linux-kernel - Re: [PATCH 1/1] cpu-hotplug: export cpu_hotplug_enable/cpu_hotplug

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Date:	Wed, 24 Jun 2015 11:54:05 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Vitaly Kuznetsov <vkuznets@...hat.com>
cc:	Peter Zijlstra <peterz@...radead.org>,
	KY Srinivasan <kys@...rosoft.com>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devel@...uxdriverproject.org" <devel@...uxdriverproject.org>,
	"mingo@...nel.org" <mingo@...nel.org>,
	"rafael.j.wysocki@...el.com" <rafael.j.wysocki@...el.com>
Subject: Re: [PATCH 1/1] cpu-hotplug: export
 cpu_hotplug_enable/cpu_hotplug_disable

On Wed, 24 Jun 2015, Vitaly Kuznetsov wrote:

> Peter Zijlstra <peterz@...radead.org> writes:
> 
> > On Tue, Jun 23, 2015 at 04:57:05PM +0000, KY Srinivasan wrote:
> >
> >> > diff --git a/kernel/cpu.c b/kernel/cpu.c
> >> > index 94bbe46..8f35ee6 100644
> >> > --- a/kernel/cpu.c
> >> > +++ b/kernel/cpu.c
> >> > @@ -190,17 +190,19 @@ void cpu_hotplug_done(void)
> >> >  void cpu_hotplug_disable(void)
> >> >  {
> >> >  	cpu_maps_update_begin();
> >> > -	cpu_hotplug_disabled = 1;
> >> > +	cpu_hotplug_disabled++;
> >> >  	cpu_maps_update_done();
> >> >  }
> >> > +EXPORT_SYMBOL_GPL(cpu_hotplug_disable);
> >> > 
> >> >  void cpu_hotplug_enable(void)
> >> >  {
> >> >  	cpu_maps_update_begin();
> >> > -	cpu_hotplug_disabled = 0;
> >> > +	if (cpu_hotplug_disabled)
> >> > +		cpu_hotplug_disabled--;
> >
> > No that just papers over bugs.
> >
> 
> Yes, but these bugs are not in Linux. I don't see any other way for a
> platform to enable/disable cpu hotplug in runtime.

What? cpu_hotplug_disable()/enable() do that today. They just do not
support recursion and we have not yet seen any argument WHY that's
required at all.

Thanks,

	tglx
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