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Message-ID: <f371f88c310654ff4a023b300c6de7b982d12b04.camel@redhat.com>
Date: Thu, 31 Oct 2024 16:54:08 -0400
From: Lyude Paul <lyude@...hat.com>
To: Boqun Feng <boqun.feng@...il.com>, Thomas Gleixner <tglx@...utronix.de>
Cc: Dirk Behme <dirk.behme@...il.com>, rust-for-linux@...r.kernel.org,
Danilo Krummrich <dakr@...hat.com>, airlied@...hat.com, Ingo Molnar
<mingo@...hat.com>, will@...nel.org, Waiman Long <longman@...hat.com>,
Peter Zijlstra <peterz@...radead.org>, linux-kernel@...r.kernel.org, Miguel
Ojeda <ojeda@...nel.org>, Alex Gaynor <alex.gaynor@...il.com>,
wedsonaf@...il.com, Gary Guo <gary@...yguo.net>, Björn
Roy Baron <bjorn3_gh@...tonmail.com>, Benno Lossin
<benno.lossin@...ton.me>, Andreas Hindborg <a.hindborg@...sung.com>,
aliceryhl@...gle.com, Trevor Gross <tmgross@...ch.edu>
Subject: Re: [POC 5/6] rust: sync: Introduce lock::Backend::Context
On Thu, 2024-10-17 at 22:51 -0700, Boqun Feng wrote:
> From: Lyude Paul <lyude@...hat.com>
>
> Now that we've introduced an `InterruptDisabled` token for marking
> contexts in which IRQs are disabled, we can have a way to avoid
> `SpinLockIrq` disabling interrupts if the interrupts have already been
> disabled. Basically, a `SpinLockIrq` should work like a `SpinLock` if
> interrupts are disabled. So a function:
>
> (&'a SpinLockIrq, &'a InterruptDisabled) -> Guard<'a, .., SpinLockBackend>
>
> makes senses. Note that due to `Guard` and `InterruptDisabled` has the
> same lifetime, interrupts cannot be enabled whiel the Guard exists.
>
> Add a `lock_with()` interface for `Lock`, and an associate type of
> `Backend` to describe the context.
>
> [Boqun: Change the interface a lot, now `SpinLockIrq` can use the
> `lock()` function, but it always disable the interrupts, reuse the
> `lock_with()` method to provide a way for locking if interrupts are
> already disabled. `lock_with()` implementation will be added later.]
>
> Co-developed-by: Lyude Paul <lyude@...hat.com>
> Signed-off-by: Lyude Paul <lyude@...hat.com>
> Signed-off-by: Boqun Feng <boqun.feng@...il.com>
> ---
> rust/kernel/sync/lock.rs | 12 +++++++++++-
> rust/kernel/sync/lock/mutex.rs | 1 +
> rust/kernel/sync/lock/spinlock.rs | 3 +++
> 3 files changed, 15 insertions(+), 1 deletion(-)
>
> diff --git a/rust/kernel/sync/lock.rs b/rust/kernel/sync/lock.rs
> index f6c34ca4d819..49b53433201c 100644
> --- a/rust/kernel/sync/lock.rs
> +++ b/rust/kernel/sync/lock.rs
> @@ -38,6 +38,9 @@ pub unsafe trait Backend {
> /// [`unlock`]: Backend::unlock
> type GuardState;
>
> + /// The context which can be provided to acquire the lock with a different backend.
> + type Context<'a>;
> +
> /// Initialises the lock.
> ///
> /// # Safety
> @@ -120,8 +123,15 @@ pub fn new(t: T, name: &'static CStr, key: &'static LockClassKey) -> impl PinIni
> }
>
> impl<T: ?Sized, B: Backend> Lock<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> {
> + todo!()
> + }
> +
> /// Acquires the lock and gives the caller access to the data protected by it.
> - pub fn lock(&self) -> Guard<'_, T, B> {
> + #[inline]
> + pub fn lock<'a>(&'a self) -> 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()) };
> diff --git a/rust/kernel/sync/lock/mutex.rs b/rust/kernel/sync/lock/mutex.rs
> index 30632070ee67..7c2c23994493 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 884d4d1cbf23..8f9e1b27e474 100644
> --- a/rust/kernel/sync/lock/spinlock.rs
> +++ b/rust/kernel/sync/lock/spinlock.rs
> @@ -3,6 +3,7 @@
> //! A kernel spinlock.
> //!
> //! This module allows Rust code to use the kernel's `spinlock_t`.
> +use crate::interrupt::InterruptDisabled;
>
> /// Creates a [`SpinLock`] initialiser with the given name and a newly-created lock class.
> ///
> @@ -92,6 +93,7 @@ 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,
> @@ -183,6 +185,7 @@ macro_rules! new_spinlock_irq {
> unsafe impl super::Backend for SpinLockIrqBackend {
> type State = bindings::spinlock_t;
> type GuardState = ();
> + type Context<'a> = &'a InterruptDisabled;
Does this actually need to be a reference here? I thought we wanted to use
just plain token types with lifetimes instead of references
>
> unsafe fn init(
> ptr: *mut Self::State,
--
Cheers,
Lyude Paul (she/her)
Software Engineer at Red Hat
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