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SubjectRe: [PATCH 4/5] sched/deadline: Cleanup on_dl_rq() handling
On Tue, Jul 30, 2019 at 08:41:15AM +0200, Juri Lelli wrote:
> On 29/07/19 18:49, Peter Zijlstra wrote:
> > On Fri, Jul 26, 2019 at 09:27:55AM +0100, Dietmar Eggemann wrote:
> > > Remove BUG_ON() in __enqueue_dl_entity() since there is already one in
> > > enqueue_dl_entity().
> > >
> > > Move the check that the dl_se is not on the dl_rq from
> > > __dequeue_dl_entity() to dequeue_dl_entity() to align with the enqueue
> > > side and use the on_dl_rq() helper function.
> > >
> > > Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
> > > ---
> > > kernel/sched/deadline.c | 8 +++-----
> > > 1 file changed, 3 insertions(+), 5 deletions(-)
> > >
> > > diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> > > index 1fa005f79307..a9cb52ceb761 100644
> > > --- a/kernel/sched/deadline.c
> > > +++ b/kernel/sched/deadline.c
> > > @@ -1407,8 +1407,6 @@ static void __enqueue_dl_entity(struct sched_dl_entity *dl_se)
> > > struct sched_dl_entity *entry;
> > > int leftmost = 1;
> > >
> > > - BUG_ON(!RB_EMPTY_NODE(&dl_se->rb_node));
> > > -
> > > while (*link) {
> > > parent = *link;
> > > entry = rb_entry(parent, struct sched_dl_entity, rb_node);
> > > @@ -1430,9 +1428,6 @@ static void __dequeue_dl_entity(struct sched_dl_entity *dl_se)
> > > {
> > > struct dl_rq *dl_rq = dl_rq_of_se(dl_se);
> > >
> > > - if (RB_EMPTY_NODE(&dl_se->rb_node))
> > > - return;
> > > -
> > > rb_erase_cached(&dl_se->rb_node, &dl_rq->root);
> > > RB_CLEAR_NODE(&dl_se->rb_node);
> > >
> > > @@ -1466,6 +1461,9 @@ enqueue_dl_entity(struct sched_dl_entity *dl_se,
> > >
> > > static void dequeue_dl_entity(struct sched_dl_entity *dl_se)
> > > {
> > > + if (!on_dl_rq(dl_se))
> > > + return;
> >
> > Why allow double dequeue instead of WARN?
>
> As I was saying to Valentin, it can currently happen that a task could
> have already been dequeued by update_curr_dl()->throttle called by
> dequeue_task_dl() before calling __dequeue_task_dl(). Do you think we
> should check for this condition before calling into dequeue_dl_entity()?

Yes, that's what ->dl_throttled is for, right? And !->dl_throttled &&
!on_dl_rq() is a BUG.

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