sync.rs

  1// SPDX-License-Identifier: GPL-2.0
  2
  3//! Synchronisation primitives.
  4//!
  5//! This module contains the kernel APIs related to synchronisation that have been ported or
  6//! wrapped for usage by Rust code in the kernel.
  7
  8use crate::prelude::*;
  9use crate::types::Opaque;
 10use pin_init;
 11
 12mod arc;
 13pub mod aref;
 14pub mod atomic;
 15pub mod barrier;
 16pub mod completion;
 17mod condvar;
 18pub mod lock;
 19mod locked_by;
 20pub mod poll;
 21pub mod rcu;
 22mod refcount;
 23mod set_once;
 24
 25pub use arc::{Arc, ArcBorrow, UniqueArc};
 26pub use completion::Completion;
 27pub use condvar::{new_condvar, CondVar, CondVarTimeoutResult};
 28pub use lock::global::{global_lock, GlobalGuard, GlobalLock, GlobalLockBackend, GlobalLockedBy};
 29pub use lock::mutex::{new_mutex, Mutex, MutexGuard};
 30pub use lock::spinlock::{new_spinlock, SpinLock, SpinLockGuard};
 31pub use locked_by::LockedBy;
 32pub use refcount::Refcount;
 33pub use set_once::SetOnce;
 34
 35/// Represents a lockdep class. It's a wrapper around C's `lock_class_key`.
 36#[repr(transparent)]
 37#[pin_data(PinnedDrop)]
 38pub struct LockClassKey {
 39    #[pin]
 40    inner: Opaque<bindings::lock_class_key>,
 41}
 42
 43// SAFETY: `bindings::lock_class_key` is designed to be used concurrently from multiple threads and
 44// provides its own synchronization.
 45unsafe impl Sync for LockClassKey {}
 46
 47impl LockClassKey {
 48    /// Initializes a dynamically allocated lock class key. In the common case of using a
 49    /// statically allocated lock class key, the static_lock_class! macro should be used instead.
 50    ///
 51    /// # Examples
 52    /// ```
 53    /// # use kernel::alloc::KBox;
 54    /// # use kernel::types::ForeignOwnable;
 55    /// # use kernel::sync::{LockClassKey, SpinLock};
 56    /// # use pin_init::stack_pin_init;
 57    ///
 58    /// let key = KBox::pin_init(LockClassKey::new_dynamic(), GFP_KERNEL)?;
 59    /// let key_ptr = key.into_foreign();
 60    ///
 61    /// {
 62    ///     stack_pin_init!(let num: SpinLock<u32> = SpinLock::new(
 63    ///         0,
 64    ///         c"my_spinlock",
 65    ///         // SAFETY: `key_ptr` is returned by the above `into_foreign()`, whose
 66    ///         // `from_foreign()` has not yet been called.
 67    ///         unsafe { <Pin<KBox<LockClassKey>> as ForeignOwnable>::borrow(key_ptr) }
 68    ///     ));
 69    /// }
 70    ///
 71    /// // SAFETY: We dropped `num`, the only use of the key, so the result of the previous
 72    /// // `borrow` has also been dropped. Thus, it's safe to use from_foreign.
 73    /// unsafe { drop(<Pin<KBox<LockClassKey>> as ForeignOwnable>::from_foreign(key_ptr)) };
 74    ///
 75    /// # Ok::<(), Error>(())
 76    /// ```
 77    pub fn new_dynamic() -> impl PinInit<Self> {
 78        pin_init!(Self {
 79            // SAFETY: lockdep_register_key expects an uninitialized block of memory
 80            inner <- Opaque::ffi_init(|slot| unsafe { bindings::lockdep_register_key(slot) })
 81        })
 82    }
 83
 84    pub(crate) fn as_ptr(&self) -> *mut bindings::lock_class_key {
 85        self.inner.get()
 86    }
 87}
 88
 89#[pinned_drop]
 90impl PinnedDrop for LockClassKey {
 91    fn drop(self: Pin<&mut Self>) {
 92        // SAFETY: self.as_ptr was registered with lockdep and self is pinned, so the address
 93        // hasn't changed. Thus, it's safe to pass to unregister.
 94        unsafe { bindings::lockdep_unregister_key(self.as_ptr()) }
 95    }
 96}
 97
 98/// Defines a new static lock class and returns a pointer to it.
 99#[doc(hidden)]
100#[macro_export]
101macro_rules! static_lock_class {
102    () => {{
103        static CLASS: $crate::sync::LockClassKey =
104            // Lockdep expects uninitialized memory when it's handed a statically allocated `struct
105            // lock_class_key`.
106            //
107            // SAFETY: `LockClassKey` transparently wraps `Opaque` which permits uninitialized
108            // memory.
109            unsafe { ::core::mem::MaybeUninit::uninit().assume_init() };
110        $crate::prelude::Pin::static_ref(&CLASS)
111    }};
112}
113
114/// Returns the given string, if one is provided, otherwise generates one based on the source code
115/// location.
116#[doc(hidden)]
117#[macro_export]
118macro_rules! optional_name {
119    () => {
120        $crate::c_str!(::core::concat!(::core::file!(), ":", ::core::line!()))
121    };
122    ($name:literal) => {
123        $crate::c_str!($name)
124    };
125}