From eaa0612e0260a6ec16aa3be1f6ced21f059dd794 Mon Sep 17 00:00:00 2001
From: qupeng <onlyqupeng@gmail.com>
Date: Fri, 20 Dec 2019 12:07:52 +0800
Subject: [PATCH] raft: abort leader transferring if the target is demoted
 (#11417)

Signed-off-by: qupeng <qupeng@pingcap.com>
---
 raft/raft.go      |  4 ++--
 raft/raft_test.go | 32 ++++++++++++++++++++++++++++++++
 2 files changed, 34 insertions(+), 2 deletions(-)

diff --git a/raft/raft.go b/raft/raft.go
index cdcb43d3f..8f570a75a 100644
--- a/raft/raft.go
+++ b/raft/raft.go
@@ -1566,8 +1566,8 @@ func (r *raft) switchToConfig(cfg tracker.Config, prs tracker.ProgressMap) pb.Co
 			r.maybeSendAppend(id, false /* sendIfEmpty */)
 		})
 	}
-	// If the the leadTransferee was removed, abort the leadership transfer.
-	if _, tOK := r.prs.Progress[r.leadTransferee]; !tOK && r.leadTransferee != 0 {
+	// If the the leadTransferee was removed or demoted, abort the leadership transfer.
+	if _, tOK := r.prs.Config.Voters.IDs()[r.leadTransferee]; !tOK && r.leadTransferee != 0 {
 		r.abortLeaderTransfer()
 	}
 
diff --git a/raft/raft_test.go b/raft/raft_test.go
index b4e935edf..87ceb99ca 100644
--- a/raft/raft_test.go
+++ b/raft/raft_test.go
@@ -3601,6 +3601,38 @@ func TestLeaderTransferRemoveNode(t *testing.T) {
 	checkLeaderTransferState(t, lead, StateLeader, 1)
 }
 
+func TestLeaderTransferDemoteNode(t *testing.T) {
+	nt := newNetwork(nil, nil, nil)
+	nt.send(pb.Message{From: 1, To: 1, Type: pb.MsgHup})
+
+	nt.ignore(pb.MsgTimeoutNow)
+
+	lead := nt.peers[1].(*raft)
+
+	// The leadTransferee is demoted when leadship transferring.
+	nt.send(pb.Message{From: 3, To: 1, Type: pb.MsgTransferLeader})
+	if lead.leadTransferee != 3 {
+		t.Fatalf("wait transferring, leadTransferee = %v, want %v", lead.leadTransferee, 3)
+	}
+
+	lead.applyConfChange(pb.ConfChangeV2{
+		Changes: []pb.ConfChangeSingle{
+			{
+				Type:   pb.ConfChangeRemoveNode,
+				NodeID: 3,
+			},
+			{
+				Type:   pb.ConfChangeAddLearnerNode,
+				NodeID: 3,
+			},
+		},
+	})
+
+	// Make the Raft group commit the LeaveJoint entry.
+	lead.applyConfChange(pb.ConfChangeV2{})
+	checkLeaderTransferState(t, lead, StateLeader, 1)
+}
+
 // TestLeaderTransferBack verifies leadership can transfer back to self when last transfer is pending.
 func TestLeaderTransferBack(t *testing.T) {
 	nt := newNetwork(nil, nil, nil)