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sched: Allow balance callbacks for check_class_changed()

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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>
Cc: ktkhai@parallels.com
Cc: rostedt@goodmis.org
Cc: juri.lelli@gmail.com
Cc: pang.xunlei@linaro.org
Cc: oleg@redhat.com
Cc: wanpeng.li@linux.intel.com
Link: http://lkml.kernel.org/r/20150611124742.615343911@infradead.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
This commit is contained in:
Peter Zijlstra 2015-06-11 14:46:39 +02:00 committed by Thomas Gleixner
parent dbc7f069b9
commit 4c9a4bc89a
1 changed files with 22 additions and 3 deletions
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25
kernel/sched/core.c
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@ -1001,7 +1001,11 @@ inline int task_curr(const struct task_struct *p)
}
/*
* 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(struct rq *rq, struct task_struct *p,
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);
@ -1491,8 +1495,12 @@ ttwu_do_wakeup(struct rq *rq, struct task_struct *p, int wake_flags)
p->state = TASK_RUNNING;
#ifdef CONFIG_SMP
if (p->sched_class->task_woken)
if (p->sched_class->task_woken) {
/*
* XXX can drop rq->lock; most likely ok.
*/
p->sched_class->task_woken(rq, p);
}
if (rq->idle_stamp) {
u64 delta = rq_clock(rq) - rq->idle_stamp;
@ -3100,7 +3108,11 @@ void rt_mutex_setprio(struct task_struct *p, int prio)
check_class_changed(rq, p, prev_class, oldprio);
out_unlock:
preempt_disable(); /* avoid rq from going away on us */
__task_rq_unlock(rq);
balance_callback(rq);
preempt_enable();
}
#endif
@ -3661,11 +3673,18 @@ change:
}
check_class_changed(rq, p, prev_class, oldprio);
preempt_disable(); /* avoid rq from going away on us */
task_rq_unlock(rq, p, &flags);
if (pi)
rt_mutex_adjust_pi(p);
/*
* Run balance callbacks after we've adjusted the PI chain.
*/
balance_callback(rq);
preempt_enable();
return 0;
}