cgroup: allow ->post_create() to fail

There could be cases where controllers want to do initialization
operations which may fail from ->post_create().  This patch makes
->post_create() return -errno to indicate failure and online_css()
relay such failures.

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

3 files changed, 23 insertions, 12 deletions

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index f4a9c9836906..03d8a92786da 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -440,7 +440,7 @@ int cgroup_taskset_size(struct cgroup_taskset *tset);
 
 struct cgroup_subsys {
         struct cgroup_subsys_state *(*create)(struct cgroup *cgrp);
-        void (*post_create)(struct cgroup *cgrp);
+        int (*post_create)(struct cgroup *cgrp);
         void (*pre_destroy)(struct cgroup *cgrp);
         void (*destroy)(struct cgroup *cgrp);
         int (*can_attach)(struct cgroup *cgrp, struct cgroup_taskset *tset);
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 027b66e66698..c389f4258681 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -4041,14 +4041,18 @@ static void init_cgroup_css(struct cgroup_subsys_state *css,
         INIT_WORK(&css->dput_work, css_dput_fn);
 }
 
-/* invoke ->post_create() on a new CSS and mark it online */
-static void online_css(struct cgroup_subsys *ss, struct cgroup *cgrp)
+/* invoke ->post_create() on a new CSS and mark it online if successful */
+static int online_css(struct cgroup_subsys *ss, struct cgroup *cgrp)
 {
+        int ret = 0;
+
         lockdep_assert_held(&cgroup_mutex);
 
         if (ss->post_create)
-                ss->post_create(cgrp);
-        cgrp->subsys[ss->subsys_id]->flags |= CSS_ONLINE;
+                ret = ss->post_create(cgrp);
+        if (!ret)
+                cgrp->subsys[ss->subsys_id]->flags |= CSS_ONLINE;
+        return ret;
 }
 
 /* if the CSS is online, invoke ->pre_destory() on it and mark it offline */
@@ -4174,12 +4178,15 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
         list_add_tail_rcu(&cgrp->sibling, &cgrp->parent->children);
         root->number_of_cgroups++;
 
-        for_each_subsys(root, ss) {
-                /* each css holds a ref to the cgroup's dentry */
+        /* each css holds a ref to the cgroup's dentry */
+        for_each_subsys(root, ss)
                 dget(dentry);
 
-                /* creation succeeded, notify subsystems */
-                online_css(ss, cgrp);
+        /* creation succeeded, notify subsystems */
+        for_each_subsys(root, ss) {
+                err = online_css(ss, cgrp);
+                if (err)
+                        goto err_destroy;
         }
 
         err = cgroup_populate_dir(cgrp, true, root->subsys_mask);
@@ -4393,7 +4400,7 @@ static void __init cgroup_init_subsys(struct cgroup_subsys *ss)
         BUG_ON(!list_empty(&init_task.tasks));
 
         ss->active = 1;
-        online_css(ss, dummytop);
+        BUG_ON(online_css(ss, dummytop));
 
         mutex_unlock(&cgroup_mutex);
 
@@ -4500,7 +4507,9 @@ int __init_or_module cgroup_load_subsys(struct cgroup_subsys *ss)
         write_unlock(&css_set_lock);
 
         ss->active = 1;
-        online_css(ss, dummytop);
+        ret = online_css(ss, dummytop);
+        if (ret)
+                goto err_unload;
 
         /* success! */
         mutex_unlock(&cgroup_mutex);
diff --git a/kernel/cgroup_freezer.c b/kernel/cgroup_freezer.c
index 670a4af7dc94..ee8bb671688c 100644
--- a/kernel/cgroup_freezer.c
+++ b/kernel/cgroup_freezer.c
@@ -112,7 +112,7 @@ static struct cgroup_subsys_state *freezer_create(struct cgroup *cgroup)
  * parent's freezing state while holding both parent's and our
  * freezer->lock.
  */
-static void freezer_post_create(struct cgroup *cgroup)
+static int freezer_post_create(struct cgroup *cgroup)
 {
         struct freezer *freezer = cgroup_freezer(cgroup);
         struct freezer *parent = parent_freezer(freezer);
@@ -136,6 +136,8 @@ static void freezer_post_create(struct cgroup *cgroup)
         spin_unlock(&freezer->lock);
         if (parent)
                 spin_unlock_irq(&parent->lock);
+
+        return 0;
 }
 
 /**