[PATCH 4.19 117/421] blk-wbt: introduce a new disable state to prevent false positive by rwb_enabled()

[Greg Kroah-Hartman]

From: Zhang Yi <yi.zhang@xxxxxxxxxx>

[ Upstream commit 1d0903d61e9645c6330b94247b96dd873dfc11c8 ]

Now that we disable wbt by simply zero out rwb->wb_normal in
wbt_disable_default() when switch elevator to bfq, but it's not safe
because it will become false positive if we change queue depth. If it
become false positive between wbt_wait() and wbt_track() when submit
write request, it will lead to drop rqw->inflight to -1 in wbt_done(),
which will end up trigger IO hung. Fix this issue by introduce a new
state which mean the wbt was disabled.

Fixes: a79050434b45 ("blk-rq-qos: refactor out common elements of blk-wbt")
Signed-off-by: Zhang Yi <yi.zhang@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20210619093700.920393-2-yi.zhang@xxxxxxxxxx
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 block/blk-wbt.c | 5 +++--
 block/blk-wbt.h | 1 +
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/block/blk-wbt.c b/block/blk-wbt.c
index 50f2abfa1a60..08623f37617f 100644
--- a/block/blk-wbt.c
+++ b/block/blk-wbt.c
@@ -76,7 +76,8 @@ enum {
 
 static inline bool rwb_enabled(struct rq_wb *rwb)
 {
-	return rwb && rwb->wb_normal != 0;
+	return rwb && rwb->enable_state != WBT_STATE_OFF_DEFAULT &&
+		      rwb->wb_normal != 0;
 }
 
 static void wb_timestamp(struct rq_wb *rwb, unsigned long *var)
@@ -764,7 +765,7 @@ void wbt_disable_default(struct request_queue *q)
 	rwb = RQWB(rqos);
 	if (rwb->enable_state == WBT_STATE_ON_DEFAULT) {
 		blk_stat_deactivate(rwb->cb);
-		rwb->wb_normal = 0;
+		rwb->enable_state = WBT_STATE_OFF_DEFAULT;
 	}
 }
 EXPORT_SYMBOL_GPL(wbt_disable_default);
diff --git a/block/blk-wbt.h b/block/blk-wbt.h
index f47218d5b3b2..dd0d0f297d1e 100644
--- a/block/blk-wbt.h
+++ b/block/blk-wbt.h
@@ -34,6 +34,7 @@ enum {
 enum {
 	WBT_STATE_ON_DEFAULT	= 1,
 	WBT_STATE_ON_MANUAL	= 2,
+	WBT_STATE_OFF_DEFAULT
 };
 
 struct rq_wb {
-- 
2.30.2