[SRU C][PATCH 8/8] blk-wbt: wake up all when we scale up, not down

[Mauricio Faria de Oliveira]

From: Josef Bacik <josef at toxicpanda.com>

BugLink: https://bugs.launchpad.net/bugs/1810998

Tetsuo brought to my attention that I screwed up the scale_up/scale_down
helpers when I factored out the rq-qos code.  We need to wake up all the
waiters when we add slots for requests to make, not when we shrink the
slots.  Otherwise we'll end up things waiting forever.  This was a
mistake and simply puts everything back the way it was.

cc: stable at vger.kernel.org
Fixes: a79050434b45 ("blk-rq-qos: refactor out common elements of blk-wbt")
eported-by: Tetsuo Handa <penguin-kernel at i-love.sakura.ne.jp>
Signed-off-by: Josef Bacik <josef at toxicpanda.com>
Signed-off-by: Jens Axboe <axboe at kernel.dk>
(cherry picked from commit 5e65a20341e02df637d1c16cd487858d2c6a876a)
Signed-off-by: Mauricio Faria de Oliveira <mfo at canonical.com>
---
 block/blk-wbt.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/block/blk-wbt.c b/block/blk-wbt.c
index d6c1d42b85c5..4e30632d3773 100644
--- a/block/blk-wbt.c
+++ b/block/blk-wbt.c
@@ -310,6 +310,7 @@ static void scale_up(struct rq_wb *rwb)
 	rq_depth_scale_up(&rwb->rq_depth);
 	calc_wb_limits(rwb);
 	rwb->unknown_cnt = 0;
+	rwb_wake_all(rwb);
 	rwb_trace_step(rwb, "scale up");
 }
 
@@ -318,7 +319,6 @@ static void scale_down(struct rq_wb *rwb, bool hard_throttle)
 	rq_depth_scale_down(&rwb->rq_depth, hard_throttle);
 	calc_wb_limits(rwb);
 	rwb->unknown_cnt = 0;
-	rwb_wake_all(rwb);
 	rwb_trace_step(rwb, "scale down");
 }
 
-- 
2.17.1