Re: [PATCH v6 2/3] rust: sync: Introduce lock::Backend::Context

From: Boqun Feng
Date: Sun Sep 29 2024 - 19:53:33 EST


On Mon, Sep 16, 2024 at 05:28:05PM -0400, Lyude Paul wrote:
> Now that we've introduced an `IrqDisabled` token for marking contexts in
> which IRQs are disabled, we need a way to be able to pass it to locks that
> require that IRQs are disabled. In order to continue using the
> `lock::Backend` type instead of inventing our own thing, we accomplish this
> by adding the associated Context type, along with a `lock_with()` function
> that can accept a Context when acquiring a lock. To allow current users of
> context-less locks to keep using the normal `lock()` method, we take an
> example from Wedson Almeida Filho's work and add a `where T<'a>: Default`
> bound to `lock()` so that it can only be called on lock types where the
> context is simply a placeholder value, then re-implement it through the new
> `lock_with()` function.
>

Given that Backend::Context and "lock() where Context: Default" are
basically Benno's idea, I think it's fair to have a Suggested-by tag
here.

> Signed-off-by: Lyude Paul <lyude@xxxxxxxxxx>
> Reviewed-by: Benno Lossin <benno.lossin@xxxxxxxxx>
> Reviewed-by: Daniel Almeida <daniel.almeida@xxxxxxxxxxxxx>
> Reviewed-by: Gary Guo <gary@xxxxxxxxxxx>
>

Reviewed-by: Boqun Feng <boqun.feng@xxxxxxxxx>

Regards,
Boqun

> ---
>
> V3:
> * Use explicit lifetimes in lock_with() to ensure self and _context have
> the same lifetime (Benno)
> * Use () for locks that don't need a Context instead of PhantomData (Benno)
> V4:
> * Fix typo (Dirk)
>
> ---
> rust/kernel/sync/lock.rs | 17 +++++++++++++++--
> rust/kernel/sync/lock/mutex.rs | 1 +
> rust/kernel/sync/lock/spinlock.rs | 1 +
> 3 files changed, 17 insertions(+), 2 deletions(-)
>
> diff --git a/rust/kernel/sync/lock.rs b/rust/kernel/sync/lock.rs
> index d6e9bab114b87..cc39a3dc3f20b 100644
> --- a/rust/kernel/sync/lock.rs
> +++ b/rust/kernel/sync/lock.rs
> @@ -43,6 +43,9 @@ pub unsafe trait Backend {
> /// [`unlock`]: Backend::unlock
> type GuardState;
>
> + /// The context which must be provided to acquire the lock.
> + type Context<'a>;
> +
> /// Initialises the lock.
> ///
> /// # Safety
> @@ -125,14 +128,24 @@ pub fn new(t: T, name: &'static CStr, key: &'static LockClassKey) -> impl PinIni
> }
>
> impl<T: ?Sized, B: Backend> Lock<T, B> {
> - /// Acquires the lock and gives the caller access to the data protected by it.
> - pub fn lock(&self) -> Guard<'_, T, B> {
> + /// Acquires the lock with the given context and gives the caller access to the data protected
> + /// by it.
> + pub fn lock_with<'a>(&'a self, _context: B::Context<'a>) -> Guard<'a, 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(self.state.get()) };
> // SAFETY: The lock was just acquired.
> unsafe { Guard::new(self, state) }
> }
> +
> + /// Acquires the lock and gives the caller access to the data protected by it.
> + #[inline]
> + pub fn lock<'a>(&'a self) -> Guard<'a, T, B>
> + where
> + B::Context<'a>: Default,
> + {
> + self.lock_with(B::Context::default())
> + }
> }
>
> /// A lock guard.
> diff --git a/rust/kernel/sync/lock/mutex.rs b/rust/kernel/sync/lock/mutex.rs
> index 30632070ee670..7c2c239944931 100644
> --- a/rust/kernel/sync/lock/mutex.rs
> +++ b/rust/kernel/sync/lock/mutex.rs
> @@ -93,6 +93,7 @@ macro_rules! new_mutex {
> unsafe impl super::Backend for MutexBackend {
> type State = bindings::mutex;
> type GuardState = ();
> + type Context<'a> = ();
>
> unsafe fn init(
> ptr: *mut Self::State,
> diff --git a/rust/kernel/sync/lock/spinlock.rs b/rust/kernel/sync/lock/spinlock.rs
> index ea5c5bc1ce12e..97d85a5576615 100644
> --- a/rust/kernel/sync/lock/spinlock.rs
> +++ b/rust/kernel/sync/lock/spinlock.rs
> @@ -92,6 +92,7 @@ macro_rules! new_spinlock {
> unsafe impl super::Backend for SpinLockBackend {
> type State = bindings::spinlock_t;
> type GuardState = ();
> + type Context<'a> = ();
>
> unsafe fn init(
> ptr: *mut Self::State,
> --
> 2.46.0
>