cgroup: drop hierarchy_id_lock

Now that hierarchy_id alloc / free are protected by the cgroup
mutexes, there's no need for this separate lock.  Drop it.

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 dbc84f7d23b816511cfb20b9ff99f09dc0529035..3ef677d314bc87b89d029d043edd92fbf9921d08 100644 (file)
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -189,9 +189,13 @@ struct cgroup_event {
 static LIST_HEAD(roots);
 static int root_count;
 
+/*
+ * Hierarchy ID allocation and mapping.  It follows the same exclusion
+ * rules as other root ops - both cgroup_mutex and cgroup_root_mutex for
+ * writes, either for reads.
+ */
 static DEFINE_IDA(hierarchy_ida);
 static int next_hierarchy_id;
-static DEFINE_SPINLOCK(hierarchy_id_lock);
 
 /* dummytop is a shorthand for the dummy hierarchy's top cgroup */
 #define dummytop (&rootnode.top_cgroup)
@@ -1430,10 +1434,12 @@ static int cgroup_init_root_id(struct cgroupfs_root *root)
 {
        int ret;
 
+       lockdep_assert_held(&cgroup_mutex);
+       lockdep_assert_held(&cgroup_root_mutex);
+
        do {
                if (!ida_pre_get(&hierarchy_ida, GFP_KERNEL))
                        return -ENOMEM;
-               spin_lock(&hierarchy_id_lock);
                /* Try to allocate the next unused ID */
                ret = ida_get_new_above(&hierarchy_ida, next_hierarchy_id,
                                        &root->hierarchy_id);
@@ -1446,18 +1452,17 @@ static int cgroup_init_root_id(struct cgroupfs_root *root)
                        /* Can only get here if the 31-bit IDR is full ... */
                        BUG_ON(ret);
                }
-               spin_unlock(&hierarchy_id_lock);
        } while (ret);
        return 0;
 }
 
 static void cgroup_exit_root_id(struct cgroupfs_root *root)
 {
+       lockdep_assert_held(&cgroup_mutex);
+       lockdep_assert_held(&cgroup_root_mutex);
+
        if (root->hierarchy_id) {
-               spin_lock(&hierarchy_id_lock);
                ida_remove(&hierarchy_ida, root->hierarchy_id);
-               spin_unlock(&hierarchy_id_lock);
-
                root->hierarchy_id = 0;
        }
 }
@@ -4656,8 +4661,14 @@ int __init cgroup_init(void)
        hash_add(css_set_table, &init_css_set.hlist, key);
 
        /* allocate id for the dummy hierarchy */
+       mutex_lock(&cgroup_mutex);
+       mutex_lock(&cgroup_root_mutex);
+
        BUG_ON(cgroup_init_root_id(&rootnode));
 
+       mutex_unlock(&cgroup_root_mutex);
+       mutex_unlock(&cgroup_mutex);
+
        cgroup_kobj = kobject_create_and_add("cgroup", fs_kobj);
        if (!cgroup_kobj) {
                err = -ENOMEM;