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Message-ID: <9596d82a-4e70-c6be-6c37-519401815e32@gmail.com>
Date: Sun, 9 Apr 2023 13:48:07 -0300
From: Martin Rodriguez Reboredo <yakoyoku@...il.com>
To: Wedson Almeida Filho <wedsonaf@...il.com>,
rust-for-linux@...r.kernel.org
Cc: Miguel Ojeda <ojeda@...nel.org>,
Alex Gaynor <alex.gaynor@...il.com>,
Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
Björn Roy Baron <bjorn3_gh@...tonmail.com>,
linux-kernel@...r.kernel.org,
Wedson Almeida Filho <walmeida@...rosoft.com>,
Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
Waiman Long <longman@...hat.com>
Subject: Re: [PATCH v3 05/13] rust: lock: introduce `SpinLock`
On 4/8/23 04:53, Wedson Almeida Filho wrote:
> From: Wedson Almeida Filho <walmeida@...rosoft.com>
>
> This is the `spinlock_t` lock backend and allows Rust code to use the
> kernel spinlock idiomatically.
>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Will Deacon <will@...nel.org>
> Cc: Waiman Long <longman@...hat.com>
> Signed-off-by: Wedson Almeida Filho <walmeida@...rosoft.com>
> ---
> v1 -> v2: No changes
> v2 -> v3: No changes
>
> rust/helpers.c | 24 +++++++
> rust/kernel/sync.rs | 2 +-
> rust/kernel/sync/lock.rs | 1 +
> rust/kernel/sync/lock/spinlock.rs | 116 ++++++++++++++++++++++++++++++
> 4 files changed, 142 insertions(+), 1 deletion(-)
> create mode 100644 rust/kernel/sync/lock/spinlock.rs
>
> diff --git a/rust/helpers.c b/rust/helpers.c
> index 3010a2ec26e2..05694e3f8f70 100644
> --- a/rust/helpers.c
> +++ b/rust/helpers.c
> @@ -22,6 +22,7 @@
> #include <linux/build_bug.h>
> #include <linux/refcount.h>
> #include <linux/mutex.h>
> +#include <linux/spinlock.h>
>
> __noreturn void rust_helper_BUG(void)
> {
> @@ -35,6 +36,29 @@ void rust_helper_mutex_lock(struct mutex *lock)
> }
> EXPORT_SYMBOL_GPL(rust_helper_mutex_lock);
>
> +void rust_helper___spin_lock_init(spinlock_t *lock, const char *name,
> + struct lock_class_key *key)
> +{
> +#ifdef CONFIG_DEBUG_SPINLOCK
> + spin_lock_init_with_key(lock, name, key);
> +#else
> + spin_lock_init(lock);
> +#endif
> +}
> +EXPORT_SYMBOL_GPL(rust_helper___spin_lock_init);
> +
> +void rust_helper_spin_lock(spinlock_t *lock)
> +{
> + spin_lock(lock);
> +}
> +EXPORT_SYMBOL_GPL(rust_helper_spin_lock);
> +
> +void rust_helper_spin_unlock(spinlock_t *lock)
> +{
> + spin_unlock(lock);
> +}
> +EXPORT_SYMBOL_GPL(rust_helper_spin_unlock);
> +
> refcount_t rust_helper_REFCOUNT_INIT(int n)
> {
> return (refcount_t)REFCOUNT_INIT(n);
> diff --git a/rust/kernel/sync.rs b/rust/kernel/sync.rs
> index 693f0b7f4e4f..c997ff7e951e 100644
> --- a/rust/kernel/sync.rs
> +++ b/rust/kernel/sync.rs
> @@ -11,7 +11,7 @@ mod arc;
> pub mod lock;
>
> pub use arc::{Arc, ArcBorrow, UniqueArc};
> -pub use lock::mutex::Mutex;
> +pub use lock::{mutex::Mutex, spinlock::SpinLock};
>
> /// Represents a lockdep class. It's a wrapper around C's `lock_class_key`.
> #[repr(transparent)]
> diff --git a/rust/kernel/sync/lock.rs b/rust/kernel/sync/lock.rs
> index 86669f771ee0..df43dff5af5c 100644
> --- a/rust/kernel/sync/lock.rs
> +++ b/rust/kernel/sync/lock.rs
> @@ -11,6 +11,7 @@ use core::{cell::UnsafeCell, marker::PhantomData, marker::PhantomPinned};
> use macros::pin_data;
>
> pub mod mutex;
> +pub mod spinlock;
>
> /// The "backend" of a lock.
