*: fix data race of Column.GeneratedExpr (#48888) (#48924)

close #44919, close #48191

Author: ti-chi-bot

br/pkg/lightning/backend/kv/sql2kv.go

@@ -115,7 +115,7 @@ func CollectGeneratedColumns(se *Session, meta *model.TableInfo, cols []*table.C
 	var genCols []GeneratedCol
 	for i, col := range cols {
 		if col.GeneratedExpr != nil {
-			expr, err := expression.RewriteAstExpr(se, col.GeneratedExpr, schema, names, true)
+			expr, err := expression.RewriteAstExpr(se, col.GeneratedExpr.Internal(), schema, names, true)
 			if err != nil {
 				return nil, err
 			}

pkg/ddl/ddl_api.go

@@ -5349,7 +5349,8 @@ func ProcessColumnOptions(ctx sessionctx.Context, col *table.Column, options []*
 			col.GeneratedExprString = sb.String()
 			col.GeneratedStored = opt.Stored
 			col.Dependences = make(map[string]struct{})
-			col.GeneratedExpr = opt.Expr
+			// Only used by checkModifyGeneratedColumn, there is no need to set a ctor for it.
+			col.GeneratedExpr = table.NewClonableExprNode(nil, opt.Expr)
 			for _, colName := range FindColumnNamesInExpr(opt.Expr) {
 				col.Dependences[colName.Name.L] = struct{}{}
 			}
@@ -5415,7 +5416,7 @@ func checkModifyColumnWithGeneratedColumnsConstraint(allCols []*table.Column, ol
 		if col.GeneratedExpr == nil {
 			continue
 		}
-		dependedColNames := FindColumnNamesInExpr(col.GeneratedExpr)
+		dependedColNames := FindColumnNamesInExpr(col.GeneratedExpr.Internal())
 		for _, name := range dependedColNames {
 			if name.Name.L == oldColName.L {
 				if col.Hidden {

pkg/ddl/generated_column.go

@@ -252,7 +252,7 @@ func checkModifyGeneratedColumn(sctx sessionctx.Context, schemaName model.CIStr,
 
 	if newCol.IsGenerated() {
 		// rule 3.
-		if err := checkIllegalFn4Generated(newCol.Name.L, typeColumn, newCol.GeneratedExpr); err != nil {
+		if err := checkIllegalFn4Generated(newCol.Name.L, typeColumn, newCol.GeneratedExpr.Internal()); err != nil {
 			return errors.Trace(err)
 		}
 

pkg/ddl/schematracker/dm_tracker.go

@@ -613,7 +613,7 @@ func (d SchemaTracker) renameColumn(_ sessionctx.Context, ident ast.Ident, spec
 		if col.GeneratedExpr == nil {
 			continue
 		}
-		dependedColNames := ddl.FindColumnNamesInExpr(col.GeneratedExpr)
+		dependedColNames := ddl.FindColumnNamesInExpr(col.GeneratedExpr.Internal())
 		for _, name := range dependedColNames {
 			if name.Name.L == oldColName.L {
 				if col.Hidden {

pkg/planner/core/logical_plan_builder.go

@@ -5358,7 +5358,7 @@ func (b *PlanBuilder) buildDataSource(ctx context.Context, tn *ast.TableName, as
 				var err error
 				originVal := b.allowBuildCastArray
 				b.allowBuildCastArray = true
-				expr, _, err = b.rewrite(ctx, columns[i].GeneratedExpr, ds, nil, true)
+				expr, _, err = b.rewrite(ctx, columns[i].GeneratedExpr.Clone(), ds, nil, true)
 				b.allowBuildCastArray = originVal
 				if err != nil {
 					return nil, err
@@ -6327,7 +6327,7 @@ func (b *PlanBuilder) buildUpdateLists(ctx context.Context, tableList []*ast.Tab
 			}
 			virtualAssignments = append(virtualAssignments, &ast.Assignment{
 				Column: &ast.ColumnName{Schema: tn.Schema, Table: tn.Name, Name: colInfo.Name},
-				Expr:   tableVal.Cols()[i].GeneratedExpr,
+				Expr:   tableVal.Cols()[i].GeneratedExpr.Clone(),
 			})
 		}
 	}

pkg/planner/core/planbuilder.go

@@ -3889,7 +3889,7 @@ func (b *PlanBuilder) resolveGeneratedColumns(ctx context.Context, columns []*ta
 
