From 01e37e005a2f362ceb26c63c853dba0eeb8f9257 Mon Sep 17 00:00:00 2001
From: Marten Seemann <martenseemann@gmail.com>
Date: Tue, 18 Dec 2018 20:55:31 +0630
Subject: [PATCH] fix deadlock when closing and receiving MAX_STREAM_DATA
 frames

---
 send_stream.go | 16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/send_stream.go b/send_stream.go
index 9e8f6954..ccb58a93 100644
--- a/send_stream.go
+++ b/send_stream.go
@@ -221,13 +221,14 @@ func (s *sendStream) getDataForWriting(maxBytes protocol.ByteCount) ([]byte, boo
 
 func (s *sendStream) Close() error {
 	s.mutex.Lock()
-	defer s.mutex.Unlock()
-
 	if s.canceledWrite {
+		s.mutex.Unlock()
 		return fmt.Errorf("Close called for canceled stream %d", s.streamID)
 	}
 	s.finishedWriting = true
-	s.sender.onHasStreamData(s.streamID) // need to send the FIN
+	s.mutex.Unlock()
+
+	s.sender.onHasStreamData(s.streamID) // need to send the FIN, must be called without holding the mutex
 	s.ctxCancel()
 	return nil
 }
@@ -238,7 +239,7 @@ func (s *sendStream) CancelWrite(errorCode protocol.ApplicationErrorCode) error
 	s.mutex.Unlock()
 
 	if completed {
-		s.sender.onStreamCompleted(s.streamID)
+		s.sender.onStreamCompleted(s.streamID) // must be called without holding the mutex
 	}
 	return err
 }
@@ -271,12 +272,13 @@ func (s *sendStream) handleStopSendingFrame(frame *wire.StopSendingFrame) {
 }
 
 func (s *sendStream) handleMaxStreamDataFrame(frame *wire.MaxStreamDataFrame) {
-	s.flowController.UpdateSendWindow(frame.ByteOffset)
 	s.mutex.Lock()
-	if s.dataForWriting != nil {
+	hasStreamData := s.dataForWriting != nil
+	s.mutex.Unlock()
+	s.flowController.UpdateSendWindow(frame.ByteOffset)
+	if hasStreamData {
 		s.sender.onHasStreamData(s.streamID)
 	}
-	s.mutex.Unlock()
 }
 
 // must be called after locking the mutex