spinlock.rs

  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
  7/// Creates a [`SpinLock`] initialiser with the given name and a newly-created lock class.
  8///
  9/// It uses the name if one is given, otherwise it generates one based on the file name and line
 10/// number.
 11#[macro_export]
 12macro_rules! new_spinlock {
 13    ($inner:expr $(, $name:literal)? $(,)?) => {
 14        $crate::sync::SpinLock::new(
 15            $inner, $crate::optional_name!($($name)?), $crate::static_lock_class!())
 16    };
 17}
 18pub use new_spinlock;
 19
 20/// A spinlock.
 21///
 22/// Exposes the kernel's [`spinlock_t`]. When multiple CPUs attempt to lock the same spinlock, only
 23/// one at a time is allowed to progress, the others will block (spinning) until the spinlock is
 24/// unlocked, at which point another CPU will be allowed to make progress.
 25///
 26/// Instances of [`SpinLock`] need a lock class and to be pinned. The recommended way to create such
 27/// instances is with the [`pin_init`](pin_init::pin_init) and [`new_spinlock`] macros.
 28///
 29/// # Examples
 30///
 31/// The following example shows how to declare, allocate and initialise a struct (`Example`) that
 32/// contains an inner struct (`Inner`) that is protected by a spinlock.
 33///
 34/// ```
 35/// use kernel::sync::{new_spinlock, SpinLock};
 36///
 37/// struct Inner {
 38///     a: u32,
 39///     b: u32,
 40/// }
 41///
 42/// #[pin_data]
 43/// struct Example {
 44///     c: u32,
 45///     #[pin]
 46///     d: SpinLock<Inner>,
 47/// }
 48///
 49/// impl Example {
 50///     fn new() -> impl PinInit<Self> {
 51///         pin_init!(Self {
 52///             c: 10,
 53///             d <- new_spinlock!(Inner { a: 20, b: 30 }),
 54///         })
 55///     }
 56/// }
 57///
 58/// // Allocate a boxed `Example`.
 59/// let e = KBox::pin_init(Example::new(), GFP_KERNEL)?;
 60/// assert_eq!(e.c, 10);
 61/// assert_eq!(e.d.lock().a, 20);
 62/// assert_eq!(e.d.lock().b, 30);
 63/// # Ok::<(), Error>(())
 64/// ```
 65///
 66/// The following example shows how to use interior mutability to modify the contents of a struct
 67/// protected by a spinlock despite only having a shared reference:
 68///
 69/// ```
 70/// use kernel::sync::SpinLock;
 71///
 72/// struct Example {
 73///     a: u32,
 74///     b: u32,
 75/// }
 76///
 77/// fn example(m: &SpinLock<Example>) {
 78///     let mut guard = m.lock();
 79///     guard.a += 10;
 80///     guard.b += 20;
 81/// }
 82/// ```
 83///
 84/// [`spinlock_t`]: srctree/include/linux/spinlock.h
 85pub type SpinLock<T> = super::Lock<T, SpinLockBackend>;
 86
 87/// A kernel `spinlock_t` lock backend.
 88pub struct SpinLockBackend;
 89
 90/// A [`Guard`] acquired from locking a [`SpinLock`].
 91///
 92/// This is simply a type alias for a [`Guard`] returned from locking a [`SpinLock`]. It will unlock
 93/// the [`SpinLock`] upon being dropped.
 94///
 95/// [`Guard`]: super::Guard
 96pub type SpinLockGuard<'a, T> = super::Guard<'a, T, SpinLockBackend>;
 97
 98// SAFETY: The underlying kernel `spinlock_t` object ensures mutual exclusion. `relock` uses the
 99// default implementation that always calls the same locking method.
100unsafe impl super::Backend for SpinLockBackend {
101    type State = bindings::spinlock_t;
102    type GuardState = ();
103
104    unsafe fn init(
105        ptr: *mut Self::State,
106        name: *const crate::ffi::c_char,
107        key: *mut bindings::lock_class_key,
108    ) {
109        // SAFETY: The safety requirements ensure that `ptr` is valid for writes, and `name` and
110        // `key` are valid for read indefinitely.
111        unsafe { bindings::__spin_lock_init(ptr, name, key) }
112    }
113
114    unsafe fn lock(ptr: *mut Self::State) -> Self::GuardState {
115        // SAFETY: The safety requirements of this function ensure that `ptr` points to valid
116        // memory, and that it has been initialised before.
117        unsafe { bindings::spin_lock(ptr) }
118    }
119
120    unsafe fn unlock(ptr: *mut Self::State, _guard_state: &Self::GuardState) {
121        // SAFETY: The safety requirements of this function ensure that `ptr` is valid and that the
122        // caller is the owner of the spinlock.
123        unsafe { bindings::spin_unlock(ptr) }
124    }
125
126    unsafe fn try_lock(ptr: *mut Self::State) -> Option<Self::GuardState> {
127        // SAFETY: The `ptr` pointer is guaranteed to be valid and initialized before use.
128        let result = unsafe { bindings::spin_trylock(ptr) };
129
130        if result != 0 {
131            Some(())
132        } else {
133            None
134        }
135    }
136
137    unsafe fn assert_is_held(ptr: *mut Self::State) {
138        // SAFETY: The `ptr` pointer is guaranteed to be valid and initialized before use.
139        unsafe { bindings::spin_assert_is_held(ptr) }
140    }
141}