linux-kernel - RE: [PATCH] Fix the race between smp_call

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Date:	Mon, 19 Mar 2012 00:58:21 +0000
From:	"Liu, Chuansheng" <chuansheng.liu@...el.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Yanmin Zhang <yanmin_zhang@...ux.intel.com>,
	"tglx@...utronix.de" <tglx@...utronix.de>
Subject: RE: [PATCH] Fix the race between smp_call_function and CPU booting



> -----Original Message-----
> From: Peter Zijlstra [mailto:peterz@...radead.org]
> Sent: Friday, March 16, 2012 5:49 PM
> To: Liu, Chuansheng
> Cc: linux-kernel@...r.kernel.org; Yanmin Zhang; tglx@...utronix.de
> Subject: RE: [PATCH] Fix the race between smp_call_function and CPU booting
> 
> On Fri, 2012-03-16 at 06:24 +0000, Liu, Chuansheng wrote:
> 
> > Based on your patch, I did a little modification, how do you think of that?
> 
> > --- a/kernel/cpu.c
> > +++ b/kernel/cpu.c
> > @@ -640,8 +640,10 @@ void set_cpu_present(unsigned int cpu, bool
> > present)
> >
> >  void set_cpu_online(unsigned int cpu, bool online)  {
> > -       if (online)
> > +       if (online) {
> >                 cpumask_set_cpu(cpu, to_cpumask(cpu_online_bits));
> > +               cpumask_set_cpu(cpu, to_cpumask(cpu_active_bits));
> > +       }
> >         else
> >                 cpumask_clear_cpu(cpu, to_cpumask(cpu_online_bits));
> > }
> 
> I'm thinking this lacks rationale. What was wrong, Why does this fix it.
> If you can't answer that stop tinkering and start thinking.
Your patch advance the setting active bit before online setting, that will cause
an warning error, I just move the setting active bit after setting online setting, it can fix
the warning error, and it can fix the race issue between smp_call_function and CPU booting.

I have tested it by some stress tests.

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