linux-kernel - Re: [PATCH v4] cpu/hotplug: Do not bail-out in DYING/STARTING sections

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Message-ID: <YtbSP21k1hTKGlqv@google.com>
Date:   Tue, 19 Jul 2022 16:48:15 +0100
From:   Vincent Donnefort <vdonnefort@...gle.com>
To:     Valentin Schneider <vschneid@...hat.com>
Cc:     peterz@...radead.org, tglx@...utronix.de,
        linux-kernel@...r.kernel.org, regressions@...mhuis.info,
        kernel-team@...roid.com, Derek Dolney <z23@...teo.net>
Subject: Re: [PATCH v4] cpu/hotplug: Do not bail-out in DYING/STARTING
 sections

On Tue, Jul 19, 2022 at 04:12:03PM +0100, Valentin Schneider wrote:
> On 04/07/22 14:13, Vincent Donnefort wrote:
> > +static int _cpuhp_invoke_callback_range(bool bringup,
> > +					unsigned int cpu,
> > +					struct cpuhp_cpu_state *st,
> > +					enum cpuhp_state target,
> > +					bool nofail)
> [...]
> > +		if (nofail) {
> > +			pr_warn("CPU %u %s state %s (%d) failed (%d)\n",
> > +				cpu, bringup ? "UP" : "DOWN",
> > +				cpuhp_get_step(st->state)->name,
> > +				st->state, err);
> > +			ret = -1;
> 
> On a single failure we'll get two warns (WARN_ON_ONCE() + pr_warn(), and
> then subsequently just the pr_warn()), is that intended?

It does, this is to keep the backtrace that used to be here... but now, giving
a second thought, we can probably get rid of it and just keep the pr_warn()?

> 
> Also, why not have ret = err here?

If two states fail, the ret wouldn't mean much, hence a default "-1" just for
the WARN_ONCE. But if we drop the latter, that would simplify the problem of
knowing which error code to return.

> 
> > +		} else {
> > +			ret = err;
> >                       break;
> > +		}
> >       }
> >
> > -	return err;
> > +	return ret;
> 
> > +static inline void cpuhp_invoke_callback_range_nofail(bool bringup,
> > +						      unsigned int cpu,
> > +						      struct cpuhp_cpu_state *st,
> > +						      enum cpuhp_state target)
> > +{
> > +	WARN_ON_ONCE(_cpuhp_invoke_callback_range(bringup, cpu, st, target, true));
> >  }
> >
>