From 6a93858125a2ece1c2cc557e11d34e51a67ada45 Mon Sep 17 00:00:00 2001
From: Till Faelligen <2353100+S7evinK@users.noreply.github.com>
Date: Thu, 20 Oct 2022 10:45:59 +0200
Subject: [PATCH] Fix race condition

---
 federationapi/queue/destinationqueue.go | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/federationapi/queue/destinationqueue.go b/federationapi/queue/destinationqueue.go
index 00e02b2d9..768ed1f2b 100644
--- a/federationapi/queue/destinationqueue.go
+++ b/federationapi/queue/destinationqueue.go
@@ -21,16 +21,17 @@ import (
 	"sync"
 	"time"
 
+	"github.com/matrix-org/gomatrix"
+	"github.com/matrix-org/gomatrixserverlib"
+	"github.com/sirupsen/logrus"
+	"go.uber.org/atomic"
+
 	fedapi "github.com/matrix-org/dendrite/federationapi/api"
 	"github.com/matrix-org/dendrite/federationapi/statistics"
 	"github.com/matrix-org/dendrite/federationapi/storage"
 	"github.com/matrix-org/dendrite/federationapi/storage/shared"
 	"github.com/matrix-org/dendrite/roomserver/api"
 	"github.com/matrix-org/dendrite/setup/process"
-	"github.com/matrix-org/gomatrix"
-	"github.com/matrix-org/gomatrixserverlib"
-	"github.com/sirupsen/logrus"
-	"go.uber.org/atomic"
 )
 
 const (
@@ -541,6 +542,8 @@ func (oq *destinationQueue) handleTransactionSuccess(pduCount int, eduCount int)
 	// the pending events and EDUs, and wipe our transaction ID.
 	oq.statistics.Success()
 	oq.pendingMutex.Lock()
+	defer oq.pendingMutex.Unlock()
+
 	for i := range oq.pendingPDUs[:pduCount] {
 		oq.pendingPDUs[i] = nil
 	}
@@ -549,7 +552,6 @@ func (oq *destinationQueue) handleTransactionSuccess(pduCount int, eduCount int)
 	}
 	oq.pendingPDUs = oq.pendingPDUs[pduCount:]
 	oq.pendingEDUs = oq.pendingEDUs[eduCount:]
-	oq.pendingMutex.Unlock()
 
 	if len(oq.pendingPDUs) > 0 || len(oq.pendingEDUs) > 0 {
 		select {