linux-kernel - Re: [patch V2 17/17] sched: Enable might_sleep() and smp_processor

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Date:   Wed, 17 May 2017 00:46:37 +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>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [patch V2 17/17] sched: Enable might_sleep() and smp_processor_id()
 checks early

On Tue, 16 May 2017, Steven Rostedt wrote:
> On Tue, 16 May 2017 20:42:48 +0200
> Thomas Gleixner <tglx@...utronix.de> wrote:
> > +
> > +	/*
> > +	 * Enable might_sleep() and smp_processor_id() checks.
> > +	 * They cannot be enabled earlier because with CONFIG_PRREMPT=y
> 
> My cat's version of CONFIG_PREEMPT, it's CONFIG_ PRR EMPT!

I don't have a cat and I don't need one for creating typos. I'm perfectly
able to do that myself :)

> > +	 * kernel_thread() would trigger might_sleep() splats. With
> > +	 * CONFIG_PREEMPT_VOLUNTARY=y the init task might have scheduled
> > +	 * already, but it's stuck on the kthreadd_done completion.
> > +	 */
> > +	system_state = SYSTEM_SCHEDULING;
> > +
> >  	complete(&kthreadd_done);
> >  
> >  	/*
> > --- a/kernel/sched/core.c
> > +++ b/kernel/sched/core.c
> > @@ -6226,8 +6226,10 @@ void ___might_sleep(const char *file, in
> >  
> >  	if ((preempt_count_equals(preempt_offset) && !irqs_disabled() &&
> >  	     !is_idle_task(current)) ||
> > -	    system_state != SYSTEM_RUNNING || oops_in_progress)
> > +	    system_state == SYSTEM_BOOTING || system_state > SYSTEM_RUNNING ||
> > +	    oops_in_progress)
> >  		return;
> > +
> >  	if (time_before(jiffies, prev_jiffy + HZ) && prev_jiffy)
> >  		return;
> >  	prev_jiffy = jiffies;
> > --- a/lib/smp_processor_id.c
> > +++ b/lib/smp_processor_id.c
> > @@ -28,7 +28,7 @@ notrace static unsigned int check_preemp
> >  	/*
> >  	 * It is valid to assume CPU-locality during early bootup:
> >  	 */
> > -	if (system_state != SYSTEM_RUNNING)
> > +	if (system_state < SYSTEM_SCHEDULING)
> 
> Do we want to ignore halting or rebooting too?

I don't think so. After setting those states, interesting stuff like
device_shutdown() gets invoked. We want the coverage there.

Thanks,

	tglx