Re: [PATCH v6 4/7] add KUnit coverage on Rust ww_mutex implementation

[Daniel Almeida <daniel.almeida@collabora.com>]

> On 3 Sep 2025, at 10:13, Onur Özkan <work@onurozkan.dev> wrote:
> 
> Adds coverage around the core `ww_mutex` functionality
> 
> Signed-off-by: Onur Özkan <work@onurozkan.dev>
> ---
> rust/kernel/sync/lock/ww_mutex.rs | 127 ++++++++++++++++++++++++++++++
> 1 file changed, 127 insertions(+)
> 
> diff --git a/rust/kernel/sync/lock/ww_mutex.rs b/rust/kernel/sync/lock/ww_mutex.rs
> index 314360632953..d289718d2c98 100644
> --- a/rust/kernel/sync/lock/ww_mutex.rs
> +++ b/rust/kernel/sync/lock/ww_mutex.rs
> @@ -421,3 +421,130 @@ fn drop(&mut self) {
>         unsafe { bindings::ww_mutex_unlock(self.mutex.as_ptr()) };
>     }
> }
> +
> +#[kunit_tests(rust_kernel_ww_mutex)]
> +mod tests {
> +    use crate::c_str;
> +    use crate::prelude::*;
> +    use crate::sync::Arc;
> +    use pin_init::stack_pin_init;
> +
> +    use super::*;
> +
> +    // A simple coverage on `define_ww_class` macro.
> +    define_ww_class!(TEST_WOUND_WAIT_CLASS, wound_wait, c_str!("test_wound_wait"));
> +    define_ww_class!(TEST_WAIT_DIE_CLASS, wait_die, c_str!("test_wait_die"));
> +
> +    #[test]
> +    fn test_ww_mutex_basic_lock_unlock() -> Result {
> +        stack_pin_init!(let class = WwClass::new_wound_wait(c_str!("test_mutex_class")));
> +
> +        let mutex = Arc::pin_init(WwMutex::new(42, &class), GFP_KERNEL)?;
> +
> +        let ctx = KBox::pin_init(WwAcquireCtx::new(&class), GFP_KERNEL)?;
> +
> +        // Lock.
> +        let guard = ctx.lock(&mutex)?;
> +        assert_eq!(*guard, 42);
> +
> +        // Drop the lock.
> +        drop(guard);
> +
> +        // Lock it again.
> +        let mut guard = ctx.lock(&mutex)?;
> +        *guard = 100;
> +        assert_eq!(*guard, 100);
> +
> +        Ok(())
> +    }
> +
> +    #[test]
> +    fn test_ww_mutex_trylock() -> Result {
> +        stack_pin_init!(let class = WwClass::new_wound_wait(c_str!("trylock_class")));
> +
> +        let mutex = Arc::pin_init(WwMutex::new(123, &class), GFP_KERNEL)?;
> +
> +        let ctx = KBox::pin_init(WwAcquireCtx::new(&class), GFP_KERNEL)?;
> +
> +        // `try_lock` on unlocked mutex should succeed.
> +        let guard = ctx.try_lock(&mutex)?;
> +        assert_eq!(*guard, 123);
> +
> +        // Now it should fail immediately as it's already locked.
> +        assert!(ctx.try_lock(&mutex).is_err());
> +
> +        Ok(())
> +    }
> +
> +    #[test]
> +    fn test_ww_mutex_is_locked() -> Result {
> +        stack_pin_init!(let class = WwClass::new_wait_die(c_str!("locked_check_class")));
> +
> +        let mutex = Arc::pin_init(WwMutex::new("hello", &class), GFP_KERNEL)?;
> +
> +        let ctx = KBox::pin_init(WwAcquireCtx::new(&class), GFP_KERNEL)?;
> +
> +        // Should not be locked initially.
> +        assert!(!mutex.is_locked());
> +
> +        let guard = ctx.lock(&mutex)?;
> +        assert!(mutex.is_locked());
> +
> +        drop(guard);
> +        assert!(!mutex.is_locked());
> +
> +        Ok(())
> +    }
> +
> +    #[test]
> +    fn test_ww_acquire_context() -> Result {
> +        stack_pin_init!(let class = WwClass::new_wound_wait(c_str!("ctx_class")));
> +
> +        let mutex1 = Arc::pin_init(WwMutex::new(1, &class), GFP_KERNEL)?;
> +        let mutex2 = Arc::pin_init(WwMutex::new(2, &class), GFP_KERNEL)?;
> +
> +        let ctx = KBox::pin_init(WwAcquireCtx::new(&class), GFP_KERNEL)?;
> +
> +        // Acquire multiple mutexes with the same context.
> +        let guard1 = ctx.lock(&mutex1)?;
> +        let guard2 = ctx.lock(&mutex2)?;
> +
> +        assert_eq!(*guard1, 1);
> +        assert_eq!(*guard2, 2);
> +
> +        ctx.done();
> +
> +        // We shouldn't be able to lock once it's `done`.
> +        assert!(ctx.lock(&mutex1).is_err());
> +        assert!(ctx.lock(&mutex2).is_err());
> +
> +        Ok(())
> +    }
> +
> +    #[test]
> +    fn test_with_global_classes() -> Result {
> +        let wound_wait_mutex =
> +            Arc::pin_init(WwMutex::new(100, &TEST_WOUND_WAIT_CLASS), GFP_KERNEL)?;
> +        let wait_die_mutex = Arc::pin_init(WwMutex::new(200, &TEST_WAIT_DIE_CLASS), GFP_KERNEL)?;
> +
> +        let ww_ctx = KBox::pin_init(WwAcquireCtx::new(&TEST_WOUND_WAIT_CLASS), GFP_KERNEL)?;
> +        let wd_ctx = KBox::pin_init(WwAcquireCtx::new(&TEST_WAIT_DIE_CLASS), GFP_KERNEL)?;
> +
> +        let ww_guard = ww_ctx.lock(&wound_wait_mutex)?;
> +        let wd_guard = wd_ctx.lock(&wait_die_mutex)?;
> +
> +        assert_eq!(*ww_guard, 100);
> +        assert_eq!(*wd_guard, 200);
> +
> +        assert!(wound_wait_mutex.is_locked());
> +        assert!(wait_die_mutex.is_locked());
> +
> +        drop(ww_guard);
> +        drop(wd_guard);
> +
> +        assert!(!wound_wait_mutex.is_locked());
> +        assert!(!wait_die_mutex.is_locked());
> +
> +        Ok(())
> +    }
> +}
> --
> 2.50.0
> 

I don’t see anything necessarily wrong here, but I’d rather wait until
the Rust API stabilizes a bit before having another look.

— Daniel