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>

1 files changed, 43 insertions, 29 deletions

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 5d452e7fcb4f..4178e45becb4 100644
--- 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();
 
         /*