cgroup: factor out cgroup_subsys_state creation into create_css()

Now that all opertations to create a css (cgroup_subsys_state) are
collected into a single loop in cgroup_create(), it's easy to factor
it out into its own function.  Factor out css creation into
create_css().  This makes the code easier to follow and will enable
decoupling css creation from cgroup creation which is necessary for
the planned unified hierarchy.

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

1 files changed, 57 insertions, 38 deletions

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 39e2295466ec..d12c29f42feb 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -4073,6 +4073,62 @@ static void offline_css(struct cgroup_subsys_state *css)
         RCU_INIT_POINTER(css->cgroup->subsys[ss->subsys_id], css);
 }
 
+/**
+ * create_css - create a cgroup_subsys_state
+ * @cgrp: the cgroup new css will be associated with
+ * @ss: the subsys of new css
+ *
+ * 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.
+ * Returns 0 on success, -errno on failure.
+ */
+static int create_css(struct cgroup *cgrp, struct cgroup_subsys *ss)
+{
+        struct cgroup *parent = cgrp->parent;
+        struct cgroup_subsys_state *css;
+        int err;
+
+        lockdep_assert_held(&cgrp->dentry->d_inode->i_mutex);
+        lockdep_assert_held(&cgroup_mutex);
+
+        css = ss->css_alloc(cgroup_css(parent, ss));
+        if (IS_ERR(css))
+                return PTR_ERR(css);
+
+        err = percpu_ref_init(&css->refcnt, css_release);
+        if (err)
+                goto err_free;
+
+        init_css(css, ss, cgrp);
+
+        err = cgroup_populate_dir(cgrp, 1 << ss->subsys_id);
+        if (err)
+                goto err_free;
+
+        err = online_css(css);
+        if (err)
+                goto err_free;
+
+        dget(cgrp->dentry);
+        css_get(css->parent);
+
+        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;
+        }
+
+        return 0;
+
+err_free:
+        percpu_ref_cancel_init(&css->refcnt);
+        ss->css_free(css);
+        return err;
+}
+
 /*
  * cgroup_create - create a cgroup
  * @parent: cgroup that will be parent of the new cgroup
@@ -4084,7 +4140,6 @@ static void offline_css(struct cgroup_subsys_state *css)
 static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
                              umode_t mode)
 {
-        struct cgroup_subsys_state *css = NULL;
         struct cgroup *cgrp;
         struct cgroup_name *name;
         struct cgroupfs_root *root = parent->root;
@@ -4175,41 +4230,9 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
 
         /* let's create and online css's */
         for_each_root_subsys(root, ss) {
-                css = ss->css_alloc(cgroup_css(parent, ss));
-                if (IS_ERR(css)) {
-                        err = PTR_ERR(css);
-                        css = NULL;
-                        goto err_destroy;
-                }
-
-                err = percpu_ref_init(&css->refcnt, css_release);
+                err = create_css(cgrp, ss);
                 if (err)
                         goto err_destroy;
-
-                init_css(css, ss, cgrp);
-
-                err = cgroup_populate_dir(cgrp, 1 << ss->subsys_id);
-                if (err)
-                        goto err_destroy;
-
-                err = online_css(css);
-                if (err)
-                        goto err_destroy;
-
-                dget(dentry);
-                css_get(css->parent);
-
-                /* mark it consumed for error path */
-                css = NULL;
-
-                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;
-                }
         }
 
         mutex_unlock(&cgroup_mutex);
@@ -4230,10 +4253,6 @@ err_free_cgrp:
         return err;
 
 err_destroy:
-        if (css) {
-                percpu_ref_cancel_init(&css->refcnt);
-                css->ss->css_free(css);
-        }
         cgroup_destroy_locked(cgrp);
         mutex_unlock(&cgroup_mutex);
         mutex_unlock(&dentry->d_inode->i_mutex);