> ///
> diff --git a/rust/kernel/sync/lock/spinlock.rs b/rust/kernel/sync/lock/spinlock.rs
> new file mode 100644
> index 000000000000..a52d20fc9755
> --- /dev/null
> +++ b/rust/kernel/sync/lock/spinlock.rs
> @@ -0,0 +1,116 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +//! A kernel spinlock.
> +//!
> +//! This module allows Rust code to use the kernel's `spinlock_t`.
> +
> +use crate::bindings;
> +
> +/// Creates a [`SpinLock`] initialiser with the given name and a newly-created lock class.
> +///
> +/// It uses the name if one is given, otherwise it generates one based on the file name and line
> +/// number.
> +#[macro_export]
> +macro_rules! new_spinlock {
> + ($inner:expr $(, $name:literal)? $(,)?) => {
> + $crate::sync::SpinLock::new(
> + $inner, $crate::optional_name!($($name)?), $crate::static_lock_class!())
> + };
> +}
> +
> +/// A spinlock.
> +///
> +/// Exposes the kernel's [`spinlock_t`]. When multiple CPUs attempt to lock the same spinlock, only
> +/// one at a time is allowed to progress, the others will block (spinning) until the spinlock is
> +/// unlocked, at which point another CPU will be allowed to make progress.
> +///
> +/// Instances of [`SpinLock`] need a lock class and to be pinned. The recommended way to create such
> +/// instances is with the [`pin_init`](crate::pin_init) and [`new_spinlock`] macros.
> +///
> +/// # Examples
> +///
> +/// The following example shows how to declare, allocate and initialise a struct (`Example`) that
> +/// contains an inner struct (`Inner`) that is protected by a spinlock.
> +///
> +/// ```
> +/// use kernel::{init::InPlaceInit, init::PinInit, new_spinlock, pin_init, sync::SpinLock};
> +///
> +/// struct Inner {
> +/// a: u32,
> +/// b: u32,
> +/// }
> +///
> +/// #[pin_data]
> +/// struct Example {
> +/// c: u32,
> +/// #[pin]
> +/// d: SpinLock<Inner>,
> +/// }
> +///
> +/// impl Example {
> +/// fn new() -> impl PinInit<Self> {
> +/// pin_init!(Self {
> +/// c: 10,
> +/// d <- new_spinlock!(Inner { a: 20, b: 30 }),
> +/// })
> +/// }
> +/// }
> +///
> +/// // Allocate a boxed `Example`.
> +/// let e = Box::pin_init(Example::new())?;
> +/// assert_eq!(e.c, 10);
> +/// assert_eq!(e.d.lock().a, 20);
> +/// assert_eq!(e.d.lock().b, 30);
> +/// ```
> +///
> +/// The following example shows how to use interior mutability to modify the contents of a struct
> +/// protected by a spinlock despite only having a shared reference:
> +///
> +/// ```
> +/// use kernel::sync::SpinLock;
> +///
> +/// struct Example {
> +/// a: u32,
> +/// b: u32,
> +/// }
> +///
> +/// fn example(m: &SpinLock<Example>) {
> +/// let mut guard = m.lock();
> +/// guard.a += 10;
> +/// guard.b += 20;
> +/// }
> +/// ```
> +///
> +/// [`spinlock_t`]: ../../../../include/linux/spinlock.h
> +pub type SpinLock<T> = super::Lock<T, SpinLockBackend>;
> +
> +/// A kernel `spinlock_t` lock backend.
> +pub struct SpinLockBackend;
> +
> +// SAFETY: The underlying kernel `spinlock_t` object ensures mutual exclusion.
> +unsafe impl super::Backend for SpinLockBackend {
> + type State = bindings::spinlock_t;
> + type GuardState = ();
> +
> + unsafe fn init(
> + ptr: *mut Self::State,
> + name: *const core::ffi::c_char,
> + key: *mut bindings::lock_class_key,
> + ) {
> + // SAFETY: The safety requirements ensure that `ptr` is valid for writes, and `name` and
> + // `key` are valid for read indefinitely.
> + unsafe { bindings::__spin_lock_init(ptr, name, key) }
> + }
> +
> + unsafe fn lock(ptr: *mut Self::State) -> Self::GuardState {
> + // SAFETY: The safety requirements of this function ensure that `ptr` points to valid
> + // memory, and that it has been initialised before.
> + unsafe { bindings::spin_lock(ptr) }
> + }
> +
> + unsafe fn unlock(ptr: *mut Self::State, _guard_state: &Self::GuardState) {
> + // SAFETY: The safety requirements of this function ensure that `ptr` is valid and that the
> + // caller is the owner of the mutex.
> + unsafe { bindings::spin_unlock(ptr) }
> + }
> +}
Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@...il.com>
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