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nohz/full, sched/rt: Fix missed tick-reenabling bug in dequeue_task_rt()

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[ Upstream commit 5c66d1b9b3 ]

dequeue_task_rt() only decrements 'rt_rq->rt_nr_running' after having
called sched_update_tick_dependency() preventing it from re-enabling the
tick on systems that no longer have pending SCHED_RT tasks but have
multiple runnable SCHED_OTHER tasks:

  dequeue_task_rt()
    dequeue_rt_entity()
      dequeue_rt_stack()
        dequeue_top_rt_rq()
	  sub_nr_running()	// decrements rq->nr_running
	    sched_update_tick_dependency()
	      sched_can_stop_tick()	// checks rq->rt.rt_nr_running,
	      ...
        __dequeue_rt_entity()
          dec_rt_tasks()	// decrements rq->rt.rt_nr_running
	  ...

Every other scheduler class performs the operation in the opposite
order, and sched_update_tick_dependency() expects the values to be
updated as such. So avoid the misbehaviour by inverting the order in
which the above operations are performed in the RT scheduler.

Fixes: 76d92ac305 ("sched: Migrate sched to use new tick dependency mask model")
Signed-off-by: Nicolas Saenz Julienne <nsaenzju@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Valentin Schneider <vschneid@redhat.com>
Reviewed-by: Phil Auld <pauld@redhat.com>
Link: https://lore.kernel.org/r/20220628092259.330171-1-nsaenzju@redhat.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Nicolas Saenz Julienne 2022-06-28 11:22:59 +02:00 committed by Greg Kroah-Hartman
parent 298417471e
commit e06a31e61f
1 changed files with 9 additions and 6 deletions
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15
kernel/sched/rt.c
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@ -437,7 +437,7 @@ static inline void rt_queue_push_tasks(struct rq *rq)
#endif /* CONFIG_SMP */
static void enqueue_top_rt_rq(struct rt_rq *rt_rq);
static void dequeue_top_rt_rq(struct rt_rq *rt_rq);
static void dequeue_top_rt_rq(struct rt_rq *rt_rq, unsigned int count);
static inline int on_rt_rq(struct sched_rt_entity *rt_se)
{
@ -558,7 +558,7 @@ static void sched_rt_rq_dequeue(struct rt_rq *rt_rq)
rt_se = rt_rq->tg->rt_se[cpu];
if (!rt_se) {
dequeue_top_rt_rq(rt_rq);
dequeue_top_rt_rq(rt_rq, rt_rq->rt_nr_running);
/* Kick cpufreq (see the comment in kernel/sched/sched.h). */
cpufreq_update_util(rq_of_rt_rq(rt_rq), 0);
}
@ -644,7 +644,7 @@ static inline void sched_rt_rq_enqueue(struct rt_rq *rt_rq)
static inline void sched_rt_rq_dequeue(struct rt_rq *rt_rq)
{
dequeue_top_rt_rq(rt_rq);
dequeue_top_rt_rq(rt_rq, rt_rq->rt_nr_running);
}
static inline int rt_rq_throttled(struct rt_rq *rt_rq)
@ -1043,7 +1043,7 @@ static void update_curr_rt(struct rq *rq)
}
static void
dequeue_top_rt_rq(struct rt_rq *rt_rq)
dequeue_top_rt_rq(struct rt_rq *rt_rq, unsigned int count)
{
struct rq *rq = rq_of_rt_rq(rt_rq);
@ -1054,7 +1054,7 @@ dequeue_top_rt_rq(struct rt_rq *rt_rq)
BUG_ON(!rq->nr_running);
sub_nr_running(rq, rt_rq->rt_nr_running);
sub_nr_running(rq, count);
rt_rq->rt_queued = 0;
}
@ -1333,18 +1333,21 @@ static void __dequeue_rt_entity(struct sched_rt_entity *rt_se, unsigned int flag
static void dequeue_rt_stack(struct sched_rt_entity *rt_se, unsigned int flags)
{
struct sched_rt_entity *back = NULL;
unsigned int rt_nr_running;
for_each_sched_rt_entity(rt_se) {
rt_se->back = back;
back = rt_se;
}
dequeue_top_rt_rq(rt_rq_of_se(back));
rt_nr_running = rt_rq_of_se(back)->rt_nr_running;
for (rt_se = back; rt_se; rt_se = rt_se->back) {
if (on_rt_rq(rt_se))
__dequeue_rt_entity(rt_se, flags);
}
dequeue_top_rt_rq(rt_rq_of_se(back), rt_nr_running);
}
static void enqueue_rt_entity(struct sched_rt_entity *rt_se, unsigned int flags)