contrail-tor-agent is struck in tbb::mutex::lock called from TcpSession::IsClosed. On looking at the lock, it seems that there is an attempt to take lock on a free'd TcpSession.

(gdb) bt
#0  __lll_lock_wait () at ../nptl/sysdeps/unix/sysv/linux/x86_64/lowlevellock.S:135
#1  0x00007f76c3b28657 in _L_lock_909 () from /lib/x86_64-linux-gnu/libpthread.so.0
#2  0x00007f76c3b28480 in __GI___pthread_mutex_lock (mutex=0x7f76980e6b98) at ../nptl/pthread_mutex_lock.c:79
#3  0x000000000100c7ec in tbb::mutex::lock (this=0x7f76980e6b98) at /usr/include/tbb/mutex.h:164
#4  0x000000000100c79e in tbb::mutex::scoped_lock::acquire (this=0x7fff60b7fc40, mutex=...) at /usr/include/tbb/mutex.h:105
#5  0x000000000100c759 in tbb::mutex::scoped_lock::scoped_lock (this=0x7fff60b7fc40, mutex=...) at /usr/include/tbb/mutex.h:91
#6  0x00000000012fce92 in TcpSession::IsClosed (this=0x7f76980e6b90) at controller/src/io/tcp_session.h:119
#7  0x0000000001859d81 in SandeshClient::SendSandesh (this=0x7f76b4070f70, snh=0x3dcdc40) at tools/sandesh/library/cpp/sandesh_client.cc:117
#8  0x000000000183f7e3 in Sandesh::SendEnqueue (this=0x3dcdc40) at tools/sandesh/library/cpp/sandesh.cc:591
#9  0x000000000183fa36 in Sandesh::Dispatch (this=0x3dcdc40, sconn=0x0) at tools/sandesh/library/cpp/sandesh.cc:611
#10 0x0000000001616f2e in XmppEventLog::Send (category=..., level=SandeshLevel::SYS_NOTICE, file=..., line=1314, f1=..., f2=..., f3=...,
    f4=...) at build/debug/xmpp/sandesh/xmpp_state_machine_sandesh_types.h:504
#11 0x000000000161305d in XmppStateMachine::OnSessionEvent (this=0x7f765c00e5b0, session=0x7f7694088de0, event=TcpSession::CONNECT_FAILED)
    at controller/src/xmpp/xmpp_state_machine.cc:1311
#12 0x0000000001631886 in boost::_mfi::mf2<void, XmppStateMachine, TcpSession*, TcpSession::Event>::operator() (this=0x7f7694088e98,
    p=0x7f765c00e5b0, a1=0x7f7694088de0, a2=TcpSession::CONNECT_FAILED) at /usr/include/boost/bind/mem_fn_template.hpp:280
#13 0x00000000016300ca in boost::_bi::list3<boost::_bi::value<XmppStateMachine*>, boost::arg<1>, boost::arg<2> >::operator()<boost::_mfi::mf2<void, XmppStateMachine, TcpSession*, TcpSession::Event>, boost::_bi::list2<TcpSession*&, TcpSession::Event&> > (this=0x7f7694088ea8, f=...,
    a=...) at /usr/include/boost/bind/bind.hpp:392
#14 0x000000000162edd8 in boost::_bi::bind_t<void, boost::_mfi::mf2<void, XmppStateMachine, TcpSession*, TcpSession::Event>, boost::_bi::list3<boost::_bi::value<XmppStateMachine*>, boost::arg<1>, boost::arg<2> > >::operator()<TcpSession*, TcpSession::Event> (this=0x7f7694088e98,
    a1=@0x7fff60b80160: 0x7f7694088de0, a2=@0x7fff60b8015c: TcpSession::CONNECT_FAILED) at /usr/include/boost/bind/bind_template.hpp:61
#15 0x000000000162def1 in boost::detail::function::void_function_obj_invoker2<boost::_bi::bind_t<void, boost::_mfi::mf2<void, XmppStateMachine, TcpSession*, TcpSession::Event>, boost::_bi::list3<boost::_bi::value<XmppStateMachine*>, boost::arg<1>, boost::arg<2> > >, void, TcpSession*, TcpSession::Event>::invoke (function_obj_ptr=..., a0=0x7f7694088de0, a1=TcpSession::CONNECT_FAILED)
    at /usr/include/boost/function/function_template.hpp:153
#16 0x000000000182e424 in boost::function2<void, TcpSession*, TcpSession::Event>::operator() (this=0x7f7694088e90, a0=0x7f7694088de0,
    a1=TcpSession::CONNECT_FAILED) at /usr/include/boost/function/function_template.hpp:767
#17 0x0000000001825028 in TcpSession::ConnectFailed (this=0x7f7694088de0) at controller/src/io/tcp_session.cc:278
#18 0x00000000018181a3 in TcpServer::ConnectHandler (this=0x7f765c00d2e0, server=..., session=..., error=...)
