Re: NULL pointer dereference in pick_next_task_fair

Peter Zijlstra
2019-11-08T12:52:25Z

On Fri, Nov 08, 2019 at 12:55:57PM +0100, Peter Zijlstra wrote:
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -3929,13 +3929,14 @@ pick_next_task(struct rq *rq, struct tas
> }
>
> restart:
> - /*
> - * Ensure that we put DL/RT tasks before the pick loop, such that they
> - * can PULL higher prio tasks when we lower the RQ 'priority'.
> - */
> - prev->sched_class->put_prev_task(rq, prev, rf);
> - if (!rq->nr_running)
> - newidle_balance(rq, rf);
> +#ifdef CONFIG_SMP
/*
* We must do the balancing pass before put_next_task(), such
* that when we release the rq->lock the task is in the same
* state as before we took rq->lock.
*
* We can terminate the balance pass as soon as we know there is
* a runnable task of @class priority or higher.
*/
> + for_class_range(class, prev->sched_class, &idle_sched_class) {
> + if (class->balance(rq, prev, rf))
> + break;
> + }
> +#endif
> +
> + put_prev_task(rq, prev);
>
> for_each_class(class) {
> p = class->pick_next_task(rq, NULL, NULL);