dnsdist: Fix a data race reported by TSAN in SNMP metrics

Unless I'm mistaken, the report (below) is a false positive since
`std::atomic<T>::operator T` is equivalent to `load()` and
`std::atomic<T>::operator=` to `store()`, but perhaps I'm missing
something.
Note that I could not reproduce the issue using clang++ 11.1.0's
TSAN, only with the one from g++ 11.1.0.

```
==================
WARNING: ThreadSanitizer: data race (pid=11157)
  Atomic read of size 8 at 0x7b7400002580 by thread T2:
    #0 __tsan_atomic64_load <null> (dnsdist+0x7a6eb0)
    #1 std::atomic<double>::load(std::memory_order) const /usr/bin/../lib/gcc/x86_64-linux-gnu/8/../../../../include/c++/8/atomic:250:2 (dnsdist+0x83c4da)
    #2 pdns::stat_t_trait<double>::operator double() const /opt/project/pdns/dnsdistdist/./stat_t.hh:67:60 (dnsdist+0xd05b2e)
    #3 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:356:54 (dnsdist+0xeceab8)
    #4 netsnmp_call_next_handler <null> (libnetsnmpagent.so.30+0x2a0cc)
    #5 SNMPAgent::handleSNMPQueryCB(int, boost::any&) /opt/project/pdns/dnsdistdist/snmp-agent.cc:96:13 (dnsdist+0xfb2417)
    #6 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+0x8956e8)
    #7 boost::function2<void, int, boost::any&>::operator()(int, boost::any&) const /usr/include/boost/function/function_template.hpp:768:14 (dnsdist+0xf9f13c)
    #8 EpollFDMultiplexer::run(timeval*, int) /opt/project/pdns/dnsdistdist/epollmplexer.cc:176:7 (dnsdist+0xfd1feb)
    #9 SNMPAgent::worker() /opt/project/pdns/dnsdistdist/snmp-agent.cc:141:24 (dnsdist+0xfb273f)
    #10 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+0xf36079)
    #11 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+0xf35f71)
    #12 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+0xf35f1e)
    #13 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+0xf35ec5)
    #14 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+0xf35c29)
    #15 <null> <null> (libstdc++.so.6+0xbbb2e)

  Previous write of size 8 at 0x7b7400002580 by thread T18:
    [failed to restore the stack]

  Location is heap block of size 2304 at 0x7b7400001e00 allocated by main thread:
    #0 operator new(unsigned long, std::align_val_t) <null> (dnsdist+0x7e8c57)
    #1 __gnu_cxx::new_allocator<std::_Sp_counted_ptr_inplace<DownstreamState, std::allocator<DownstreamState>, (__gnu_cxx::_Lock_policy)2> >::allocate(unsigned long, void const*) /usr/bin/../lib/gcc/x86_64-linux-gnu/8/../../../../include/c++/8/ext/new_allocator.h:108:31 (dnsdist+0xe6b4e2)
    #2 std::allocator_traits<std::allocator<std::_Sp_counted_ptr_inplace<DownstreamState, std::allocator<DownstreamState>, (__gnu_cxx::_Lock_policy)2> > >::allocate(std::allocator<std::_Sp_counted_ptr_inplace<DownstreamState, std::allocator<DownstreamState>, (__gnu_cxx::_Lock_policy)2> >&, unsigned long) /usr/bin/../lib/gcc/x86_64-linux-gnu/8/../../../../include/c++/8/bits/alloc_traits.h:436:20 (dnsdist+0xe6b430)
    #3 std::__allocated_ptr<std::allocator<std::_Sp_counted_ptr_inplace<DownstreamState, std::allocator<DownstreamState>, (__gnu_cxx::_Lock_policy)2> > > std::__allocate_guarded<std::allocator<std::_Sp_counted_ptr_inplace<DownstreamState, std::allocator<DownstreamState>, (__gnu_cxx::_Lock_policy)2> > >(std::allocator<std::_Sp_counted_ptr_inplace<DownstreamState, std::allocator<DownstreamState>, (__gnu_cxx::_Lock_policy)2> >&) /usr/bin/../lib/gcc/x86_64-linux-gnu/8/../../../../include/c++/8/bits/allocated_ptr.h:97:21 (dnsdist+0xe6b1d0)
    #4 std::__shared_count<(__gnu_cxx::_Lock_policy)2>::__shared_count<DownstreamState, std::allocator<DownstreamState>, ComboAddress&, ComboAddress&, unsigned int&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >&, unsigned long&, bool>(DownstreamState*&, std::_Sp_alloc_shared_tag<std::allocator<DownstreamState> >, ComboAddress&, ComboAddress&, unsigned int&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >&, unsigned long&, bool&&) /usr/bin/../lib/gcc/x86_64-linux-gnu/8/../../../../include/c++/8/bits/shared_ptr_base.h:675:19 (dnsdist+0xe6fb0a)
    #5 std::__shared_ptr<DownstreamState, (__gnu_cxx::_Lock_policy)2>::__shared_ptr<std::allocator<DownstreamState>, ComboAddress&, ComboAddress&, unsigned int&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >&, unsigned long&, bool>(std::_Sp_alloc_shared_tag<std::allocator<DownstreamState> >, ComboAddress&, ComboAddress&, unsigned int&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >&, unsigned long&, bool&&) /usr/bin/../lib/gcc/x86_64-linux-gnu/8/../../../../include/c++/8/bits/shared_ptr_base.h:1342:14 (dnsdist+0xe6fa7a)
