On Mon, Jun 26, 2017 at 03:18:03PM -0700, Vikram Mulukutla wrote:
> kernel/kthread.c | 13 ++++++++++++-
> 1 file changed, 12 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/kthread.c b/kernel/kthread.c
> index 26db528..7ad3354 100644
> --- a/kernel/kthread.c
> +++ b/kernel/kthread.c
> @@ -171,9 +171,20 @@ static void __kthread_parkme(struct kthread *self)
> {
> __set_current_state(TASK_PARKED);
> while (test_bit(KTHREAD_SHOULD_PARK, &self->flags)) {
> + /*
> + * Why the preempt_disable?
> + * Hotplug needs to ensure that 'self' is off of the runqueue
> + * as well, before scheduling the stopper thread that will
> + * migrate tasks off of the runqeue that 'self' was running on.
> + * This avoids unnecessary migration work and also ensures that
> + * kthread_unpark in the cpu_up path doesn't race with
> + * __kthread_parkme.
> + */
> + preempt_disable();
> if (!test_and_set_bit(KTHREAD_IS_PARKED, &self->flags))
> complete(&self->parked);
> + schedule_preempt_disabled();
This is broken. schedule_preempt_disable() doesn't guarantee no
preemptions, just makes it less likely.
> + preempt_enable();
> __set_current_state(TASK_PARKED);
> }
> clear_bit(KTHREAD_IS_PARKED, &self->flags);