119 lines
3.6 KiB
Rust
119 lines
3.6 KiB
Rust
// SPDX-License-Identifier: GPL-2.0
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//! A kernel spinlock.
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//!
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//! This module allows Rust code to use the kernel's `spinlock_t`.
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use crate::bindings;
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/// Creates a [`SpinLock`] initialiser with the given name and a newly-created lock class.
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///
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/// It uses the name if one is given, otherwise it generates one based on the file name and line
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/// number.
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#[macro_export]
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macro_rules! new_spinlock {
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($inner:expr $(, $name:literal)? $(,)?) => {
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$crate::sync::SpinLock::new(
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$inner, $crate::optional_name!($($name)?), $crate::static_lock_class!())
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};
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}
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/// A spinlock.
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///
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/// Exposes the kernel's [`spinlock_t`]. When multiple CPUs attempt to lock the same spinlock, only
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/// one at a time is allowed to progress, the others will block (spinning) until the spinlock is
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/// unlocked, at which point another CPU will be allowed to make progress.
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///
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/// Instances of [`SpinLock`] need a lock class and to be pinned. The recommended way to create such
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/// instances is with the [`pin_init`](crate::pin_init) and [`new_spinlock`] macros.
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///
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/// # Examples
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///
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/// The following example shows how to declare, allocate and initialise a struct (`Example`) that
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/// contains an inner struct (`Inner`) that is protected by a spinlock.
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///
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/// ```
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/// use kernel::{init::InPlaceInit, init::PinInit, new_spinlock, pin_init, sync::SpinLock};
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///
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/// struct Inner {
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/// a: u32,
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/// b: u32,
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/// }
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///
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/// #[pin_data]
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/// struct Example {
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/// c: u32,
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/// #[pin]
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/// d: SpinLock<Inner>,
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/// }
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///
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/// impl Example {
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/// fn new() -> impl PinInit<Self> {
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/// pin_init!(Self {
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/// c: 10,
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/// d <- new_spinlock!(Inner { a: 20, b: 30 }),
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/// })
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/// }
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/// }
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///
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/// // Allocate a boxed `Example`.
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/// let e = Box::pin_init(Example::new())?;
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/// assert_eq!(e.c, 10);
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/// assert_eq!(e.d.lock().a, 20);
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/// assert_eq!(e.d.lock().b, 30);
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/// # Ok::<(), Error>(())
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/// ```
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///
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/// The following example shows how to use interior mutability to modify the contents of a struct
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/// protected by a spinlock despite only having a shared reference:
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///
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/// ```
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/// use kernel::sync::SpinLock;
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///
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/// struct Example {
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/// a: u32,
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/// b: u32,
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/// }
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///
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/// fn example(m: &SpinLock<Example>) {
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/// let mut guard = m.lock();
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/// guard.a += 10;
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/// guard.b += 20;
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/// }
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/// ```
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///
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/// [`spinlock_t`]: srctree/include/linux/spinlock.h
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pub type SpinLock<T> = super::Lock<T, SpinLockBackend>;
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/// A kernel `spinlock_t` lock backend.
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pub struct SpinLockBackend;
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// SAFETY: The underlying kernel `spinlock_t` object ensures mutual exclusion. `relock` uses the
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// default implementation that always calls the same locking method.
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unsafe impl super::Backend for SpinLockBackend {
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type State = bindings::spinlock_t;
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type GuardState = ();
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unsafe fn init(
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ptr: *mut Self::State,
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name: *const core::ffi::c_char,
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key: *mut bindings::lock_class_key,
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) {
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// SAFETY: The safety requirements ensure that `ptr` is valid for writes, and `name` and
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// `key` are valid for read indefinitely.
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unsafe { bindings::__spin_lock_init(ptr, name, key) }
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}
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unsafe fn lock(ptr: *mut Self::State) -> Self::GuardState {
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// SAFETY: The safety requirements of this function ensure that `ptr` points to valid
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// memory, and that it has been initialised before.
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unsafe { bindings::spin_lock(ptr) }
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}
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unsafe fn unlock(ptr: *mut Self::State, _guard_state: &Self::GuardState) {
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// SAFETY: The safety requirements of this function ensure that `ptr` is valid and that the
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// caller is the owner of the mutex.
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unsafe { bindings::spin_unlock(ptr) }
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}
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}
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