[PATCH 08/14] block: bypass blkg_tryget_closest for the root_blkg
From: Christoph Hellwig <hch@lst.de>
Date: 2020-06-27 07:32:59
Also in:
cgroups, dm-devel, linux-mm, lkml
Subsystem:
block layer, control group - block io controller (blkio), the rest · Maintainers:
Jens Axboe, Tejun Heo, Josef Bacik, Linus Torvalds
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. Signed-off-by: Christoph Hellwig <hch@lst.de> --- block/blk-cgroup.c | 15 ++++++++++----- 1 file changed, 10 insertions(+), 5 deletions(-)
diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index 6aedb73ffbf473..0912820d4f8194 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c@@ -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);
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2.26.2