nfsd: fix refcount leak when file is unhashed after being found

If we wait_for_construction and find that the file is no longer hashed,
and we're going to retry the open, the old nfsd_file reference is
currently leaked. Put the reference before retrying.

Fixes: c6593366 ("nfsd: don't kill nfsd_files because of lease break error")
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Tested-by: Youzhong Yang <youzhong@gmail.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

fs/nfsd/filecache.c

@@ -1051,6 +1051,7 @@ nfsd_file_do_acquire(struct svc_rqst *rqstp, struct svc_fh *fhp,
 			status = nfserr_jukebox;
 			goto construction_err;
 		}
+		nfsd_file_put(nf);
 		open_retry = false;
 		fh_put(fhp);
 		goto retry;