Re: [PATCH v3 1/4] rv/reactors: use context-sensitive lockdep wait type in rv_react()

[Gabriele Monaco <gmonaco@redhat.com>]

On Mon, 2026-08-17 at 10:18 +0200, Nam Cao wrote:
> Gabriele Monaco <gmonaco@redhat.com> writes:
> 
> > On Mon, 2026-08-10 at 01:10 +0800, wen.yang@linux.dev wrote:
> > > From: Wen Yang <wen.yang@linux.dev>
> > > 
> > > Reactors must not explicitly take locks, so they should comply with
> > > LD_WAIT_FREE.  However, reactor callbacks can run with preemption
> > > enabled on any kernel (not just PREEMPT_RT).  If a timer interrupt
> > > fires during the callback, the interrupt exit path schedules and
> > > acquires rq->__lock (LD_WAIT_SPIN) while the lockdep override map that
> > > declared LD_WAIT_FREE is still held, triggering a spurious
> > > "Invalid wait context" warning:
> ...
> > Anyway, I'd appreciate comments/acks from the other folks in the loop
> 
> Sorry, I do not know enough about lockdep to comment on this.
> 
> FWIW, I would rather just use LD_WAIT_SPIN and keep things
> simple. Context-sensitive code paths "feels wrong" to me. Spinning
> should either be allowed or forbidden. Making it dynamic "feels like" it
> will bring further complications down the road.
> 
> But that's just my intuition.

I don't have a strong opinion on this, but since there's no one in the kernel
using LD_WAIT_FREE as inner type, that feels like a hint to go down the simple
route too and allow LD_WAIT_SPIN.

If a reactor ever uses spinlocks, lockdep would already complain on its own if
that ends up being an issue, wouldn't it?

Gabriele