    #6 std::shared_ptr<DownstreamState>::shared_ptr<std::allocator<DownstreamState>, ComboAddress&, ComboAddress&, unsigned int&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >&, unsigned long&, bool>(std::_Sp_alloc_shared_tag<std::allocator<DownstreamState> >, ComboAddress&, ComboAddress&, unsigned int&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >&, unsigned long&, bool&&) /usr/bin/../lib/gcc/x86_64-linux-gnu/8/../../../../include/c++/8/bits/shared_ptr.h:359:4 (dnsdist+0xe6f99d)
    #7 std::shared_ptr<DownstreamState> std::allocate_shared<DownstreamState, std::allocator<DownstreamState>, ComboAddress&, ComboAddress&, unsigned int&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >&, unsigned long&, bool>(std::allocator<DownstreamState> const&, ComboAddress&, ComboAddress&, unsigned int&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >&, unsigned long&, bool&&) /usr/bin/../lib/gcc/x86_64-linux-gnu/8/../../../../include/c++/8/bits/shared_ptr.h:705:14 (dnsdist+0xe6f8e0)
    #8 std::shared_ptr<DownstreamState> std::make_shared<DownstreamState, ComboAddress&, ComboAddress&, unsigned int&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >&, unsigned long&, bool>(ComboAddress&, ComboAddress&, unsigned int&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >&, unsigned long&, bool&&) /usr/bin/../lib/gcc/x86_64-linux-gnu/8/../../../../include/c++/8/bits/shared_ptr.h:721:14 (dnsdist+0xe6a726)
    #9 setupLuaConfig(LuaContext&, bool, bool)::$_2::operator()(boost::variant<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::unordered_map<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, boost::variant<bool, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::vector<std::pair<int, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::allocator<std::pair<int, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > > > >, std::function<std::tuple<DNSName, unsigned short, unsigned short> (DNSName const&, unsigned short, unsigned short, dnsheader*)> >, std::hash<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::equal_to<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::allocator<std::pair<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const, boost::variant<bool, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::vector<std::pair<int, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::allocator<std::pair<int, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > > > >, std::function<std::tuple<DNSName, unsigned short, unsigned short> (DNSName const&, unsigned short, unsigned short, dnsheader*)> > > > > >, boost::optional<int>) const /opt/project/pdns/dnsdistdist/dnsdist-lua.cc:356:11 (dnsdist+0xdf9166)
    #10 _ZN10LuaContext6BinderIRZL14setupLuaConfigRS_bbE3$_2RKN5boost7variantINSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEEJSt13unordered_mapISB_NS5_IbJSB_St6vectorISt4pairIiSB_ESaISF_EESt8functionIFSt5tupleIJ7DNSNamettEERKSK_ttP9dnsheaderEEEEESt4hashISB_ESt8equal_toISB_ESaISE_IKSB_SS_EEEEEEEclIJRKNS4_8optionalIiEEEEEDTcldtdefpT8functiondtdefpT5paramspclsr3stdE7forwardIT_Efp_EEEDpOS1A_ /opt/project/pdns/dnsdistdist/./ext/luawrapper/include/LuaContext.hpp:1846:20 (dnsdist+0xdf89af)
    #11 _ZN10LuaContext6BinderIRNS0_IRZL14setupLuaConfigRS_bbE3$_2RKN5boost7variantINSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEEJSt13unordered_mapISB_NS5_IbJSB_St6vectorISt4pairIiSB_ESaISF_EESt8functionIFSt5tupleIJ7DNSNamettEERKSK_ttP9dnsheaderEEEEESt4hashISB_ESt8equal_toISB_ESaISE_IKSB_SS_EEEEEEEERKNS4_8optionalIiEEEclIJEEEDTcldtdefpT8functiondtdefpT5paramspclsr3stdE7forwardIT_Efp_EEEDpOS1C_ /opt/project/pdns/dnsdistdist/./ext/luawrapper/include/LuaContext.hpp:1846:20 (dnsdist+0xdf8917)
    #12 std::shared_ptr<DownstreamState> LuaContext::readIntoFunction<std::shared_ptr<DownstreamState>, LuaContext::Binder<LuaContext::Binder<setupLuaConfig(LuaContext&, bool, bool)::$_2&, boost::variant<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::unordered_map<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, boost::variant<bool, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::vector<std::pair<int, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::allocator<std::pair<int, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > > > >, std::function<std::tuple<DNSName, unsigned short, unsigned short> (DNSName const&, unsigned short, unsigned