Hi Kirill,
On 27/09/14 09:40, Kirill Tkhai wrote:
> From: Kirill Tkhai <ktk...@parallels.com>
>
> hrtimer_try_to_cancel() may bring a suprise, and even two its calls
> may fail.
>
> So, let's implement 100% guaranteed way to cancel the timer and let's
> be sure we are safe even in very unlikely situations.
>
Could you give more details about the unlikely situations in the
changelog? It would be nice to have some more information for future
reference.
Thanks,
- Juri
> We do not create any problem with rq unlocking, because it already
> may happed below in pull_dl_task(). No problem with deadline tasks
> balancing too.
>
> Signed-off-by: Kirill Tkhai <ktk...@parallels.com>
> ---
> kernel/sched/deadline.c | 33 ++++++++++++++++++++++++++-------
> 1 file changed, 26 insertions(+), 7 deletions(-)
>
> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> index abfaf3d..63f8b4a 100644
> --- a/kernel/sched/deadline.c
> +++ b/kernel/sched/deadline.c
> @@ -555,11 +555,6 @@ void init_dl_task_timer(struct sched_dl_entity *dl_se)
> {
> struct hrtimer *timer = &dl_se->dl_timer;
>
> - if (hrtimer_active(timer)) {
> - hrtimer_try_to_cancel(timer);
> - return;
> - }
> -
> hrtimer_init(timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
> timer->function = dl_task_timer;
> }
> @@ -1567,10 +1562,34 @@ void init_sched_dl_class(void)
>
> #endif /* CONFIG_SMP */
>
> +/*
> + * Surely cancel task's dl_timer. May drop rq->lock.
> + */
> +static void cancel_dl_timer(struct rq *rq, struct task_struct *p)
> +{
> + struct hrtimer *dl_timer = &p->dl.dl_timer;
> +
> + /* Nobody will change task's class if pi_lock is held */
> + lockdep_assert_held(&p->pi_lock);
> +
> + if (hrtimer_active(dl_timer)) {
> + int ret = hrtimer_try_to_cancel(dl_timer);
> +
> + if (unlikely(ret == -1)) {
> + /*
> + * Note, p may migrate OR new deadline tasks
> + * may appear in rq when we are unlocking it.
> + */
> + raw_spin_unlock(&rq->lock);
> + hrtimer_cancel(dl_timer);
> + raw_spin_lock(&rq->lock);
> + }
> + }
> +}
> +
> static void switched_from_dl(struct rq *rq, struct task_struct *p)
> {
> - if (hrtimer_active(&p->dl.dl_timer) && !dl_policy(p->policy))
> - hrtimer_try_to_cancel(&p->dl.dl_timer);
> + cancel_dl_timer(rq, p);
>
> __dl_clear_params(p);
>
>
>
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