Re: [patch 17/18] sched: Enable might_sleep() checks early

Steven Rostedt
2017-05-15T15:10:13Z

On Sun, 14 May 2017 20:27:33 +0200
Thomas Gleixner <tglx@linutronix.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@linutronix.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;
>