nvme-multipath: set bdi capabilities once

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>

drivers/nvme/host/core.c

@@ -1909,13 +1909,6 @@ static void __nvme_revalidate_disk(struct gendisk *disk, struct nvme_id_ns *id)
 	if (ns->head->disk) {
 		nvme_update_disk_info(ns->head->disk, ns, id);
 		blk_queue_stack_limits(ns->head->disk->queue, ns->queue);
-		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;
-		}
-
 		revalidate_disk(ns->head->disk);
 	}
 #endif

drivers/nvme/host/multipath.c

@@ -3,6 +3,7 @@
  * Copyright (c) 2017-2018 Christoph Hellwig.
  */
 
+#include <linux/backing-dev.h>
 #include <linux/moduleparam.h>
 #include <trace/events/block.h>
 #include "nvme.h"
@@ -666,6 +667,13 @@ 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)