From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: From: Kirill Tkhai To: "linux-kernel@vger.kernel.org" Cc: Ingo Molnar , Peter Zijlstra , Steven Rostedt , stable@vger.kernel.org Subject: [PATCH] sched/rt: Fix rq's cpupri leak while enqueue/dequeue child RT entities MIME-Version: 1.0 Message-Id: <49231385567953@web4m.yandex.ru> Date: Wed, 27 Nov 2013 19:59:13 +0400 Content-Transfer-Encoding: 7bit Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org List-ID: This patch touches RT group scheduling case. Functions inc_rt_prio_smp() and dec_rt_prio_smp() change (global) rq's priority, while rt_rq passed to them may be not the top-level rt_rq. This is wrong, because changing of priority on a child level does not guarantee that the priority is the highest all over the rq. So, this leak makes RT balancing unusable. The short example: the task having the highest priority among all rq's RT tasks (no one other task has the same priority) are waking on a throttle rt_rq. The rq's cpupri is set to the task's priority equivalent, but real rq->rt.highest_prio.curr is less. The patch below fixes the problem. It looks like all version have this bug, so I CC'ed stable mailing list. Signed-off-by: Kirill Tkhai CC: Ingo Molnar CC: Peter Zijlstra CC: Steven Rostedt CC: stable@vger.kernel.org --- kernel/sched/rt.c | 14 ++++++++++++++ 1 files changed, 14 insertions(+), 0 deletions(-) diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c index 7d57275..1c40655 100644 --- a/kernel/sched/rt.c +++ b/kernel/sched/rt.c @@ -901,6 +901,13 @@ inc_rt_prio_smp(struct rt_rq *rt_rq, int prio, int prev_prio) { struct rq *rq = rq_of_rt_rq(rt_rq); +#ifdef CONFIG_RT_GROUP_SCHED + /* + * Change rq's cpupri only if rt_rq is the top queue. + */ + if (&rq->rt != rt_rq) + return; +#endif if (rq->online && prio < prev_prio) cpupri_set(&rq->rd->cpupri, rq->cpu, prio); } @@ -910,6 +917,13 @@ dec_rt_prio_smp(struct rt_rq *rt_rq, int prio, int prev_prio) { struct rq *rq = rq_of_rt_rq(rt_rq); +#ifdef CONFIG_RT_GROUP_SCHED + /* + * Change rq's cpupri only if rt_rq is the top queue. + */ + if (&rq->rt != rt_rq) + return; +#endif if (rq->online && rt_rq->highest_prio.curr != prev_prio) cpupri_set(&rq->rd->cpupri, rq->cpu, rt_rq->highest_prio.curr); }