[PATCH] Make a basic error check for failure in register_disk()

[Zdenek Kabelac <zdenek.kabelac@gmail.com>]

Make a basic error check for failure in register_disk() to avoid kernel BUG
when sysfs entry could not be created (i.e. duplicate filename).
Fix is not perfect as register_disk() and add_disk() should probably return
error code in this case but avoids this BUG message:

kernel BUG at fs/sysfs/group.c:65!
 [<ffffffff812d6eac>] ? device_add+0x3c/0x5a0
 [<ffffffff811767c3>] sysfs_create_group+0x13/0x20
 [<ffffffff810c6c14>] blk_trace_init_sysfs+0x14/0x20
 [<ffffffff8121e3b0>] blk_register_queue+0x40/0x100
 [<ffffffff81223438>] add_disk+0xf8/0x170
 [<ffffffffa00bb3aa>] dm_create+0x37a/0x5b0 [dm_mod]
 ...

Problem has been noticed during check of some dm error code path.

Signed-off-by: Zdenek Kabelac <zkabelac@redhat.com>

---
 block/genhd.c |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)

diff --git a/block/genhd.c b/block/genhd.c
index f4c64c2..317f961 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -544,6 +544,10 @@ void add_disk(struct gendisk *disk)
 	blk_register_region(disk_devt(disk), disk->minors, NULL,
 			    exact_match, exact_lock, disk);
 	register_disk(disk);
+	if (!disk_to_dev(disk)->kobj.parent) {
+		WARN_ON(1);
+		return;
+	}
 	blk_register_queue(disk);

 	bdi = &disk->queue->backing_dev_info;