[PATCH] block: fix attribute_group lost if set before add_disk

[Sun Feng <loyou85@gmail.com>]

after commit 52b85909f85d("block: fold register_disk into device_add_disk")
when set attribute_group with following code:

  disk_to_dev(disk)->groups = attr_groups;
  err = add_disk(disk);

disk_to_dev(disk)->groups will set to NULL in device_add_disk,

  static inline int __must_check add_disk(struct gendisk *disk)
  {
       	return device_add_disk(NULL, disk, NULL);
  }
  int __must_check device_add_disk(struct device *parent, ...
                                 const struct attribute_group **groups)
  {
	…
	ddev->groups = groups

and it will lose attribute group set.

Signed-off-by: Sun Feng <loyou85@gmail.com>
---
 block/genhd.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/block/genhd.c b/block/genhd.c
index 27205ae..6b76f67 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -459,7 +459,10 @@ int __must_check device_add_disk(struct device *parent, struct gendisk *disk,
 	dev_set_uevent_suppress(ddev, 1);
 
 	ddev->parent = parent;
-	ddev->groups = groups;
+	if (groups) {
+		WARN_ON(ddev->groups);
+		ddev->groups = groups;
+	}
 	dev_set_name(ddev, "%s", disk->disk_name);
 	if (!(disk->flags & GENHD_FL_HIDDEN))
 		ddev->devt = MKDEV(disk->major, disk->first_minor);
-- 
2.7.4