Re: NULL pointer dereference in pick_next_task_fair

[Peter Zijlstra]

On Thu, Nov 07, 2019 at 06:12:07PM +0300, Kirill Tkhai wrote:
> On 07.11.2019 16:26, Peter Zijlstra wrote:

> > Urgh... throttling.

> One more thing about current code in git. After rq->lock became able to
> be unlocked after put_prev_task() is commited, we got a new corner case.
> We usually had the same order for running task:
> 
>   dequeue_task()
>   put_prev_task()
> 
> Now the order may be reversed (this is also in case of throttling):
> 
>   put_prev_task() (called from pick_next_task())
>   dequeue_task()  (called from another cpu)
> 
> This is more theoretically, since I don't see a problem here. But there are
> too many statistics and counters in sched_class methods, that it is impossible
> to be sure all of them work as expected.

Hmm,.. where does throttling happen on a remote CPU? I through both
cfs-bandwidth and dl throttle locally.

Or are you talking about NO_HZ_FULL's sched_remote_tick() ?