From 7b49e431c16606dc7da5806c60590443fc767f74 Mon Sep 17 00:00:00 2001
From: Jack Yu <jackysp@gmail.com>
Date: Mon, 9 Dec 2019 13:41:09 +0800
Subject: [PATCH] session: if txn invalid do not active it and return an error
 (#13935)

---
 executor/builder.go       | 2 +-
 executor/executor_test.go | 2 +-
 executor/point_get.go     | 2 +-
 executor/simple.go        | 2 +-
 session/session.go        | 3 +++
 session/session_test.go   | 8 +++++---
 6 files changed, 12 insertions(+), 7 deletions(-)

diff --git a/executor/builder.go b/executor/builder.go
index 902b1d42d7e28..be008f078a0c5 100644
--- a/executor/builder.go
+++ b/executor/builder.go
@@ -1269,7 +1269,7 @@ func (b *executorBuilder) getStartTS() (uint64, error) {
 	if err != nil {
 		return 0, errors.Trace(err)
 	}
-	if startTS == 0 && txn.Valid() {
+	if startTS == 0 {
 		startTS = txn.StartTS()
 	}
 	b.startTS = startTS
diff --git a/executor/executor_test.go b/executor/executor_test.go
index 399ca9990d7c4..8631f2673aed9 100644
--- a/executor/executor_test.go
+++ b/executor/executor_test.go
@@ -2345,7 +2345,7 @@ func (s *testSuite) TestSelectForUpdate(c *C) {
 	tk.MustExec("drop table if exists t, t1")
 
 	txn, err := tk.Se.Txn(true)
-	c.Assert(err, IsNil)
+	c.Assert(kv.ErrInvalidTxn.Equal(err), IsTrue)
 	c.Assert(txn.Valid(), IsFalse)
 	tk.MustExec("create table t (c1 int, c2 int, c3 int)")
 	tk.MustExec("insert t values (11, 2, 3)")
diff --git a/executor/point_get.go b/executor/point_get.go
index e9dbed0617865..db506dfb55bf0 100644
--- a/executor/point_get.go
+++ b/executor/point_get.go
@@ -154,7 +154,7 @@ func (e *PointGetExecutor) encodeIndexKey() (_ []byte, err error) {
 }
 
 func (e *PointGetExecutor) get(key kv.Key) (val []byte, err error) {
-	txn, err := e.ctx.Txn(true)
+	txn, err := e.ctx.Txn(false)
 	if err != nil {
 		return nil, errors.Trace(err)
 	}
diff --git a/executor/simple.go b/executor/simple.go
index cfd19af0cce49..e0ddc88911b1c 100644
--- a/executor/simple.go
+++ b/executor/simple.go
@@ -139,7 +139,7 @@ func (e *SimpleExec) executeRollback(s *ast.RollbackStmt) error {
 	sessVars := e.ctx.GetSessionVars()
 	logutil.Logger(context.Background()).Debug("execute rollback statement", zap.Uint64("conn", sessVars.ConnectionID))
 	sessVars.SetStatusFlag(mysql.ServerStatusInTrans, false)
-	txn, err := e.ctx.Txn(true)
+	txn, err := e.ctx.Txn(false)
 	if err != nil {
 		return errors.Trace(err)
 	}
diff --git a/session/session.go b/session/session.go
index 68e611689f4a8..1f8aa53d12276 100644
--- a/session/session.go
+++ b/session/session.go
@@ -1028,6 +1028,9 @@ func (s *session) DropPreparedStmt(stmtID uint32) error {
 }
 
 func (s *session) Txn(active bool) (kv.Transaction, error) {
+	if !s.txn.validOrPending() && active {
+		return &s.txn, kv.ErrInvalidTxn
+	}
 	if s.txn.pending() && active {
 		// Transaction is lazy initialized.
 		// PrepareTxnCtx is called to get a tso future, makes s.txn a pending txn,
diff --git a/session/session_test.go b/session/session_test.go
index 88cc6300ae270..186e3d59ca994 100644
--- a/session/session_test.go
+++ b/session/session_test.go
@@ -242,7 +242,7 @@ func (s *testSessionSuite) TestRowLock(c *C) {
 
 	tk.MustExec("drop table if exists t")
 	txn, err := tk.Se.Txn(true)
-	c.Assert(err, IsNil)
+	c.Assert(kv.ErrInvalidTxn.Equal(err), IsTrue)
 	c.Assert(txn.Valid(), IsFalse)
 	tk.MustExec("create table t (c1 int, c2 int, c3 int)")
 	tk.MustExec("insert t values (11, 2, 3)")
@@ -330,7 +330,9 @@ func (s *testSessionSuite) TestTxnLazyInitialize(c *C) {
 	tk.MustExec("create table t (id int)")
 
 	tk.MustExec("set @@autocommit = 0")
-	txn, err := tk.Se.Txn(false)
+	txn, err := tk.Se.Txn(true)
+	c.Assert(kv.ErrInvalidTxn.Equal(err), IsTrue)
+	txn, err = tk.Se.Txn(false)
 	c.Assert(err, IsNil)
 	c.Assert(txn.Valid(), IsFalse)
 	tk.MustQuery("select @@tidb_current_ts").Check(testkit.Rows("0"))
@@ -623,7 +625,7 @@ func (s *testSessionSuite) TestRetryPreparedStmt(c *C) {
 
 	tk.MustExec("drop table if exists t")
 	txn, err := tk.Se.Txn(true)
-	c.Assert(err, IsNil)
+	c.Assert(kv.ErrInvalidTxn.Equal(err), IsTrue)
 	c.Assert(txn.Valid(), IsFalse)
 	tk.MustExec("create table t (c1 int, c2 int, c3 int)")
 	tk.MustExec("insert t values (11, 2, 3)")