[PATCH v2] sched: fix first task of a task group is attached twice

[Vincent Guittot <vincent.guittot@linaro.org>]

The cfs_rq->avg.last_update_time is initialize to 0 with the main effect
that the 1st sched_entity that will be attached, will keep its
last_update_time set to 0 and will attached once again during the
enqueue.
Initialize cfs_rq->avg.last_update_time to 1 instead.

Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
---

v2:
- rq_clock_task(rq_of(cfs_rq)) can't be used because lock is not held

 kernel/sched/fair.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 218f8e8..3724656 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -8586,6 +8586,14 @@ void init_tg_cfs_entry(struct task_group *tg, struct cfs_rq *cfs_rq,
 		se->depth = parent->depth + 1;
 	}
 
+	/*
+	 * Set last_update_time to something different from 0 to make
+	 * sure the 1st sched_entity will not be attached twice: once
+	 * when attaching the task to the group and one more time when
+	 * enqueueing the task.
+	 */
+	tg->cfs_rq[cpu]->avg.last_update_time = 1;
+
 	se->my_q = cfs_rq;
 	/* guarantee group entities always have weight */
 	update_load_set(&se->load, NICE_0_LOAD);
-- 
1.9.1