Re: [RFC][PATCH 0/7] sched: balance callbacks

[Peter Zijlstra]

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.
> 
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/