[RFC PATCH 12/12] rcu: Nocb (de)activate through sysfs

[Frederic Weisbecker <frederic@kernel.org>]

Not for merge.

Make nocb toggable for a given CPU using:
	/sys/devices/system/cpu/cpu*/hotplug/nocb

This is only intended for those who want to test this patchset. The real
interfaces will be cpuset/isolation and rcutorture.

Not-Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Cc: Paul E. McKenney <paulmck@kernel.org>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: Joel Fernandes <joel@joelfernandes.org>
---
 kernel/cpu.c | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/kernel/cpu.c b/kernel/cpu.c
index 6ff2578ecf17..a36634113b8e 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -2224,10 +2224,33 @@ static ssize_t show_cpuhp_fail(struct device *dev,
 
 static DEVICE_ATTR(fail, 0644, show_cpuhp_fail, write_cpuhp_fail);
 
+static ssize_t write_nocb(struct device *dev,
+			  struct device_attribute *attr,
+			  const char *buf, size_t count)
+{
+	int val, ret;
+
+	ret = kstrtoint(buf, 10, &val);
+	if (ret)
+		return ret;
+
+	if (val == 0)
+		rcu_nocb_cpu_deoffload(dev->id);
+	else if (val == 1)
+		rcu_nocb_cpu_offload(dev->id);
+	else
+		return -EINVAL;
+
+	return count;
+}
+
+static DEVICE_ATTR(nocb, 0644, NULL, write_nocb);
+
 static struct attribute *cpuhp_cpu_attrs[] = {
 	&dev_attr_state.attr,
 	&dev_attr_target.attr,
 	&dev_attr_fail.attr,
+	&dev_attr_nocb.attr,
 	NULL
 };
 
-- 
2.28.0