Comment # 1 on bug 1230635 from heming zhao

root cause is patch bsc1226510-fix-build-err-against-6.9.3.patch is wrong.

the patch:
-       if (handle != nbc->backing_bdev_handle) {
-               err = link_backing_dev(device, new_disk_conf->meta_dev,
handle);
+       if (file != nbc->backing_bdev_file) {                                   
+               err = link_backing_dev(device, new_disk_conf->meta_dev, file);

should be:
-       if (handle != nbc->backing_bdev_handle) {
-               err = link_backing_dev(device, new_disk_conf->meta_dev,
handle);
+       if (file_bdev(file) != nbc->backing_bdev) {                             
+               err = link_backing_dev(device, new_disk_conf->meta_dev, file);

previous code 'if (file != nbc->backing_bdev_file)' usually can be triggered. 
i.e.: the 'file' is meta_dev file handle, the backing_bdev_file is another file
handle, but they point to same device. previous code will increase sysfs refcnt
one more. new code 'file_bdev(file) != nbc->backing_bdev' compares device (not
file handle) logic is correct.