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

[Boqun Feng <boqun.feng@gmail.com>]

On Mon, Nov 25, 2024 at 03:40:58PM -0500, Lyude Paul wrote:
> 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@redhat.com>
> 

Queued for more testing and reviews, thanks!

Regards,
Boqun

> ---
> 
> 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
>