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

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Message-ID: <59803e6abd88dc29c402ff2b7ed020e45f4df1df.camel@redhat.com>
Date: Sat, 05 Oct 2024 14:19:38 -0400
From: Lyude Paul <lyude@...hat.com>
To: Thomas Gleixner <tglx@...utronix.de>, rust-for-linux@...r.kernel.org
Cc: Danilo Krummrich <dakr@...hat.com>, airlied@...hat.com, Ingo Molnar
 <mingo@...hat.com>, Will Deacon <will@...nel.org>, Waiman Long
 <longman@...hat.com>, Peter Zijlstra <peterz@...radead.org>, 
 linux-kernel@...r.kernel.org, Benno Lossin <benno.lossin@...ton.me>, Daniel
 Almeida <daniel.almeida@...labora.com>, Gary Guo <gary@...yguo.net>, Miguel
 Ojeda <ojeda@...nel.org>,  Alex Gaynor <alex.gaynor@...il.com>, Wedson
 Almeida Filho <wedsonaf@...il.com>, Boqun Feng <boqun.feng@...il.com>,
 Björn Roy Baron <bjorn3_gh@...tonmail.com>, Andreas
 Hindborg <a.hindborg@...sung.com>, Alice Ryhl <aliceryhl@...gle.com>,
 Trevor Gross <tmgross@...ch.edu>, Martin Rodriguez Reboredo
 <yakoyoku@...il.com>, Valentin Obst <kernel@...entinobst.de>
Subject: Re: [PATCH v6 3/3] rust: sync: Add SpinLockIrq

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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