From ed2a37447ab51060a063362f53f730f909aee08f Mon Sep 17 00:00:00 2001
From: Remi Gacogne <remi.gacogne@powerdns.com>
Date: Tue, 1 Dec 2020 15:08:52 +0100
Subject: [PATCH] dnsdist: Clarify what DynBlockMaintenance::s_topsMutex
 protects

---
 pdns/dnsdist-dynblocks.hh             | 2 ++
 pdns/dnsdistdist/dnsdist-dynblocks.cc | 9 +++------
 2 files changed, 5 insertions(+), 6 deletions(-)

diff --git a/pdns/dnsdist-dynblocks.hh b/pdns/dnsdist-dynblocks.hh
index 87027a47ce..8f031f457a 100644
--- a/pdns/dnsdist-dynblocks.hh
+++ b/pdns/dnsdist-dynblocks.hh
@@ -394,6 +394,8 @@ private:
     std::map<std::string, std::list<std::pair<DNSName, unsigned int>>> smtData;
   };
 
+  /* Protects s_topNMGsByReason and s_topSMTsByReason. s_metricsData should only be accessed
+     by the dynamic blocks maintenance thread so it does not need a lock. */
   static std::mutex s_topsMutex;
   // need N+1 datapoints to be able to do the diff after a collection point has been reached
   static std::list<MetricsSnapshot> s_metricsData;
diff --git a/pdns/dnsdistdist/dnsdist-dynblocks.cc b/pdns/dnsdistdist/dnsdist-dynblocks.cc
index 900a25cfaf..574cd4c4c2 100644
--- a/pdns/dnsdistdist/dnsdist-dynblocks.cc
+++ b/pdns/dnsdistdist/dnsdist-dynblocks.cc
@@ -475,13 +475,10 @@ void DynBlockMaintenance::collectMetrics()
   snapshot.smtData = getTopSuffixes(s_topN * 5);
   snapshot.nmgData = getTopNetmasks(s_topN * 5);
 
-  {
-    std::lock_guard<std::mutex> lock(s_topsMutex);
-    if (s_metricsData.size() >= 7) {
-      s_metricsData.pop_front();
-    }
-    s_metricsData.push_back(std::move(snapshot));
+  if (s_metricsData.size() >= 7) {
+    s_metricsData.pop_front();
   }
+  s_metricsData.push_back(std::move(snapshot));
 }
 
 void DynBlockMaintenance::generateMetrics()
-- 
2.47.2