1)Single cpu machine case.
When rq has only RT tasks, but no one of them can be picked
because of throttling, we enter in endless loop.
pick_next_task_{dl,rt} return NULL.
In pick_next_task_fair() we permanently go to retry
if (rq->nr_running != rq->cfs.h_nr_running)
return RETRY_TASK;
(rq->nr_running is not being decremented when rt_rq becomes
throttled).
No chances to unthrottle any rt_rq or to wake fair here,
because of rq is locked permanently and interrupts are
disabled.
2)In case of SMP this can cause a hang too. Although we unlock
rq in idle_balance(), interrupts are still disabled.
The solution is to check for available tasks in DL and RT
classes instead of checking for sum.
Signed-off-by: Kirill Tkhai <ktk...@parallels.com>
CC: Peter Zijlstra <pet...@infradead.org>
CC: Ingo Molnar <mi...@redhat.com>
---
kernel/sched/fair.c | 4 +++-
kernel/sched/rt.c | 10 ----------
kernel/sched/sched.h | 12 ++++++++++++
3 files changed, 15 insertions(+), 11 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index b956e70..10db4a8 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6728,7 +6728,9 @@ static int idle_balance(struct rq *this_rq)
out:
/* Is there a task of a high priority class? */
- if (this_rq->nr_running != this_rq->cfs.h_nr_running)
+ if (this_rq->nr_running != this_rq->cfs.h_nr_running &&
+ (this_rq->dl.dl_nr_running ||
+ (this_rq->rt.rt_nr_running && !rt_rq_throttled(&this_rq->rt))))
pulled_task = -1;
if (pulled_task) {
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index f3cee0a..d8cdf16 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -470,11 +470,6 @@ static void sched_rt_rq_dequeue(struct rt_rq *rt_rq)
dequeue_rt_entity(rt_se);
}
-static inline int rt_rq_throttled(struct rt_rq *rt_rq)
-{
- return rt_rq->rt_throttled && !rt_rq->rt_nr_boosted;
-}
-
static int rt_se_boosted(struct sched_rt_entity *rt_se)
{
struct rt_rq *rt_rq = group_rt_rq(rt_se);
@@ -545,11 +540,6 @@ static inline void sched_rt_rq_dequeue(struct rt_rq *rt_rq)
{
}
-static inline int rt_rq_throttled(struct rt_rq *rt_rq)
-{
- return rt_rq->rt_throttled;
-}
-
static inline const struct cpumask *sched_rt_period_mask(void)
{
return cpu_online_mask;
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 378bff7..f2de7a1 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -423,6 +423,18 @@ struct rt_rq {
#endif
};
+#ifdef CONFIG_RT_GROUP_SCHED
+static inline int rt_rq_throttled(struct rt_rq *rt_rq)
+{
+ return rt_rq->rt_throttled && !rt_rq->rt_nr_boosted;
+}
+#else
+static inline int rt_rq_throttled(struct rt_rq *rt_rq)
+{
+ return rt_rq->rt_throttled;
+}
+#endif
+
/* Deadline class' related fields in a runqueue */
struct dl_rq {
/* runqueue is an rbtree, ordered by deadline */
--
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