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

Greg Kroah-Hartman
2021-07-19T16:09:35Z

From: Zhang Yi <yi.zhang@huawei.com>

[ 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@huawei.com>
Link: https://lore.kernel.org/r/20210619093700.920393-2-yi.zhang@huawei.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
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