NFSD: send OP_CB_RECALL_ANY to clients when number of delegations reaches its limit

The NFS server should ask clients to voluntarily return unused
delegations when the number of granted delegations reaches the
max_delegations. This is so that the server can continue to
grant delegations for new requests.
Signed-off-by: Dai Ngo <dai.ngo@oracle.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Tested-by: Chen Hanxiao <chenhx.fnst@fujitsu.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

fs/nfsd/nfs4state.c

@@ -87,6 +87,7 @@ static void nfs4_free_ol_stateid(struct nfs4_stid *stid);
 void nfsd4_end_grace(struct nfsd_net *nn);
 static void _free_cpntf_state_locked(struct nfsd_net *nn, struct nfs4_cpntf_state *cps);
 static void nfsd4_file_hash_remove(struct nfs4_file *fi);
+static void deleg_reaper(struct nfsd_net *nn);
 
 /* Locking: */
 
@@ -6550,6 +6551,8 @@ nfs4_laundromat(struct nfsd_net *nn)
 	/* service the server-to-server copy delayed unmount list */
 	nfsd4_ssc_expire_umount(nn);
 #endif
+	if (atomic_long_read(&num_delegations) >= max_delegations)
+		deleg_reaper(nn);
 out:
 	return max_t(time64_t, lt.new_timeo, NFSD_LAUNDROMAT_MINTIMEOUT);
 }