loopdev: update block device size in loop_set_status()

Loop device driver sometimes fails to impose the size limit on the
device. Keep issuing following two commands:

losetup --offset 7517244416 --sizelimit 3224971264 /dev/loop0 backed_file
blockdev --getsize64 /dev/loop0

blockdev reports file size instead of sizelimit several out of 100 times.

The problems are:

	- losetup set up the device in two ioctl:
		  LOOP_SET_FD and LOOP_SET_STATUS64.

	- LOOP_SET_STATUS64 only update size of gendisk.

Block device size will be updated lazily when device comes to use. If udev
rushes in between the two ioctl, it will bring in a block device whose
size is backing file size. If the device is not released after
LOOP_SET_STATUS64 ioctl, blockdev will not see the updated size.

Update block size in LOOP_SET_STATUS64 ioctl.
Signed-off-by: Guo Chao <yan@linux.vnet.ibm.com>
Reported-by: M. Hindess <hindessm@uk.ibm.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Guo Chao <yan@linux.vnet.ibm.com>
Cc: Nikanth Karthikesan <knikanth@suse.de>
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/block/loop.c

@@ -1092,8 +1092,13 @@ loop_set_status(struct loop_device *lo, const struct loop_info64 *info)
 
 	if (lo->lo_offset != info->lo_offset ||
 	    lo->lo_sizelimit != info->lo_sizelimit) {
+		struct block_device *bdev = lo->lo_device;
+
 		if (figure_loop_size(lo, info->lo_offset, info->lo_sizelimit))
 			return -EFBIG;
+
+		bd_set_size(bdev, (loff_t)get_capacity(bdev->bd_disk) << 9);
+		kobject_uevent(&disk_to_dev(bdev->bd_disk)->kobj, KOBJ_CHANGE);
 	}
 	loop_config_discard(lo);