Merge tag 'lockdep-for-tip.20241220' of git://git.kernel.org/pub/scm/linux/kernel/git/boqun/linux into locking/core

Lockdep changes for v6.14:

- Use swap() macro in the ww_mutex test.
- Minor fixes and documentation for lockdep configs on internal data structure sizes.
- Some "-Wunused-function" warning fixes for Clang.

Rust locking changes for v6.14:

- Add Rust locking files into LOCKING PRIMITIVES maintainer entry.
- Add `Lock<(), ..>::from_raw()` function to support abstraction on low level locking.
- Expose `Guard::new()` for public usage and add type alias for spinlock and mutex guards.
- Add lockdep checking when creating a new lock `Guard`.

6 files changed, 72 insertions, 3 deletions

diff --git a/rust/helpers/mutex.c b/rust/helpers/mutex.c
index 7e00680958ef..06575553eda5 100644
--- a/rust/helpers/mutex.c
+++ b/rust/helpers/mutex.c
@@ -12,3 +12,8 @@ void rust_helper___mutex_init(struct mutex *mutex, const char *name,
 {
 	__mutex_init(mutex, name, key);
 }
+
+void rust_helper_mutex_assert_is_held(struct mutex *mutex)
+{
+	lockdep_assert_held(mutex);
+}
diff --git a/rust/helpers/spinlock.c b/rust/helpers/spinlock.c
index 5971fdf6f755..42c4bf01a23e 100644
--- a/rust/helpers/spinlock.c
+++ b/rust/helpers/spinlock.c
@@ -30,3 +30,8 @@ int rust_helper_spin_trylock(spinlock_t *lock)
 {
 	return spin_trylock(lock);
 }
+
+void rust_helper_spin_assert_is_held(spinlock_t *lock)
+{
+	lockdep_assert_held(lock);
+}
diff --git a/rust/kernel/sync.rs b/rust/kernel/sync.rs
index 1eab7ebf25fd..dffdaad972ce 100644
--- a/rust/kernel/sync.rs
+++ b/rust/kernel/sync.rs
@@ -16,8 +16,8 @@ pub mod poll;
 pub use arc::{Arc, ArcBorrow, UniqueArc};
 pub use condvar::{new_condvar, CondVar, CondVarTimeoutResult};
 pub use lock::global::{global_lock, GlobalGuard, GlobalLock, GlobalLockBackend, GlobalLockedBy};
-pub use lock::mutex::{new_mutex, Mutex};
-pub use lock::spinlock::{new_spinlock, SpinLock};
+pub use lock::mutex::{new_mutex, Mutex, MutexGuard};
+pub use lock::spinlock::{new_spinlock, SpinLock, SpinLockGuard};
 pub use locked_by::LockedBy;
 
 /// Represents a lockdep class. It's a wrapper around C's `lock_class_key`.
diff --git a/rust/kernel/sync/lock.rs b/rust/kernel/sync/lock.rs
index 41dcddac69e2..eb80048e0110 100644
--- a/rust/kernel/sync/lock.rs
+++ b/rust/kernel/sync/lock.rs
@@ -90,12 +90,20 @@ pub unsafe trait Backend {
         // SAFETY: The safety requirements ensure that the lock is initialised.
         *guard_state = unsafe { Self::lock(ptr) };
     }
+
+    /// Asserts that the lock is held using lockdep.
+    ///
+    /// # Safety
+    ///
+    /// Callers must ensure that [`Backend::init`] has been previously called.
+    unsafe fn assert_is_held(ptr: *mut Self::State);
 }
 
 /// 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`.
+#[repr(C)]
 #[pin_data]
 pub struct Lock<T: ?Sized, B: Backend> {
     /// The kernel lock object.
@@ -134,6 +142,28 @@ impl<T, B: Backend> Lock<T, B> {
     }
 }
 