short, dnsheader*)> >, std::hash<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::equal_to<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::allocator<std::pair<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const, boost::variant<bool, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::vector<std::pair<int, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::allocator<std::pair<int, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > > > >, std::function<std::tuple<DNSName, unsigned short, unsigned short> (DNSName const&, unsigned short, unsigned short, dnsheader*)> > > > > > const&>&, boost::optional<int> const&>&>(lua_State*, LuaContext::tag<std::shared_ptr<DownstreamState> >, LuaContext::Binder<LuaContext::Binder<setupLuaConfig(LuaContext&, bool, bool)::$_2&, boost::variant<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::unordered_map<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, boost::variant<bool, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::vector<std::pair<int, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::allocator<std::pair<int, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > > > >, std::function<std::tuple<DNSName, unsigned short, unsigned short> (DNSName const&, unsigned short, unsigned short, dnsheader*)> >, std::hash<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::equal_to<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::allocator<std::pair<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const, boost::variant<bool, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::vector<std::pair<int, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::allocator<std::pair<int, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > > > >, std::function<std::tuple<DNSName, unsigned short, unsigned short> (DNSName const&, unsigned short, unsigned short, dnsheader*)> > > > > > const&>&, boost::optional<int> const&>&, int) /opt/project/pdns/dnsdistdist/./ext/luawrapper/include/LuaContext.hpp:1766:16 (dnsdist+0xdf88be)
    #13 std::enable_if<IsOptional<boost::optional<int> >::value, std::shared_ptr<DownstreamState> >::type LuaContext::readIntoFunction<std::shared_ptr<DownstreamState>, LuaContext::Binder<setupLuaConfig(LuaContext&, bool, bool)::$_2&, boost::variant<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::unordered_map<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, boost::variant<bool, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::vector<std::pair<int, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::allocator<std::pair<int, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > > > >, std::function<std::tuple<DNSName, unsigned short, unsigned short> (DNSName const&, unsigned short, unsigned short, dnsheader*)> >, std::hash<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::equal_to<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::allocator<std::pair<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const, boost::variant<bool, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::vector<std::pair<int, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::allocator<std::pair<int, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > > > >, std::function<std::tuple<DNSName, unsigned short, unsigned short> (DNSName const&, unsigned short, unsigned short, dnsheader*)> > > > > > const&>&, boost::optional<int> >(lua_State*, LuaContext::tag<std::shared_ptr<DownstreamState> >, LuaContext::Binder<setupLuaConfig(LuaContext&, bool, bool)::$_2&, boost::variant<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::unordered_map<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, boost::variant<bool, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::vector<std::pair<int, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::allocator<std::pair<int, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > > > >, std::function<std::tuple<DNSName, unsigned short, unsigned short> (DNSName const&, unsigned short, unsigned short, dnsheader*)> >, std::hash<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::equal_to<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::allocator<std::pair<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const, boost::variant<bool, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::vector<std::pair<int, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::allocator<std::pair<int, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > > > >, std::function<std::tuple<DNSName, unsigned short, unsigned short> (DNSName const&, unsigned short, unsigned short, dnsheader*)> > > > > > const&>&, int, LuaContext::tag<boost::optional<int> >) /opt/project/pdns/dnsdistdist/./ext/luawrapper/include/LuaContext.hpp:1774:20 (dnsdist+0xdf8624)
