executor: fix panic during update stmt

executor/builder.go

@@ -2057,6 +2057,7 @@ func (b *executorBuilder) buildUpdate(v *plannercore.Update) Executor {
 	b.inUpdateStmt = true
 	tblID2table := make(map[int64]table.Table, len(v.TblColPosInfos))
 	multiUpdateOnSameTable := make(map[int64]bool)
+	failpoint.Inject("injectAlterTable", func() {})
 	for _, info := range v.TblColPosInfos {
 		tbl, _ := b.is.TableByID(info.TblID)
 		if _, ok := tblID2table[info.TblID]; ok {

executor/executor_test.go

@@ -24,11 +24,13 @@ import (
 	"runtime"
 	"strconv"
 	"strings"
+	"sync"
 	"testing"
 	"time"
 
 	"github.com/golang/protobuf/proto"
 	"github.com/pingcap/errors"
+	"github.com/pingcap/failpoint"
 	"github.com/pingcap/tidb/config"
 	"github.com/pingcap/tidb/ddl"
 	"github.com/pingcap/tidb/domain"
@@ -6071,3 +6073,26 @@ func TestIsFastPlan(t *testing.T) {
 		require.Equal(t, ca.isFastPlan, ok)
 	}
 }
+
+func TestUpdateStmtWhileSchemaChanged(t *testing.T) {
+	store, _, clean := testkit.CreateMockStoreAndDomain(t)
+	defer clean()
+	tk := testkit.NewTestKit(t, store)
+	tk.MustExec("use test")
+	tk.MustExec("drop table if exists t")
+	tk.MustExec("create table t(a int, b int)")
+	tk.MustExec("insert into t(a,b) values(1,1), (3,3), (7,7)")
+	failpoint.Enable("github.com/pingcap/tidb/executor/injectAlterTable", `pause`)
+	wg := sync.WaitGroup{}
+	go func() {
+		wg.Add(1)
+		tk2 := testkit.NewTestKit(t, store)
+		tk2.MustExec("use test")
+		tk2.MustExec("update t set a = 2 where b = 1;")
+		wg.Done()
+	}()
+	tk.MustExec("alter table t add column c int NOT NULL")
+	failpoint.Disable("github.com/pingcap/tidb/executor/injectAlterTable")
+	wg.Wait()
+	tk.MustQuery("select a,c from t where b = 1").Check(testkit.Rows("2 0"))
+}

planner/core/logical_plan_builder.go

@@ -5179,6 +5179,9 @@ func CheckUpdateList(assignFlags []int, updt *Update, newTblID2Table map[int64]t
 		}
 
 		for i, col := range tbl.WritableCols() {
+			if i >= len(flags) {
+				continue
+			}
 			if flags[i] < 0 {
 				continue
 			}