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

Steven Rostedt
2017-05-16T19:12:41Z

On Tue, 16 May 2017 20:42:48 +0200
Thomas Gleixner <tglx@linutronix.de> 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 <tglx@linutronix.de>
> ---
> 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

My cat's version of CONFIG_PREEMPT, it's CONFIG_ PRR EMPT!

> + * 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?

-- Steve

> goto out;
>
> /*
>