executor: fix panic when fetching processlist table data in some ca…

…ses (#11688) (#16309)

server/server.go

@@ -448,6 +448,7 @@ func (cc *clientConn) connectInfo() *variable.ConnectionInfo {
 // ShowProcessList implements the SessionManager interface.
 func (s *Server) ShowProcessList() map[uint64]*util.ProcessInfo {
 	s.rwlock.RLock()
+	defer s.rwlock.RUnlock()
 	rs := make(map[uint64]*util.ProcessInfo, len(s.clients))
 	for _, client := range s.clients {
 		if atomic.LoadInt32(&client.status) == connStatusWaitShutdown {
@@ -457,7 +458,6 @@ func (s *Server) ShowProcessList() map[uint64]*util.ProcessInfo {
 			rs[pi.ID] = pi
 		}
 	}
-	s.rwlock.RUnlock()
 	return rs
 }
 

util/processinfo.go

@@ -77,7 +77,11 @@ func (pi *ProcessInfo) txnStartTs(tz *time.Location) (txnStart string) {
 // ToRow returns []interface{} for the row data of
 // "SELECT * FROM INFORMATION_SCHEMA.PROCESSLIST".
 func (pi *ProcessInfo) ToRow(tz *time.Location) []interface{} {
-	return append(pi.ToRowForShow(true), pi.StmtCtx.MemTracker.BytesConsumed(), pi.txnStartTs(tz))
+	bytesConsumed := int64(0)
+	if pi.StmtCtx.MemTracker != nil {
+		bytesConsumed = pi.StmtCtx.MemTracker.BytesConsumed()
+	}
+	return append(pi.ToRowForShow(true), bytesConsumed, pi.txnStartTs(tz))
 }
 
 // SessionManager is an interface for session manage. Show processlist and