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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Tejun Heo <tj@kernel.org>,
        Josef Bacik <jbacik@fb.com>, Jens Axboe <axboe@kernel.dk>
Subject: [PATCH 4.19 267/271] blk-iolatency: clear use_delay when io.latency is set to zero
Date:   Wed, 24 Jul 2019 21:22:16 +0200
Message-Id: <20190724191718.116443451@linuxfoundation.org>
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From: Tejun Heo <tj@kernel.org>

commit 5de0073fcd50cc1f150895a7bb04d3cf8067b1d7 upstream.

If use_delay was non-zero when the latency target of a cgroup was set
to zero, it will stay stuck until io.latency is enabled on the cgroup
again.  This keeps readahead disabled for the cgroup impacting
performance negatively.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Josef Bacik <jbacik@fb.com>
Fixes: d70675121546 ("block: introduce blk-iolatency io controller")
Cc: stable@vger.kernel.org # v4.19+
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 block/blk-iolatency.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/block/blk-iolatency.c
+++ b/block/blk-iolatency.c
@@ -746,8 +746,10 @@ static int iolatency_set_min_lat_nsec(st
 
 	if (!oldval && val)
 		return 1;
-	if (oldval && !val)
+	if (oldval && !val) {
+		blkcg_clear_delay(blkg);
 		return -1;
+	}
 	return 0;
 }