cgroup: separate out interface file creation from css creation

Currently, interface files are created when a css is created depending
on whether @visible is set.  This patch separates out the two into
separate steps to help code refactoring and eventually allow cgroups
which aren't visible through cgroup fs.

Move css_populate_dir() out of create_css() and drop @visible.  While
at it, rename the function to css_create() for consistency.

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

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 5d452e7fcb4fecabfe09c667ffd37ce5c59f21ab..4178e45becb45de4ac81191e432d536d3b196267 100644 (file)
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -222,8 +222,8 @@ static struct cftype cgroup_legacy_base_files[];
 static int rebind_subsystems(struct cgroup_root *dst_root, u16 ss_mask);
 static void css_task_iter_advance(struct css_task_iter *it);
 static int cgroup_destroy_locked(struct cgroup *cgrp);
-static int create_css(struct cgroup *cgrp, struct cgroup_subsys *ss,
-                     bool visible);
+static struct cgroup_subsys_state *css_create(struct cgroup *cgrp,
+                                             struct cgroup_subsys *ss);
 static void css_release(struct percpu_ref *ref);
 static void kill_css(struct cgroup_subsys_state *css);
 static int cgroup_addrm_files(struct cgroup_subsys_state *css,
@@ -3082,14 +3082,26 @@ static ssize_t cgroup_subtree_control_write(struct kernfs_open_file *of,
         */
        do_each_subsys_mask(ss, ssid, enable) {
                cgroup_for_each_live_child(child, cgrp) {
-                       if (css_enable & (1 << ssid))
-                               ret = create_css(child, ss,
-                                       cgrp->subtree_control & (1 << ssid));
-                       else
+                       if (css_enable & (1 << ssid)) {
+                               struct cgroup_subsys_state *css;
+
+                               css = css_create(child, ss);
+                               if (IS_ERR(css)) {
+                                       ret = PTR_ERR(css);
+                                       goto err_undo_css;
+                               }
+
+                               if (cgrp->subtree_control & (1 << ssid)) {
+                                       ret = css_populate_dir(css, NULL);
+                                       if (ret)
+                                               goto err_undo_css;
+                               }
+                       } else {
                                ret = css_populate_dir(cgroup_css(child, ss),
                                                       NULL);
-                       if (ret)
-                               goto err_undo_css;
+                               if (ret)
+                                       goto err_undo_css;
+                       }
                }
        } while_each_subsys_mask();
 
@@ -4717,7 +4729,9 @@ static void css_release_work_fn(struct work_struct *work)
                 * Those are supported by RCU protecting clearing of
                 * cgrp->kn->priv backpointer.
                 */
-               RCU_INIT_POINTER(*(void __rcu __force **)&cgrp->kn->priv, NULL);
+               if (cgrp->kn)
+                       RCU_INIT_POINTER(*(void __rcu __force **)&cgrp->kn->priv,
+                                        NULL);
        }
 
        mutex_unlock(&cgroup_mutex);
@@ -4801,17 +4815,16 @@ static void offline_css(struct cgroup_subsys_state *css)
 }
 
 /**
- * create_css - create a cgroup_subsys_state
+ * css_create - create a cgroup_subsys_state
  * @cgrp: the cgroup new css will be associated with
  * @ss: the subsys of new css
- * @visible: whether to create control knobs for the new css or not
  *
  * Create a new css associated with @cgrp - @ss pair.  On success, the new
- * css is online and installed in @cgrp with all interface files created if
- * @visible.  Returns 0 on success, -errno on failure.
+ * css is online and installed in @cgrp.  This function doesn't create the
+ * interface files.  Returns 0 on success, -errno on failure.
  */
-static int create_css(struct cgroup *cgrp, struct cgroup_subsys *ss,
-                     bool visible)
+static struct cgroup_subsys_state *css_create(struct cgroup *cgrp,
+                                             struct cgroup_subsys *ss)
 {
        struct cgroup *parent = cgroup_parent(cgrp);
        struct cgroup_subsys_state *parent_css = cgroup_css(parent, ss);
@@ -4822,7 +4835,7 @@ static int create_css(struct cgroup *cgrp, struct cgroup_subsys *ss,
 
        css = ss->css_alloc(parent_css);
        if (IS_ERR(css))
-               return PTR_ERR(css);
+               return css;
 
        init_and_link_css(css, ss, cgrp);
 
@@ -4835,12 +4848,6 @@ static int create_css(struct cgroup *cgrp, struct cgroup_subsys *ss,
                goto err_free_percpu_ref;
        css->id = err;
 
-       if (visible) {
-               err = css_populate_dir(css, NULL);
-               if (err)
-                       goto err_free_id;
-       }
-
        /* @css is ready to be brought online now, make it visible */
        list_add_tail_rcu(&css->sibling, &parent_css->children);
        cgroup_idr_replace(&ss->css_idr, css, css->id);
@@ -4858,18 +4865,16 @@ static int create_css(struct cgroup *cgrp, struct cgroup_subsys *ss,
                ss->warned_broken_hierarchy = true;
        }
 
-       return 0;
+       return css;
 
 err_list_del:
        list_del_rcu(&css->sibling);
-       css_clear_dir(css, NULL);
-err_free_id:
        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;
+       return ERR_PTR(err);
 }
 
 static int cgroup_mkdir(struct kernfs_node *parent_kn, const char *name,
@@ -4966,10 +4971,19 @@ static int cgroup_mkdir(struct kernfs_node *parent_kn, const char *name,
 
        /* let's create and online css's */
        do_each_subsys_mask(ss, ssid, parent->subtree_ss_mask) {
-               ret = create_css(cgrp, ss,
-                                parent->subtree_control & (1 << ssid));
-               if (ret)
+               struct cgroup_subsys_state *css;
+
+               css = css_create(cgrp, ss);
+               if (IS_ERR(css)) {
+                       ret = PTR_ERR(css);
                        goto out_destroy;
+               }
+
+               if (parent->subtree_control & (1 << ssid)) {
+                       ret = css_populate_dir(css, NULL);
+                       if (ret)
+                               goto out_destroy;
+               }
        } while_each_subsys_mask();
 
        /*