Fix data race between read APIs and finshiSplit/finishMerge in keyspa…

…ce group manager (tikv#6723)

close tikv#6721

checkTSOMerge and checkTSOSplit will read from kgm.getKeyspaceGroupMeta

finishMergeKeyspaceGroup and finishSplitKeyspaceGroup will update kgm

so just return a copy to avoid data race

Signed-off-by: Bin Shi <binshi.bing@gmail.com>

pkg/tso/keyspace_group_manager.go

@@ -112,6 +112,39 @@ func (s *state) getKeyspaceGroupMeta(
 	return s.ams[groupID], s.kgs[groupID]
 }
 
+func (s *state) checkTSOSplit(
+	targetGroupID uint32,
+) (splitTargetAM, splitSourceAM *AllocatorManager, err error) {
+	s.RLock()
+	defer s.RUnlock()
+	splitTargetAM, splitTargetGroup := s.ams[targetGroupID], s.kgs[targetGroupID]
+	// Only the split target keyspace group needs to check the TSO split.
+	if !splitTargetGroup.IsSplitTarget() {
+		return nil, nil, nil // it isn't in the split state
+	}
+	sourceGroupID := splitTargetGroup.SplitSource()
+	splitSourceAM, splitSourceGroup := s.ams[sourceGroupID], s.kgs[sourceGroupID]
+	if splitSourceAM == nil || splitSourceGroup == nil {
+		log.Error("the split source keyspace group is not initialized",
+			zap.Uint32("source", sourceGroupID))
+		return nil, nil, errs.ErrKeyspaceGroupNotInitialized.FastGenByArgs(sourceGroupID)
+	}
+	return splitTargetAM, splitSourceAM, nil
+}
+
+// Reject any request if the keyspace group is in merging state,
+// we need to wait for the merging checker to finish the TSO merging.
+func (s *state) checkTSOMerge(
+	groupID uint32,
+) error {
+	s.RLock()
+	defer s.RUnlock()
+	if s.kgs[groupID] == nil || !s.kgs[groupID].IsMerging() {
+		return nil
+	}
+	return errs.ErrKeyspaceGroupIsMerging.FastGenByArgs(groupID)
+}
+
 // getKeyspaceGroupMetaWithCheck returns the keyspace group meta of the given keyspace.
 // It also checks if the keyspace is served by the given keyspace group. If not, it returns the meta
 // of the keyspace group to which the keyspace currently belongs and returns NotServed (by the given
@@ -957,7 +990,7 @@ func (kgm *KeyspaceGroupManager) HandleTSORequest(
 	if err != nil {
 		return pdpb.Timestamp{}, curKeyspaceGroupID, err
 	}
-	err = kgm.checkTSOMerge(curKeyspaceGroupID)
+	err = kgm.state.checkTSOMerge(curKeyspaceGroupID)
 	if err != nil {
 		return pdpb.Timestamp{}, curKeyspaceGroupID, err
 	}
@@ -1032,27 +1065,19 @@ func (kgm *KeyspaceGroupManager) checkTSOSplit(
 	keyspaceGroupID uint32,
 	dcLocation string,
 ) error {
-	splitAM, splitGroup := kgm.getKeyspaceGroupMeta(keyspaceGroupID)
-	// Only the split target keyspace group needs to check the TSO split.
-	if !splitGroup.IsSplitTarget() {
-		return nil
-	}
-	splitSource := splitGroup.SplitSource()
-	splitSourceAM, splitSourceGroup := kgm.getKeyspaceGroupMeta(splitSource)
-	if splitSourceAM == nil || splitSourceGroup == nil {
-		log.Error("the split source keyspace group is not initialized",
-			zap.Uint32("source", splitSource))
-		return errs.ErrKeyspaceGroupNotInitialized.FastGenByArgs(splitSource)
+	splitTargetAM, splitSourceAM, err := kgm.state.checkTSOSplit(keyspaceGroupID)
+	if err != nil || splitTargetAM == nil {
+		return err
 	}
-	splitAllocator, err := splitAM.GetAllocator(dcLocation)
+	splitTargetAllocator, err := splitTargetAM.GetAllocator(dcLocation)
 	if err != nil {
 		return err
 	}
 	splitSourceAllocator, err := splitSourceAM.GetAllocator(dcLocation)
 	if err != nil {
 		return err
 	}
-	splitTSO, err := splitAllocator.GenerateTSO(1)
+	splitTargetTSO, err := splitTargetAllocator.GenerateTSO(1)
 	if err != nil {
 		return err
 	}
@@ -1061,19 +1086,19 @@ func (kgm *KeyspaceGroupManager) checkTSOSplit(
 		return err
 	}
 	// If the split source TSO is not greater than the newly split TSO, we don't need to do anything.
-	if tsoutil.CompareTimestamp(&splitSourceTSO, &splitTSO) <= 0 {
+	if tsoutil.CompareTimestamp(&splitSourceTSO, &splitTargetTSO) <= 0 {
 		log.Info("the split source tso is less than the newly split tso",
 			zap.Int64("split-source-tso-physical", splitSourceTSO.Physical),
 			zap.Int64("split-source-tso-logical", splitSourceTSO.Logical),
-			zap.Int64("split-tso-physical", splitTSO.Physical),
-			zap.Int64("split-tso-logical", splitTSO.Logical))
+			zap.Int64("split-tso-physical", splitTargetTSO.Physical),
+			zap.Int64("split-tso-logical", splitTargetTSO.Logical))
 		// Finish the split state directly.
 		return kgm.finishSplitKeyspaceGroup(keyspaceGroupID)
 	}
 	// If the split source TSO is greater than the newly split TSO, we need to update the split
 	// TSO to make sure the following TSO will be greater than the split keyspaces ever had
 	// in the past.
-	err = splitAllocator.SetTSO(tsoutil.GenerateTS(&pdpb.Timestamp{
+	err = splitTargetAllocator.SetTSO(tsoutil.GenerateTS(&pdpb.Timestamp{
 		Physical: splitSourceTSO.Physical + 1,
 		Logical:  splitSourceTSO.Logical,
 	}), true, true)
@@ -1083,8 +1108,8 @@ func (kgm *KeyspaceGroupManager) checkTSOSplit(
 	log.Info("the split source tso is greater than the newly split tso",
 		zap.Int64("split-source-tso-physical", splitSourceTSO.Physical),
 		zap.Int64("split-source-tso-logical", splitSourceTSO.Logical),
-		zap.Int64("split-tso-physical", splitTSO.Physical),
-		zap.Int64("split-tso-logical", splitTSO.Logical))
+		zap.Int64("split-tso-physical", splitTargetTSO.Physical),
+		zap.Int64("split-tso-logical", splitTargetTSO.Logical))
 	// Finish the split state.
 	return kgm.finishSplitKeyspaceGroup(keyspaceGroupID)
 }
@@ -1116,9 +1141,13 @@ func (kgm *KeyspaceGroupManager) finishSplitKeyspaceGroup(id uint32) error {
 			zap.Int("status-code", statusCode))
 		return errs.ErrSendRequest.FastGenByArgs()
 	}
-	// Pre-update the split keyspace group split state in memory.
-	splitGroup.SplitState = nil
-	kgm.kgs[id] = splitGroup
+	// Pre-update the split keyspace group's split state in memory.
+	// Note: to avoid data race with state read APIs, we always replace the group in memory as a whole.
+	// For now, we only have scenarios to update split state/merge state, and the other fields are always
+	// loaded from etcd without any modification, so we can simply copy the group and replace the state.
+	newSplitGroup := *splitGroup
+	newSplitGroup.SplitState = nil
+	kgm.kgs[id] = &newSplitGroup
 	return nil
 }
 
