zloop: use READ_ONCE() to read lo->lo_state in queue_rq path

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 <[e-mail]>
Reviewed-by: Christoph Hellwig <[e-mail]>
Signed-off-by: Yongpeng Yang <[e-mail]>
Signed-off-by: Jens Axboe <[e-mail]>

drivers/block/zloop.c

···
 	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;
 
 	/*
···
 		ret = -ENOMEM;
 		goto out;
 	}
-	zlo->state = Zlo_creating;
+	WRITE_ONCE(zlo->state, Zlo_creating);
 
 	ret = mutex_lock_killable(&zloop_ctl_mutex);
 	if (ret)
···
 	}
 
 	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",
···
 		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);