blkcg: remove bio->bi_css and instead use bio->bi_blkg

Prior patches ensured that any bio that interacts with a request_queue
is properly associated with a blkg. This makes bio->bi_css unnecessary
as blkg maintains a reference to blkcg already.

This removes the bio field bi_css and transfers corresponding uses to
access via bi_blkg.

Signed-off-by: Dennis Zhou <dennis@kernel.org>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

3 files changed, 12 insertions, 14 deletions

diff --git a/include/linux/bio.h b/include/linux/bio.h
index f0438061a5a3..84e1c4dc703a 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -498,7 +498,7 @@ do {						\
 do {						\
 	(dst)->bi_disk = (src)->bi_disk;	\
 	(dst)->bi_partno = (src)->bi_partno;	\
-	bio_clone_blkcg_association(dst, src);	\
+	bio_clone_blkg_association(dst, src);	\
 } while (0)
 
 #define bio_dev(bio) \
@@ -512,24 +512,21 @@ static inline void bio_associate_blkg_from_page(struct bio *bio,
 #endif
 
 #ifdef CONFIG_BLK_CGROUP
-int bio_associate_blkcg(struct bio *bio, struct cgroup_subsys_state *blkcg_css);
 void bio_disassociate_blkg(struct bio *bio);
 void bio_associate_blkg(struct bio *bio);
 void bio_associate_blkg_from_css(struct bio *bio,
 				 struct cgroup_subsys_state *css);
 void bio_disassociate_task(struct bio *bio);
-void bio_clone_blkcg_association(struct bio *dst, struct bio *src);
+void bio_clone_blkg_association(struct bio *dst, struct bio *src);
 #else	/* CONFIG_BLK_CGROUP */
-static inline int bio_associate_blkcg(struct bio *bio,
-			struct cgroup_subsys_state *blkcg_css) { return 0; }
 static inline void bio_disassociate_blkg(struct bio *bio) { }
 static inline void bio_associate_blkg(struct bio *bio) { }
 static inline void bio_associate_blkg_from_css(struct bio *bio,
 					       struct cgroup_subsys_state *css)
 { }
 static inline void bio_disassociate_task(struct bio *bio) { }
-static inline void bio_clone_blkcg_association(struct bio *dst,
-			struct bio *src) { }
+static inline void bio_clone_blkg_association(struct bio *dst,
+					      struct bio *src) { }
 #endif	/* CONFIG_BLK_CGROUP */
 
 #ifdef CONFIG_HIGHMEM
diff --git a/include/linux/blk-cgroup.h b/include/linux/blk-cgroup.h
index 8b069c3775ee..f11c37f8ce09 100644
--- a/include/linux/blk-cgroup.h
+++ b/include/linux/blk-cgroup.h
@@ -309,8 +309,8 @@ static inline struct blkcg *css_to_blkcg(struct cgroup_subsys_state *css)
  */
 static inline struct blkcg *__bio_blkcg(struct bio *bio)
 {
-	if (bio && bio->bi_css)
-		return css_to_blkcg(bio->bi_css);
+	if (bio && bio->bi_blkg)
+		return bio->bi_blkg->blkcg;
 	return css_to_blkcg(blkcg_css());
 }
 
@@ -324,8 +324,8 @@ static inline struct blkcg *__bio_blkcg(struct bio *bio)
  */
 static inline struct blkcg *bio_blkcg(struct bio *bio)
 {
-	if (bio && bio->bi_css)
-		return css_to_blkcg(bio->bi_css);
+	if (bio && bio->bi_blkg)
+		return bio->bi_blkg->blkcg;
 	return NULL;
 }
 
diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
index c0ba1a038ff3..46c005d601ac 100644
--- a/include/linux/blk_types.h
+++ b/include/linux/blk_types.h
@@ -174,10 +174,11 @@ struct bio {
 	void			*bi_private;
 #ifdef CONFIG_BLK_CGROUP
 	/*
-	 * Optional css associated with this bio.  Put on bio
-	 * release.  Read comment on top of bio_associate_current().
+	 * Represents the association of the css and request_queue for the bio.
+	 * If a bio goes direct to device, it will not have a blkg as it will
+	 * not have a request_queue associated with it.  The reference is put
+	 * on release of the bio.
 	 */
-	struct cgroup_subsys_state *bi_css;
 	struct blkcg_gq		*bi_blkg;
 	struct bio_issue	bi_issue;
 #endif