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SubjectRe: [RFC][PATCH 0/7] sched: balance callbacks
On Mon, Jun 01, 2015 at 03:58:18PM +0200, Peter Zijlstra wrote:
> Hi,
>
> Mike stumbled over a cute bug where the RT/DL balancing ops caused a bug.
>
> The exact scenario is __sched_setscheduler() changing a (runnable) task from
> FIFO to OTHER. In swiched_from_rt(), where we do pull_rt_task() we temporarity
> drop rq->lock. This gap allows regular cfs load-balancing to step in and
> migrate our.

s/\./ task&/

> However, check_class_changed() will happily continue with switched_to_fair()
> which assumes our task is still on the old rq and makes the kernel go boom.
>
> Instead of trying to patch this up and make things complicated; simply disallow
> these methods to drop rq->lock and extend the current post_schedule stuff into
> a balancing callback list, and use that.
>
> This survives Mike's testcase for well over an hour on my ivb-ep. I've not yet
> tested it on anything bigger.
>


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