blk-cgroup: remove __bio_blkcg

Remove the unused and deprecated __bio_blkcg helper.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Tejun Heo <tj@kernel.org>
Link: https://lore.kernel.org/r/20220420042723.1010598-2-hch@lst.deSigned-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-cgroup.h

@@ -139,27 +139,6 @@ static inline struct cgroup_subsys_state *blkcg_css(void)
 	return task_css(current, io_cgrp_id);
 }
 
-/**
- * __bio_blkcg - internal, inconsistent version to get blkcg
- *
- * DO NOT USE.
- * This function is inconsistent and consequently is dangerous to use.  The
- * first part of the function returns a blkcg where a reference is owned by the
- * bio.  This means it does not need to be rcu protected as it cannot go away
- * with the bio owning a reference to it.  However, the latter potentially gets
- * it from task_css().  This can race against task migration and the cgroup
- * dying.  It is also semantically different as it must be called rcu protected
- * and is susceptible to failure when trying to get a reference to it.
- * Therefore, it is not ok to assume that *_get() will always succeed on the
- * blkcg returned here.
- */
-static inline struct blkcg *__bio_blkcg(struct bio *bio)
-{
-	if (bio && bio->bi_blkg)
-		return bio->bi_blkg->blkcg;
-	return css_to_blkcg(blkcg_css());
-}
-
 /**
  * bio_issue_as_root_blkg - see if this bio needs to be issued as root blkg
  * @return: true if this bio needs to be submitted with the root blkg context.
@@ -471,8 +450,6 @@ static inline int blkcg_activate_policy(struct request_queue *q,
 static inline void blkcg_deactivate_policy(struct request_queue *q,
 					   const struct blkcg_policy *pol) { }
 
-static inline struct blkcg *__bio_blkcg(struct bio *bio) { return NULL; }
-
 static inline struct blkg_policy_data *blkg_to_pd(struct blkcg_gq *blkg,
 						  struct blkcg_policy *pol) { return NULL; }
 static inline struct blkcg_gq *pd_to_blkg(struct blkg_policy_data *pd) { return NULL; }