[RFC PATCH nohz] return NOTIFY_BAD in cpu down call back to stop offlining the cpu

[Li Zhong <zhong@linux.vnet.ibm.com>]

In tick_nohz_cpu_down_callback() if the cpu is the one handling
timekeeping , it seems that we should return something that could stop
notify CPU_DOWN_PREPARE, and then start notify CPU_DOWN_FAILED on the
already called notifier call backs.

-EINVAL will be converted to 0 by notifier_to_errno(), then the cpu
would be taken down with part of the DOWN_PREPARE notifier callbacks
called, and something bad could happen after that.

Signed-off-by: Li Zhong <zhong@linux.vnet.ibm.com>
---
 kernel/time/tick-sched.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index bc67d42..17b8155 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -306,7 +306,7 @@ static int __cpuinit tick_nohz_cpu_down_callback(struct notifier_block *nfb,
 		 * we can't safely shutdown that CPU.
 		 */
 		if (have_nohz_full_mask && tick_do_timer_cpu == cpu)
-			return -EINVAL;
+			return NOTIFY_BAD;
 		break;
 	}
 	return NOTIFY_OK;
-- 
1.7.1