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>

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 46dcdbd..b186a7e 100644 (file)
--- 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);