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+// SPDX-License-Identifier: GPL-2.0
+
+//! Generic kernel lock and guard.
+//!
+//! It contains a generic Rust lock and guard that allow for different backends (e.g., mutexes,
+//! spinlocks, raw spinlocks) to be provided with minimal effort.
+
+use super::LockClassKey;
+use crate::{bindings, init::PinInit, pin_init, str::CStr, types::Opaque, types::ScopeGuard};
+use core::{cell::UnsafeCell, marker::PhantomData, marker::PhantomPinned};
+use macros::pin_data;
+
+pub mod mutex;
+pub mod spinlock;
+
+/// The "backend" of a lock.
+///
+/// It is the actual implementation of the lock, without the need to repeat patterns used in all
+/// locks.
+///
+/// # Safety
+///
+/// - Implementers must ensure that only one thread/CPU may access the protected data once the lock
+/// is owned, that is, between calls to `lock` and `unlock`.
+/// - Implementers must also ensure that `relock` uses the same locking method as the original
+/// lock operation.
+pub unsafe trait Backend {
+ /// The state required by the lock.
+ type State;
+
+ /// The state required to be kept between lock and unlock.
+ type GuardState;
+
+ /// Initialises the lock.
+ ///
+ /// # Safety
+ ///
+ /// `ptr` must be valid for write for the duration of the call, while `name` and `key` must
+ /// remain valid for read indefinitely.
+ unsafe fn init(
+ ptr: *mut Self::State,
+ name: *const core::ffi::c_char,
+ key: *mut bindings::lock_class_key,
+ );
+
+ /// Acquires the lock, making the caller its owner.
+ ///
+ /// # Safety
+ ///
+ /// Callers must ensure that [`Backend::init`] has been previously called.
+ #[must_use]
+ unsafe fn lock(ptr: *mut Self::State) -> Self::GuardState;
+
+ /// Releases the lock, giving up its ownership.
+ ///
+ /// # Safety
+ ///
+ /// It must only be called by the current owner of the lock.
+ unsafe fn unlock(ptr: *mut Self::State, guard_state: &Self::GuardState);
+
+ /// Reacquires the lock, making the caller its owner.
+ ///
+ /// # Safety
+ ///
+ /// Callers must ensure that `guard_state` comes from a previous call to [`Backend::lock`] (or
+ /// variant) that has been unlocked with [`Backend::unlock`] and will be relocked now.
+ unsafe fn relock(ptr: *mut Self::State, guard_state: &mut Self::GuardState) {
+ // SAFETY: The safety requirements ensure that the lock is initialised.
+ *guard_state = unsafe { Self::lock(ptr) };
+ }
+}
+
+/// A mutual exclusion primitive.
+///
+/// Exposes one of the kernel locking primitives. Which one is exposed depends on the lock backend
+/// specified as the generic parameter `B`.
+#[pin_data]
+pub struct Lock<T: ?Sized, B: Backend> {
+ /// The kernel lock object.
+ #[pin]
+ state: Opaque<B::State>,
+
+ /// Some locks are known to be self-referential (e.g., mutexes), while others are architecture
+ /// or config defined (e.g., spinlocks). So we conservatively require them to be pinned in case
+ /// some architecture uses self-references now or in the future.
+ #[pin]
+ _pin: PhantomPinned,
+
+ /// The data protected by the lock.
+ pub(crate) data: UnsafeCell<T>,
+}
+
+// SAFETY: `Lock` can be transferred across thread boundaries iff the data it protects can.
+unsafe impl<T: ?Sized + Send, B: Backend> Send for Lock<T, B> {}
+
+// SAFETY: `Lock` serialises the interior mutability it provides, so it is `Sync` as long as the
+// data it protects is `Send`.
+unsafe impl<T: ?Sized + Send, B: Backend> Sync for Lock<T, B> {}
+
+impl<T, B: Backend> Lock<T, B> {
+ /// Constructs a new lock initialiser.
+ #[allow(clippy::new_ret_no_self)]
+ pub fn new(t: T, name: &'static CStr, key: &'static LockClassKey) -> impl PinInit<Self> {
+ pin_init!(Self {
+ data: UnsafeCell::new(t),
+ _pin: PhantomPinned,
+ // SAFETY: `slot` is valid while the closure is called and both `name` and `key` have
+ // static lifetimes so they live indefinitely.
+ state <- Opaque::ffi_init(|slot| unsafe {
+ B::init(slot, name.as_char_ptr(), key.as_ptr())
+ }),
+ })
+ }
+}
+
+impl<T: ?Sized, B: Backend> Lock<T, B> {
+ /// Acquires the lock and gives the caller access to the data protected by it.
+ pub fn lock(&self) -> Guard<'_, T, B> {
+ // SAFETY: The constructor of the type calls `init`, so the existence of the object proves
+ // that `init` was called.
+ let state = unsafe { B::lock(self.state.get()) };
+ // SAFETY: The lock was just acquired.
+ unsafe { Guard::new(self, state) }
+ }
+}
+
+/// A lock guard.
+///
+/// Allows mutual exclusion primitives that implement the `Backend` trait to automatically unlock
+/// when a guard goes out of scope. It also provides a safe and convenient way to access the data
+/// protected by the lock.
+#[must_use = "the lock unlocks immediately when the guard is unused"]
+pub struct Guard<'a, T: ?Sized, B: Backend> {
+ pub(crate) lock: &'a Lock<T, B>,
+ pub(crate) state: B::GuardState,
+ _not_send: PhantomData<*mut ()>,
+}
+
+// SAFETY: `Guard` is sync when the data protected by the lock is also sync.
+unsafe impl<T: Sync + ?Sized, B: Backend> Sync for Guard<'_, T, B> {}
+
+impl<T: ?Sized, B: Backend> Guard<'_, T, B> {
+ pub(crate) fn do_unlocked(&mut self, cb: impl FnOnce()) {
+ // SAFETY: The caller owns the lock, so it is safe to unlock it.
+ unsafe { B::unlock(self.lock.state.get(), &self.state) };
+
+ // SAFETY: The lock was just unlocked above and is being relocked now.
+ let _relock =
+ ScopeGuard::new(|| unsafe { B::relock(self.lock.state.get(), &mut self.state) });
+
+ cb();
+ }
+}
+
+impl<T: ?Sized, B: Backend> core::ops::Deref for Guard<'_, T, B> {
+ type Target = T;
+
+ fn deref(&self) -> &Self::Target {
+ // SAFETY: The caller owns the lock, so it is safe to deref the protected data.
+ unsafe { &*self.lock.data.get() }
+ }
+}
+
+impl<T: ?Sized, B: Backend> core::ops::DerefMut for Guard<'_, T, B> {
+ fn deref_mut(&mut self) -> &mut Self::Target {
+ // SAFETY: The caller owns the lock, so it is safe to deref the protected data.
+ unsafe { &mut *self.lock.data.get() }
+ }
+}
+
+impl<T: ?Sized, B: Backend> Drop for Guard<'_, T, B> {
+ fn drop(&mut self) {
+ // SAFETY: The caller owns the lock, so it is safe to unlock it.
+ unsafe { B::unlock(self.lock.state.get(), &self.state) };
+ }
+}
+
+impl<'a, T: ?Sized, B: Backend> Guard<'a, T, B> {
+ /// Constructs a new immutable lock guard.
+ ///
+ /// # Safety
+ ///
+ /// The caller must ensure that it owns the lock.
+ pub(crate) unsafe fn new(lock: &'a Lock<T, B>, state: B::GuardState) -> Self {
+ Self {
+ lock,
+ state,
+ _not_send: PhantomData,
+ }
+ }
+}