1// SPDX-License-Identifier: GPL-2.0
  2
  3//! A kernel spinlock.
  4//!
  5//! This module allows Rust code to use the kernel's `spinlock_t`.
  6
  7use crate::bindings;
  8
  9/// Creates a [`SpinLock`] initialiser with the given name and a newly-created lock class.
 10///
 11/// It uses the name if one is given, otherwise it generates one based on the file name and line
 12/// number.
 13#[macro_export]
 14macro_rules! new_spinlock {
 15    ($inner:expr $(, $name:literal)? $(,)?) => {
 16        $crate::sync::SpinLock::new(
 17            $inner, $crate::optional_name!($($name)?), $crate::static_lock_class!())
 18    };
 19}
 20pub use new_spinlock;
 21
 22/// A spinlock.
 23///
 24/// Exposes the kernel's [`spinlock_t`]. When multiple CPUs attempt to lock the same spinlock, only
 25/// one at a time is allowed to progress, the others will block (spinning) until the spinlock is
 26/// unlocked, at which point another CPU will be allowed to make progress.
 27///
 28/// Instances of [`SpinLock`] need a lock class and to be pinned. The recommended way to create such
 29/// instances is with the [`pin_init`](crate::pin_init) and [`new_spinlock`] macros.
 30///
 31/// # Examples
 32///
 33/// The following example shows how to declare, allocate and initialise a struct (`Example`) that
 34/// contains an inner struct (`Inner`) that is protected by a spinlock.
 35///
 36/// ```
 37/// use kernel::sync::{new_spinlock, SpinLock};
 38///
 39/// struct Inner {
 40///     a: u32,
 41///     b: u32,
 42/// }
 43///
 44/// #[pin_data]
 45/// struct Example {
 46///     c: u32,
 47///     #[pin]
 48///     d: SpinLock<Inner>,
 49/// }
 50///
 51/// impl Example {
 52///     fn new() -> impl PinInit<Self> {
 53///         pin_init!(Self {
 54///             c: 10,
 55///             d <- new_spinlock!(Inner { a: 20, b: 30 }),
 56///         })
 57///     }
 58/// }
 59///
 60/// // Allocate a boxed `Example`.
 61/// let e = Box::pin_init(Example::new())?;
 62/// assert_eq!(e.c, 10);
 63/// assert_eq!(e.d.lock().a, 20);
 64/// assert_eq!(e.d.lock().b, 30);
 65/// # Ok::<(), Error>(())
 66/// ```
 67///
 68/// The following example shows how to use interior mutability to modify the contents of a struct
 69/// protected by a spinlock despite only having a shared reference:
 70///
 71/// ```
 72/// use kernel::sync::SpinLock;
 73///
 74/// struct Example {
 75///     a: u32,
 76///     b: u32,
 77/// }
 78///
 79/// fn example(m: &SpinLock<Example>) {
 80///     let mut guard = m.lock();
 81///     guard.a += 10;
 82///     guard.b += 20;
 83/// }
 84/// ```
 85///
 86/// [`spinlock_t`]: srctree/include/linux/spinlock.h
 87pub type SpinLock<T> = super::Lock<T, SpinLockBackend>;
 88
 89/// A kernel `spinlock_t` lock backend.
 90pub struct SpinLockBackend;
 91
 92// SAFETY: The underlying kernel `spinlock_t` object ensures mutual exclusion. `relock` uses the
 93// default implementation that always calls the same locking method.
 94unsafe impl super::Backend for SpinLockBackend {
 95    type State = bindings::spinlock_t;
 96    type GuardState = ();
 97
 98    unsafe fn init(
 99        ptr: *mut Self::State,
100        name: *const core::ffi::c_char,
101        key: *mut bindings::lock_class_key,
102    ) {
103        // SAFETY: The safety requirements ensure that `ptr` is valid for writes, and `name` and
104        // `key` are valid for read indefinitely.
105        unsafe { bindings::__spin_lock_init(ptr, name, key) }
106    }
107
108    unsafe fn lock(ptr: *mut Self::State) -> Self::GuardState {
109        // SAFETY: The safety requirements of this function ensure that `ptr` points to valid
110        // memory, and that it has been initialised before.
111        unsafe { bindings::spin_lock(ptr) }
112    }
113
114    unsafe fn unlock(ptr: *mut Self::State, _guard_state: &Self::GuardState) {
115        // SAFETY: The safety requirements of this function ensure that `ptr` is valid and that the
116        // caller is the owner of the spinlock.
117        unsafe { bindings::spin_unlock(ptr) }
118    }
119}