kernel/
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.
36///
37/// Wraps the kernel's `struct lock_class_key`.
38#[repr(transparent)]
39#[pin_data(PinnedDrop)]
40pub struct LockClassKey {
41    #[pin]
42    inner: Opaque<bindings::lock_class_key>,
43}
44
45// SAFETY: Unregistering a lock class key from a different thread than where it was registered is
46// allowed.
47unsafe impl Send for LockClassKey {}
48
49// SAFETY: `bindings::lock_class_key` is designed to be used concurrently from multiple threads and
50// provides its own synchronization.
51unsafe impl Sync for LockClassKey {}
52
53impl LockClassKey {
54    /// Initializes a statically allocated lock class key.
55    ///
56    /// This is usually used indirectly through the [`static_lock_class!`] macro. See its
57    /// documentation for more information.
58    ///
59    /// # Safety
60    ///
61    /// * Before using the returned value, it must be pinned in a static memory location.
62    /// * The destructor must never run on the returned `LockClassKey`.
63    pub const unsafe fn new_static() -> Self {
64        LockClassKey {
65            inner: Opaque::uninit(),
66        }
67    }
68
69    /// Initializes a dynamically allocated lock class key.
70    ///
71    /// In the common case of using a statically allocated lock class key, the
72    /// [`static_lock_class!`] macro should be used instead.
73    ///
74    /// # Examples
75    ///
76    /// ```
77    /// use kernel::alloc::KBox;
78    /// use kernel::types::ForeignOwnable;
79    /// use kernel::sync::{LockClassKey, SpinLock};
80    /// use pin_init::stack_pin_init;
81    ///
82    /// let key = KBox::pin_init(LockClassKey::new_dynamic(), GFP_KERNEL)?;
83    /// let key_ptr = key.into_foreign();
84    ///
85    /// {
86    ///     stack_pin_init!(let num: SpinLock<u32> = SpinLock::new(
87    ///         0,
88    ///         c"my_spinlock",
89    ///         // SAFETY: `key_ptr` is returned by the above `into_foreign()`, whose
90    ///         // `from_foreign()` has not yet been called.
91    ///         unsafe { <Pin<KBox<LockClassKey>> as ForeignOwnable>::borrow(key_ptr) }
92    ///     ));
93    /// }
94    ///
95    /// // SAFETY: We dropped `num`, the only use of the key, so the result of the previous
96    /// // `borrow` has also been dropped. Thus, it's safe to use from_foreign.
97    /// unsafe { drop(<Pin<KBox<LockClassKey>> as ForeignOwnable>::from_foreign(key_ptr)) };
98    /// # Ok::<(), Error>(())
99    /// ```
100    pub fn new_dynamic() -> impl PinInit<Self> {
101        pin_init!(Self {
102            // SAFETY: lockdep_register_key expects an uninitialized block of memory
103            inner <- Opaque::ffi_init(|slot| unsafe { bindings::lockdep_register_key(slot) })
104        })
105    }
106
107    /// Returns a raw pointer to the inner C struct.
108    ///
109    /// It is up to the caller to use the raw pointer correctly.
110    pub fn as_ptr(&self) -> *mut bindings::lock_class_key {
111        self.inner.get()
112    }
113}
114
115#[pinned_drop]
116impl PinnedDrop for LockClassKey {
117    fn drop(self: Pin<&mut Self>) {
118        // SAFETY: `self.as_ptr()` was registered with lockdep and `self` is pinned, so the address
119        // hasn't changed. Thus, it's safe to pass it to unregister.
120        unsafe { bindings::lockdep_unregister_key(self.as_ptr()) }
121    }
122}
123
124/// Defines a new static lock class and returns a pointer to it.
125///
126/// # Examples
127///
128/// ```
129/// use kernel::c_str;
130/// use kernel::sync::{static_lock_class, Arc, SpinLock};
131///
132/// fn new_locked_int() -> Result<Arc<SpinLock<u32>>> {
133///     Arc::pin_init(SpinLock::new(
134///         42,
135///         c_str!("new_locked_int"),
136///         static_lock_class!(),
137///     ), GFP_KERNEL)
138/// }
139/// ```
140#[macro_export]
141macro_rules! static_lock_class {
142    () => {{
143        static CLASS: $crate::sync::LockClassKey =
144            // SAFETY: The returned `LockClassKey` is stored in static memory and we pin it. Drop
145            // never runs on a static global.
146            unsafe { $crate::sync::LockClassKey::new_static() };
147        $crate::prelude::Pin::static_ref(&CLASS)
148    }};
149}
150pub use static_lock_class;
151
152/// Returns the given string, if one is provided, otherwise generates one based on the source code
153/// location.
154#[doc(hidden)]
155#[macro_export]
156macro_rules! optional_name {
157    () => {
158        $crate::c_str!(::core::concat!(::core::file!(), ":", ::core::line!()))
159    };
160    ($name:literal) => {
161        $crate::c_str!($name)
162    };
163}
kernel/sync.rs

kernel/
sync.rs
