Re: [PATCH v3 06/13] rust: lock: add support for `Lock::lock_irqsave`

[Martin Rodriguez Reboredo <yakoyoku@gmail.com>]

On 4/8/23 04:53, Wedson Almeida Filho wrote:
> From: Wedson Almeida Filho <walmeida@microsoft.com>
> 
> This allows locks like spinlocks and raw spinlocks to expose a
> `lock_irqsave` variant in Rust that corresponds to the C version.
> 
> Signed-off-by: Wedson Almeida Filho <walmeida@microsoft.com>
> ---
> v1 -> v2: No changes
> v2 -> v3: No changes
> 
>  rust/kernel/sync/lock.rs | 38 ++++++++++++++++++++++++++++++++++++++
>  1 file changed, 38 insertions(+)
> 
> diff --git a/rust/kernel/sync/lock.rs b/rust/kernel/sync/lock.rs
> index df43dff5af5c..690429561f0e 100644
> --- a/rust/kernel/sync/lock.rs
> +++ b/rust/kernel/sync/lock.rs
> @@ -57,6 +57,29 @@ pub unsafe trait Backend {
>      unsafe fn unlock(ptr: *mut Self::State, guard_state: &Self::GuardState);
>  }
>  
> +/// The "backend" of a lock that supports the irq-save variant.
> +///
> +/// # Safety
> +///
> +/// The same requirements wrt mutual exclusion in [`Backend`] apply for acquiring the lock via
> +/// [`IrqSaveBackend::lock_irqsave`].
> +///
> +/// Additionally, when [`IrqSaveBackend::lock_irqsave`] is used to acquire the lock, implementers
> +/// must disable interrupts on lock, and restore interrupt state on unlock. Implementers may use
> +/// [`Backend::GuardState`] to store state needed to keep track of the interrupt state.
> +pub unsafe trait IrqSaveBackend: Backend {
> +    /// Acquires the lock, making the caller its owner.
> +    ///
> +    /// Before acquiring the lock, it disables interrupts, and returns the previous interrupt state
> +    /// as its guard state so that the guard can restore it when it is dropped.
> +    ///
> +    /// # Safety
> +    ///
> +    /// Callers must ensure that [`Backend::init`] has been previously called.
> +    #[must_use]
> +    unsafe fn lock_irqsave(ptr: *mut Self::State) -> Self::GuardState;
> +}
> +
>  /// A mutual exclusion primitive.
>  ///
>  /// Exposes one of the kernel locking primitives. Which one is exposed depends on the lock banckend
> @@ -111,6 +134,21 @@ impl<T: ?Sized, B: Backend> Lock<T, B> {
>      }
>  }
>  
> +impl<T: ?Sized, B: IrqSaveBackend> Lock<T, B> {
> +    /// Acquires the lock and gives the caller access to the data protected by it.
> +    ///
> +    /// Before acquiring the lock, it disables interrupts. When the guard is dropped, the interrupt
> +    /// state (either enabled or disabled) is restored to its state before
> +    /// [`lock_irqsave`](Self::lock_irqsave) was called.
> +    pub fn lock_irqsave(&self) -> Guard<'_, T, B> {
> +        // SAFETY: The constructor of the type calls `init`, so the existence of the object proves
> +        // that `init` was called.
> +        let state = unsafe { B::lock_irqsave(self.state.get()) };
> +        // SAFETY: The lock was just acquired.
> +        unsafe { Guard::new(self, state) }
> +    }
> +}
> +
>  /// A lock guard.
>  ///
>  /// Allows mutual exclusion primitives that implement the `Backend` trait to automatically unlock

Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com>