blkcg: let blkio_group point to blkio_cgroup directly

Currently, blkg points to the associated blkcg via its css_id.  This
unnecessarily complicates dereferencing blkcg.  Let blkg hold a
reference to the associated blkcg and point directly to it and disable
css_id on blkio_subsys.

This change requires splitting blkiocg_destroy() into
blkiocg_pre_destroy() and blkiocg_destroy() so that all blkg's can be
destroyed and all the blkcg references held by them dropped during
cgroup removal.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 1 insertions, 1 deletions

diff --git a/block/blk-cgroup.h b/block/blk-cgroup.h
index 7ebecf6ea8f1..ca1fc637bd6e 100644
--- a/block/blk-cgroup.h
+++ b/block/blk-cgroup.h
@@ -163,7 +163,7 @@ struct blkio_group {
         /* Pointer to the associated request_queue, RCU protected */
         struct request_queue __rcu *q;
         struct hlist_node blkcg_node;
-        unsigned short blkcg_id;
+        struct blkio_cgroup *blkcg;
         /* Store cgroup path */
         char path[128];
         /* policy which owns this blk group */