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

Prior patches ensured that all bios are now associated with some blkg.
This now makes bio->bi_css unnecessary as blkg maintains a reference to
the blkcg already.

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

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

2 files changed, 12 insertions, 46 deletions

diff --git a/block/bio.c b/block/bio.c
index 387480de6992..71cfe3720ea7 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -609,7 +609,7 @@ 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);
 }
@@ -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_associate_blkg - associate a bio with the a blkg
  * @bio: target bio
  * @blkg: the blkg to associate
@@ -2033,7 +2005,6 @@ int bio_associate_blkg_from_css(struct bio *bio,
 				struct cgroup_subsys_state *css)
 {
 	css_get(css);
-	bio->bi_css = css;
 	return __bio_associate_blkg_from_css(bio, css);
 }
 EXPORT_SYMBOL_GPL(bio_associate_blkg_from_css);
@@ -2054,12 +2025,11 @@ int bio_associate_blkg_from_page(struct bio *bio, struct page *page)
 {
 	struct cgroup_subsys_state *css;
 
-	if (unlikely(bio->bi_css))
+	if (unlikely(bio->bi_blkg))
 		return -EBUSY;
 	if (!page->mem_cgroup)
 		return 0;
 	css = cgroup_get_e_css(page->mem_cgroup->css.cgroup, &io_cgrp_subsys);
-	bio->bi_css = css;
 
 	return __bio_associate_blkg_from_css(bio, css);
 }
@@ -2085,8 +2055,7 @@ int bio_associate_create_blkg(struct request_queue *q, struct bio *bio)
 
 	rcu_read_lock();
 
-	bio_associate_blkcg(bio, NULL);
-	blkcg = bio_blkcg(bio);
+	blkcg = css_to_blkcg(blkcg_get_css());
 
 	if (!blkcg->css.parent) {
 		ret = bio_associate_blkg(bio, q->root_blkg);
@@ -2110,30 +2079,27 @@ void bio_disassociate_task(struct bio *bio)
 		put_io_context(bio->bi_ioc);
 		bio->bi_ioc = NULL;
 	}
-	if (bio->bi_css) {
-		css_put(bio->bi_css);
-		bio->bi_css = NULL;
-	}
 	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;
 	}
 }
 
 /**
- * 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)
diff --git a/block/bounce.c b/block/bounce.c
index 7a08703b1204..b30071ac4ec6 100644
--- a/block/bounce.c
+++ b/block/bounce.c
@@ -257,7 +257,7 @@ 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);