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>

block/bio.c

@@ -610,7 +610,7 @@ void __bio_clone_fast(struct bio *bio, struct bio *bio_src)
 	bio->bi_iter = bio_src->bi_iter;
 	bio->bi_io_vec = bio_src->bi_io_vec;
 
-	bio_clone_blkcg_association(bio, bio_src);
+	bio_clone_blkg_association(bio, bio_src);
 	blkcg_bio_issue_init(bio);
 }
 EXPORT_SYMBOL(__bio_clone_fast);
@@ -1957,34 +1957,6 @@ EXPORT_SYMBOL(bioset_init_from_src);
 
 #ifdef CONFIG_BLK_CGROUP
 
-/**
- * bio_associate_blkcg - associate a bio with the specified blkcg
- * @bio: target bio
- * @blkcg_css: css of the blkcg to associate
- *
- * Associate @bio with the blkcg specified by @blkcg_css.  Block layer will
- * treat @bio as if it were issued by a task which belongs to the blkcg.
- *
- * This function takes an extra reference of @blkcg_css which will be put
- * when @bio is released.  The caller must own @bio and is responsible for
- * synchronizing calls to this function.  If @blkcg_css is %NULL, a call to
- * blkcg_get_css() finds the current css from the kthread or task.
- */
-int bio_associate_blkcg(struct bio *bio, struct cgroup_subsys_state *blkcg_css)
-{
-	if (unlikely(bio->bi_css))
-		return -EBUSY;
-
-	if (blkcg_css)
-		css_get(blkcg_css);
-	else
-		blkcg_css = blkcg_get_css();
-
-	bio->bi_css = blkcg_css;
-	return 0;
-}
-EXPORT_SYMBOL_GPL(bio_associate_blkcg);
-
 /**
  * bio_disassociate_blkg - puts back the blkg reference if associated
  * @bio: target bio
@@ -1994,6 +1966,8 @@ EXPORT_SYMBOL_GPL(bio_associate_blkcg);
 void bio_disassociate_blkg(struct bio *bio)
 {
 	if (bio->bi_blkg) {
+		/* a ref is always taken on css */
+		css_put(&bio_blkcg(bio)->css);
 		blkg_put(bio->bi_blkg);
 		bio->bi_blkg = NULL;
 	}
@@ -2047,7 +2021,6 @@ void bio_associate_blkg_from_css(struct bio *bio,
 				 struct cgroup_subsys_state *css)
 {
 	css_get(css);
-	bio->bi_css = css;
 	__bio_associate_blkg_from_css(bio, css);
 }
 EXPORT_SYMBOL_GPL(bio_associate_blkg_from_css);
@@ -2066,13 +2039,10 @@ void bio_associate_blkg_from_page(struct bio *bio, struct page *page)
 {
 	struct cgroup_subsys_state *css;
 
-	if (unlikely(bio->bi_css))
-		return;
 	if (!page->mem_cgroup)
 		return;
 
 	css = cgroup_get_e_css(page->mem_cgroup->css.cgroup, &io_cgrp_subsys);
-	bio->bi_css = css;
 	__bio_associate_blkg_from_css(bio, css);
 }
 #endif /* CONFIG_MEMCG */
@@ -2094,8 +2064,10 @@ void bio_associate_blkg(struct bio *bio)
 
 	rcu_read_lock();
 
-	bio_associate_blkcg(bio, NULL);
-	blkcg = bio_blkcg(bio);
+	if (bio->bi_blkg)
+		blkcg = bio->bi_blkg->blkcg;
+	else
+		blkcg = css_to_blkcg(blkcg_get_css());
 
 	if (!blkcg->css.parent) {
 		__bio_associate_blkg(bio, q->root_blkg);
@@ -2115,27 +2087,22 @@ EXPORT_SYMBOL_GPL(bio_associate_blkg);
  */
 void bio_disassociate_task(struct bio *bio)
 {
-	if (bio->bi_css) {
-		css_put(bio->bi_css);
-		bio->bi_css = NULL;
-	}
 	bio_disassociate_blkg(bio);
 }
 
 /**
- * bio_clone_blkcg_association - clone blkcg association from src to dst bio
+ * bio_clone_blkg_association - clone blkg association from src to dst bio
  * @dst: destination bio
  * @src: source bio
  */
-void bio_clone_blkcg_association(struct bio *dst, struct bio *src)
+void bio_clone_blkg_association(struct bio *dst, struct bio *src)
 {
-	if (src->bi_css)
-		WARN_ON(bio_associate_blkcg(dst, src->bi_css));
-
-	if (src->bi_blkg)
+	if (src->bi_blkg) {
+		css_get(&bio_blkcg(src)->css);
 		__bio_associate_blkg(dst, src->bi_blkg);
+	}
 }
-EXPORT_SYMBOL_GPL(bio_clone_blkcg_association);
+EXPORT_SYMBOL_GPL(bio_clone_blkg_association);
 #endif /* CONFIG_BLK_CGROUP */
 
 static void __init biovec_init_slabs(void)

block/bounce.c

@@ -277,7 +277,7 @@ static struct bio *bounce_clone_bio(struct bio *bio_src, gfp_t gfp_mask,
 		}
 	}
 
-	bio_clone_blkcg_association(bio, bio_src);
+	bio_clone_blkg_association(bio, bio_src);
 	blkcg_bio_issue_init(bio);
 
 	return bio;

drivers/block/loop.c

@@ -77,6 +77,7 @@
 #include <linux/falloc.h>
 #include <linux/uio.h>
 #include <linux/ioprio.h>
+#include <linux/blk-cgroup.h>
 
 #include "loop.h"
 
@@ -1820,8 +1821,8 @@ static blk_status_t loop_queue_rq(struct blk_mq_hw_ctx *hctx,
 
 	/* always use the first bio's css */
 #ifdef CONFIG_BLK_CGROUP
-	if (cmd->use_aio && rq->bio && rq->bio->bi_css) {
-		cmd->css = rq->bio->bi_css;
+	if (cmd->use_aio && rq->bio && rq->bio->bi_blkg) {
+		cmd->css = &bio_blkcg(rq->bio)->css;
 		css_get(cmd->css);
 	} else
 #endif

drivers/md/raid0.c

@@ -542,7 +542,7 @@ static void raid0_handle_discard(struct mddev *mddev, struct bio *bio)
 		    !discard_bio)
 			continue;
 		bio_chain(discard_bio, bio);
-		bio_clone_blkcg_association(discard_bio, bio);
+		bio_clone_blkg_association(discard_bio, bio);
 		if (mddev->gendisk)
 			trace_block_bio_remap(bdev_get_queue(rdev->bdev),
 				discard_bio, disk_devt(mddev->gendisk),

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

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;
 }
 

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

kernel/trace/blktrace.c

@@ -764,9 +764,9 @@ blk_trace_bio_get_cgid(struct request_queue *q, struct bio *bio)
 	if (!bt || !(blk_tracer_flags.val & TRACE_BLK_OPT_CGROUP))
 		return NULL;
 
-	if (!bio->bi_css)
+	if (!bio->bi_blkg)
 		return NULL;
-	return cgroup_get_kernfs_id(bio->bi_css->cgroup);
+	return cgroup_get_kernfs_id(bio_blkcg(bio)->css.cgroup);
 }
 #else
 static union kernfs_node_id *