linux-kernel - Re: [patch 17/18] sched: Enable might

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Message-ID: <20170515111008.1215e489@gandalf.local.home>
Date:   Mon, 15 May 2017 11:10:08 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Thomas Gleixner <tglx@...utronix.de>
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 17/18] sched: Enable might_sleep() checks early

On Sun, 14 May 2017 20:27:33 +0200
Thomas Gleixner <tglx@...utronix.de> wrote:

> might_sleep() checks are enabled after the boot process is done. That hides
> bugs in the smp bringup and driver initialization code.
> 
> Enable it right when the scheduler starts working, i.e. when init task and
> kthreadd have been created and right before the idle task enables
> preemption.

Looking at commit b433c3d4549ae749, it appears that on very slow
machines, there is a possibility that the init task can start running.
Should system_state be updated before that complete() is called?

-- Steve

> 
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> ---
>  init/main.c         |    2 ++
>  kernel/sched/core.c |    4 +++-
>  2 files changed, 5 insertions(+), 1 deletion(-)
> 
> --- a/init/main.c
> +++ b/init/main.c
> @@ -410,6 +410,8 @@ static noinline void __ref rest_init(voi
>  	 * at least once to get things moving:
>  	 */
>  	init_idle_bootup_task(current);
> +	/* Enable might_sleep() checks */
> +	system_state = SYSTEM_BOOTING_UP;
>  	schedule_preempt_disabled();
>  	/* Call into cpu_idle with preempt disabled */
>  	cpu_startup_entry(CPUHP_ONLINE);
> --- 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;
>