On Tue, Jul 04, 2017 at 09:27:07AM +0200, Peter Zijlstra wrote: > 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 ?
Hmm,.. could you give a little more detail? Because if ->on_rq=0, we'll have done dequeue_task() which will have done update_curr() with ->on_rq, weight and ->running consistently. Then the above, inconsistent update should not happen, because delta=0.
