nvme: fix a crash in nvme_mpath_add_disk

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@wdc.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Max Gurtovoy <maxg@mellanox.com>

diff --git a/drivers/nvme/host/multipath.c b/drivers/nvme/host/multipath.c
index 18d084e..6650947 100644 (file)
--- a/drivers/nvme/host/multipath.c
+++ b/drivers/nvme/host/multipath.c
@@ -672,10 +672,11 @@ 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->capabilities |=
+                                       BDI_CAP_STABLE_WRITES;
        }
 }