Messages in this thread |  | | Date | Fri, 05 Jun 2015 10:48:36 +0200 | From | Peter Zijlstra <> | Subject | [PATCH 00/14] sched: balance callbacks |
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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 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.
Changes since -v2: - reworked the hrtimer patch. -- Kirill, tglx - added lock pinning
Changes since -v1: - make SMP=n build, - cured switched_from_dl()'s cancel_dl_timer().
no real tests on the new parts other than booting / building kernels.
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