@@ -1146,9 +1175,14 @@ func (kgm *KeyspaceGroupManager) finishMergeKeyspaceGroup(id uint32) error {
 			zap.Int("status-code", statusCode))
 		return errs.ErrSendRequest.FastGenByArgs()
 	}
-	// Pre-update the split keyspace group split state in memory.
-	mergeTarget.MergeState = nil
-	kgm.kgs[id] = mergeTarget
+
+	// Pre-update the merge target keyspace group's merge state in memory.
+	// Note: to avoid data race with state read APIs, we always replace the group in memory as a whole.
+	// For now, we only have scenarios to update split state/merge state, and the other fields are always
+	// loaded from etcd without any modification, so we can simply copy the group and replace the state.
+	newTargetGroup := *mergeTarget
+	newTargetGroup.MergeState = nil
+	kgm.kgs[id] = &newTargetGroup
 	return nil
 }
 
@@ -1286,15 +1320,3 @@ func (kgm *KeyspaceGroupManager) mergingChecker(ctx context.Context, mergeTarget
 		return
 	}
 }
-
-// Reject any request if the keyspace group is in merging state,
-// we need to wait for the merging checker to finish the TSO merging.
-func (kgm *KeyspaceGroupManager) checkTSOMerge(
-	keyspaceGroupID uint32,
-) error {
-	_, group := kgm.getKeyspaceGroupMeta(keyspaceGroupID)
-	if !group.IsMerging() {
-		return nil
-	}
-	return errs.ErrKeyspaceGroupIsMerging.FastGenByArgs(keyspaceGroupID)
-}