From 26f2704f6669f13c6c03664acae1c3e44cebbbbf Mon Sep 17 00:00:00 2001
From: buffer <1045931706@qq.com>
Date: Thu, 28 Sep 2023 17:42:21 +0800
Subject: [PATCH] This is an automated cherry-pick of #7143

close tikv/pd#4399

Signed-off-by: ti-chi-bot <ti-community-prow-bot@tidb.io>
---
 server/core/region.go      | 24 ++++++++++++++++++++++--
 server/core/region_test.go | 13 +++++++++++++
 2 files changed, 35 insertions(+), 2 deletions(-)

diff --git a/server/core/region.go b/server/core/region.go
index 81b3e1bacaa..90b5d904ddc 100644
--- a/server/core/region.go
+++ b/server/core/region.go
@@ -22,11 +22,13 @@ import (
 	"sort"
 	"strings"
 	"sync/atomic"
+	"time"
 	"unsafe"
 
 	"github.com/docker/go-units"
 	"github.com/gogo/protobuf/proto"
 	"github.com/pingcap/errors"
+	"github.com/pingcap/failpoint"
 	"github.com/pingcap/kvproto/pkg/metapb"
 	"github.com/pingcap/kvproto/pkg/pdpb"
 	"github.com/pingcap/kvproto/pkg/replication_modepb"
@@ -885,7 +887,16 @@ func (r *RegionsInfo) setRegionLocked(region *RegionInfo) (*RegionInfo, []*Regio
 }
 
 // UpdateSubTree updates the subtree.
+<<<<<<< HEAD:server/core/region.go
 func (r *RegionsInfo) UpdateSubTree(region, origin *RegionInfo, toRemove []*RegionInfo, rangeChanged bool) {
+=======
+func (r *RegionsInfo) UpdateSubTree(region, origin *RegionInfo, overlaps []*RegionInfo, rangeChanged bool) {
+	failpoint.Inject("UpdateSubTree", func() {
+		if origin == nil {
+			time.Sleep(time.Second)
+		}
+	})
+>>>>>>> 54219d649 (region: fix the potential panic .  (#7143)):pkg/core/region.go
 	r.st.Lock()
 	defer r.st.Unlock()
 	if origin != nil {
@@ -894,8 +905,17 @@ func (r *RegionsInfo) UpdateSubTree(region, origin *RegionInfo, toRemove []*Regi
 			// TODO: Improve performance by deleting only the different peers.
 			r.removeRegionFromSubTreeLocked(origin)
 		} else {
-			r.updateSubTreeStat(origin, region)
-			r.subRegions[region.GetID()].RegionInfo = region
+			// The region tree and the subtree update is not atomic and the region tree is updated first.
+			// If there are two thread needs to update region tree,
+			// t1: thread-A  update region tree
+			// 										t2: thread-B: update region tree again
+			//										t3: thread-B: update subtree
+			// t4: thread-A: update region subtree
+			// to keep region tree consistent with subtree, we need to drop this update.
+			if tree, ok := r.subRegions[region.GetID()]; ok {
+				r.updateSubTreeStat(origin, region)
+				tree.RegionInfo = region
+			}
 			return
 		}
 	}
diff --git a/server/core/region_test.go b/server/core/region_test.go
index e6535b6f423..505df4394fc 100644
--- a/server/core/region_test.go
+++ b/server/core/region_test.go
@@ -22,6 +22,7 @@ import (
 	"testing"
 	"time"
 
+	"github.com/pingcap/failpoint"
 	"github.com/pingcap/kvproto/pkg/metapb"
 	"github.com/pingcap/kvproto/pkg/pdpb"
 	"github.com/stretchr/testify/require"
@@ -451,6 +452,18 @@ func TestRegionKey(t *testing.T) {
 	}
 }
 
+func TestSetRegionConcurrence(t *testing.T) {
+	re := require.New(t)
+	re.NoError(failpoint.Enable("github.com/tikv/pd/pkg/core/UpdateSubTree", `return()`))
+	regions := NewRegionsInfo()
+	region := NewTestRegionInfo(1, 1, []byte("a"), []byte("b"))
+	go func() {
+		regions.AtomicCheckAndPutRegion(region)
+	}()
+	regions.AtomicCheckAndPutRegion(region)
+	re.NoError(failpoint.Disable("github.com/tikv/pd/pkg/core/UpdateSubTree"))
+}
+
 func TestSetRegion(t *testing.T) {
 	re := require.New(t)
 	regions := NewRegionsInfo()