    #14 std::enable_if<!(IsOptional<boost::variant<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::unordered_map<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, boost::variant<bool, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::vector<std::pair<int, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::allocator<std::pair<int, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > > > >, std::function<std::tuple<DNSName, unsigned short, unsigned short> (DNSName const&, unsigned short, unsigned short, dnsheader*)> >, std::hash<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::equal_to<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::allocator<std::pair<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const, boost::variant<bool, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::vector<std::pair<int, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::allocator<std::pair<int, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > > > >, std::function<std::tuple<DNSName, unsigned short, unsigned short> (DNSName const&, unsigned short, unsigned short, dnsheader*)> > > > > > >::value), std::shared_ptr<DownstreamState> >::type LuaContext::readIntoFunction<std::shared_ptr<DownstreamState>, setupLuaConfig(LuaContext&, bool, bool)::$_2&, boost::variant<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::unordered_map<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, boost::variant<bool, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::vector<std::pair<int, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::allocator<std::pair<int, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > > > >, std::function<std::tuple<DNSName, unsigned short, unsigned short> (DNSName const&, unsigned short, unsigned short, dnsheader*)> >, std::hash<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::equal_to<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::allocator<std::pair<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const, boost::variant<bool, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::vector<std::pair<int, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::allocator<std::pair<int, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > > > >, std::function<std::tuple<DNSName, unsigned short, unsigned short> (DNSName const&, unsigned short, unsigned short, dnsheader*)> > > > > >, boost::optional<int> >(lua_State*, LuaContext::tag<std::shared_ptr<DownstreamState> >, setupLuaConfig(LuaContext&, bool, bool)::$_2&, int, LuaContext::tag<boost::variant<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::unordered_map<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, boost::variant<bool, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::vector<std::pair<int, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::allocator<std::pair<int, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > > > >, std::function<std::tuple<DNSName, unsigned short, unsigned short> (DNSName const&, unsigned short, unsigned short, dnsheader*)> >, std::hash<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::equal_to<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::allocator<std::pair<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const, boost::variant<bool, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::vector<std::pair<int, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::allocator<std::pair<int, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > > > >, std::function<std::tuple<DNSName, unsigned short, unsigned short> (DNSName const&, unsigned short, unsigned short, dnsheader*)> > > > > > >, LuaContext::tag<boost::optional<int> >) /opt/project/pdns/dnsdistdist/./ext/luawrapper/include/LuaContext.hpp:1796:16 (dnsdist+0xdf848d)
    #15 std::enable_if<(!(std::integral_constant<bool, false>::value)) && (!(std::is_void<bool>::value)), LuaContext::PushedObject>::type LuaContext::Pusher<std::shared_ptr<DownstreamState> (boost::variant<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::unordered_map<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, boost::variant<bool, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::vector<std::pair<int, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::allocator<std::pair<int, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > > > >, std::function<std::tuple<DNSName, unsigned short, unsigned short> (DNSName const&, unsigned short, unsigned short, dnsheader*)> >, std::hash<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::equal_to<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::allocator<std::pair<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const, boost::variant<bool, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::vector<std::pair<int, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::allocator<std::pair<int, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > > > >, std::function<std::tuple<DNSName, unsigned short, unsigned short> (DNSName const&, unsigned short, unsigned short, dnsheader*)> > > > > >, boost::optional<int>), void>::callback2<setupLuaConfig(LuaContext&, bool, bool)::$_2&>(lua_State*, bool&&, int) /opt/project/pdns/dnsdistdist/./ext/luawrapper/include/LuaContext.hpp:2429:31 (dnsdist+0xdf83c2)
