cgroup: warn about broken hierarchies only after css_online

If everything goes right, it shouldn't really matter if we are spitting
this warning after css_alloc or css_online. If we fail between then,
there are some ill cases where we would previously see the message and
now we won't (like if the files fail to be created).

I believe it really shouldn't matter: this message is intended in spirit
to be shown when creation succeeds, but with insane settings.

Signed-off-by: Glauber Costa <glommer@parallels.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

1 files changed, 9 insertions, 9 deletions

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 46dcdbd7485b..b186a7e25b0a 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -4151,15 +4151,6 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
                         if (err)
                                 goto err_free_all;
                 }
-
-                if (ss->broken_hierarchy && !ss->warned_broken_hierarchy &&
-                    parent->parent) {
-                        pr_warning("cgroup: %s (%d) created nested cgroup for controller \"%s\" which has incomplete hierarchy support. Nested cgroups may change behavior in the future.\n",
-                                   current->comm, current->pid, ss->name);
-                        if (!strcmp(ss->name, "memory"))
-                                pr_warning("cgroup: \"memory\" requires setting use_hierarchy to 1 on the root.\n");
-                        ss->warned_broken_hierarchy = true;
-                }
         }
 
         /*
@@ -4188,6 +4179,15 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
                 err = online_css(ss, cgrp);
                 if (err)
                         goto err_destroy;
+
+                if (ss->broken_hierarchy && !ss->warned_broken_hierarchy &&
+                    parent->parent) {
+                        pr_warning("cgroup: %s (%d) created nested cgroup for controller \"%s\" which has incomplete hierarchy support. Nested cgroups may change behavior in the future.\n",
+                                   current->comm, current->pid, ss->name);
+                        if (!strcmp(ss->name, "memory"))
+                                pr_warning("cgroup: \"memory\" requires setting use_hierarchy to 1 on the root.\n");
+                        ss->warned_broken_hierarchy = true;
+                }
         }
 
         err = cgroup_populate_dir(cgrp, true, root->subsys_mask);