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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20150624102733.GK3644@twins.programming.kicks-ass.net>
Date:	Wed, 24 Jun 2015 12:27:33 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:	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>,
	"tglx@...utronix.de" <tglx@...utronix.de>
Subject: Re: [PATCH  1/1] cpu-hotplug: export
 cpu_hotplug_enable/cpu_hotplug_disable

On Wed, Jun 24, 2015 at 11:43:33AM +0200, 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.

Any code using this had better be open source, if not I really don't
care anyway.

That really ought to be:

	WARN_ON(--cpu_hotplug_disabled < 0);

You do not make underflows go away.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/