    #16 LuaContext::PushedObject LuaContext::Pusher<std::shared_ptr<DownstreamState> (boost::variant<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::unordered_map<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, boost::variant<bool, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::vector<std::pair<int, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::allocator<std::pair<int, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > > > >, std::function<std::tuple<DNSName, unsigned short, unsigned short> (DNSName const&, unsigned short, unsigned short, dnsheader*)> >, std::hash<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::equal_to<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::allocator<std::pair<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const, boost::variant<bool, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::vector<std::pair<int, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::allocator<std::pair<int, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > > > >, std::function<std::tuple<DNSName, unsigned short, unsigned short> (DNSName const&, unsigned short, unsigned short, dnsheader*)> > > > > >, boost::optional<int>), void>::callback<setupLuaConfig(LuaContext&, bool, bool)::$_2>(lua_State*, setupLuaConfig(LuaContext&, bool, bool)::$_2*, int) /opt/project/pdns/dnsdistdist/./ext/luawrapper/include/LuaContext.hpp:2398:20 (dnsdist+0xdf8169)
    #17 std::enable_if<boost::has_trivial_destructor<setupLuaConfig(LuaContext&, bool, bool)::$_2>::value, LuaContext::PushedObject>::type LuaContext::Pusher<std::shared_ptr<DownstreamState> (boost::variant<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::unordered_map<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, boost::variant<bool, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::vector<std::pair<int, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::allocator<std::pair<int, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > > > >, std::function<std::tuple<DNSName, unsigned short, unsigned short> (DNSName const&, unsigned short, unsigned short, dnsheader*)> >, std::hash<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::equal_to<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::allocator<std::pair<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const, boost::variant<bool, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::vector<std::pair<int, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::allocator<std::pair<int, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > > > >, std::function<std::tuple<DNSName, unsigned short, unsigned short> (DNSName const&, unsigned short, unsigned short, dnsheader*)> > > > > >, boost::optional<int>), void>::push<setupLuaConfig(LuaContext&, bool, bool)::$_2>(lua_State*, setupLuaConfig(LuaContext&, bool, bool)::$_2)::'lambda'(lua_State*)::operator()(lua_State*) const /opt/project/pdns/dnsdistdist/./ext/luawrapper/include/LuaContext.hpp:2327:20 (dnsdist+0xdf80c9)
    #18 std::enable_if<boost::has_trivial_destructor<setupLuaConfig(LuaContext&, bool, bool)::$_2>::value, LuaContext::PushedObject>::type LuaContext::Pusher<std::shared_ptr<DownstreamState> (boost::variant<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::unordered_map<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, boost::variant<bool, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::vector<std::pair<int, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::allocator<std::pair<int, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > > > >, std::function<std::tuple<DNSName, unsigned short, unsigned short> (DNSName const&, unsigned short, unsigned short, dnsheader*)> >, std::hash<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::equal_to<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::allocator<std::pair<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const, boost::variant<bool, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::vector<std::pair<int, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::allocator<std::pair<int, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > > > >, std::function<std::tuple<DNSName, unsigned short, unsigned short> (DNSName const&, unsigned short, unsigned short, dnsheader*)> > > > > >, boost::optional<int>), void>::push<setupLuaConfig(LuaContext&, bool, bool)::$_2>(lua_State*, setupLuaConfig(LuaContext&, bool, bool)::$_2)::'lambda'(lua_State*)::__invoke(lua_State*) /opt/project/pdns/dnsdistdist/./ext/luawrapper/include/LuaContext.hpp:2323:31 (dnsdist+0xdf8055)
