From 912cb5421de602c1794f9620524665502dc866b0 Mon Sep 17 00:00:00 2001
From: tiancaiamao <tiancaiamao@gmail.com>
Date: Tue, 9 Oct 2018 13:23:30 +0800
Subject: [PATCH 1/3] domain: close slow query channel after closing session
 pool

If slow query channel is closed before session pool, some session's goroutine may still
writing to the channel. Writing to a closed channel would cause TiDB panic.
---
 domain/domain.go          | 2 +-
 domain/topn_slow_query.go | 8 ++++++++
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/domain/domain.go b/domain/domain.go
index 865214c5972c3..cd6734b34c3e2 100644
--- a/domain/domain.go
+++ b/domain/domain.go
@@ -457,8 +457,8 @@ func (do *Domain) Close() {
 	if do.etcdClient != nil {
 		terror.Log(errors.Trace(do.etcdClient.Close()))
 	}
-	do.slowQuery.Close()
 	do.sysSessionPool.Close()
+	do.slowQuery.Close()
 	do.wg.Wait()
 	log.Info("[domain] close")
 }
diff --git a/domain/topn_slow_query.go b/domain/topn_slow_query.go
index 52251d34475f2..e86c61f192af9 100644
--- a/domain/topn_slow_query.go
+++ b/domain/topn_slow_query.go
@@ -196,6 +196,14 @@ func (q *topNSlowQueries) QueryTop(count int, kind ast.ShowSlowKind) []*SlowQuer
 }
 
 func (q *topNSlowQueries) Close() {
+	done := false
+	for !done {
+		select {
+		case <-q.ch:
+		default:
+			done = true
+		}
+	}
 	close(q.ch)
 }
 

From 477672a5f0adfef26408d4d4db9baa536222827e Mon Sep 17 00:00:00 2001
From: tiancaiamao <tiancaiamao@gmail.com>
Date: Wed, 10 Oct 2018 15:53:53 +0800
Subject: [PATCH 2/3] address comment

---
 domain/topn_slow_query.go | 8 --------
 1 file changed, 8 deletions(-)

diff --git a/domain/topn_slow_query.go b/domain/topn_slow_query.go
index e86c61f192af9..52251d34475f2 100644
--- a/domain/topn_slow_query.go
+++ b/domain/topn_slow_query.go
@@ -196,14 +196,6 @@ func (q *topNSlowQueries) QueryTop(count int, kind ast.ShowSlowKind) []*SlowQuer
 }
 
 func (q *topNSlowQueries) Close() {
-	done := false
-	for !done {
-		select {
-		case <-q.ch:
-		default:
-			done = true
-		}
-	}
 	close(q.ch)
 }
 

From 5ebd9282f2b42280e8b8e1fd7cc8751a3ea6e5a4 Mon Sep 17 00:00:00 2001
From: tiancaiamao <tiancaiamao@gmail.com>
Date: Thu, 11 Oct 2018 12:56:45 +0800
Subject: [PATCH 3/3] address comment

---
 domain/domain.go          | 6 ++++++
 domain/topn_slow_query.go | 9 +++++++++
 2 files changed, 15 insertions(+)

diff --git a/domain/domain.go b/domain/domain.go
index cd6734b34c3e2..8b0b98929aaad 100644
--- a/domain/domain.go
+++ b/domain/domain.go
@@ -335,6 +335,12 @@ func (do *Domain) Reload() error {
 
 // LogSlowQuery keeps topN recent slow queries in domain.
 func (do *Domain) LogSlowQuery(query *SlowQueryInfo) {
+	do.slowQuery.mu.RLock()
+	defer do.slowQuery.mu.RUnlock()
+	if do.slowQuery.mu.closed {
+		return
+	}
+
 	select {
 	case do.slowQuery.ch <- query:
 	default:
diff --git a/domain/topn_slow_query.go b/domain/topn_slow_query.go
index 52251d34475f2..f8ae69c0be67e 100644
--- a/domain/topn_slow_query.go
+++ b/domain/topn_slow_query.go
@@ -115,6 +115,11 @@ type topNSlowQueries struct {
 	period   time.Duration
 	ch       chan *SlowQueryInfo
 	msgCh    chan *showSlowMessage
+
+	mu struct {
+		sync.RWMutex
+		closed bool
+	}
 }
 
 func newTopNSlowQueries(topN int, period time.Duration, queueSize int) *topNSlowQueries {
@@ -196,6 +201,10 @@ func (q *topNSlowQueries) QueryTop(count int, kind ast.ShowSlowKind) []*SlowQuer
 }
 
 func (q *topNSlowQueries) Close() {
+	q.mu.Lock()
+	q.mu.closed = true
+	q.mu.Unlock()
+
 	close(q.ch)
 }