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SubjectRe: [PATCH] sched/fair: do not announce throttled next buddy in dequeue_task_fair
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Konstantin Khlebnikov <khlebnikov@yandex-team.ru> writes:

> Hierarchy could be already throttled at this point. Throttled next
> buddy could trigger null pointer dereference in pick_next_task_fair().
>
> Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>

Reviewed-by: Ben Segall <bsegall@google.com>

> Cc: Stable <stable@vger.kernel.org> # v3.2+
> ---
> kernel/sched/fair.c | 9 ++++-----
> 1 file changed, 4 insertions(+), 5 deletions(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index fe809fe169d2..3c6b038cb734 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -4519,15 +4519,14 @@ static void dequeue_task_fair(struct rq *rq, struct task_struct *p, int flags)
>
> /* Don't dequeue parent if it has other entities besides us */
> if (cfs_rq->load.weight) {
> + /* avoid re-evaluating load for this entity */
> + se = parent_entity(se);
> /*
> * Bias pick_next to pick a task from this cfs_rq, as
> * p is sleeping when it is within its sched_slice.
> */
> - if (task_sleep && parent_entity(se))
> - set_next_buddy(parent_entity(se));
> -
> - /* avoid re-evaluating load for this entity */
> - se = parent_entity(se);
> + if (task_sleep && se && !throttled_hierarchy(cfs_rq))
> + set_next_buddy(se);
> break;
> }
> flags |= DEQUEUE_SLEEP;

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