[PATCH v2] rust: sync: Add lock::Backend::assert_is_held()

From: Lyude Paul
Date: Mon Nov 25 2024 - 15:42:23 EST


Since we've exposed Lock::from_raw() and Guard::new() publically, we want
to be able to make sure that we assert that a lock is actually held when
constructing a Guard for it to handle instances of unsafe Guard::new()
calls outside of our lock module.

So, let's do this by adding a new method assert_is_held to Backend, which
uses lockdep to check whether or not a lock has been acquired. When lockdep
is disabled, this has no overhead.

Signed-off-by: Lyude Paul <lyude@xxxxxxxxxx>

---

V2
* Use lockdep instead of is_locked() functions
* Drop is_locked, replace with assert_is_held()
---
rust/helpers/mutex.c | 5 +++++
rust/helpers/spinlock.c | 5 +++++
rust/kernel/sync/lock.rs | 10 ++++++++++
rust/kernel/sync/lock/mutex.rs | 7 +++++++
rust/kernel/sync/lock/spinlock.rs | 7 +++++++
5 files changed, 34 insertions(+)

diff --git a/rust/helpers/mutex.c b/rust/helpers/mutex.c
index 7e00680958ef1..06575553eda5c 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 b7b0945e8b3cb..b26953d0d65b5 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);
}
+
+void rust_helper_spin_assert_is_held(spinlock_t *lock)
+{
+ lockdep_assert_held(lock);
+}
diff --git a/rust/kernel/sync/lock.rs b/rust/kernel/sync/lock.rs
index 6d3c8874eb26a..bc71fda87b104 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) };
}
+
+ /// 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.
@@ -207,6 +214,9 @@ impl<'a, T: ?Sized, B: Backend> Guard<'a, T, B> {
///
/// The caller must ensure that it owns the lock.
pub(crate) 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 0e946ebefce12..8ee079f6ae0ac 100644
--- a/rust/kernel/sync/lock/mutex.rs
+++ b/rust/kernel/sync/lock/mutex.rs
@@ -126,4 +126,11 @@ unsafe fn try_lock(ptr: *mut Self::State) -> Option<Self::GuardState> {
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 9f4d128bed983..b2c1343aabee3 100644
--- a/rust/kernel/sync/lock/spinlock.rs
+++ b/rust/kernel/sync/lock/spinlock.rs
@@ -125,4 +125,11 @@ unsafe fn try_lock(ptr: *mut Self::State) -> Option<Self::GuardState> {
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);
+ }
+ }
}

base-commit: b7ed2b6f4e8d7f64649795e76ee9db67300de8eb
--
2.47.0