blob: 753fea50c00c2b7687f15f9074e51e05ce5d37a2 [file] [log] [blame]
From 9f606b627f6be0a88302fa42425bf568293463a7 Mon Sep 17 00:00:00 2001
From: Vincent Guittot <>
Date: Tue, 14 Jan 2020 15:13:56 +0100
Subject: [PATCH] sched/fair: Prevent unlimited runtime on throttled group
commit 2a4b03ffc69f2dedc6388e9a6438b5f4c133a40d upstream.
When a running task is moved on a throttled task group and there is no
other task enqueued on the CPU, the task can keep running using 100% CPU
whatever the allocated bandwidth for the group and although its cfs rq is
throttled. Furthermore, the group entity of the cfs_rq and its parents are
not enqueued but only set as curr on their respective cfs_rqs.
We have the following sequence:
-dequeue_task: dequeue task and group_entities.
-put_prev_task: put task and group entities.
-sched_change_group: move task to new group.
-enqueue_task: enqueue only task but not group entities because cfs_rq is
-set_next_task : set task and group_entities as current sched_entity of
their cfs_rq.
Another impact is that the root cfs_rq runnable_load_avg at root rq stays
null because the group_entities are not enqueued. This situation will stay
the same until an "external" event triggers a reschedule. Let trigger it
immediately instead.
Signed-off-by: Vincent Guittot <>
Signed-off-by: Peter Zijlstra (Intel) <>
Signed-off-by: Ingo Molnar <>
Acked-by: Ben Segall <>
Signed-off-by: Paul Gortmaker <>
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index d5a45c112773..1ffd4103fbf4 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6434,8 +6434,15 @@ void sched_move_task(struct task_struct *tsk)
if (queued)
enqueue_task(rq, tsk, queue_flags);
- if (running)
+ if (running) {
set_curr_task(rq, tsk);
+ /*
+ * After changing group, the running task may have joined a
+ * throttled one but it's still the running task. Trigger a
+ * resched to make sure that task can still run.
+ */
+ resched_curr(rq);
+ }
task_rq_unlock(rq, tsk, &rf);