[PATCH] block: Fixup condition detecting exclusive opener during partition rescan

[Jan Kara <jack@suse.cz>]

The condition detecting whether somebody else has the device exclusively
open in disk_scan_partitions() has a brownpaper bag bug. It triggers also
when nobody has the device exclusively open and we are coming from
BLKRRPART path. Interestingly this didn't have any adverse effects
during testing because tools update kernel's notion of the partition
table using ioctls and don't rely on BLKRRPART. Fix the bug before
somebody trips over it.

Fixes: 8d67fc20caf8 ("block: Do not reread partition table on exclusively open device")
CC: stable@vger.kernel.org
Signed-off-by: Jan Kara <jack@suse.cz>
---
 block/genhd.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/block/genhd.c b/block/genhd.c
index 012529d36f5b..29fb2c98b401 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -367,7 +367,7 @@ int disk_scan_partitions(struct gendisk *disk, fmode_t mode, void *owner)
 	if (disk->open_partitions)
 		return -EBUSY;
 	/* Someone else has bdev exclusively open? */
-	if (disk->part0->bd_holder != owner)
+	if (disk->part0->bd_holder && disk->part0->bd_holder != owner)
 		return -EBUSY;
 
 	set_bit(GD_NEED_PART_SCAN, &disk->state);
-- 
2.35.3