dnsdist: Make the backend queryLoad and dropRate values atomic

So that there is no race when these vaues are read by the SNMP or
web threads and updated by the health check thread at the same time.
Reported by Thread Sanitizer:

WARNING: ThreadSanitizer: data race (pid=11167)
  Write of size 8 at 0x7b7400002558 by thread T18:
    #0 healthChecksThread() /opt/project/pdns/dnsdistdist/dnsdist.cc:1712:22 (dnsdist+0xf2a4a2)
    #1 void std::__invoke_impl<void, void (*)()>(std::__invoke_other, void (*&&)()) /usr/bin/../lib/gcc/x86_64-linux-gnu/8/../../../../include/c++/8/bits/invoke.h:60:14 (dnsdist+0xf40ea2)
    #2 std::__invoke_result<void (*)()>::type std::__invoke<void (*)()>(void (*&&)()) /usr/bin/../lib/gcc/x86_64-linux-gnu/8/../../../../include/c++/8/bits/invoke.h:95:14 (dnsdist+0xf40e0d)
    #3 decltype(std::__invoke(_S_declval<0ul>())) std::thread::_Invoker<std::tuple<void (*)()> >::_M_invoke<0ul>(std::_Index_tuple<0ul>) /usr/bin/../lib/gcc/x86_64-linux-gnu/8/../../../../include/c++/8/thread:244:13 (dnsdist+0xf40dd5)
    #4 std::thread::_Invoker<std::tuple<void (*)()> >::operator()() /usr/bin/../lib/gcc/x86_64-linux-gnu/8/../../../../include/c++/8/thread:253:11 (dnsdist+0xf40d95)
    #5 std::thread::_State_impl<std::thread::_Invoker<std::tuple<void (*)()> > >::_M_run() /usr/bin/../lib/gcc/x86_64-linux-gnu/8/../../../../include/c++/8/thread:196:13 (dnsdist+0xf40c29)
    #6 <null> <null> (libstdc++.so.6+0xbbb2e)

  Previous read of size 8 at 0x7b7400002558 by thread T2:
    #0 backendStatTable_handler(netsnmp_mib_handler_s*, netsnmp_handler_registration_s*, netsnmp_agent_request_info_s*, netsnmp_request_info_s*) /opt/project/pdns/dnsdistdist/dnsdist-snmp.cc:356:62 (dnsdist+0xeccf98)
    #1 netsnmp_call_next_handler <null> (libnetsnmpagent.so.30+0x2a0cc)
    #2 SNMPAgent::handleSNMPQueryCB(int, boost::any&) /opt/project/pdns/dnsdistdist/snmp-agent.cc:96:13 (dnsdist+0xfb0847)
    #3 boost::detail::function::void_function_invoker2<void (*)(int, boost::any&), void, int, boost::any&>::invoke(boost::detail::function::function_buffer&, int, boost::any&) /usr/include/boost/function/function_template.hpp:118:11 (dnsdist+0x8937d8)
    #4 boost::function2<void, int, boost::any&>::operator()(int, boost::any&) const /usr/include/boost/function/function_template.hpp:768:14 (dnsdist+0xf9d56c)
    #5 EpollFDMultiplexer::run(timeval*, int) /opt/project/pdns/dnsdistdist/epollmplexer.cc:176:7 (dnsdist+0xfd041b)
    #6 SNMPAgent::worker() /opt/project/pdns/dnsdistdist/snmp-agent.cc:141:24 (dnsdist+0xfb0b6f)
    #7 void std::__invoke_impl<void, void (SNMPAgent::*)(), SNMPAgent*>(std::__invoke_memfun_deref, void (SNMPAgent::*&&)(), SNMPAgent*&&) /usr/bin/../lib/gcc/x86_64-linux-gnu/8/../../../../include/c++/8/bits/invoke.h:73:14 (dnsdist+0xf344c9)
    #8 std::__invoke_result<void (SNMPAgent::*)(), SNMPAgent*>::type std::__invoke<void (SNMPAgent::*)(), SNMPAgent*>(void (SNMPAgent::*&&)(), SNMPAgent*&&) /usr/bin/../lib/gcc/x86_64-linux-gnu/8/../../../../include/c++/8/bits/invoke.h:95:14 (dnsdist+0xf343c1)
    #9 decltype(std::__invoke(_S_declval<0ul>(), _S_declval<1ul>())) std::thread::_Invoker<std::tuple<void (SNMPAgent::*)(), SNMPAgent*> >::_M_invoke<0ul, 1ul>(std::_Index_tuple<0ul, 1ul>) /usr/bin/../lib/gcc/x86_64-linux-gnu/8/../../../../include/c++/8/thread:244:13 (dnsdist+0xf3436e)
    #10 std::thread::_Invoker<std::tuple<void (SNMPAgent::*)(), SNMPAgent*> >::operator()() /usr/bin/../lib/gcc/x86_64-linux-gnu/8/../../../../include/c++/8/thread:253:11 (dnsdist+0xf34315)
    #11 std::thread::_State_impl<std::thread::_Invoker<std::tuple<void (SNMPAgent::*)(), SNMPAgent*> > >::_M_run() /usr/bin/../lib/gcc/x86_64-linux-gnu/8/../../../../include/c++/8/thread:196:13 (dnsdist+0xf34079)
    #12 <null> <null> (libstdc++.so.6+0xbbb2e)

diff --git a/pdns/dnsdist.hh b/pdns/dnsdist.hh
index f89734d2b3f1f2efe8c4bc82a4d6c848a4102845..e2448fab46268b169967e5e3a59fd9a8a96630cc 100644 (file)
--- a/pdns/dnsdist.hh
+++ b/pdns/dnsdist.hh
@@ -944,8 +944,8 @@ struct DownstreamState
   size_t socketsOffset{0};
   size_t d_maxInFlightQueriesPerConn{1};
   size_t d_tcpConcurrentConnectionsLimit{0};
-  double queryLoad{0.0};
-  double dropRate{0.0};
+  pdns::stat_t_trait<double> queryLoad{0.0};
+  pdns::stat_t_trait<double> dropRate{0.0};
   double latencyUsec{0.0};
   int order{1};
   int weight{1};