[PATCH 2/2] cpu hotplug: fix ksoftirqd termination on cpu hotplug with naughty realtime process

[Satoru Takeuchi <takeuchi_satoru@jp.fujitsu.com>]

Fix ksoftirqd termination on cpu hotplug with naughty real time process.

Assuming the following case:

 - Try to hot remove CPU2 from CPU1.
 - There is a real time process on CPU2, and that process doesn't sleep at all.
 - That rt process and ksoftirqd/2 is migrated to the CPU0

Then ksoftirqd/2 can't stop becasue that rt process runs everlastingly on CPU0,
and CPU1 waiting the ksoftirqd/2's termination hangs up. To fix this problem, set
the priority of ksoftirqd/2 to max one before kthread_stop().

Signed-off-by: Satoru Takeuchi <takeuchi_satoru@jp.fujitsu.com>

Index: linux-2.6.21/kernel/softirq.c
===================================================================
--- linux-2.6.21.orig/kernel/softirq.c	2007-05-11 13:45:34.000000000 +0900
+++ linux-2.6.21/kernel/softirq.c	2007-05-11 17:19:12.000000000 +0900
@@ -590,6 +590,7 @@ static int __cpuinit cpu_callback(struct
 {
 	int hotcpu = (unsigned long)hcpu;
 	struct task_struct *p;
+	struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 };
 
 	switch (action) {
 	case CPU_UP_PREPARE:
@@ -614,6 +615,7 @@ static int __cpuinit cpu_callback(struct
 	case CPU_DEAD:
 		p = per_cpu(ksoftirqd, hotcpu);
 		per_cpu(ksoftirqd, hotcpu) = NULL;
+		sched_setscheduler(p, SCHED_FIFO, &param);
 		kthread_stop(p);
 		takeover_tasklets(hotcpu);
 		break;