linux-kernel - Re: [PATCH] [x86, msr]: remove code duplication

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Message-ID: <20090707103723.GD5668@aftab>
Date:	Tue, 7 Jul 2009 12:37:23 +0200
From:	Borislav Petkov <borislav.petkov@....com>
To:	"H. Peter Anvin" <hpa@...or.com>
CC:	x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] [x86, msr]: remove code duplication

On Mon, Jul 06, 2009 at 02:31:36PM -0700, H. Peter Anvin wrote:
> Borislav Petkov wrote:
> > -
> > -	smp_call_function_many(mask, __rdmsr_on_cpu, &rv, 1);
> > +	smp_call_function_single(this_cpu, msr_func, &rv, 1);
> > +	smp_call_function_many(mask, msr_func, &rv, 1);
> >  	preempt_enable();
> 
> Why are you using smp_call_function_single() to execute something *on
> your own CPU*?

Actually, the more important question is why am I executing anything on
my own CPU without first checking if it is in the cpumask _at_ _all_?!
/me ducks behind the sofa.

The right thing to do should be something like the following:

preempt_disable();
this_cpu = raw_smp_processor_id();

if (cpumask_test_cpu(this_cpu, mask)) {
	local_irq_disable();
	msr_func(&rv);
	local_irq_enable();
}

smp_call_function_many(mask, msr_func, &rv, 1);
preempt_enable();

Patch coming up...

-- 
Regards/Gruss,
Boris.

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