cpu hotplug: fix ksoftirqd termination on cpu hotplug with naughty realtime process

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().

[akpm@linux-foundation.org: fix warning]
Signed-off-by: Satoru Takeuchi <takeuchi_satoru@jp.fujitsu.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Ashok Raj <ashok.raj@intel.com>
Cc: Gautham R Shenoy <ego@in.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 5 insertions, 1 deletions

diff --git a/kernel/softirq.c b/kernel/softirq.c
index 73217a9e2875..8de267790166 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -614,12 +614,16 @@ static int __cpuinit cpu_callback(struct notifier_block *nfb,
                 kthread_bind(per_cpu(ksoftirqd, hotcpu),
                              any_online_cpu(cpu_online_map));
         case CPU_DEAD:
-        case CPU_DEAD_FROZEN:
+        case CPU_DEAD_FROZEN: {
+                struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 };
+
                 p = per_cpu(ksoftirqd, hotcpu);
                 per_cpu(ksoftirqd, hotcpu) = NULL;
+                sched_setscheduler(p, SCHED_FIFO, &param);
                 kthread_stop(p);
                 takeover_tasklets(hotcpu);
                 break;
+        }
 #endif /* CONFIG_HOTPLUG_CPU */
         }
         return NOTIFY_OK;