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mutex.rs
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mutex.rs
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// SPDX-License-Identifier: GPL-2.0
//! A kernel mutex.
//!
//! This module allows Rust code to use the kernel's [`struct mutex`].
use super::{Guard, Lock, NeedsLockClass};
use crate::{bindings, CStr};
use core::{cell::UnsafeCell, marker::PhantomPinned, pin::Pin};
/// Safely initialises a [`Mutex`] with the given name, generating a new lock class.
#[macro_export]
macro_rules! mutex_init {
($mutex:expr, $name:literal) => {
$crate::init_with_lockdep!($mutex, $name)
};
}
/// Exposes the kernel's [`struct mutex`]. When multiple threads attempt to lock the same mutex,
/// only one at a time is allowed to progress, the others will block (sleep) until the mutex is
/// unlocked, at which point another thread will be allowed to wake up and make progress.
///
/// A [`Mutex`] must first be initialised with a call to [`Mutex::init`] before it can be used. The
/// [`mutex_init`] macro is provided to automatically assign a new lock class to a mutex instance.
///
/// Since it may block, [`Mutex`] needs to be used with care in atomic contexts.
///
/// [`struct mutex`]: ../../../include/linux/mutex.h
pub struct Mutex<T: ?Sized> {
/// The kernel `struct mutex` object.
mutex: UnsafeCell<bindings::mutex>,
/// A mutex needs to be pinned because it contains a [`struct list_head`] that is
/// self-referential, so it cannot be safely moved once it is initialised.
_pin: PhantomPinned,
/// The data protected by the mutex.
data: UnsafeCell<T>,
}
// SAFETY: `Mutex` can be transferred across thread boundaries iff the data it protects can.
unsafe impl<T: ?Sized + Send> Send for Mutex<T> {}
// SAFETY: `Mutex` serialises the interior mutability it provides, so it is `Sync` as long as the
// data it protects is `Send`.
unsafe impl<T: ?Sized + Send> Sync for Mutex<T> {}
impl<T> Mutex<T> {
/// Constructs a new mutex.
///
/// # Safety
///
/// The caller must call [`Mutex::init`] before using the mutex.
pub unsafe fn new(t: T) -> Self {
Self {
mutex: UnsafeCell::new(bindings::mutex::default()),
data: UnsafeCell::new(t),
_pin: PhantomPinned,
}
}
}
impl<T: ?Sized> Mutex<T> {
/// Locks the mutex and gives the caller access to the data protected by it. Only one thread at
/// a time is allowed to access the protected data.
pub fn lock(&self) -> Guard<Self> {
self.lock_noguard();
// SAFETY: The mutex was just acquired.
unsafe { Guard::new(self) }
}
}
impl<T: ?Sized> NeedsLockClass for Mutex<T> {
unsafe fn init(self: Pin<&Self>, name: CStr<'static>, key: *mut bindings::lock_class_key) {
bindings::__mutex_init(self.mutex.get(), name.as_ptr() as _, key);
}
}
impl<T: ?Sized> Lock for Mutex<T> {
type Inner = T;
#[cfg(not(CONFIG_DEBUG_LOCK_ALLOC))]
fn lock_noguard(&self) {
// SAFETY: `mutex` points to valid memory.
unsafe { bindings::mutex_lock(self.mutex.get()) };
}
#[cfg(CONFIG_DEBUG_LOCK_ALLOC)]
fn lock_noguard(&self) {
// SAFETY: `mutex` points to valid memory.
unsafe { bindings::mutex_lock_nested(self.mutex.get(), 0) };
}
unsafe fn unlock(&self) {
bindings::mutex_unlock(self.mutex.get());
}
fn locked_data(&self) -> &UnsafeCell<T> {
&self.data
}
}