[PATCH 10/14] blkcg: remove bio->bi_css and instead use bio->bi_blkg

From: Dennis Zhou
Date: Wed Dec 05 2018 - 12:11:02 EST

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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@xxxxxxxxxx>
Reviewed-by: Josef Bacik <josef@xxxxxxxxxxxxxx>
Acked-by: Tejun Heo <tj@xxxxxxxxxx>
---
block/bio.c | 59 +++++++++-----------------------------
block/bounce.c | 2 +-
drivers/block/loop.c | 5 ++--
drivers/md/raid0.c | 2 +-
include/linux/bio.h | 11 +++----
include/linux/blk-cgroup.h | 8 +++---
include/linux/blk_types.h | 7 +++--
kernel/trace/blktrace.c | 4 +--
8 files changed, 32 insertions(+), 66 deletions(-)

diff --git a/block/bio.c b/block/bio.c
index b42477b6a225..2b6bc7b805ec 100644
--- a/block/bio.c
+++ b/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)
diff --git a/block/bounce.c b/block/bounce.c
index cfb96d5170d0..ffb9e9ecfa7e 100644
--- a/block/bounce.c
+++ b/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;
diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 176ab1f28eca..0770004616de 100644
--- a/drivers/block/loop.c
+++ b/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
diff --git a/drivers/md/raid0.c b/drivers/md/raid0.c
index ac1cffd2a09b..f3fb5bb8c82a 100644
--- a/drivers/md/raid0.c
+++ b/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),
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
diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c
index 2868d85f1fb1..fac0ddf8a8e2 100644
--- a/kernel/trace/blktrace.c
+++ b/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 *
--
2.17.1

Next message: Dennis Zhou: "[PATCH 13/14] blkcg: change blkg reference counting to use percpu_ref"
Previous message: Dennis Zhou: "[PATCH 01/14] blkcg: fix ref count issue with bio_blkcg() using task_css"
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Next in thread: Dennis Zhou: "[PATCH 13/14] blkcg: change blkg reference counting to use percpu_ref"
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