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,
16 /// The "backend" of a lock.
18 /// It is the actual implementation of the lock, without the need to repeat patterns used in all
23 /// - Implementers must ensure that only one thread/CPU may access the protected data once the lock
24 /// is owned, that is, between calls to `lock` and `unlock`.
25 /// - Implementers must also ensure that `relock` uses the same locking method as the original
26 /// lock operation.
28     /// The state required by the lock.
29     type State;  typedef
31     /// The state required to be kept between lock and unlock.
34     /// Initialises the lock.
41         ptr: *mut Self::State,  in init()  argument
46     /// Acquires the lock, making the caller its owner.
52     unsafe fn lock(ptr: *mut Self::State) -> Self::GuardState;  in lock()  method
54     /// Releases the lock, giving up its ownership.
58     /// It must only be called by the current owner of the lock.
59     unsafe fn unlock(ptr: *mut Self::State, guard_state: &Self::GuardState);  in unlock()  argument
61     /// Reacquires the lock, making the caller its owner.
65     /// Callers must ensure that `guard_state` comes from a previous call to [`Backend::lock`] (or
67     unsafe fn relock(ptr: *mut Self::State, guard_state: &mut Self::GuardState) {  in relock()  argument
68         // SAFETY: The safety requirements ensure that the lock is initialised.  in relock()
69         *guard_state = unsafe { Self::lock(ptr) };  in relock()
75 /// Exposes one of the kernel locking primitives. Which one is exposed depends on the lock
78 pub struct Lock<T: ?Sized, B: Backend> {  struct
79     /// The kernel lock object.
81     state: Opaque<B::State>,  field
83     /// Some locks are known to be self-referential (e.g., mutexes), while others are architecture
85     /// some architecture uses self-references now or in the future.
89     /// The data protected by the lock.
93 // SAFETY: `Lock` can be transferred across thread boundaries iff the data it protects can.  argument
94 unsafe impl<T: ?Sized + Send, B: Backend> Send for Lock<T, B> {}  implementation
96 // SAFETY: `Lock` serialises the interior mutability it provides, so it is `Sync` as long as the
98 unsafe impl<T: ?Sized + Send, B: Backend> Sync for Lock<T, B> {}  implementation
100 impl<T, B: Backend> Lock<T, B> {  implementation
101     /// Constructs a new lock initialiser.
102     pub fn new(t: T, name: &'static CStr, key: &'static LockClassKey) -> impl PinInit<Self> {  in new()
108             state <- Opaque::ffi_init(|slot| unsafe {  in new()
115 impl<T: ?Sized, B: Backend> Lock<T, B> {  impl
116     /// Acquires the lock and gives the caller access to the data protected by it.
117     pub fn lock(&self) -> Guard<'_, T, B> {  in lock()  method
120         let state = unsafe { B::lock(self.state.get()) };  in lock()  localVariable
121         // SAFETY: The lock was just acquired.  in lock()
122         unsafe { Guard::new(self, state) }  in lock()
126 /// A lock guard.
130 /// protected by the lock.
131 #[must_use = "the lock unlocks immediately when the guard is unused"]
133     pub(crate) lock: &'a Lock<T, B>,  field
134     pub(crate) state: B::GuardState,  field
138 // SAFETY: `Guard` is sync when the data protected by the lock is also sync.
143         // SAFETY: The caller owns the lock, so it is safe to unlock it.  in do_unlocked()
144         unsafe { B::unlock(self.lock.state.get(), &self.state) };  in do_unlocked()
146         // SAFETY: The lock was just unlocked above and is being relocked now.  in do_unlocked()
148             ScopeGuard::new(|| unsafe { B::relock(self.lock.state.get(), &mut self.state) });  in do_unlocked()
157     fn deref(&self) -> &Self::Target {  in deref()
158         // SAFETY: The caller owns the lock, so it is safe to deref the protected data.  in deref()
159         unsafe { &*self.lock.data.get() }  in deref()
164     fn deref_mut(&mut self) -> &mut Self::Target {  in deref_mut()
165         // SAFETY: The caller owns the lock, so it is safe to deref the protected data.  in deref_mut()
166         unsafe { &mut *self.lock.data.get() }  in deref_mut()
172         // SAFETY: The caller owns the lock, so it is safe to unlock it.  in drop()
173         unsafe { B::unlock(self.lock.state.get(), &self.state) };  in drop()
178     /// Constructs a new immutable lock guard.
182     /// The caller must ensure that it owns the lock.
183     pub(crate) unsafe fn new(lock: &'a Lock<T, B>, state: B::GuardState) -> Self {  in new()
185             lock,  in new()
186             state,  in new()