    at controller/src/io/tcp_server.cc:388
#19 0x0000000001822f35 in boost::_mfi::mf3<void, TcpServer, boost::intrusive_ptr<TcpServer>, boost::intrusive_ptr<TcpSession>, boost::system::error_code const&>::operator() (this=0x7fff60b806c0, p=0x7f765c00d2e0, a1=..., a2=..., a3=...)
    at /usr/include/boost/bind/mem_fn_template.hpp:393
#20 0x0000000001822e11 in boost::_bi::list4<boost::_bi::value<TcpServer*>, boost::_bi::value<boost::intrusive_ptr<TcpServer> >, boost::_bi::value<boost::intrusive_ptr<TcpSession> >, boost::arg<1> (*)()>::operator()<boost::_mfi::mf3<void, TcpServer, boost::intrusive_ptr<TcpServer>, boost::intrusive_ptr<TcpSession>, boost::system::error_code const&>, boost::_bi::list1<boost::system::error_code const&> > (this=0x7fff60b806d0,
    f=..., a=...) at /usr/include/boost/bind/bind.hpp:457
#21 0x0000000001822d30 in boost::_bi::bind_t<void, boost::_mfi::mf3<void, TcpServer, boost::intrusive_ptr<TcpServer>, boost::intrusive_ptr<TcpSession>, boost::system::error_code const&>, boost::_bi::list4<boost::_bi::value<TcpServer*>, boost::_bi::value<boost::intrusive_ptr<TcpServer> >, boost::_bi::value<boost::intrusive_ptr<TcpSession> >, boost::arg<1> (*)()> >::operator()<boost::system::error_code> (this=0x7fff60b806c0,
    a1=...) at /usr/include/boost/bind/bind_template.hpp:47
#22 0x0000000001822bc1 in boost::asio::detail::binder1<boost::_bi::bind_t<void, boost::_mfi::mf3<void, TcpServer, boost::intrusive_ptr<TcpServer>, boost::intrusive_ptr<TcpSession>, boost::system::error_code const&>, boost::_bi::list4<boost::_bi::value<TcpServer*>, boost::_bi::value<boost::intrusive_ptr<TcpServer> >, boost::_bi::value<boost::intrusive_ptr<TcpSession> >, boost::arg<1> (*)()> >, boost::system::error_code>::operator() (this=0x7fff60b806c0) at /usr/include/boost/asio/detail/bind_handler.hpp:47
#23 0x0000000001822ad9 in boost::asio::asio_handler_invoke<boost::asio::detail::binder1<boost::_bi::bind_t<void, boost::_mfi::mf3<void, TcpServ---Type <return> to continue, or q <return> to quit---
er, boost::intrusive_ptr<TcpServer>, boost::intrusive_ptr<TcpSession>, boost::system::error_code const&>, boost::_bi::list4<boost::_bi::value<TcpServer*>, boost::_bi::value<boost::intrusive_ptr<TcpServer> >, boost::_bi::value<boost::intrusive_ptr<TcpSession> >, boost::arg<1> (*)()> >, boost::system::error_code> > (function=...) at /usr/include/boost/asio/handler_invoke_hook.hpp:64
