cgroup: use cgroup_apply_enable_control() in cgroup creation path

cgroup_create() manually updates control masks and creates child csses
which cgroup_mkdir() then manually populates.  Both can be simplified
by using cgroup_apply_enable_control() and friends.  The only catch is
that it calls css_populate_dir() with NULL cgroup->kn during
cgroup_create().  This is worked around by making the function noop on
NULL kn.

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 bbeb35f..ee6951b 100644 (file)
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -1490,7 +1490,7 @@ static int css_populate_dir(struct cgroup_subsys_state *css,
        struct cftype *cfts, *failed_cfts;
        int ret;
 
-       if (css->flags & CSS_VISIBLE)
+       if ((css->flags & CSS_VISIBLE) || !cgrp->kn)
                return 0;
 
        if (!css->ss) {
@@ -5042,10 +5042,9 @@ err_free_css:
 static struct cgroup *cgroup_create(struct cgroup *parent)
 {
        struct cgroup_root *root = parent->root;
-       struct cgroup_subsys *ss;
        struct cgroup *cgrp, *tcgrp;
        int level = parent->level + 1;
-       int ssid, ret;
+       int ret;
 
        /* allocate the cgroup and its ID, 0 is reserved for the root */
        cgrp = kzalloc(sizeof(*cgrp) +
@@ -5095,25 +5094,19 @@ static struct cgroup *cgroup_create(struct cgroup *parent)
         */
        cgroup_idr_replace(&root->cgroup_idr, cgrp, cgrp->id);
 
-       /* create the csses */
-       do_each_subsys_mask(ss, ssid, cgroup_ss_mask(cgrp)) {
-               struct cgroup_subsys_state *css;
-
-               css = css_create(cgrp, ss);
-               if (IS_ERR(css)) {
-                       ret = PTR_ERR(css);
-                       goto out_destroy;
-               }
-       } while_each_subsys_mask();
-
        /*
         * On the default hierarchy, a child doesn't automatically inherit
         * subtree_control from the parent.  Each is configured manually.
         */
-       if (!cgroup_on_dfl(cgrp)) {
+       if (!cgroup_on_dfl(cgrp))
                cgrp->subtree_control = cgroup_control(cgrp);
-               cgroup_refresh_subtree_ss_mask(cgrp);
-       }
+
+       cgroup_propagate_control(cgrp);
+
+       /* @cgrp doesn't have dir yet so the following will only create csses */
+       ret = cgroup_apply_control_enable(cgrp);
+       if (ret)
+               goto out_destroy;
 
        return cgrp;
 
@@ -5131,9 +5124,8 @@ static int cgroup_mkdir(struct kernfs_node *parent_kn, const char *name,
                        umode_t mode)
 {
        struct cgroup *parent, *cgrp;
-       struct cgroup_subsys *ss;
        struct kernfs_node *kn;
-       int ssid, ret;
+       int ret;
 
        /* do not accept '\n' to prevent making /proc/<pid>/cgroup unparsable */
        if (strchr(name, '\n'))
@@ -5171,11 +5163,9 @@ static int cgroup_mkdir(struct kernfs_node *parent_kn, const char *name,
        if (ret)
                goto out_destroy;
 
-       do_each_subsys_mask(ss, ssid, cgroup_control(cgrp)) {
-               ret = css_populate_dir(cgroup_css(cgrp, ss), NULL);
-               if (ret)
-                       goto out_destroy;
-       } while_each_subsys_mask();
+       ret = cgroup_apply_control_enable(cgrp);
+       if (ret)
+               goto out_destroy;
 
        /* let's create and online css's */
        kernfs_activate(kn);