Re: [PATCH 1/7] sched/core: uclamp: add CPU clamp groups accounting

[Peter Zijlstra]

On Fri, Apr 13, 2018 at 12:47:45PM +0100, Patrick Bellasi wrote:
> In the past I remember some funny dance in cgroup callbacks when a
> task was terminating (like being moved in the root-rq just before
> exiting). But, as you say, if we always have the task_rq_lock we
> should be safe.

The syscall does the whole:

	task_rq_lock();
	queued = task_on_rq_queued();
	running = task_current();
	if (queued)
		dequeue_task();
	if (running)
		put_prev_task();

	/*
	 * task is in invariant state here,
	 * muck with it.
	 */

	if (queued)
		enqueue_task();
	if (running)
		set_curr_task()
	task_rq_unlock();

pattern; which because C sucks, we've not found a good template for yet.

Without the dequeue/put,enqueue/set you have to jump a few extra hoops.