Re: [PATCH v6 3/3] rust: sync: Add SpinLockIrq

[Lyude Paul]

On Fri, 2024-10-04 at 14:48 -0400, Lyude Paul wrote:
> 
> FWIW: I agree we want things to map C closely wherever we can, but part of the
> reason of having rust in the kernel at all is to take advantage of the
> features it provides us that aren't in C - so there's always going to be
> differences in some places. This being said though, I'm more then happy to
> minimize those as much as possible and explore ways to figure out how to make
> it so that correctly using these interfaces is as obvious and not-error prone
> as possible. The last thing I want is to encourage bad patterns in drivers
> that maintainers have to deal with the headaches of for ages to come,
> especially when rust should be able to help with this as opposed to harm :).

I was thinking about this a bit more today and I realized I might actually
have a better solution that I think would actually map a lot closer to the C
primitives and I feel a bit silly it didn't occur to me before.

What if instead of with_interrupts_disabled, we extended Lock so that types
like SpinLockIrq that require a context like IrqDisabled can require the use
of two new methods:

* first_lock<R>(&self, cb: impl for<'a> FnOnce(Guard<'a, T, B>, B::Context<'a>) -> R) -> R
* lock_with(&self, B::Context<'a>) -> T

The first begins the locking context, in this case turning local interrupts
off on non-PREEMPT_RT kernels, and otherwise acts like
with_interrupts_disabled would. lock_with would be the same as what we have
now.
> 
> > 
> > Thanks,
> > 
> >         tglx
> > 
> > 
> 

-- 
Cheers,
 Lyude Paul (she/her)
 Software Engineer at Red Hat

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