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

["Gary Guo" <gary@garyguo.net>]

On Tue Sep 29, 2026 at 3:45 PM BST, Andreas Hindborg wrote:
> 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 {

Do we want to keep the name `do_unlocked` now this is public?

I think we can drop "do_" and just call this `unlocked`, consistent with popular
Rust ecosystem crates like parking_lot and spin.

Best,
Gary


>          // 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>