Extend comment
diff --git a/src/cpp/server/server.cc b/src/cpp/server/server.cc
index 8b21337..e039c07 100644
--- a/src/cpp/server/server.cc
+++ b/src/cpp/server/server.cc
@@ -332,6 +332,8 @@
// Spin, eating requests until the completion queue is completely shutdown.
// If the deadline expires then cancel anything that's pending and keep
// spinning forever until the work is actually drained.
+ // Since nothing else needs to touch state guarded by mu_, holding it
+ // through this loop is fine.
SyncRequest* request;
bool ok;
while (SyncRequest::AsyncWait(&cq_, &request, &ok, deadline)) {