[PATCH 4.6 48/96] cgroup: remove redundant cleanup in css_create

[Greg Kroah-Hartman]

4.6-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Wenwei Tao <ww.tao0320@xxxxxxxxx>

commit b00c52dae6d9ee8d0f2407118ef6544ae5524781 upstream.

When create css failed, before call css_free_rcu_fn, we remove the css
id and exit the percpu_ref, but we will do these again in
css_free_work_fn, so they are redundant.  Especially the css id, that
would cause problem if we remove it twice, since it may be assigned to
another css after the first remove.

tj: This was broken by two commits updating the free path without
    synchronizing the creation failure path.  This can be easily
    triggered by trying to create more than 64k memory cgroups.

Signed-off-by: Wenwei Tao <ww.tao0320@xxxxxxxxx>
Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
Cc: Vladimir Davydov <vdavydov@xxxxxxxxxxxxx>
Fixes: 9a1049da9bd2 ("percpu-refcount: require percpu_ref to be exited explicitly")
Fixes: 01e586598b22 ("cgroup: release css->id after css_free")
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 kernel/cgroup.c |    5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -5150,7 +5150,7 @@ static struct cgroup_subsys_state *css_c
 
 	err = cgroup_idr_alloc(&ss->css_idr, NULL, 2, 0, GFP_KERNEL);
 	if (err < 0)
-		goto err_free_percpu_ref;
+		goto err_free_css;
 	css->id = err;
 
 	/* @css is ready to be brought online now, make it visible */
@@ -5174,9 +5174,6 @@ static struct cgroup_subsys_state *css_c
 
 err_list_del:
 	list_del_rcu(&css->sibling);
-	cgroup_idr_remove(&ss->css_idr, css->id);
-err_free_percpu_ref:
-	percpu_ref_exit(&css->refcnt);
 err_free_css:
 	call_rcu(&css->rcu_head, css_free_rcu_fn);
 	return ERR_PTR(err);