[PATCH] cgroups: remove rcu_read_lock() in cgroupstats_build()

[Lai Jiangshan <laijs@cn.fujitsu.com>]

cgroup_iter_* do not need rcu_read_lock().

In cgroup_enable_task_cg_lists(), do_each_thread() and
while_each_thread() are protected by RCU,
it's OK, for write_lock(&css_set_lock) implies rcu_read_lock() in non-RT kernel.

If we need explicit rcu_read_lock(), we should add rcu_read_lock()
in cgroup_enable_task_cg_lists(), not cgroup_iter_*.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
---
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 358e775..e6d92a5 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -2047,7 +2047,6 @@ int cgroupstats_build(struct cgroupstats *stats, struct dentry *dentry)
 
 	ret = 0;
 	cgrp = dentry->d_fsdata;
-	rcu_read_lock();
 
 	cgroup_iter_start(cgrp, &it);
 	while ((tsk = cgroup_iter_next(cgrp, &it))) {
@@ -2072,7 +2071,6 @@ int cgroupstats_build(struct cgroupstats *stats, struct dentry *dentry)
 	}
 	cgroup_iter_end(cgrp, &it);
 
-	rcu_read_unlock();
 err:
 	return ret;
 }