    #19 _init <null> (libluajit-5.1.so.2+0x9dd6)
    #20 std::tuple<> LuaContext::call<std::tuple<> >(lua_State*, LuaContext::PushedObject) /opt/project/pdns/dnsdistdist/./ext/luawrapper/include/LuaContext.hpp:1413:29 (dnsdist+0xc9ae67)
    #21 LuaContext::executeCode(std::istream&) /opt/project/pdns/dnsdistdist/./ext/luawrapper/include/LuaContext.hpp:267:9 (dnsdist+0xe6077a)
    #22 setupLua(LuaContext&, bool, bool, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&) /opt/project/pdns/dnsdistdist/dnsdist-lua.cc:2599:10 (dnsdist+0xdf4ff3)
    #23 main /opt/project/pdns/dnsdistdist/dnsdist.cc:2235:17 (dnsdist+0xf282ea)

  Thread T2 'dnsdist/SNMP' (tid=11160, running) created by main thread at:
    #0 pthread_create <null> (dnsdist+0x75f2d5)
    #1 std::thread::_M_start_thread(std::unique_ptr<std::thread::_State, std::default_delete<std::thread::_State> >, void (*)()) <null> (libstdc++.so.6+0xbbdb4)
    #2 SNMPAgent::run() /opt/project/pdns/dnsdistdist/./snmp-agent.hh:36:14 (dnsdist+0xf3087c)
    #3 main /opt/project/pdns/dnsdistdist/dnsdist.cc:2373:20 (dnsdist+0xf28f32)

  Thread T18 'dnsdist/healthC' (tid=11176, running) created by main thread at:
    #0 pthread_create <null> (dnsdist+0x75f2d5)
    #1 std::thread::_M_start_thread(std::unique_ptr<std::thread::_State, std::default_delete<std::thread::_State> >, void (*)()) <null> (libstdc++.so.6+0xbbdb4)
    #2 main /opt/project/pdns/dnsdistdist/dnsdist.cc:2463:12 (dnsdist+0xf29769)

SUMMARY: ThreadSanitizer: data race (/opt/dnsdist-with-tsan/bin/dnsdist+0x7a6eb0) in __tsan_atomic64_load
```

diff --git a/pdns/dnsdist-snmp.cc b/pdns/dnsdist-snmp.cc
index 6aedb06ee62058750fd223b7acd0d559ecbbf47f..d4f4937d6db378b9dcf4e84b1c0962fd090f89ba 100644 (file)
--- a/pdns/dnsdist-snmp.cc
+++ b/pdns/dnsdist-snmp.cc
@@ -311,14 +311,14 @@ static int backendStatTable_handler(netsnmp_mib_handler* handler,
         break;
       case COLUMN_BACKENDOUTSTANDING:
         DNSDistSNMPAgent::setCounter64Value(request,
-                                            server->outstanding);
+                                            server->outstanding.load());
         break;
       case COLUMN_BACKENDQPSLIMIT:
         DNSDistSNMPAgent::setCounter64Value(request,
                                             server->qps.getRate());
         break;
       case COLUMN_BACKENDREUSED:
-        DNSDistSNMPAgent::setCounter64Value(request, server->reuseds);
+        DNSDistSNMPAgent::setCounter64Value(request, server->reuseds.load());
         break;
       case COLUMN_BACKENDSTATE:
       {
@@ -353,10 +353,10 @@ static int backendStatTable_handler(netsnmp_mib_handler* handler,
         break;
       }
       case COLUMN_BACKENDQPS:
-        DNSDistSNMPAgent::setCounter64Value(request, server->queryLoad);
+        DNSDistSNMPAgent::setCounter64Value(request, server->queryLoad.load());
         break;
       case COLUMN_BACKENDQUERIES:
-        DNSDistSNMPAgent::setCounter64Value(request, server->queries);
+        DNSDistSNMPAgent::setCounter64Value(request, server->queries.load());
         break;
       case COLUMN_BACKENDORDER:
         DNSDistSNMPAgent::setCounter64Value(request, server->order);

diff --git a/pdns/dnsdist.cc b/pdns/dnsdist.cc
index 0b4c5b316b559fe182a62718e6e7ff6bb8cf686c..9a2ac0a23f228aa879a236a9653edc13e68e4eb4 100644 (file)
--- a/pdns/dnsdist.cc
+++ b/pdns/dnsdist.cc
@@ -1709,8 +1709,8 @@ static void healthChecksThread()
       }
 
       auto delta = dss->sw.udiffAndSet()/1000000.0;
-      dss->queryLoad = 1.0*(dss->queries.load() - dss->prev.queries.load())/delta;
-      dss->dropRate = 1.0*(dss->reuseds.load() - dss->prev.reuseds.load())/delta;
+      dss->queryLoad.store(1.0*(dss->queries.load() - dss->prev.queries.load())/delta);
+      dss->dropRate.store(1.0*(dss->reuseds.load() - dss->prev.reuseds.load())/delta);
       dss->prev.queries.store(dss->queries.load());
       dss->prev.reuseds.store(dss->reuseds.load());