cgroup: fix broken css_has_online_children()

After running:

  # mount -t cgroup cpu xxx /cgroup && mkdir /cgroup/sub && \
    rmdir /cgroup/sub && umount /cgroup

I found the cgroup root still existed:

  # cat /proc/cgroups
  #subsys_name    hierarchy       num_cgroups     enabled
  cpuset  0       1       1
  cpu     1       1       1
  ...

It turned out css_has_online_children() is broken.

Signed-off-by: Li Zefan <lizefan@huawei.com>
Sigend-off-by: Tejun Heo <tj@kernel.org>

1 files changed, 1 insertions, 1 deletions

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 7868fc3c0bc5..d9a8be911f5b 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -3328,7 +3328,7 @@ bool css_has_online_children(struct cgroup_subsys_state *css)
 
         rcu_read_lock();
         css_for_each_child(child, css) {
-                if (css->flags & CSS_ONLINE) {
+                if (child->flags & CSS_ONLINE) {
                         ret = true;
                         break;
                 }