Merge pull request #4362 from tonistiigi/history-listener-hang

llbsolver: fix possible deadlock in history listen

solver/llbsolver/history.go

@@ -762,21 +762,30 @@ func (h *HistoryQueue) Listen(ctx context.Context, req *controlapi.BuildHistoryR
  }()
  }
 
+ // make a copy of events for active builds so we don't keep a lock during grpc send
+ actives := make([]*controlapi.BuildHistoryEvent, 0, len(h.active))
+
  for _, e := range h.active {
  if req.Ref != "" && e.Ref != req.Ref {
  continue
  }
  if _, ok := h.deleted[e.Ref]; ok {
  continue
  }
- sub.send(&controlapi.BuildHistoryEvent{
+ actives = append(actives, &controlapi.BuildHistoryEvent{
  Type: controlapi.BuildHistoryEventType_STARTED,
  Record: e,
  })
  }
 
  h.mu.Unlock()
 
+ for _, e := range actives {
+ if err := f(e); err != nil {
+ return err
+ }
+ }
+
  if !req.ActiveOnly {
  events := []*controlapi.BuildHistoryEvent{}
  if err := h.opt.DB.View(func(tx *bolt.Tx) error {