cgroup: convert cgroup_ida to cgroup_idr

This enables us to lookup a cgroup by its id.

v4:
- add a comment for idr_remove() in cgroup_offline_fn().

v3:
- on success, idr_alloc() returns the id but not 0, so fix the BUG_ON()
  in cgroup_init().
- pass the right value to idr_alloc() so that the id for dummy cgroup is 0.

Signed-off-by: Li Zefan <lizefan@huawei.com>
Reviewed-by: Michal Hocko <mhocko@suse.cz>
Signed-off-by: Tejun Heo <tj@kernel.org>

1 files changed, 2 insertions, 2 deletions

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 00a7e07a1567..cca570e188fb 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -161,7 +161,7 @@ struct cgroup_name {
 struct cgroup {
         unsigned long flags;            /* "unsigned long" so bitops work */
 
-        int id;                         /* ida allocated in-hierarchy ID */
+        int id;                         /* idr allocated in-hierarchy ID */
 
         /*
          * We link our 'sibling' struct into our parent's 'children'.
@@ -322,7 +322,7 @@ struct cgroupfs_root {
         unsigned long flags;
 
         /* IDs for cgroups in this hierarchy */
-        struct ida cgroup_ida;
+        struct idr cgroup_idr;
 
         /* The path to use for release notifications. */
         char release_agent_path[PATH_MAX];