cfq: Remove useless css reference get

There's no need to take css reference here, for the caller
has already called rcu_read_lock() to prevent cgroup from
being removed.

Signed-off-by: Gui Jianfeng <guijianfeng@cn.fujitsu.com>
Reviewed-by: Li Zefan <lizf@cn.fujitsu.com>
Acked-by: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

block/blk-cgroup.c

@@ -23,20 +23,6 @@ static LIST_HEAD(blkio_list);
 struct blkio_cgroup blkio_root_cgroup = { .weight = 2*BLKIO_WEIGHT_DEFAULT };
 EXPORT_SYMBOL_GPL(blkio_root_cgroup);
 
-bool blkiocg_css_tryget(struct blkio_cgroup *blkcg)
-{
-	if (!css_tryget(&blkcg->css))
-		return false;
-	return true;
-}
-EXPORT_SYMBOL_GPL(blkiocg_css_tryget);
-
-void blkiocg_css_put(struct blkio_cgroup *blkcg)
-{
-	css_put(&blkcg->css);
-}
-EXPORT_SYMBOL_GPL(blkiocg_css_put);
-
 struct blkio_cgroup *cgroup_to_blkio_cgroup(struct cgroup *cgroup)
 {
 	return container_of(cgroup_subsys_state(cgroup, blkio_subsys_id),

block/blk-cgroup.h

@@ -43,9 +43,6 @@ struct blkio_group {
 	unsigned long sectors;
 };
 
-extern bool blkiocg_css_tryget(struct blkio_cgroup *blkcg);
-extern void blkiocg_css_put(struct blkio_cgroup *blkcg);
-
 typedef void (blkio_unlink_group_fn) (void *key, struct blkio_group *blkg);
 typedef void (blkio_update_group_weight_fn) (struct blkio_group *blkg,
 						unsigned int weight);

block/cfq-iosched.c

@@ -951,10 +951,6 @@ cfq_find_alloc_cfqg(struct cfq_data *cfqd, struct cgroup *cgroup, int create)
 	struct backing_dev_info *bdi = &cfqd->queue->backing_dev_info;
 	unsigned int major, minor;
 
-	/* Do we need to take this reference */
-	if (!blkiocg_css_tryget(blkcg))
-		return NULL;;
-
 	cfqg = cfqg_of_blkg(blkiocg_lookup_group(blkcg, key));
 	if (cfqg || !create)
 		goto done;
@@ -985,7 +981,6 @@ cfq_find_alloc_cfqg(struct cfq_data *cfqd, struct cgroup *cgroup, int create)
 	hlist_add_head(&cfqg->cfqd_node, &cfqd->cfqg_list);
 
 done:
-	blkiocg_css_put(blkcg);
 	return cfqg;
 }