NFSD: Add documenting comment for nfsd4_release_lockowner()

And return explicit nfserr values that match what is documented in the
new comment / API contract.
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

fs/nfsd/nfs4state.c

@@ -7524,6 +7524,23 @@ check_for_locks(struct nfs4_file *fp, struct nfs4_lockowner *lowner)
 	return status;
 }
 
+/**
+ * nfsd4_release_lockowner - process NFSv4.0 RELEASE_LOCKOWNER operations
+ * @rqstp: RPC transaction
+ * @cstate: NFSv4 COMPOUND state
+ * @u: RELEASE_LOCKOWNER arguments
+ *
+ * The lockowner's so_count is bumped when a lock record is added
+ * or when copying a conflicting lock. The latter case is brief,
+ * but can lead to fleeting false positives when looking for
+ * locks-in-use.
+ *
+ * Return values:
+ *   %nfs_ok: lockowner released or not found
+ *   %nfserr_locks_held: lockowner still in use
+ *   %nfserr_stale_clientid: clientid no longer active
+ *   %nfserr_expired: clientid not recognized
+ */
 __be32
 nfsd4_release_lockowner(struct svc_rqst *rqstp,
 			struct nfsd4_compound_state *cstate,
@@ -7550,7 +7567,7 @@ nfsd4_release_lockowner(struct svc_rqst *rqstp,
 	lo = find_lockowner_str_locked(clp, &rlockowner->rl_owner);
 	if (!lo) {
 		spin_unlock(&clp->cl_lock);
-		return status;
+		return nfs_ok;
 	}
 	if (atomic_read(&lo->lo_owner.so_count) != 2) {
 		spin_unlock(&clp->cl_lock);
@@ -7566,11 +7583,11 @@ nfsd4_release_lockowner(struct svc_rqst *rqstp,
 		put_ol_stateid_locked(stp, &reaplist);
 	}
 	spin_unlock(&clp->cl_lock);
+
 	free_ol_stateid_reaplist(&reaplist);
 	remove_blocked_locks(lo);
 	nfs4_put_stateowner(&lo->lo_owner);
-
-	return status;
+	return nfs_ok;
 }
 
 static inline struct nfs4_client_reclaim *