linux-kernel - [PATCH] sched: unthrottle rt_rq in migrate

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Date:	Fri, 18 May 2012 11:56:51 -0700
From:	Peter Boonstoppel <pboonstoppel@...dia.com>
To:	"a.p.zijlstra@...llo.nl" <a.p.zijlstra@...llo.nl>,
	"mingo@...nel.org" <mingo@...nel.org>,
	"pjt@...gle.com" <pjt@...gle.com>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"seto.hidetoshi@...fujitsu.com" <seto.hidetoshi@...fujitsu.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:	Peter De Schrijver <pdeschrijver@...dia.com>
Subject: [PATCH] sched: unthrottle rt_rq in migrate_tasks()

migrate_tasks() uses _pick_next_task_rt() to get tasks from the
real-time runqueue to be migrated. When rt_rq is throttled
_pick_next_task_rt() won't return anything, in which case
migrate_tasks() can't move all threads over and gets stuck in an
infinite loop.

Instead unthrottle rt_rq before migrating tasks.

Signed-off-by: Peter Boonstoppel <pboonstoppel@...dia.com>
---
 kernel/sched/core.c |    6 ++++++
 1 files changed, 6 insertions(+), 0 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 9236a48..b37e0b3 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -5159,6 +5159,12 @@ static void migrate_tasks(unsigned int dead_cpu)
 	/* Ensure any throttled groups are reachable by pick_next_task */
 	unthrottle_offline_cfs_rqs(rq);
 
+	/*
+	 * Ensure rt_rq is not throttled so its threads can be migrated using
+	 * pick_next_task_rt
+	 */
+	rq->rt.rt_throttled = 0;
+
 	for ( ; ; ) {
 		/*
 		 * There's this thread running, bail when that's the only
-- 
1.7.4.1
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