[PATCH v5 17/45] softirq: 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 preempt_disable() or local_irq_disable() 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: Frederic Weisbecker <fweisbec at gmail.com>
Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat at linux.vnet.ibm.com>
---

 kernel/softirq.c |    3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/softirq.c b/kernel/softirq.c
index ed567ba..98c3e27 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -631,6 +631,7 @@ static void remote_softirq_receive(void *data)
 
 static int __try_remote_softirq(struct call_single_data *cp, int cpu, int softirq)
 {
+	get_online_cpus_atomic();
 	if (cpu_online(cpu)) {
 		cp->func = remote_softirq_receive;
 		cp->info = cp;
@@ -638,8 +639,10 @@ static int __try_remote_softirq(struct call_single_data *cp, int cpu, int softir
 		cp->priv = softirq;
 
 		__smp_call_function_single(cpu, cp, 0);
+		put_online_cpus_atomic();
 		return 0;
 	}
+	put_online_cpus_atomic();
 	return 1;
 }
 #else /* CONFIG_USE_GENERIC_SMP_HELPERS */