block: return -EBUSY when there are open partitions in blkdev_reread_part

stable inclusion
from stable-5.10.33
commit fc2454cc0c4bbf3ab7556c8b38e042c6c7651e42
bugzilla: 51834
CVE: NA

--------------------------------

[ Upstream commit 68e6582e ]

The switch to go through blkdev_get_by_dev means we now ignore the
return value from bdev_disk_changed in __blkdev_get.  Add a manual
check to restore the old semantics.

Fixes: 4601b4b1 ("block: reopen the device in blkdev_reread_part")
Reported-by: NKarel Zak <kzak@redhat.com>
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20210421160502.447418-1-hch@lst.deSigned-off-by: NJens Axboe <axboe@kernel.dk>
Signed-off-by: NSasha Levin <sashal@kernel.org>
Signed-off-by: NChen Jun <chenjun102@huawei.com>
Acked-by: NWeilong Chen <chenweilong@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

block/ioctl.c

@@ -98,6 +98,8 @@ static int blkdev_reread_part(struct block_device *bdev, fmode_t mode)
 		return -EINVAL;
 	if (!capable(CAP_SYS_ADMIN))
 		return -EACCES;
+	if (bdev->bd_part_count)
+		return -EBUSY;
 
 	/*
 	 * Reopen the device to revalidate the driver state and force a