cgroup: make hierarchy_id use cyclic idr

We want to be able to lookup a hierarchy from its id and cyclic
allocation is a whole lot simpler with idr.  Convert to idr and use
idr_alloc_cyclc().

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>
Change-Id: Ibd20ebe71ddb452178302cf86a22572b18cd82df
Origin: https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=1a574231669f8c3065c83974e9557fcbbd94b8a6
Backported-by: Maciej Wereski <m.wereski@partner.samsung.com>
Signed-off-by: Maciej Wereski <m.wereski@partner.samsung.com>

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 62f9551..d9acb52 100644 (file)
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -202,8 +202,7 @@ static int root_count;
  * 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_IDR(cgroup_hierarchy_idr);
 
 /* dummytop is a shorthand for the dummy hierarchy's top cgroup */
 #define dummytop (&rootnode.top_cgroup)
@@ -1440,27 +1439,16 @@ static void init_cgroup_root(struct cgroupfs_root *root)
 
 static int cgroup_init_root_id(struct cgroupfs_root *root)
 {
-       int ret;
+       int id;
 
        lockdep_assert_held(&cgroup_mutex);
        lockdep_assert_held(&cgroup_root_mutex);
 
-       do {
-               if (!ida_pre_get(&hierarchy_ida, GFP_KERNEL))
-                       return -ENOMEM;
-               /* Try to allocate the next unused ID */
-               ret = ida_get_new_above(&hierarchy_ida, next_hierarchy_id,
-                                       &root->hierarchy_id);
-               if (ret == -ENOSPC)
-                       /* Try again starting from 0 */
-                       ret = ida_get_new(&hierarchy_ida, &root->hierarchy_id);
-               if (!ret) {
-                       next_hierarchy_id = root->hierarchy_id + 1;
-               } else if (ret != -EAGAIN) {
-                       /* Can only get here if the 31-bit IDR is full ... */
-                       BUG_ON(ret);
-               }
-       } while (ret);
+       id = idr_alloc_cyclic(&cgroup_hierarchy_idr, root, 2, 0, GFP_KERNEL);
+       if (id < 0)
+               return id;
+
+       root->hierarchy_id = id;
        return 0;
 }
 
@@ -1470,7 +1458,7 @@ static void cgroup_exit_root_id(struct cgroupfs_root *root)
        lockdep_assert_held(&cgroup_root_mutex);
 
        if (root->hierarchy_id) {
-               ida_remove(&hierarchy_ida, root->hierarchy_id);
+               idr_remove(&cgroup_hierarchy_idr, root->hierarchy_id);
                root->hierarchy_id = 0;
        }
 }