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block: move the initial blkg lookup into blkg_tryget_closest 

By moving the initial blkg lookup into blkg_tryget_closest we get
a nicely self contained routines that does all the RCU locking.

Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Christoph Hellwig 2020-06-27 09:31:54 +02:00 committed by Jens Axboe
parent a5b97526bf
commit 13c7863d48
1 changed files with 14 additions and 19 deletions
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33
block/blk-cgroup.c
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@ -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);