NVMe: Clear QUEUE_FLAG_STACKABLE

The nvme namespace request_queue's flags are initialized to
QUEUE_FLAG_DEFAULT, which currently sets QUEUE_FLAG_STACKABLE. The
device-mapper indicates this flag means the block driver is requset
based, though this driver is bio-based and problems will occur if an nvme
namespace is used with a request based dm device. This patch clears the
stackable flag.

Signed-off-by: Keith Busch <keith.busch@intel.com>
Signed-off-by: Matthew Wilcox <matthew.r.wilcox@intel.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

drivers/block/nvme-core.c

@@ -2030,6 +2030,7 @@ static struct nvme_ns *nvme_alloc_ns(struct nvme_dev *dev, unsigned nsid,
 	if (!ns->queue)
 		goto out_free_ns;
 	ns->queue->queue_flags = QUEUE_FLAG_DEFAULT;
+	queue_flag_clear_unlocked(QUEUE_FLAG_STACKABLE, ns->queue);
 	queue_flag_set_unlocked(QUEUE_FLAG_NOMERGES, ns->queue);
 	queue_flag_set_unlocked(QUEUE_FLAG_NONROT, ns->queue);
 	queue_flag_clear_unlocked(QUEUE_FLAG_ADD_RANDOM, ns->queue);