Re: [patch V2 17/17] sched: Enable might_sleep() and smp_processor_id() checks early

[Mark Rutland]

On Tue, May 16, 2017 at 08:42:48PM +0200, Thomas Gleixner wrote:
> might_sleep() and 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 when the scheduler starts working, i.e. when init task and
> kthreadd have been created and right before the idle task enables
> preemption.
> 
> Signed-off-by: Thomas Gleixner <t...@linutronix.de>

Modulo Steve's comments, FWIW:

Acked-by: Mark Rutland <mark.rutl...@arm.com>

Mark.

> ---
>  init/main.c            |   10 ++++++++++
>  kernel/sched/core.c    |    4 +++-
>  lib/smp_processor_id.c |    2 +-
>  3 files changed, 14 insertions(+), 2 deletions(-)
> 
> --- a/init/main.c
> +++ b/init/main.c
> @@ -414,6 +414,16 @@ static noinline void __ref rest_init(voi
>       rcu_read_lock();
>       kthreadd_task = find_task_by_pid_ns(pid, &init_pid_ns);
>       rcu_read_unlock();
> +
> +     /*
> +      * Enable might_sleep() and smp_processor_id() checks.
> +      * They cannot be enabled earlier because with CONFIG_PRREMPT=y
> +      * 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)
>               goto out;
>  
>       /*
> 
>