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block: bypass blkg_tryget_closest for the root_blkg

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The root_blkg is only torn down at the very end of removing a queue.
So in the I/O submission path is always has a life reference and we
can just grab another one using blkg_get instead of doing a tryget
and parent walk that won't lead anywhere.

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 09:31:53 +02:00 committed by Jens Axboe
parent 8c54628752
commit a5b97526bf
1 changed files with 10 additions and 5 deletions
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15
block/blk-cgroup.c
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@ -1758,16 +1758,21 @@ void bio_associate_blkg_from_css(struct bio *bio,
struct cgroup_subsys_state *css)
{
struct request_queue *q = bio->bi_disk->queue;
struct blkcg_gq *blkg = q->root_blkg;
if (bio->bi_blkg)
blkg_put(bio->bi_blkg);
rcu_read_lock();
if (css && css->parent)
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(blkg);
rcu_read_unlock();
} else {
blkg_get(q->root_blkg);
bio->bi_blkg = q->root_blkg;
}
}
EXPORT_SYMBOL_GPL(bio_associate_blkg_from_css);