[Devel] [PATCH RHEL7 COMMIT] sched: add WARN_ON's to debug task boosting

[Konstantin Khorenko]

The commit is pushed to "branch-rh7-3.10.0-327.22.2.vz7.16.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-327.22.2.vz7.16.4
------>
commit 1894f10ee1c3fb7c8bfdf46c226d05c3f65e90de
Author: Vladimir Davydov <vdavydov at virtuozzo.com>
Date:   Wed Aug 10 18:40:01 2016 +0400

    sched: add WARN_ON's to debug task boosting
    
    This patch ports
    
    * diff-sched-add-WARN_ONs-to-debug-task-boosting
    Added to 042stab114_2
    
    Assert that we never have a boosted entity under a throttled hierarchy.
    Also, do not panic if on set_next_entity we find a boosted entity being
    not on the list - just warn and carry on as if nothing happened.
    
    https://jira.sw.ru/browse/PSBM-44475
    https://jira.sw.ru/browse/PSBM-50077
    
    Signed-off-by: Vladimir Davydov <vdavydov at virtuozzo.com>
    Reviewed-by: Kirill Tkhai <ktkhai at virtuozzo.com>
---
 kernel/sched/fair.c | 22 +++++++++++++++++-----
 1 file changed, 17 insertions(+), 5 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index a87bacf..4cebf60 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -909,9 +909,10 @@ update_stats_curr_start(struct cfs_rq *cfs_rq, struct sched_entity *se)
 #ifdef CONFIG_CFS_BANDWIDTH
 static inline void update_entity_boost(struct sched_entity *se)
 {
-	if (!entity_is_task(se))
+	if (!entity_is_task(se)) {
 		se->boosted = cfs_rq_has_boosted_entities(group_cfs_rq(se));
-	else {
+		WARN_ON(se->boosted && cfs_rq_throttled(group_cfs_rq(se)));
+	} else {
 		struct task_struct *p = task_of(se);
 
 		if (unlikely(p != current))
@@ -943,6 +944,8 @@ static inline void __enqueue_boosted_entity(struct cfs_rq *cfs_rq,
 static inline void __dequeue_boosted_entity(struct cfs_rq *cfs_rq,
 					    struct sched_entity *se)
 {
+	if (WARN_ON(se->boost_node.next == LIST_POISON1))
+		return;
 	list_del(&se->boost_node);
 }
 
@@ -953,8 +956,11 @@ static int enqueue_boosted_entity(struct cfs_rq *cfs_rq,
 		if (se != cfs_rq->curr)
 			__enqueue_boosted_entity(cfs_rq, se);
 		se->boosted = 1;
+		WARN_ON(!entity_is_task(se) &&
+			cfs_rq_throttled(group_cfs_rq(se)));
 		return 1;
-	}
+	} else
+		WARN_ON(cfs_rq_throttled(group_cfs_rq(se)));
 
 	return 0;
 }
@@ -3847,6 +3853,8 @@ static void do_sched_cfs_slack_timer(struct cfs_bandwidth *cfs_b)
  */
 static void check_enqueue_throttle(struct cfs_rq *cfs_rq)
 {
+	WARN_ON(cfs_rq_has_boosted_entities(cfs_rq));
+
 	if (!cfs_bandwidth_used())
 		return;
 
@@ -4170,8 +4178,10 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags)
 	} else if (boost) {
 		for_each_sched_entity(se) {
 			cfs_rq = cfs_rq_of(se);
-			if (!enqueue_boosted_entity(cfs_rq, se))
+			if (!enqueue_boosted_entity(cfs_rq, se)) {
+				WARN_ON(throttled_hierarchy(cfs_rq));
 				break;
+			}
 			if (cfs_rq_throttled(cfs_rq))
 				unthrottle_cfs_rq(cfs_rq);
 		}
@@ -4232,8 +4242,10 @@ static void dequeue_task_fair(struct rq *rq, struct task_struct *p, int flags)
 		cfs_rq = cfs_rq_of(se);
 		cfs_rq->h_nr_running--;
 
-		if (cfs_rq_throttled(cfs_rq))
+		if (cfs_rq_throttled(cfs_rq)) {
+			WARN_ON(boosted);
 			break;
+		}
 
 		if (boosted)
 			boosted = dequeue_boosted_entity(cfs_rq, se);