sched: Make sure timers have migrated before killing the migration_thread

Amit K. Arora · Ingo Molnar · commit 54e88fad223c · 2010-05-31T08:37:44.000+02:00
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 &lt;aarora@in.ibm.com&gt;
Signed-off-by: Gautham R Shenoy &lt;ego@in.ibm.com&gt;
Acked-by: Tejun Heo &lt;tj@kernel.org&gt;
Signed-off-by: Peter Zijlstra &lt;a.p.zijlstra@chello.nl&gt;
Cc: Thomas Gleixner &lt;tglx@linutronix.de&gt;
LKML-Reference: &lt;20100525132346.GA14986@amitarora.in.ibm.com&gt;
Signed-off-by: Ingo Molnar &lt;mingo@elte.hu&gt;
diff --git 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;
 

Original file line number	Diff line number	Diff line change
`@@ -321,7 +321,7 @@ static int __cpuinit cpu_stop_cpu_callback(struct notifier_block *nfb,`
`321`	`321`
`322`	`322`	`#ifdef CONFIG_HOTPLUG_CPU`
`323`	`323`	`case CPU_UP_CANCELED:`
`324`		`- case CPU_DEAD:`
	`324`	`+ case CPU_POST_DEAD:`
`325`	`325`	`{`
`326`	`326`	`struct cpu_stop_work *work;`
`327`	`327`