linux-kernel - Re: [patch 18/18] sched: Enable smp_processor

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Date:   Mon, 15 May 2017 17:36:29 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Steven Rostedt <rostedt@...dmis.org>
cc:     LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Mark Rutland <mark.rutland@....com>
Subject: Re: [patch 18/18] sched: Enable smp_processor_id() checks early

On Mon, 15 May 2017, Steven Rostedt wrote:

> On Sun, 14 May 2017 20:27:34 +0200
> Thomas Gleixner <tglx@...utronix.de> wrote:
> 
> > smp_processor_id() checks are enabled after the boot process is done. That
> > hides bugs in the smp bringup and driver initialization code.
> > 
> > Enable it right before the first non-boot CPU is brought up.
> > 
> > Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> > ---
> >  init/main.c            |    3 +++
> >  lib/smp_processor_id.c |    2 +-
> >  2 files changed, 4 insertions(+), 1 deletion(-)
> > 
> > 
> > Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> > ---
> >  init/main.c            |    3 +++
> >  lib/smp_processor_id.c |    2 +-
> >  2 files changed, 4 insertions(+), 1 deletion(-)
> > 
> > --- a/init/main.c
> > +++ b/init/main.c
> > @@ -1025,6 +1025,9 @@ static noinline void __init kernel_init_
> >  	 */
> >  	set_cpus_allowed_ptr(current, cpumask_of(raw_smp_processor_id()));
> >  
> > +	/* Enable smp_processor_id() checks */
> > +	system_state = SYSTEM_BOOTING_SMP;
> > +
> 
> Just a nit, but why set this here and not just before
> smp_prepare_cpus()? Anyway...

Because smp_prepare_cpus() is full of "UP" assumptions. Thinking more about
it, we just can set the cpus allowed ptr right after creating it and just
have a single state which enables both checks. I'll have a look.

Thanks,

	tglx