1 // SPDX-License-Identifier: GPL-2.0
3 //! Generic kernel lock and guard.
5 //! It contains a generic Rust lock and guard that allow for different backends (e.g., mutexes,
24 /// The "backend" of a lock.
26 /// It is the actual implementation of the lock, without the need to repeat patterns used in all
31 /// - Implementers must ensure that only one thread/CPU may access the protected data once the lock
32 ///   is owned, that is, between calls to [`lock`] and [`unlock`].
33 /// - Implementers must also ensure that [`relock`] uses the same locking method as the original
34 ///   lock operation.
36 /// [`lock`]: Backend::lock
40     /// The state required by the lock.
41     type State;  typedef
43     /// The state required to be kept between [`lock`] and [`unlock`].
45     /// [`lock`]: Backend::lock
49     /// Initialises the lock.
56         ptr: *mut Self::State,  in init()  argument
61     /// Acquires the lock, making the caller its owner.
67     unsafe fn lock(ptr: *mut Self::State) -> Self::GuardState;  in lock()  method
69     /// Tries to acquire the lock.
74     unsafe fn try_lock(ptr: *mut Self::State) -> Option<Self::GuardState>;  in try_lock()
76     /// Releases the lock, giving up its ownership.
80     /// It must only be called by the current owner of the lock.
81     unsafe fn unlock(ptr: *mut Self::State, guard_state: &Self::GuardState);  in unlock()  argument
83     /// Reacquires the lock, making the caller its owner.
87     /// Callers must ensure that `guard_state` comes from a previous call to [`Backend::lock`] (or
89     unsafe fn relock(ptr: *mut Self::State, guard_state: &mut Self::GuardState) {  in relock()  argument
90         // SAFETY: The safety requirements ensure that the lock is initialised.  in relock()
91         *guard_state = unsafe { Self::lock(ptr) };  in relock()
94     /// Asserts that the lock is held using lockdep.
99     unsafe fn assert_is_held(ptr: *mut Self::State);  in assert_is_held()  argument
104 /// Exposes one of the kernel locking primitives. Which one is exposed depends on the lock
108 pub struct Lock<T: ?Sized, B: Backend> {  struct
109     /// The kernel lock object.
111     state: Opaque<B::State>,  field
113     /// Some locks are known to be self-referential (e.g., mutexes), while others are architecture
115     /// some architecture uses self-references now or in the future.
119     /// The data protected by the lock.
123 // SAFETY: `Lock` can be transferred across thread boundaries iff the data it protects can.  argument
124 unsafe impl<T: ?Sized + Send, B: Backend> Send for Lock<T, B> {}  implementation
126 // SAFETY: `Lock` serialises the interior mutability it provides, so it is `Sync` as long as the
128 unsafe impl<T: ?Sized + Send, B: Backend> Sync for Lock<T, B> {}  implementation
130 impl<T, B: Backend> Lock<T, B> {  implementation
131     /// Constructs a new lock initialiser.
132     pub fn new(t: T, name: &'static CStr, key: &'static LockClassKey) -> impl PinInit<Self> {  in new()
138             state <- Opaque::ffi_init(|slot| unsafe {  in new()
145 impl<B: Backend> Lock<(), B> {  impl
146     /// Constructs a [`Lock`] from a raw pointer.
148     /// This can be useful for interacting with a lock which was initialised outside of Rust.
152     /// The caller promises that `ptr` points to a valid initialised instance of [`State`] during
155     /// [`State`]: Backend::State
156     pub unsafe fn from_raw<'a>(ptr: *mut B::State) -> &'a Self {  in from_raw()
158         // - By the safety contract `ptr` must point to a valid initialised instance of `B::State`  in from_raw()
159         // - Since the lock data type is `()` which is a ZST, `state` is the only non-ZST member of  in from_raw()
161         // - Combined with `#[repr(C)]`, this guarantees `Self` has an equivalent data layout to  in from_raw()
162         //   `B::State`.  in from_raw()
167 impl<T: ?Sized, B: Backend> Lock<T, B> {  impl
168     /// Acquires the lock and gives the caller access to the data protected by it.
169     pub fn lock(&self) -> Guard<'_, T, B> {  in lock()  method
172         let state = unsafe { B::lock(self.state.get()) };  in lock()  localVariable
173         // SAFETY: The lock was just acquired.  in lock()
174         unsafe { Guard::new(self, state) }  in lock()
177     /// Tries to acquire the lock.
179     /// Returns a guard that can be used to access the data protected by the lock if successful.
180     pub fn try_lock(&self) -> Option<Guard<'_, T, B>> {  in try_lock()
183         unsafe { B::try_lock(self.state.get()).map(|state| Guard::new(self, state)) }  in try_lock()
187 /// A lock guard.
191 /// protected by the lock.
192 #[must_use = "the lock unlocks immediately when the guard is unused"]
194     pub(crate) lock: &'a Lock<T, B>,  field
195     pub(crate) state: B::GuardState,  field
199 // SAFETY: `Guard` is sync when the data protected by the lock is also sync.
203     pub(crate) fn do_unlocked<U>(&mut self, cb: impl FnOnce() -> U) -> U {  in do_unlocked()
204         // SAFETY: The caller owns the lock, so it is safe to unlock it.  in do_unlocked()
205         unsafe { B::unlock(self.lock.state.get(), &self.state) };  in do_unlocked()
208                 // SAFETY: The lock was just unlocked above and is being relocked now.  in do_unlocked()
209                 unsafe { B::relock(self.lock.state.get(), &mut self.state) });  in do_unlocked()
218     fn deref(&self) -> &Self::Target {  in deref()
219         // SAFETY: The caller owns the lock, so it is safe to deref the protected data.  in deref()
220         unsafe { &*self.lock.data.get() }  in deref()
225     fn deref_mut(&mut self) -> &mut Self::Target {  in deref_mut()
226         // SAFETY: The caller owns the lock, so it is safe to deref the protected data.  in deref_mut()
227         unsafe { &mut *self.lock.data.get() }  in deref_mut()
233         // SAFETY: The caller owns the lock, so it is safe to unlock it.  in drop()
234         unsafe { B::unlock(self.lock.state.get(), &self.state) };  in drop()
239     /// Constructs a new immutable lock guard.
243     /// The caller must ensure that it owns the lock.
244     pub unsafe fn new(lock: &'a Lock<T, B>, state: B::GuardState) -> Self {  in new()
245         // SAFETY: The caller can only hold the lock if `Backend::init` has already been called.  in new()
246         unsafe { B::assert_is_held(lock.state.get()) };  in new()
249             lock,  in new()
250             state,  in new()