Re: [PATCH v2] sched/pelt: fix false running accounting

From: Peter Zijlstra
Date: Tue Jul 04 2017 - 03:27:17 EST

On Sat, Jul 01, 2017 at 07:06:13AM +0200, Vincent Guittot wrote:
> The running state is a subset of runnable state which means that running
> can't be set if runnable (weight) is cleared. There are corner cases
> where the current sched_entity has been already dequeued but cfs_rq->curr
> has not been updated yet and still points to the dequeued sched_entity.
> If ___update_load_avg is called at that time, weight will be 0 and running
> will be set which is not possible.
> This case happens during pick_next_task_fair() when a cfs_rq becomes idles.
> The current sched_entity has been dequeued so se->on_rq is cleared and
> cfs_rq->weight is null. But cfs_rq->curr still points to se (it will be
> cleared when picking the idle thread). Because the cfs_rq becomes idle,
> idle_balance() is called and ends up to call update_blocked_averages()
> with these wrong running and runnable states.
> Add a test in ___update_load_avg to correct the running state in this case.

Cute, however did you find that ?