Re: [PATCH v12 5/6] rust: ww_mutex: implement LockSet

[Gary Guo]

On Mon Oct 12, 2026 at 11:26 AM BST, Onur Özkan wrote:
> LockSet is a high-level and safe API built on top of
> ww_mutex which provides a safe and easy to use API
> while keeping the ww_mutex semantics.
>
> When EDEADLK is hit it drops all held locks and waits for the
> contended mutex. It then retries the given (by the user)
> locking algorithm with that mutex held and the same acquire
> context until it succeeds.

Do we really need this, or this can be achieved by simple retry loops?

    fn retry_if_deadlock<R>(f: impl FnOnce() -> Result<R>) -> Result<R> {
        loop {
            match f() {
                Err(EDEADLK) => (),
                e => return e,
            }
        }
    }

    stack_pin_init!(let acq_ctx = AcquireCtx::new(&class));
    retry_if_deadlock(|| {
        let mut gaurd1 = acq_ctx.lock(&mutex1)?;
        let mut guard2 = acq_ctx.lock(&mutex2)?;

        acq_ctx.done();

        *guard1 += 1;
        *guard2 += 1;
    });

I think the only difference is that the `LockSet` acquires the contending mutex
first. However, I imagine we can solve this by having a wrapped `AcquireCtx`
that provides that.

Best,
Gary

>
> Signed-off-by: Onur Özkan <work@xxxxxxxxxxxxx>
> ---
>  rust/kernel/sync/lock/ww_mutex.rs          |   6 +
>  rust/kernel/sync/lock/ww_mutex/lock_set.rs | 449 +++++++++++++++++++++
>  2 files changed, 455 insertions(+)
>  create mode 100644 rust/kernel/sync/lock/ww_mutex/lock_set.rs