+impl<B: Backend> Lock<(), B> {
+    /// Constructs a [`Lock`] from a raw pointer.
+    ///
+    /// This can be useful for interacting with a lock which was initialised outside of Rust.
+    ///
+    /// # Safety
+    ///
+    /// The caller promises that `ptr` points to a valid initialised instance of [`State`] during
+    /// the whole lifetime of `'a`.
+    ///
+    /// [`State`]: Backend::State
+    pub unsafe fn from_raw<'a>(ptr: *mut B::State) -> &'a Self {
+        // SAFETY:
+        // - By the safety contract `ptr` must point to a valid initialised instance of `B::State`
+        // - Since the lock data type is `()` which is a ZST, `state` is the only non-ZST member of
+        //   the struct
+        // - Combined with `#[repr(C)]`, this guarantees `Self` has an equivalent data layout to
+        //   `B::State`.
+        unsafe { &*ptr.cast() }
+    }
+}
+
 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> {
@@ -211,7 +241,10 @@ impl<'a, T: ?Sized, B: Backend> Guard<'a, T, B> {
     /// # Safety
     ///
     /// The caller must ensure that it owns the lock.
-    pub(crate) unsafe fn new(lock: &'a Lock<T, B>, state: B::GuardState) -> Self {
+    pub unsafe fn new(lock: &'a Lock<T, B>, state: B::GuardState) -> Self {
+        // SAFETY: The caller can only hold the lock if `Backend::init` has already been called.
+        unsafe { B::assert_is_held(lock.state.get()) };
+
         Self {
             lock,
             state,
diff --git a/rust/kernel/sync/lock/mutex.rs b/rust/kernel/sync/lock/mutex.rs
index 0e946ebefce1..70cadbc2e8e2 100644
--- a/rust/kernel/sync/lock/mutex.rs
+++ b/rust/kernel/sync/lock/mutex.rs
@@ -86,6 +86,14 @@ pub use new_mutex;
 /// [`struct mutex`]: srctree/include/linux/mutex.h
 pub type Mutex<T> = super::Lock<T, MutexBackend>;
 
+/// A [`Guard`] acquired from locking a [`Mutex`].
+///
+/// This is simply a type alias for a [`Guard`] returned from locking a [`Mutex`]. It will unlock
+/// the [`Mutex`] upon being dropped.
+///
+/// [`Guard`]: super::Guard
+pub type MutexGuard<'a, T> = super::Guard<'a, T, MutexBackend>;
+
 /// A kernel `struct mutex` lock backend.
 pub struct MutexBackend;
 
@@ -126,4 +134,9 @@ unsafe impl super::Backend for MutexBackend {
             None
         }
     }
+
+    unsafe fn assert_is_held(ptr: *mut Self::State) {
+        // SAFETY: The `ptr` pointer is guaranteed to be valid and initialized before use.
+        unsafe { bindings::mutex_assert_is_held(ptr) }
+    }
 }
diff --git a/rust/kernel/sync/lock/spinlock.rs b/rust/kernel/sync/lock/spinlock.rs
index 9f4d128bed98..ab2f8d075311 100644
--- a/rust/kernel/sync/lock/spinlock.rs
+++ b/rust/kernel/sync/lock/spinlock.rs
@@ -87,6 +87,14 @@ pub type SpinLock<T> = super::Lock<T, SpinLockBackend>;
 /// A kernel `spinlock_t` lock backend.
 pub struct SpinLockBackend;
 
+/// A [`Guard`] acquired from locking a [`SpinLock`].
+///
+/// This is simply a type alias for a [`Guard`] returned from locking a [`SpinLock`]. It will unlock
+/// the [`SpinLock`] upon being dropped.
+///
+/// [`Guard`]: super::Guard
+pub type SpinLockGuard<'a, T> = super::Guard<'a, T, SpinLockBackend>;
+
 // SAFETY: The underlying kernel `spinlock_t` object ensures mutual exclusion. `relock` uses the
 // default implementation that always calls the same locking method.
 unsafe impl super::Backend for SpinLockBackend {
@@ -125,4 +133,9 @@ unsafe impl super::Backend for SpinLockBackend {
             None
         }
     }
+
+    unsafe fn assert_is_held(ptr: *mut Self::State) {
+        // SAFETY: The `ptr` pointer is guaranteed to be valid and initialized before use.
+        unsafe { bindings::spin_assert_is_held(ptr) }
+    }
 }