From 4bff8d959e290e90b790e139b94a6011a1c8d482 Mon Sep 17 00:00:00 2001
From: Remi Gacogne <remi.gacogne@powerdns.com>
Date: Tue, 16 Feb 2021 11:43:40 +0100
Subject: [PATCH] dnsdist: Create TCP worker threads before acceptors ones

Otherwise we might crash when the first TCP query arrives because
we are dividing by zero when trying to select a worker.
---
 pdns/dnsdist.cc | 11 +++++++----
 pdns/dnsdist.hh |  4 ++++
 2 files changed, 11 insertions(+), 4 deletions(-)

diff --git a/pdns/dnsdist.cc b/pdns/dnsdist.cc
index d6c6aa9ac5..bf68654f2c 100644
--- a/pdns/dnsdist.cc
+++ b/pdns/dnsdist.cc
@@ -2418,6 +2418,13 @@ int main(int argc, char** argv)
     }
     handleQueuedHealthChecks(mplexer, true);
 
+    /* we need to create the TCP worker threads before the
+       acceptor ones, otherwise we might crash when processing
+       the first TCP query */
+    while (!g_tcpclientthreads->hasReachedMaxThreads()) {
+      g_tcpclientthreads->addTCPClientThread();
+    }
+
     for(auto& cs : g_frontends) {
       if (cs->dohFrontend != nullptr) {
 #ifdef HAVE_DNS_OVER_HTTPS
@@ -2445,10 +2452,6 @@ int main(int argc, char** argv)
       }
     }
 
-    while (!g_tcpclientthreads->hasReachedMaxThreads()) {
-      g_tcpclientthreads->addTCPClientThread();
-    }
-
     thread carbonthread(carbonDumpThread);
     carbonthread.detach();
 
diff --git a/pdns/dnsdist.hh b/pdns/dnsdist.hh
index d93340a371..a98c7324d3 100644
--- a/pdns/dnsdist.hh
+++ b/pdns/dnsdist.hh
@@ -857,6 +857,10 @@ public:
   }
   int getThread()
   {
+    if (d_numthreads == 0) {
+      throw std::runtime_error("No TCP worker thread yet");
+    }
+
     uint64_t pos = d_pos++;
     ++d_queued;
     return d_tcpclientthreads.at(pos % d_numthreads);
-- 
2.47.2