Take the account session lock when deleting from map

Signed-off-by: Neil Twigg <neil@nats.io>

server/mqtt.go

@@ -3274,7 +3274,7 @@ func (s *Server) mqttCheckPubRetainedPerms() {
 		// Get all of the retained messages. Then we will sort them so
 		// that they are in sequence order, which should help the file
 		// store to not have to load out-of-order blocks so often.
-		asm.mu.Lock()
+		asm.mu.RLock()
 		rms = rms[:0] // reuse slice
 		for subj, rf := range asm.retmsgs {
 			rms = append(rms, retainedMsg{
@@ -3282,7 +3282,7 @@ func (s *Server) mqttCheckPubRetainedPerms() {
 				rmsg: rf,
 			})
 		}
-		asm.mu.Unlock()
+		asm.mu.RUnlock()
 		sort.Slice(rms, func(i, j int) bool {
 			return rms[i].rmsg.sseq < rms[j].rmsg.sseq
 		})
@@ -3319,8 +3319,10 @@ func (s *Server) mqttCheckPubRetainedPerms() {
 			// Not present or permissions have changed such that the source can't
 			// publish on that subject anymore: remove it from the map.
 			if u == nil {
+				asm.mu.Lock()
 				delete(asm.retmsgs, rf.subj)
 				asm.sl.Remove(rf.rmsg.sub)
+				asm.mu.Unlock()
 				deletes[rf.subj] = rf.rmsg.sseq
 			}
 		}