From: Vincent Guittot vincent.guittot@linaro.org
[ Upstream commit 2a4b03ffc69f2dedc6388e9a6438b5f4c133a40d ]
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:
sched_move_task -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 throttled. -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 vincent.guittot@linaro.org Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Signed-off-by: Ingo Molnar mingo@kernel.org Acked-by: Ben Segall bsegall@google.com Link: https://lkml.kernel.org/r/1579011236-31256-1-git-send-email-vincent.guittot@... Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/sched/core.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 1f4f8e850cab7..4b6b916ec1be4 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -7067,8 +7067,15 @@ void sched_move_task(struct task_struct *tsk)
if (queued) enqueue_task(rq, tsk, queue_flags); - if (running) + if (running) { set_next_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); }