6447452 re-creating zfs files can lead to failure to unmount

[neil.per...@sun.com]

Author: perrin
Repository: /hg/onnv/onnv-gate
Revision: 61420810b69c00d91d0c9eb3944a1bf9b0d9f8a4
Log message:
6447452 re-creating zfs files can lead to failure to unmount

Files:
        update: usr/src/uts/common/fs/zfs/zfs_vnops.c