[RFC PATCH v2 07/10] kick_process(), cpu-hotplug: Prevent offlining of target CPU properly

["Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>]

Once stop_machine() is gone from the CPU offline path, we won't be able to
depend on preempt_disable() to prevent CPUs from going offline from under us.

Use the get/put_online_cpus_atomic_light() APIs to prevent changes to the
cpu_online_mask, while invoking from atomic context.

Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
---

 kernel/sched/core.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index c9a331e..84a8579 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1091,11 +1091,11 @@ void kick_process(struct task_struct *p)
 {
 	int cpu;
 
-	preempt_disable();
+	get_online_cpus_atomic_light();
 	cpu = task_cpu(p);
 	if ((cpu != smp_processor_id()) && task_curr(p))
 		smp_send_reschedule(cpu);
-	preempt_enable();
+	put_online_cpus_atomic_light();
 }
 EXPORT_SYMBOL_GPL(kick_process);
 #endif /* CONFIG_SMP */