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

[Wanpeng Li]

Hi Konstantin, Xunlei,
2016-07-11 16:42 GMT+08:00 Xunlei Pang <xpang@xxxxxxxxxx>:
> On 2016/07/11 at 16:22, Xunlei Pang wrote:
>> On 2016/07/11 at 15:25, 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?
>> I guess it's the following code leading to a NULL se returned:
>
> s/NULL/empty-entity cfs_rq se/
>
>> pick_next_entity():
>>     if (cfs_rq->next && wakeup_preempt_entity(cfs_rq->next, left) < 1)
            ^^^^^^^^^^^^^
I think this will return false.

Regards,
Wanpeng Li