linux-kernel - [PATCH 03/14] block: really clone the block cgroup in bio_clone_blkg

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Message-Id: <20200627073159.2447325-4-hch@lst.de>
Date:   Sat, 27 Jun 2020 09:31:48 +0200
From:   Christoph Hellwig <hch@....de>
To:     Jens Axboe <axboe@...nel.dk>, Tejun Heo <tj@...nel.org>
Cc:     Dennis Zhou <dennis@...nel.org>, Li Zefan <lizefan@...wei.com>,
        Johannes Weiner <hannes@...xchg.org>, dm-devel@...hat.com,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        cgroups@...r.kernel.org, linux-mm@...ck.org
Subject: [PATCH 03/14] block: really clone the block cgroup in bio_clone_blkg_association

bio_clone_blkg_association is supposed to clone the associatation, but
actually ends up doing a search with a tryget.  As we know we have a
reference on the source cgroup just get an unconditional additional
reference to it and call it a day.  That also removes the need for
a RCU critical section.

Signed-off-by: Christoph Hellwig <hch@....de>
---
 block/bio.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/block/bio.c b/block/bio.c
index 8aef4460b32e0e..e1d01acce8070c 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -1737,12 +1737,12 @@ EXPORT_SYMBOL_GPL(bio_associate_blkg);
  */
 void bio_clone_blkg_association(struct bio *dst, struct bio *src)
 {
-	rcu_read_lock();
-
-	if (src->bi_blkg)
-		__bio_associate_blkg(dst, src->bi_blkg);
-
-	rcu_read_unlock();
+	if (src->bi_blkg) {
+		if (dst->bi_blkg)
+			blkg_put(dst->bi_blkg);
+		blkg_get(src->bi_blkg);
+		dst->bi_blkg = src->bi_blkg;
+	}
 }
 EXPORT_SYMBOL_GPL(bio_clone_blkg_association);
 #endif /* CONFIG_BLK_CGROUP */
-- 
2.26.2