On Mon, Oct 27, 2014 at 05:40:52PM +0300, Kirill Tkhai wrote:
> +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.
> + * A caller of us must be fine with that.
> + */
> + 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)
> {
> + cancel_dl_timer(rq, p);
>
> __dl_clear_params(p);
>
I added the below comments; just to make sure we all remember this...
---
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1008,6 +1008,9 @@ inline int task_curr(const struct task_s
return cpu_curr(task_cpu(p)) == p;
}
+/*
+ * Can drop rq->lock because from sched_class::switched_from() methods drop it.
+ */
static inline void check_class_changed(struct rq *rq, struct task_struct *p,
const struct sched_class *prev_class,
int oldprio)
@@ -1015,6 +1018,7 @@ static inline void check_class_changed(s
if (prev_class != p->sched_class) {
if (prev_class->switched_from)
prev_class->switched_from(rq, p);
+ /* Possble rq->lock 'hole'. */
p->sched_class->switched_to(rq, p);
} else if (oldprio != p->prio || dl_task(p))
p->sched_class->prio_changed(rq, p, oldprio);
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1157,6 +1157,11 @@ struct sched_class {
void (*task_fork) (struct task_struct *p);
void (*task_dead) (struct task_struct *p);
+ /*
+ * The switched_from() call is allowed to drop rq->lock, therefore we
+ * cannot assume the switched_from/switched_to pair is serliazed by
+ * rq->lock. They are however serialized by p->pi_lock.
+ */
void (*switched_from) (struct rq *this_rq, struct task_struct *task);
void (*switched_to) (struct rq *this_rq, struct task_struct *task);
void (*prio_changed) (struct rq *this_rq, struct task_struct *task,
--
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