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SubjectRe: [PATCH v2 4/7] sched/deadline: reschedule if stop task slip in after pull operations
On Wed, May 13, 2015 at 02:01:04PM +0800, Wanpeng Li wrote:
> pull_dl_task can drop (and re-acquire) rq->lock, this means a stop task
> can slip in, in which case we need to reschedule. This patch add the
> reschedule when the scenario occurs.
>
> Signed-off-by: Wanpeng Li <wanpeng.li@linux.intel.com>
> ---
> kernel/sched/deadline.c | 16 +++++++++++++++-
> 1 file changed, 15 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> index e49b1e6..7d4c4fc 100644
> --- a/kernel/sched/deadline.c
> +++ b/kernel/sched/deadline.c
> @@ -1750,7 +1750,13 @@ static void switched_from_dl(struct rq *rq, struct task_struct *p)
> if (!task_on_rq_queued(p) || rq->dl.dl_nr_running)
> return;
>
> - if (pull_dl_task(rq))
> + /*
> + * pull_dl_task() can drop (and re-acquire) rq->lock; this
> + * means a stop task can slip in, in which case we need to
> + * reschedule.
> + */
> + if (pull_dl_task(rq) ||
> + (rq->stop && task_on_rq_queued(rq->stop)))
> resched_curr(rq);

But, the waking of the stop task will already have done the preemption
check and won (obviously). So the wakeup should already have done the
resched_curr().

So why?



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