Messages in this thread | | | From | Kirill Tkhai <> | Subject | Re: [RFC][PATCH 3/7] sched: Allow balance callbacks for check_class_changed() | Date | Tue, 02 Jun 2015 16:58:34 +0300 |
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01.06.2015, 17:13, "Peter Zijlstra" <peterz@infradead.org>: > In order to remove dropping rq->lock from the > switched_{to,from}()/prio_changed() sched_class methods, run the > balance callbacks after it. > > We need to remove dropping rq->lock because its buggy, > suppose using sched_setattr()/sched_setscheduler() to change a running > task from FIFO to OTHER. > > By the time we get to switched_from_rt() the task is already enqueued > on the cfs runqueues. If switched_from_rt() does pull_rt_task() and > drops rq->lock, load-balancing can come in and move our task @p to > another rq. > > The subsequent switched_to_fair() still assumes @p is on @rq and bad > things will happen. > > By using balance callbacks we delay the load-balancing operations > {rt,dl}x{push,pull} until we've done all the important work and the > task is fully set up. > > Furthermore, the balance callbacks do not know about @p, therefore > they cannot get confused like this. > > Reported-by: Mike Galbraith <umgwanakikbuti@gmail.com> > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> > --- > kernel/sched/core.c | 25 ++++++++++++++++++++++--- > 1 file changed, 22 insertions(+), 3 deletions(-) > > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -1001,7 +1001,11 @@ inline int task_curr(const struct task_s > } > > /* > - * Can drop rq->lock because from sched_class::switched_from() methods drop it. > + * switched_from, switched_to and prio_changed must _NOT_ drop rq->lock, > + * use the balance_callback list if you want balancing. > + * > + * this means any call to check_class_changed() must be followed by a call to > + * balance_callback(). > */ > static inline void check_class_changed(struct rq *rq, struct task_struct *p, > const struct sched_class *prev_class, > @@ -1010,7 +1014,7 @@ 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'. */ > +
But switched_from_dl()->cancel_dl_timer() still unlocks rq->lock.
It seems we should drop it (cancel_dl_timer) and move hrtimer_cancel() from switched_from_dl() to finish_task_switch(). It will be executed for all classes and completely take the functionality we implement cancel_dl_timer() for.
> p->sched_class->switched_to(rq, p); > } else if (oldprio != p->prio || dl_task(p)) > p->sched_class->prio_changed(rq, p, oldprio);
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