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sched/fair: Prevent unlimited runtime on throttled group
[ Upstream commit 2a4b03ffc6
]
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@linaro.org
Signed-off-by: Sasha Levin <sashal@kernel.org>
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1 changed files with 8 additions and 1 deletions
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@ -7058,8 +7058,15 @@ void sched_move_task(struct task_struct *tsk)
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if (queued)
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enqueue_task(rq, tsk, queue_flags);
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if (running)
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if (running) {
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set_next_task(rq, tsk);
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/*
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* After changing group, the running task may have joined a
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* throttled one but it's still the running task. Trigger a
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* resched to make sure that task can still run.
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*/
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resched_curr(rq);
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}
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task_rq_unlock(rq, tsk, &rf);
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}
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