linux-kernel - Re: [PATCH 3/4] cpu/hotplug: Add cpuhp_invoke_callback

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Date:   Wed, 20 Jan 2021 18:54:43 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     vincent.donnefort@....com
Cc:     tglx@...utronix.de, linux-kernel@...r.kernel.org,
        valentin.schneider@....com
Subject: Re: [PATCH 3/4] cpu/hotplug: Add cpuhp_invoke_callback_range()

On Wed, Jan 20, 2021 at 02:11:14PM +0100, Peter Zijlstra wrote:
> On Mon, Jan 11, 2021 at 05:10:46PM +0000, vincent.donnefort@....com wrote:
> > @@ -157,26 +162,24 @@ static int cpuhp_invoke_callback(unsigned int cpu, enum cpuhp_state state,
> >  
> >  	if (st->fail == state) {
> >  		st->fail = CPUHP_INVALID;
> > -
> > -		if (!(bringup ? step->startup.single : step->teardown.single))
> > -			return 0;
> > -
> >  		return -EAGAIN;
> >  	}
> >  
> > +	if (cpuhp_step_empty(bringup, step)) {
> > +		WARN_ON_ONCE(1);
> > +		return 0;
> > +	}
> 
> This changes the behaviour of fail.. might be best to refactor without
> changing behaviour.
> 

Aah, the trick is in cpuhp_next_state() skipping empty states, so we'll
never get there.