staging: lustre: lmv: correctly iput lmo_root

staging: lustre: lmv: correctly iput lmo_root

[ Upstream commit 17556cdbe6ed70a6a20e597b228628f7f34387f8 ]

Commit 8f18c8a48b73 ("staging: lustre: lmv: separate master object
with master stripe") changed how lmo_root inodes were managed,
particularly when LMV_HASH_FLAG_MIGRATION is not set.
Previously lsm_md_oinfo[0].lmo_root was always a borrowed
inode reference and didn't need to by iput().
Since the change, that special case only applies when
LMV_HASH_FLAG_MIGRATION is set

In the upstream (lustre-release) version of this patch [Commit
60e07b972114 ("LU-4690 lod: separate master object with master
stripe")] the for loop in the lmv_unpack_md() was changed to count
from 0 and to ignore entry 0 if LMV_HASH_FLAG_MIGRATION is set.
In the patch that got applied to Linux, that change was missing,
so lsm_md_oinfo[0].lmo_root is never iput().
This results in a "VFS: Busy inodes" warning at unmount.

Fixes: 8f18c8a48b73 ("staging: lustre: lmv: separate master object with master stripe")
Signed-off-by: NeilBrown <neilb@suse.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>