[PATCH v4 2/2] zloop: use READ_ONCE() to read lo->lo_state in queue_rq path

[Yongpeng Yang <yangyongpeng.storage@gmail.com>]

From: Yongpeng Yang <yangyongpeng@xiaomi.com>

In the queue_rq path, zlo->state is accessed without locking, and direct
access may read stale data. This patch uses READ_ONCE() to read
zlo->state and data_race() to silence code checkers, and changes all
assignments to use WRITE_ONCE().

Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Yongpeng Yang <yangyongpeng@xiaomi.com>
---
v3:
- Use WRITE_ONCE() instead of assignments to update state.
v2:
- Use READ_ONCE() instead of converting state to atomic_t type.
---
 drivers/block/zloop.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/block/zloop.c b/drivers/block/zloop.c
index 77bd6081b244..8e334f5025fc 100644
--- a/drivers/block/zloop.c
+++ b/drivers/block/zloop.c
@@ -697,7 +697,7 @@ static blk_status_t zloop_queue_rq(struct blk_mq_hw_ctx *hctx,
 	struct zloop_cmd *cmd = blk_mq_rq_to_pdu(rq);
 	struct zloop_device *zlo = rq->q->queuedata;
 
-	if (zlo->state == Zlo_deleting)
+	if (data_race(READ_ONCE(zlo->state)) == Zlo_deleting)
 		return BLK_STS_IOERR;
 
 	/*
@@ -1002,7 +1002,7 @@ static int zloop_ctl_add(struct zloop_options *opts)
 		ret = -ENOMEM;
 		goto out;
 	}
-	zlo->state = Zlo_creating;
+	WRITE_ONCE(zlo->state, Zlo_creating);
 
 	ret = mutex_lock_killable(&zloop_ctl_mutex);
 	if (ret)
@@ -1113,7 +1113,7 @@ static int zloop_ctl_add(struct zloop_options *opts)
 	}
 
 	mutex_lock(&zloop_ctl_mutex);
-	zlo->state = Zlo_live;
+	WRITE_ONCE(zlo->state, Zlo_live);
 	mutex_unlock(&zloop_ctl_mutex);
 
 	pr_info("zloop: device %d, %u zones of %llu MiB, %u B block size\n",
@@ -1177,7 +1177,7 @@ static int zloop_ctl_remove(struct zloop_options *opts)
 		ret = -EINVAL;
 	} else {
 		idr_remove(&zloop_index_idr, zlo->id);
-		zlo->state = Zlo_deleting;
+		WRITE_ONCE(zlo->state, Zlo_deleting);
 	}
 
 	mutex_unlock(&zloop_ctl_mutex);
-- 
2.43.0