[PATCH 1/1] Fix NULL pointer dereference in register_disk

[zhengbin <zhengbin13@xxxxxxxxxx>]

If __device_add_disk-->bdi_register_owner-->bdi_register-->
bdi_register_va-->device_create_vargs fails, bdi->dev is still
NULL, __device_add_disk-->register_disk will visit bdi->dev->kobj.
This patch fixes that.

Signed-off-by: zhengbin <zhengbin13@xxxxxxxxxx>
---
 block/genhd.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/block/genhd.c b/block/genhd.c
index 1dd8fd6..78b82d2 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -655,10 +655,12 @@ static void register_disk(struct device *parent, struct gendisk *disk,
 		kobject_uevent(&part_to_dev(part)->kobj, KOBJ_ADD);
 	disk_part_iter_exit(&piter);

-	err = sysfs_create_link(&ddev->kobj,
-				&disk->queue->backing_dev_info->dev->kobj,
-				"bdi");
-	WARN_ON(err);
+	if (disk->queue->backing_dev_info->dev) {
+		err = sysfs_create_link(&ddev->kobj,
+			  &disk->queue->backing_dev_info->dev->kobj,
+			  "bdi");
+		WARN_ON(err);
+	}
 }

 /**
--
2.7.4