linux-kernel - [tip:sched/urgent] sched: Make sure timers have migrated before killing the migration

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Message-ID: <tip-54e88fad223c4e1d94289611a90c7fe3ebe5631b@git.kernel.org>
Date:	Mon, 31 May 2010 07:18:52 GMT
From:	"tip-bot for Amit K. Arora" <aarora@...ux.vnet.ibm.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, ego@...ibm.com,
	aarora@...ux.vnet.ibm.com, hpa@...or.com, mingo@...hat.com,
	a.p.zijlstra@...llo.nl, tj@...nel.org, tglx@...utronix.de,
	aarora@...ibm.com, mingo@...e.hu
Subject: [tip:sched/urgent] sched: Make sure timers have migrated before killing the migration_thread

Commit-ID:  54e88fad223c4e1d94289611a90c7fe3ebe5631b
Gitweb:     http://git.kernel.org/tip/54e88fad223c4e1d94289611a90c7fe3ebe5631b
Author:     Amit K. Arora <aarora@...ux.vnet.ibm.com>
AuthorDate: Tue, 25 May 2010 18:53:46 +0530
Committer:  Ingo Molnar <mingo@...e.hu>
CommitDate: Mon, 31 May 2010 08:37:44 +0200

sched: Make sure timers have migrated before killing the migration_thread

Problem: In a stress test where some heavy tests were running along with
regular CPU offlining and onlining, a hang was observed. The system seems
to be hung at a point where migration_call() tries to kill the
migration_thread of the dying CPU, which just got moved to the current
CPU. This migration thread does not get a chance to run (and die) since
rt_throttled is set to 1 on current, and it doesn't get cleared as the
hrtimer which is supposed to reset the rt bandwidth
(sched_rt_period_timer) is tied to the CPU which we just marked dead!

Solution: This patch pushes the killing of migration thread to
"CPU_POST_DEAD" event. By then all the timers (including
sched_rt_period_timer) should have got migrated (along with other
callbacks).

Signed-off-by: Amit Arora <aarora@...ibm.com>
Signed-off-by: Gautham R Shenoy <ego@...ibm.com>
Acked-by: Tejun Heo <tj@...nel.org>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc: Thomas Gleixner <tglx@...utronix.de>
LKML-Reference: <20100525132346.GA14986@...tarora.in.ibm.com>
Signed-off-by: Ingo Molnar <mingo@...e.hu>
---
 kernel/stop_machine.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c
index b4e7431..70f8d90 100644
--- a/kernel/stop_machine.c
+++ b/kernel/stop_machine.c
@@ -321,7 +321,7 @@ static int __cpuinit cpu_stop_cpu_callback(struct notifier_block *nfb,
 
 #ifdef CONFIG_HOTPLUG_CPU
 	case CPU_UP_CANCELED:
-	case CPU_DEAD:
+	case CPU_POST_DEAD:
 	{
 		struct cpu_stop_work *work;
 
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