linux-kernel - Re: [PATCH 14/36] cpuidle: Fix rcu_idle

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Message-ID: <Yqi6Fd38ZCsDUnQG@hirez.programming.kicks-ass.net>
Date:   Tue, 14 Jun 2022 18:40:53 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Mark Rutland <mark.rutland@....com>
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Subject: Re: [PATCH 14/36] cpuidle: Fix rcu_idle_*() usage

On Tue, Jun 14, 2022 at 01:41:13PM +0100, Mark Rutland wrote:
> On Wed, Jun 08, 2022 at 04:27:37PM +0200, Peter Zijlstra wrote:
> > --- a/kernel/time/tick-broadcast.c
> > +++ b/kernel/time/tick-broadcast.c
> > @@ -622,9 +622,13 @@ struct cpumask *tick_get_broadcast_onesh
> >   * to avoid a deep idle transition as we are about to get the
> >   * broadcast IPI right away.
> >   */
> > -int tick_check_broadcast_expired(void)
> > +noinstr int tick_check_broadcast_expired(void)
> >  {
> > +#ifdef _ASM_GENERIC_BITOPS_INSTRUMENTED_NON_ATOMIC_H
> > +	return arch_test_bit(smp_processor_id(), cpumask_bits(tick_broadcast_force_mask));
> > +#else
> >  	return cpumask_test_cpu(smp_processor_id(), tick_broadcast_force_mask);
> > +#endif
> >  }
> 
> This is somewhat not-ideal. :/

I'll say.

> Could we unconditionally do the arch_test_bit() variant, with a comment, or
> does that not exist in some cases?

Loads of build errors ensued, which is how I ended up with this mess ...