sched: fix hotplug cpus on ia64

Cliff Wickman wrote:

> I built an ia64 kernel from Andrew's tree (2.6.26-rc2-mm1)
> and get a very predictable hotplug cpu problem.
> billberry1:/tmp/cpw # ./dis
> disabled cpu 17
> enabled cpu 17
> billberry1:/tmp/cpw # ./dis
> disabled cpu 17
> enabled cpu 17
> billberry1:/tmp/cpw # ./dis
>
> The script that disables the cpu always hangs (unkillable)
> on the 3rd attempt.
>
> And a bit further:
> The kstopmachine thread always sits on the run queue (real time) for about
> 30 minutes before running.

this fix solves some (but not all) issues between CPU hotplug and
RT bandwidth throttling.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 11 insertions, 4 deletions

diff --git a/kernel/sched.c b/kernel/sched.c
index 727bdef7616..e9c24a12865 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -7513,21 +7513,28 @@ int sched_create_sysfs_power_savings_entries(struct sysdev_class *cls)
 static int update_sched_domains(struct notifier_block *nfb,
                                 unsigned long action, void *hcpu)
 {
+        int cpu = (int)(long)hcpu;
+
         switch (action) {
-        case CPU_UP_PREPARE:
-        case CPU_UP_PREPARE_FROZEN:
         case CPU_DOWN_PREPARE:
         case CPU_DOWN_PREPARE_FROZEN:
+                disable_runtime(cpu_rq(cpu));
+                /* fall-through */
+        case CPU_UP_PREPARE:
+        case CPU_UP_PREPARE_FROZEN:
                 detach_destroy_domains(&cpu_online_map);
                 free_sched_domains();
                 return NOTIFY_OK;
 
-        case CPU_UP_CANCELED:
-        case CPU_UP_CANCELED_FROZEN:
+
         case CPU_DOWN_FAILED:
         case CPU_DOWN_FAILED_FROZEN:
         case CPU_ONLINE:
         case CPU_ONLINE_FROZEN:
+                enable_runtime(cpu_rq(cpu));
+                /* fall-through */
+        case CPU_UP_CANCELED:
+        case CPU_UP_CANCELED_FROZEN:
         case CPU_DEAD:
         case CPU_DEAD_FROZEN:
                 /*