin_init;
+    ///
+    /// stack_pin_init!{
+    ///     let lock = new_spinlock!(())
+    /// }
+    ///
+    /// let mut guard = lock.lock();
+    /// let mut buffer = KVec::new();
+    /// // Temporarily unlock to allocate memory, which should not be done while holding a spinlock.
+    /// guard.do_unlocked(|| {
+    ///     buffer.push(5u32, GFP_KERNEL)
+    /// })?;
+    /// # Ok::<(), Error>(())
+    /// ```
+    pub fn do_unlocked<U>(&mut self, cb: impl FnOnce() -> U) -> U {
         // SAFETY: The caller owns the lock, so it is safe to unlock it.
         unsafe { B::unlock(self.lock.state.get(), &self.state) };
 

---
base-commit: 72d3fcf802c45d00b300f25b848a93c3a2bd7c7e
change-id: 20260215-export-do-unlocked-00a6ac9373d4

Best regards,
--  
Andreas Hindborg <a.hindborg@kernel.org>