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Date: Fri, 05 Jun 2015 10:48:36 +0200 From: Peter Zijlstra <peterz@...radead.org> To: umgwanakikbuti@...il.com, mingo@...e.hu Cc: ktkhai@...allels.com, rostedt@...dmis.org, tglx@...utronix.de, juri.lelli@...il.com, pang.xunlei@...aro.org, oleg@...hat.com, wanpeng.li@...ux.intel.com, linux-kernel@...r.kernel.org, peterz@...radead.org Subject: [PATCH 00/14] sched: balance callbacks 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. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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