cgroup: update init_css() into init_and_link_css()

init_css() takes the cgroup the new css belongs to as an argument and
initializes the new css's ->cgroup and ->parent pointers but doesn't
acquire the matching reference counts.  After the previous patch,
create_css() puts init_css() and reference acquisition right next to
each other.  Let's move reference acquistion into init_css() and
rename the function to init_and_link_css().  This makes sense and is
easier to follow.  This makes the root csses to hold a reference on
cgrp_dfl_root.cgrp, which is harmless.

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

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 0e2c401ed7b954e633a4742a0332e343cac87423..f1c98c527b2d7243e89883626a38787d3ee198b2 100644 (file)
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -4109,17 +4109,21 @@ static void css_release(struct percpu_ref *ref)
        call_rcu(&css->rcu_head, css_free_rcu_fn);
 }
 
-static void init_css(struct cgroup_subsys_state *css, struct cgroup_subsys *ss,
-                    struct cgroup *cgrp)
+static void init_and_link_css(struct cgroup_subsys_state *css,
+                             struct cgroup_subsys *ss, struct cgroup *cgrp)
 {
+       cgroup_get(cgrp);
+
        css->cgroup = cgrp;
        css->ss = ss;
        css->flags = 0;
 
-       if (cgrp->parent)
+       if (cgrp->parent) {
                css->parent = cgroup_css(cgrp->parent, ss);
-       else
+               css_get(css->parent);
+       } else {
                css->flags |= CSS_ROOT;
+       }
 
        BUG_ON(cgroup_css(cgrp, ss));
 }
@@ -4185,9 +4189,7 @@ static int create_css(struct cgroup *cgrp, struct cgroup_subsys *ss)
        if (IS_ERR(css))
                return PTR_ERR(css);
 
-       init_css(css, ss, cgrp);
-       cgroup_get(cgrp);
-       css_get(css->parent);
+       init_and_link_css(css, ss, cgrp);
 
        err = percpu_ref_init(&css->refcnt, css_release);
        if (err)
@@ -4656,7 +4658,7 @@ static void __init cgroup_init_subsys(struct cgroup_subsys *ss)
        css = ss->css_alloc(cgroup_css(&cgrp_dfl_root.cgrp, ss));
        /* We don't handle early failures gracefully */
        BUG_ON(IS_ERR(css));
-       init_css(css, ss, &cgrp_dfl_root.cgrp);
+       init_and_link_css(css, ss, &cgrp_dfl_root.cgrp);
 
        /* Update the init_css_set to contain a subsys
         * pointer to this state - since the subsystem is