nfsd: extra checks when freeing delegation stateids

We've had some reports of problems in the refcounting for delegation
stateids that we've yet to track down. Add some extra checks to ensure
that we've removed the object from various lists before freeing it.

Link: https://bugzilla.redhat.com/show_bug.cgi?id=2127067
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

fs/nfsd/nfs4state.c

@@ -1060,7 +1060,12 @@ static struct nfs4_ol_stateid * nfs4_alloc_open_stateid(struct nfs4_client *clp)
 
 static void nfs4_free_deleg(struct nfs4_stid *stid)
 {
-	WARN_ON(!list_empty(&stid->sc_cp_list));
+	struct nfs4_delegation *dp = delegstateid(stid);
+
+	WARN_ON_ONCE(!list_empty(&stid->sc_cp_list));
+	WARN_ON_ONCE(!list_empty(&dp->dl_perfile));
+	WARN_ON_ONCE(!list_empty(&dp->dl_perclnt));
+	WARN_ON_ONCE(!list_empty(&dp->dl_recall_lru));
 	kmem_cache_free(deleg_slab, stid);
 	atomic_long_dec(&num_delegations);
 }