#24 0x000000000182294e in boost_asio_handler_invoke_helpers::invoke<boost::asio::detail::binder1<boost::_bi::bind_t<void, boost::_mfi::mf3<void, TcpServer, boost::intrusive_ptr<TcpServer>, boost::intrusive_ptr<TcpSession>, boost::system::error_code const&>, boost::_bi::list4<boost::_bi::value<TcpServer*>, boost::_bi::value<boost::intrusive_ptr<TcpServer> >, boost::_bi::value<boost::intrusive_ptr<TcpSession> >, boost::arg<1> (*)()> >, boost::system::error_code>, boost::_bi::bind_t<void, boost::_mfi::mf3<void, TcpServer, boost::intrusive_ptr<TcpServer>, boost::intrusive_ptr<TcpSession>, boost::system::error_code const&>, boost::_bi::list4<boost::_bi::value<TcpServer*>, boost::_bi::value<boost::intrusive_ptr<TcpServer> >, boost::_bi::value<boost::intrusive_ptr<TcpSession> >, boost::arg<1> (*)()> > > (function=..., context=...)
    at /usr/include/boost/asio/detail/handler_invoke_helpers.hpp:37
#25 0x000000000182275b in boost::asio::detail::asio_handler_invoke<boost::asio::detail::binder1<boost::_bi::bind_t<void, boost::_mfi::mf3<void, TcpServer, boost::intrusive_ptr<TcpServer>, boost::intrusive_ptr<TcpSession>, boost::system::error_code const&>, boost::_bi::list4<boost::_bi::value<TcpServer*>, boost::_bi::value<boost::intrusive_ptr<TcpServer> >, boost::_bi::value<boost::intrusive_ptr<TcpSession> >, boost::arg<1> (*)()> >, boost::system::error_code>, boost::_bi::bind_t<void, boost::_mfi::mf3<void, TcpServer, boost::intrusive_ptr<TcpServer>, boost::intrusive_ptr<TcpSession>, boost::system::error_code const&>, boost::_bi::list4<boost::_bi::value<TcpServer*>, boost::_bi::value<boost::intrusive_ptr<TcpServer> >, boost::_bi::value<boost::intrusive_ptr<TcpSession> >, boost::arg<1> (*)()> >, boost::system::error_code> (function=...,
    this_handler=0x7fff60b807b0) at /usr/include/boost/asio/detail/bind_handler.hpp:88
#26 0x00000000018222bc in boost_asio_handler_invoke_helpers::invoke<boost::asio::detail::binder1<boost::_bi::bind_t<void, boost::_mfi::mf3<void, TcpServer, boost::intrusive_ptr<TcpServer>, boost::intrusive_ptr<TcpSession>, boost::system::error_code const&>, boost::_bi::list4<boost::_bi::value<TcpServer*>, boost::_bi::value<boost::intrusive_ptr<TcpServer> >, boost::_bi::value<boost::intrusive_ptr<TcpSession> >, boost::arg<1> (*)()> >, boost::system::error_code>, boost::asio::detail::binder1<boost::_bi::bind_t<void, boost::_mfi::mf3<void, TcpServer, boost::intrusive_ptr<TcpServer>, boost::intrusive_ptr<TcpSession>, boost::system::error_code const&>, boost::_bi::list4<boost::_bi::value<TcpServer*>, boost::_bi::value<boost::intrusive_ptr<TcpServer> >, boost::_bi::value<boost::intrusive_ptr<TcpSession> >, boost::arg<1> (*)()> >, boost::system::error_code> > (function=..., context=...) at /usr/include/boost/asio/detail/handler_invoke_helpers.hpp:37
#27 0x00000000018218a0 in boost::asio::detail::reactive_socket_connect_op<boost::asio::ip::tcp, boost::_bi::bind_t<void, boost::_mfi::mf3<void, TcpServer, boost::intrusive_ptr<TcpServer>, boost::intrusive_ptr<TcpSession>, boost::system::error_code const&>, boost::_bi::list4<boost::_bi::value<TcpServer*>, boost::_bi::value<boost::intrusive_ptr<TcpServer> >, boost::_bi::value<boost::intrusive_ptr<TcpSession> >, boost::arg<1> (*)()> > >::do_complete (owner=0x3da16f0, base=0x7f7694204620) at /usr/include/boost/asio/detail/reactive_socket_connect_op.hpp:100
