base: ensure that a SQL instance ID is not set to conflicting value

Prior to this patch, a SQL instance ID container could be
assigned successively different values. This would make it possible
for erroneous code to mistakenly initialize the instance ID twice,
without any evidence that something was amiss.

This patch fixes this by using the same prevention logic that we
already use for node IDs.

Release note: None

pkg/base/node_id.go

@@ -199,11 +199,27 @@ func NewSQLIDContainer(sqlInstanceID SQLInstanceID, nodeID *NodeIDContainer) *SQ
 // SetSQLInstanceID sets the SQL instance ID. It returns an error if
 // we attempt to set an instance ID when the nodeID has already been
 // initialized.
-func (c *SQLIDContainer) SetSQLInstanceID(sqlInstanceID SQLInstanceID) error {
+func (c *SQLIDContainer) SetSQLInstanceID(ctx context.Context, sqlInstanceID SQLInstanceID) error {
 	if _, ok := c.OptionalNodeID(); ok {
 		return errors.New("attempting to initialize instance ID when node ID is set")
 	}
-	c.sqlInstanceID = sqlInstanceID
+
+	// Use the same logic to set the instance ID as for the node ID.
+	//
+	// TODO(knz): All this could be advantageously simplified if we agreed
+	// to use the same type for NodeIDContainer and SQLIDContainer.
+	if sqlInstanceID <= 0 {
+		log.Fatalf(ctx, "trying to set invalid SQLInstanceID: %d", sqlInstanceID)
+	}
+	oldVal := atomic.SwapInt32((*int32)(&c.sqlInstanceID), int32(sqlInstanceID))
+	if oldVal == 0 {
+		if log.V(2) {
+			log.Infof(ctx, "SQLInstanceID set to %d", sqlInstanceID)
+		}
+	} else if oldVal != int32(sqlInstanceID) {
+		log.Fatalf(ctx, "different SQLInstanceIDs set: %d, then %d", oldVal, sqlInstanceID)
+	}
+
 	c.str.Store(strconv.Itoa(int(sqlInstanceID)))
 	return nil
 }

pkg/server/server_sql.go

@@ -974,7 +974,7 @@ func (s *SQLServer) initInstanceID(ctx context.Context) error {
 	if err != nil {
 		return err
 	}
-	err = s.sqlIDContainer.SetSQLInstanceID(instanceID)
+	err = s.sqlIDContainer.SetSQLInstanceID(ctx, instanceID)
 	if err != nil {
 		return err
 	}