nfsd: eliminate special handling of NFS4ERR_SEQ_MISORDERED

On a SEQ_MISORDERED error, the current code will reattempt the call, but
set the slot sequence ID to 1. I can find no mention of this remedy in
the spec, and it seems potentially dangerous. It's possible that the
last call was sent with seqid 1, and doing this will cause a
retransmission of the reply.

Drop this special handling, and always treat SEQ_MISORDERED like
BADSLOT. Retry the call, but leak the slot so that it is no longer used.

Signed-off-by: Jeff Layton <[e-mail]>
Signed-off-by: Chuck Lever <[e-mail]>

fs/nfsd/nfs4callback.c

···
 			goto requeue;
 		rpc_delay(task, 2 * HZ);
 		return false;
+	case -NFS4ERR_SEQ_MISORDERED:
 	case -NFS4ERR_BADSLOT:
 		/*
-		 * BADSLOT means that the client and server are out of sync
-		 * as to the backchannel parameters. Mark the backchannel faulty
-		 * and restart the RPC, but leak the slot so no one uses it.
+		 * A SEQ_MISORDERED or BADSLOT error means that the client and
+		 * server are out of sync as to the backchannel parameters. Mark
+		 * the backchannel faulty and restart the RPC, but leak the slot
+		 * so that it's no longer used.
 		 */
 		nfsd4_mark_cb_fault(cb->cb_clp);
 		cb->cb_held_slot = -1;
 		goto retry_nowait;
-	case -NFS4ERR_SEQ_MISORDERED:
-		if (session->se_cb_seq_nr[cb->cb_held_slot] != 1) {
-			session->se_cb_seq_nr[cb->cb_held_slot] = 1;
-			goto retry_nowait;
-		}
-		break;
 	default:
 		nfsd4_mark_cb_fault(cb->cb_clp);
 	}