#28 0x000000000119a8b8 in boost::asio::detail::task_io_service_operation::complete (this=0x7f7694204620, owner=..., ec=...,
    bytes_transferred=0) at /usr/include/boost/asio/detail/task_io_service_operation.hpp:37
#29 0x00000000011f6b9f in boost::asio::detail::epoll_reactor::descriptor_state::do_complete (owner=0x3da16f0, base=0x3db02e0, ec=...,
    bytes_transferred=29) at /usr/include/boost/asio/detail/impl/epoll_reactor.ipp:651
#30 0x000000000119a8b8 in boost::asio::detail::task_io_service_operation::complete (this=0x3db02e0, owner=..., ec=..., bytes_transferred=29)
    at /usr/include/boost/asio/detail/task_io_service_operation.hpp:37
#31 0x000000000119b933 in boost::asio::detail::task_io_service::do_run_one (this=0x3da16f0, lock=..., this_thread=..., ec=...)
    at /usr/include/boost/asio/detail/impl/task_io_service.ipp:384
#32 0x000000000119b493 in boost::asio::detail::task_io_service::run (this=0x3da16f0, ec=...)
    at /usr/include/boost/asio/detail/impl/task_io_service.ipp:153
#33 0x00000000017f914b in boost::asio::io_service::run (this=0x3da16d0, ec=...) at /usr/include/boost/asio/impl/io_service.ipp:66
#34 0x00000000017f7e62 in EventManager::RunWithExceptionHandling (this=0x3da16d0) at controller/src/io/event_manager.cc:51
#35 0x00000000012d1a19 in main (argc=3, argv=0x7fff60b81508) at controller/src/vnsw/agent/ovs_tor_agent/main.cc:75 

(gdb) frame 6
#6  0x00000000012fce92 in TcpSession::IsClosed (this=0x7f76980e6b90) at controller/src/io/tcp_session.h:119
119	controller/src/io/tcp_session.h: No such file or directory.
(gdb) p refcount_
$8 = {
  <tbb::internal::atomic_impl_with_arithmetic<int, int, char>> = {
    <tbb::internal::atomic_impl<int>> = {
      my_storage = {
        my_value = 0
      }
    }, <No data fields>}, <No data fields>}
(gdb)
(gdb) frame 3
#3  0x000000000100c7ec in tbb::mutex::lock (this=0x7f76980e6b98) at /usr/include/tbb/mutex.h:164
164	/usr/include/tbb/mutex.h: No such file or directory.
(gdb) p *this
$11 = {
  static is_rw_mutex = false,
  static is_recursive_mutex = false,
  static is_fair_mutex = false,
  impl = {
    __data = {
      __lock = 2,
      __count = 32630,
      __owner = 0,
      __nusers = 0,
      __kind = -1,
      __spins = 0,
      __elision = 0,
      __list = {
        __prev = 0x0,
        __next = 0x0
      }
    },
    __size = "\002\000\000\000v\177\000\000\000\000\000\000\000\000\000\000\377\377\377\377", '\000' <repeats 19 times>,
    __align = 140144782868482
  }
}
(gdb)