 		originalVal := b.allowBuildCastArray
 		b.allowBuildCastArray = true
-		expr, _, err := b.rewrite(ctx, column.GeneratedExpr, mockPlan, nil, true)
+		expr, _, err := b.rewrite(ctx, column.GeneratedExpr.Clone(), mockPlan, nil, true)
 		b.allowBuildCastArray = originalVal
 		if err != nil {
 			return igc, err

pkg/table/column.go

@@ -46,11 +46,39 @@ import (
 type Column struct {
 	*model.ColumnInfo
 	// If this column is a generated column, the expression will be stored here.
-	GeneratedExpr ast.ExprNode
+	GeneratedExpr *ClonableExprNode
 	// If this column has default expr value, this expression will be stored here.
 	DefaultExpr ast.ExprNode
 }
 
+// ClonableExprNode is a wrapper for ast.ExprNode.
+type ClonableExprNode struct {
+	ctor     func() ast.ExprNode
+	internal ast.ExprNode
+}
+
+// NewClonableExprNode creates a ClonableExprNode.
+func NewClonableExprNode(ctor func() ast.ExprNode, internal ast.ExprNode) *ClonableExprNode {
+	return &ClonableExprNode{
+		ctor:     ctor,
+		internal: internal,
+	}
+}
+
+// Clone makes a "copy" of internal ast.ExprNode by reconstructing it.
+func (n *ClonableExprNode) Clone() ast.ExprNode {
+	if n.ctor == nil {
+		return n.internal
+	}
+	return n.ctor()
+}
+
+// Internal returns the reference of the internal ast.ExprNode.
+// Note: only use this method when you are sure that the internal ast.ExprNode is not modified concurrently.
+func (n *ClonableExprNode) Internal() ast.ExprNode {
+	return n.internal
+}
+
 // String implements fmt.Stringer interface.
 func (c *Column) String() string {
 	ans := []string{c.Name.O, types.TypeToStr(c.GetType(), c.GetCharset())}

pkg/table/tables/tables.go

@@ -33,6 +33,7 @@ import (
 	"github.com/pingcap/tidb/pkg/kv"
 	"github.com/pingcap/tidb/pkg/meta"
 	"github.com/pingcap/tidb/pkg/meta/autoid"
+	"github.com/pingcap/tidb/pkg/parser/ast"
 	"github.com/pingcap/tidb/pkg/parser/model"
 	"github.com/pingcap/tidb/pkg/parser/mysql"
 	"github.com/pingcap/tidb/pkg/sessionctx"
@@ -138,15 +139,21 @@ func TableFromMeta(allocs autoid.Allocators, tblInfo *model.TableInfo) (table.Ta
 
 		col := table.ToColumn(colInfo)
 		if col.IsGenerated() {
-			expr, err := generatedexpr.ParseExpression(colInfo.GeneratedExprString)
+			genStr := colInfo.GeneratedExprString
+			expr, err := buildGeneratedExpr(tblInfo, genStr)
 			if err != nil {
 				return nil, err
 			}
-			expr, err = generatedexpr.SimpleResolveName(expr, tblInfo)
-			if err != nil {
-				return nil, err
-			}
-			col.GeneratedExpr = expr
+			col.GeneratedExpr = table.NewClonableExprNode(func() ast.ExprNode {
+				newExpr, err1 := buildGeneratedExpr(tblInfo, genStr)
+				if err1 != nil {
+					logutil.BgLogger().Warn("unexpected parse generated string error",
+						zap.String("generatedStr", genStr),
+						zap.Error(err1))
+					return expr
+				}
+				return newExpr
+			}, expr)
 		}
 		// default value is expr.
 		if col.DefaultIsExpr {
@@ -177,6 +184,18 @@ func TableFromMeta(allocs autoid.Allocators, tblInfo *model.TableInfo) (table.Ta
 	return newPartitionedTable(&t, tblInfo)
 }
 
+func buildGeneratedExpr(tblInfo *model.TableInfo, genExpr string) (ast.ExprNode, error) {
+	expr, err := generatedexpr.ParseExpression(genExpr)
+	if err != nil {
+		return nil, err
+	}
+	expr, err = generatedexpr.SimpleResolveName(expr, tblInfo)
+	if err != nil {
+		return nil, err
+	}
+	return expr, nil
+}
+
 // initTableCommon initializes a TableCommon struct.
 func initTableCommon(t *TableCommon, tblInfo *model.TableInfo, physicalTableID int64, cols []*table.Column, allocs autoid.Allocators, constraints []*table.Constraint) {
 	t.tableID = tblInfo.ID