cgroup: simplify cgroup_load_subsys() failure path

Now that cgroup_unload_subsys() can tell whether the root css is
online or not, we can safely call cgroup_unload_subsys() after idr
init failure in cgroup_load_subsys().

Replace the manual unrolling and invoke cgroup_unload_subsys() on
failure.  This drops cgroup_mutex inbetween but should be safe as the
subsystem will fail try_module_get() and thus can't be mounted
inbetween.  As this means that cgroup_unload_subsys() can be called
before css_sets are rehashed, remove BUG_ON() on %NULL
css_set->subsys[] from cgroup_unload_subsys().

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

1 files changed, 10 insertions, 11 deletions

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 78a3d5c0968e..166b5141f3d4 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -4400,8 +4400,8 @@ static void __init cgroup_init_subsys(struct cgroup_subsys *ss)
  */
 int __init_or_module cgroup_load_subsys(struct cgroup_subsys *ss)
 {
-        int i;
         struct cgroup_subsys_state *css;
+        int i, ret;
 
         /* check name and function validity */
         if (ss->name == NULL || strlen(ss->name) > MAX_CGROUP_TYPE_NAMELEN ||
@@ -4452,15 +4452,9 @@ int __init_or_module cgroup_load_subsys(struct cgroup_subsys *ss)
         init_cgroup_css(css, ss, dummytop);
         /* init_idr must be after init_cgroup_css because it sets css->id. */
         if (ss->use_id) {
-                int ret = cgroup_init_idr(ss, css);
-                if (ret) {
-                        ss->destroy(dummytop);
-                        dummytop->subsys[ss->subsys_id] = NULL;
-                        subsys[ss->subsys_id] = NULL;
-                        list_del_init(&ss->sibling);
-                        mutex_unlock(&cgroup_mutex);
-                        return ret;
-                }
+                ret = cgroup_init_idr(ss, css);
+                if (ret)
+                        goto err_unload;
         }
 
         /*
@@ -4498,6 +4492,12 @@ int __init_or_module cgroup_load_subsys(struct cgroup_subsys *ss)
         /* success! */
         mutex_unlock(&cgroup_mutex);
         return 0;
+
+err_unload:
+        mutex_unlock(&cgroup_mutex);
+        /* @ss can't be mounted here as try_module_get() would fail */
+        cgroup_unload_subsys(ss);
+        return ret;
 }
 EXPORT_SYMBOL_GPL(cgroup_load_subsys);
 
@@ -4548,7 +4548,6 @@ void cgroup_unload_subsys(struct cgroup_subsys *ss)
                 struct css_set *cg = link->cg;
 
                 hlist_del(&cg->hlist);
-                BUG_ON(!cg->subsys[ss->subsys_id]);
                 cg->subsys[ss->subsys_id] = NULL;
                 hhead = css_set_hash(cg->subsys);
                 hlist_add_head(&cg->hlist, hhead);