[PATCH 1/3] rust: sync: Add Lock::is_locked()

Lyude Paul
2024-11-20T22:35:06Z

Now that we've added a Lock::from_raw() function and exposed Guard::new(),
it would be good to actually add the ability to assert the current state
of a lock to ensure correctness for unsafe code using these functions.

To do so, let's add Lock::is_locked() which simply returns whether or not a
Lock is acquired. We'll use this in the next few commits to add some debug
assertions.

Signed-off-by: Lyude Paul <lyude@redhat.com>
---
rust/helpers/spinlock.c | 5 +++++
rust/kernel/sync/lock.rs | 18 ++++++++++++++++++
rust/kernel/sync/lock/mutex.rs | 5 +++++
rust/kernel/sync/lock/spinlock.rs | 5 +++++
4 files changed, 33 insertions(+)

diff --git a/rust/helpers/spinlock.c b/rust/helpers/spinlock.c
index b7b0945e8b3cb..90216a69e3ea1 100644
--- a/rust/helpers/spinlock.c
+++ b/rust/helpers/spinlock.c
@@ -26,3 +26,8 @@ int rust_helper_spin_trylock(spinlock_t *lock)
{
return spin_trylock(lock);
}
+
+bool rust_helper_spin_is_locked(spinlock_t *lock)
+{
+ return spin_is_locked(lock);
+}
diff --git a/rust/kernel/sync/lock.rs b/rust/kernel/sync/lock.rs
index 139f17f2ec86b..542f846ac02b2 100644
--- a/rust/kernel/sync/lock.rs
+++ b/rust/kernel/sync/lock.rs
@@ -85,6 +85,13 @@ 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) };
}
+
+ /// Returns whether or not the lock is currently acquired.
+ ///
+ /// # Safety
+ ///
+ /// Callers must ensure that `ptr` is a valid initialised pointer to this lock type.
+ unsafe fn is_locked(ptr: *mut Self::State) -> bool;
}

/// A mutual exclusion primitive.
@@ -170,6 +177,17 @@ pub fn try_lock(&self) -> Option<Guard<'_, T, B>> {
// that `init` was called.
unsafe { B::try_lock(self.state.get()).map(|state| Guard::new(self, state)) }
}
+
+ /// Return whether or not the lock is currently acquired.
+ ///
+ /// Keep in mind that this function is inherently racy: a lock could immediately be acquired or
+ /// released after this function returns. As such, the return value from this function should be
+ /// treated as a snapshot for debugging purposes.
+ pub fn is_locked(&self) -> bool {
+ // SAFETY: The constructor of the type calls `init`, so the existence of the object proves
+ // that `init` was called.
+ unsafe { B::is_locked(self.state.get()) }
+ }
}

/// A lock guard.
diff --git a/rust/kernel/sync/lock/mutex.rs b/rust/kernel/sync/lock/mutex.rs
index 0e946ebefce12..f21b1f14cbe1b 100644
--- a/rust/kernel/sync/lock/mutex.rs
+++ b/rust/kernel/sync/lock/mutex.rs
@@ -126,4 +126,9 @@ unsafe fn try_lock(ptr: *mut Self::State) -> Option<Self::GuardState> {
None
}
}
+
+ unsafe fn is_locked(ptr: *mut Self::State) -> bool {
+ // SAFETY: The `ptr` pointer is guaranteed to be valid and initialized before use.
+ unsafe { bindings::mutex_is_locked(ptr) }
+ }
}
diff --git a/rust/kernel/sync/lock/spinlock.rs b/rust/kernel/sync/lock/spinlock.rs
index 9f4d128bed983..cfccf5e900b80 100644
--- a/rust/kernel/sync/lock/spinlock.rs
+++ b/rust/kernel/sync/lock/spinlock.rs
@@ -125,4 +125,9 @@ unsafe fn try_lock(ptr: *mut Self::State) -> Option<Self::GuardState> {
None
}
}
+
+ unsafe fn is_locked(ptr: *mut Self::State) -> bool {
+ // SAFETY: The `ptr` pointer is guaranteed to be valid and initialized before use.
+ unsafe { bindings::spin_is_locked(ptr) }
+ }
}
--
2.47.0