[PATCH 5.1 366/371] blk-iolatency: clear use_delay when io.latency is set to zero

[Greg Kroah-Hartman]

From: Tejun Heo <tj@xxxxxxxxxx>

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@xxxxxxxxxx>
Cc: Josef Bacik <jbacik@xxxxxx>
Fixes: d70675121546 ("block: introduce blk-iolatency io controller")
Cc: stable@xxxxxxxxxxxxxxx # v4.19+
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

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

--- a/block/blk-iolatency.c
+++ b/block/blk-iolatency.c
@@ -758,8 +758,10 @@ 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;
 }