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Subject[PATCH 09/14] block: move the initial blkg lookup into blkg_tryget_closest
Date
By moving the initial blkg lookup into blkg_tryget_closest we get
a nicely self contained routines that does all the RCU locking.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
block/blk-cgroup.c | 33 ++++++++++++++-------------------
1 file changed, 14 insertions(+), 19 deletions(-)

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index 0912820d4f8194..d21ec2acd716e7 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -1716,19 +1716,20 @@ void blkcg_add_delay(struct blkcg_gq *blkg, u64 now, u64 delta)

/**
* blkg_tryget_closest - try and get a blkg ref on the closet blkg
- * @blkg: blkg to get
+ * @bio: target bio
+ * @css: target css
*
- * This needs to be called rcu protected. As the failure mode here is to walk
- * up the blkg tree, this ensure that the blkg->parent pointers are always
- * valid. This returns the blkg that it ended up taking a reference on or %NULL
- * if no reference was taken.
+ * As the failure mode here is to walk up the blkg tree, this ensure that the
+ * blkg->parent pointers are always valid. This returns the blkg that it ended
+ * up taking a reference on or %NULL if no reference was taken.
*/
-static inline struct blkcg_gq *blkg_tryget_closest(struct blkcg_gq *blkg)
+static inline struct blkcg_gq *blkg_tryget_closest(struct bio *bio,
+ struct cgroup_subsys_state *css)
{
- struct blkcg_gq *ret_blkg = NULL;
-
- WARN_ON_ONCE(!rcu_read_lock_held());
+ struct blkcg_gq *blkg, *ret_blkg = NULL;

+ rcu_read_lock();
+ blkg = blkg_lookup_create(css_to_blkcg(css), bio->bi_disk->queue);
while (blkg) {
if (blkg_tryget(blkg)) {
ret_blkg = blkg;
@@ -1736,6 +1737,7 @@ static inline struct blkcg_gq *blkg_tryget_closest(struct blkcg_gq *blkg)
}
blkg = blkg->parent;
}
+ rcu_read_unlock();

return ret_blkg;
}
@@ -1757,21 +1759,14 @@ static inline struct blkcg_gq *blkg_tryget_closest(struct blkcg_gq *blkg)
void bio_associate_blkg_from_css(struct bio *bio,
struct cgroup_subsys_state *css)
{
- struct request_queue *q = bio->bi_disk->queue;
-
if (bio->bi_blkg)
blkg_put(bio->bi_blkg);

if (css && css->parent) {
- struct blkcg_gq *blkg;
-
- rcu_read_lock();
- blkg = blkg_lookup_create(css_to_blkcg(css), q);
- bio->bi_blkg = blkg_tryget_closest(blkg);
- rcu_read_unlock();
+ bio->bi_blkg = blkg_tryget_closest(bio, css);
} else {
- blkg_get(q->root_blkg);
- bio->bi_blkg = q->root_blkg;
+ blkg_get(bio->bi_disk->queue->root_blkg);
+ bio->bi_blkg = bio->bi_disk->queue->root_blkg;
}
}
EXPORT_SYMBOL_GPL(bio_associate_blkg_from_css);
--
2.26.2
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