Re: Re: NULL pointer dereference in pick_next_task_fair

[Peter Zijlstra]

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.