cgroup: re-hash init_css_set after subsystems are initialized

css_sets are hashed by their subsys[] contents and in cgroup_init()
init_css_set is hashed early, before subsystem inits, when all entries
in its subsys[] are NULL, so that cgroup_dfl_root initialization can
find and link to it.  As subsystems are initialized,
init_css_set.subsys[] is filled up but the hashing is never updated
making init_css_set hashed in the wrong place.  While incorrect, this
doesn't cause a critical failure as css_set management code would
create an identical css_set dynamically.

Fix it by rehashing init_css_set after subsystems are initialized.
While at it, drop unnecessary @key local variable.

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 46529502e9d5ad427a92f0da24ebf98dd3805852..e97772b42dfb796f22bbd86dc6d600dae1f38f8e 100644 (file)
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -5266,7 +5266,6 @@ static u16 cgroup_disable_mask __initdata;
 int __init cgroup_init(void)
 {
        struct cgroup_subsys *ss;
-       unsigned long key;
        int ssid;
 
        BUILD_BUG_ON(CGROUP_SUBSYS_COUNT > 16);
@@ -5276,9 +5275,12 @@ int __init cgroup_init(void)
 
        mutex_lock(&cgroup_mutex);
 
-       /* Add init_css_set to the hash table */
-       key = css_set_hash(init_css_set.subsys);
-       hash_add(css_set_table, &init_css_set.hlist, key);
+       /*
+        * Add init_css_set to the hash table so that dfl_root can link to
+        * it during init.
+        */
+       hash_add(css_set_table, &init_css_set.hlist,
+                css_set_hash(init_css_set.subsys));
 
        BUG_ON(cgroup_setup_root(&cgrp_dfl_root, 0));
 
@@ -5331,6 +5333,11 @@ int __init cgroup_init(void)
                        ss->bind(init_css_set.subsys[ssid]);
        }
 
+       /* init_css_set.subsys[] has been updated, re-hash */
+       hash_del(&init_css_set.hlist);
+       hash_add(css_set_table, &init_css_set.hlist,
+                css_set_hash(init_css_set.subsys));
+
        WARN_ON(sysfs_create_mount_point(fs_kobj, "cgroup"));
        WARN_ON(register_filesystem(&cgroup_fs_type));
        WARN_ON(register_filesystem(&cgroup2_fs_type));