restore async split

tikv/region.go

@@ -320,15 +320,15 @@ func (rm *RaftRegionManager) OnSplitRegion(derived *metapb.Region, regions []*me
 	// Run in another goroutine to avoid deadlock.
 	// TODO need investigations, make `newRegionCtx` running in another goroutine may lead to that
 	// regionId corresponding `region` can't be found in  `rm.regions`, when calling `OnRoleChange`
-	{
+	go func() {
 		oldRegion.waitParent()
 		rm.mu.Lock()
 		for i, region := range regions {
 			rm.regions[region.Id] = newRegionCtx(region, oldRegion, peers[i].LeaderChecker)
 		}
 		rm.mu.Unlock()
 		oldRegion.refCount.Done()
-	}
+	}()
 }
 
 func (rm *RaftRegionManager) OnRegionConfChange(ctx *raftstore.PeerEventContext, epoch *metapb.RegionEpoch) {