[PATCH 16/45] tick-broadcast: Use get/put_online_cpus_atomic() to prevent CPU offline

[Srivatsa S. Bhat]

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

Use the get/put_online_cpus_atomic() APIs to prevent CPUs from going
offline, while invoking from atomic context.

Cc: Thomas Gleixner <tglx at linutronix.de>
Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat at linux.vnet.ibm.com>
---

 kernel/time/tick-broadcast.c |    8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/kernel/time/tick-broadcast.c b/kernel/time/tick-broadcast.c
index d66f554..53493a6 100644
--- a/kernel/time/tick-broadcast.c
+++ b/kernel/time/tick-broadcast.c
@@ -227,12 +227,14 @@ static void tick_do_broadcast(struct cpumask *mask)
  */
 static void tick_do_periodic_broadcast(void)
 {
+	get_online_cpus_atomic();
 	raw_spin_lock(&tick_broadcast_lock);
 
 	cpumask_and(tmpmask, cpu_online_mask, tick_broadcast_mask);
 	tick_do_broadcast(tmpmask);
 
 	raw_spin_unlock(&tick_broadcast_lock);
+	put_online_cpus_atomic();
 }
 
 /*
@@ -335,11 +337,13 @@ out:
  */
 void tick_broadcast_on_off(unsigned long reason, int *oncpu)
 {
+	get_online_cpus_atomic();
 	if (!cpumask_test_cpu(*oncpu, cpu_online_mask))
 		printk(KERN_ERR "tick-broadcast: ignoring broadcast for "
 		       "offline CPU #%d\n", *oncpu);
 	else
 		tick_do_broadcast_on_off(&reason);
+	put_online_cpus_atomic();
 }
 
 /*
@@ -505,6 +509,7 @@ static void tick_handle_oneshot_broadcast(struct clock_event_device *dev)
 	ktime_t now, next_event;
 	int cpu, next_cpu = 0;
 
+	get_online_cpus_atomic();
 	raw_spin_lock(&tick_broadcast_lock);
 again:
 	dev->next_event.tv64 = KTIME_MAX;
@@ -562,6 +567,7 @@ again:
 			goto again;
 	}
 	raw_spin_unlock(&tick_broadcast_lock);
+	put_online_cpus_atomic();
 }
 
 /*
@@ -753,6 +759,7 @@ void tick_broadcast_switch_to_oneshot(void)
 	struct clock_event_device *bc;
 	unsigned long flags;
 
+	get_online_cpus_atomic();
 	raw_spin_lock_irqsave(&tick_broadcast_lock, flags);
 
 	tick_broadcast_device.mode = TICKDEV_MODE_ONESHOT;
@@ -761,6 +768,7 @@ void tick_broadcast_switch_to_oneshot(void)
 		tick_broadcast_setup_oneshot(bc);
 
 	raw_spin_unlock_irqrestore(&tick_broadcast_lock, flags);
+	put_online_cpus_atomic();
 }