Re: [PATCH] sched/fair: do not announce throttled next buddy in dequeue_task_fair

[Konstantin Khlebnikov]

On 11.07.2016 10:25, Wanpeng Li wrote:
> 2016-06-16 20:57 GMT+08:00 Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx>:
> > Hierarchy could be already throttled at this point. Throttled next
> > buddy could trigger null pointer dereference in pick_next_task_fair().
>
> There is cfs_rq->next check in pick_next_entity(), so how can null
> pointer dereference happen?

If we nominate task from throttled hiearchy as a next buddy then at some
level in pick_next_task_fair we could pick cfs_rq which has no runnable
entities - in pick_next_entiry both "curr" and "left" are NULL.

--
Konstantin