[PATCH] nvme: fix a crash in nvme_mpath_add_disk

[Christoph Hellwig]

For private namespaces ns->head_disk is NULL, so add a NULL check
before updating the BDI capabilities.

Fixes: b2ce4d90690b ("nvme-multipath: set bdi capabilities once")
Reported-by: Avinash M N <Avinash.M.N at wdc.com>
Signed-off-by: Christoph Hellwig <hch at lst.de>
---
 drivers/nvme/host/multipath.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/nvme/host/multipath.c b/drivers/nvme/host/multipath.c
index 18d084ed497ef3..e3eaff10444f00 100644
--- a/drivers/nvme/host/multipath.c
+++ b/drivers/nvme/host/multipath.c
@@ -672,10 +672,10 @@ void nvme_mpath_add_disk(struct nvme_ns *ns, struct nvme_id_ns *id)
 	}
 
 	if (bdi_cap_stable_pages_required(ns->queue->backing_dev_info)) {
-		struct backing_dev_info *info =
-					ns->head->disk->queue->backing_dev_info;
+		struct gendisk *disk = ns->head->disk;
 
-		info->capabilities |= BDI_CAP_STABLE_WRITES;
+		if (disk)
+			disk->queue->backing_dev_info |= BDI_CAP_STABLE_WRITES;
 	}
 }
 
-- 
2.26.2