nvme-multipath: set bdi capabilities once

[ Upstream commit b2ce4d90 ]

The queues' backing device info capabilities don't change with each
namespace revalidation. Set it only when each path's request_queue
is initially added to a multipath queue.
Signed-off-by: Keith Busch <kbusch@kernel.org>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>

drivers/nvme/host/multipath.c

@@ -11,6 +11,7 @@
  * more details.
  */
 
+#include <linux/backing-dev.h>
 #include <linux/moduleparam.h>
 #include <trace/events/block.h>
 #include "nvme.h"
@@ -521,6 +522,13 @@ void nvme_mpath_add_disk(struct nvme_ns *ns, struct nvme_id_ns *id)
 		nvme_mpath_set_live(ns);
 		mutex_unlock(&ns->head->lock);
 	}
+
+	if (bdi_cap_stable_pages_required(ns->queue->backing_dev_info)) {
+		struct backing_dev_info *info =
+					ns->head->disk->queue->backing_dev_info;
+
+		info->capabilities |= BDI_CAP_STABLE_WRITES;
+	}
 }
 
 void nvme_mpath_remove_disk(struct nvme_ns_head *head)