Re: Re: NULL pointer dereference in pick_next_task_fair

Peter Zijlstra
2019-11-06T16:54:55Z

On Wed, Nov 06, 2019 at 06:51:40PM +0300, Kirill Tkhai wrote:
> > +#ifdef CONFIG_SMP
> > + if (!rq->nr_running) {
> > + /*
> > + * Make sure task_on_rq_curr() fails, such that we don't do
> > + * put_prev_task() + set_next_task() on this task again.
> > + */
> > + prev->on_cpu = 2;
> > newidle_balance(rq, rf);
>
> Shouldn't we restore prev->on_cpu = 1 after newidle_balance()? Can't prev
> become pickable again after newidle_balance() releases rq->lock, and we
> take it again, so this on_cpu == 2 never will be cleared?

Indeed so.