cgroup: add sparse annotation to cgroup_iter_start() and cgroup_iter_end()

Signed-off-by: Kirill A. Shutemov <kirill@shutemov.name>
Acked-by: Li Zefan <lizf@cn.fujitsu.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

kernel/cgroup.c

@@ -2825,6 +2825,7 @@ static void cgroup_enable_task_cg_lists(void)
 }
 
 void cgroup_iter_start(struct cgroup *cgrp, struct cgroup_iter *it)
+	__acquires(css_set_lock)
 {
 	/*
 	 * The first time anyone tries to iterate across a cgroup,
@@ -2864,6 +2865,7 @@ struct task_struct *cgroup_iter_next(struct cgroup *cgrp,
 }
 
 void cgroup_iter_end(struct cgroup *cgrp, struct cgroup_iter *it)
+	__releases(css_set_lock)
 {
 	read_unlock(&css_set_lock);
 }