On Fri, 2018-02-23 at 12:22 +0100, Francesco wrote:
> Hi all,
> I'm trying to further debug the problem I described in my earlier
> mail (
> https://lists.zeromq.org/pipermail/zeromq-dev/2018-February/032303.ht
> ml) so
> I decided to use Helgrind to find race conditions in my code.
> 
> My problem is that apparently Helgrind 3.12.0 is reporting race
> conditions
> against zmq::atomic_ptr_t<> implementation.
> Now I know that Helgrind has troubles with C++11 atomics but by
> looking at
> the code I see that ZMQ is not using them (note: I do have
> ZMQ_ATOMIC_PTR_CXX11 defined but I also have ZMQ_ATOMIC_PTR_INTRINSIC
> defined, so the latter wins!).
> 
> In particular Helgrind 3.12.0 tells me that:
> 
> 
> ==00:00:00:11.885 29399==
> ==00:00:00:11.885 29399== *Possible data race during read of size 8
> at
> 0xB373BF0 by thread #4*
> ==00:00:00:11.885 29399== Locks held: none
> ==00:00:00:11.885 29399==    at 0x6BD79AB:
> *zmq::atomic_ptr_t<zmq::command_t>::cas*(zmq::command_t*,
> zmq::command_t*)
> (atomic_ptr.hpp:150)
> ==00:00:00:11.885 29399==    by 0x6BD7874:
> zmq::ypipe_t<zmq::command_t,
> 16>::check_read() (ypipe.hpp:147)
> ==00:00:00:11.885 29399==    by 0x6BD7288:
> zmq::ypipe_t<zmq::command_t,
> 16>::read(zmq::command_t*) (ypipe.hpp:165)
> ==00:00:00:11.885 29399==    by 0x6BD6FE7:
> zmq::mailbox_t::recv(zmq::command_t*, int) (mailbox.cpp:98)
> ==00:00:00:11.885 29399==    by 0x6BD29FC:
> zmq::io_thread_t::in_event()
> (io_thread.cpp:81)
> ==00:00:00:11.885 29399==    by 0x6BD05C1: zmq::epoll_t::loop()
> (epoll.cpp:188)
> ==00:00:00:11.885 29399==    by 0x6BD06C3:
> zmq::epoll_t::worker_routine(void*) (epoll.cpp:203)
> ==00:00:00:11.885 29399==    by 0x6C18BA5: thread_routine
> (thread.cpp:109)
> ==00:00:00:11.885 29399==    by 0x4C2F837: mythread_wrapper
> (hg_intercepts.c:389)
> ==00:00:00:11.885 29399==    by 0x6E72463: start_thread
> (pthread_create.c:334)
> ==00:00:00:11.885 29399==    by 0x92F901C: clone (clone.S:109)
> ==00:00:00:11.885 29399==
> ==00:00:00:11.885 29399== This conflicts with a previous write of
> size 8 by
> thread #2
> ==00:00:00:11.885 29399== Locks held: 1, at address 0xB373C08
> ==00:00:00:11.885 29399==    at 0x6BD77F4:
> *zmq::atomic_ptr_t<zmq::command_t>::set*(zmq::command_t*)
> (atomic_ptr.hpp:90)
> ==00:00:00:11.885 29399==    by 0x6BD7422:
> zmq::ypipe_t<zmq::command_t,
> 16>::flush() (ypipe.hpp:125)
> ==00:00:00:11.885 29399==    by 0x6BD6DF5:
> zmq::mailbox_t::send(zmq::command_t const&) (mailbox.cpp:63)
> ==00:00:00:11.885 29399==    by 0x6BB9128:
> zmq::ctx_t::send_command(unsigned int, zmq::command_t const&)
> (ctx.cpp:438)
> ==00:00:00:11.885 29399==    by 0x6BE34CE:
> zmq::object_t::send_command(zmq::command_t&) (object.cpp:474)
> ==00:00:00:11.885 29399==    by 0x6BE26F8:
> zmq::object_t::send_plug(zmq::own_t*, bool) (object.cpp:220)
> ==00:00:00:11.885 29399==    by 0x6BE68E2:
> zmq::own_t::launch_child(zmq::own_t*) (own.cpp:87)
> ==00:00:00:11.885 29399==    by 0x6C03D6C:
> zmq::socket_base_t::add_endpoint(char const*, zmq::own_t*,
> zmq::pipe_t*)
> (socket_base.cpp:1006)
> ==00:00:00:11.885 29399==  Address 0xb373bf0 is 128 bytes inside a
> block of
> size 224 alloc'd
> ==00:00:00:11.885 29399==    at 0x4C2A6FD: operator new(unsigned
> long,
> std::nothrow_t const&) (vg_replace_malloc.c:376)
> ==00:00:00:11.885 29399==    by 0x6BB8B8D:
> zmq::ctx_t::create_socket(int)
> (ctx.cpp:351)
> ==00:00:00:11.885 29399==    by 0x6C284D5: zmq_socket (zmq.cpp:267)
> ==00:00:00:11.885 29399==    by 0x6143809:
> ZmqClientSocket::Config(PubSubSocketConfig const&)
> (ZmqRequestReply.cpp:303)
> ==00:00:00:11.885 29399==    by 0x6144069:
> ZmqClientMultiSocket::Config(PubSubSocketConfig const&)
> (ZmqRequestReply.cpp:407)
> ==00:00:00:11.885 29399==    by 0x61684EF: client_thread_main(void*)
> (ZmqRequestReplyUnitTests.cpp:132)
> ==00:00:00:11.886 29399==    by 0x4C2F837: mythread_wrapper
> (hg_intercepts.c:389)
> ==00:00:00:11.886 29399==    by 0x6E72463: start_thread
> (pthread_create.c:334)
> ==00:00:00:11.886 29399==    by 0x92F901C: clone (clone.S:109)
> ==00:00:00:11.886 29399==  Block was alloc'd by thread #2
> 
> 
> Is this a known (and ignorable) issue with  zmq::atomic_ptr_t<>?
> 
> Thanks,
> Francesco

Yeah I started trying to put together a suppression file but never
finished it:

https://github.com/bluca/libzmq/commit/fb9ee9da7631f9506cbfcd6db29a284ae6e9651e

Hope to have time to finish working on it eventually (feel free to
contribute!) as it's very noisy right now, as it can't know about our
lock-free queue implementation without the custom suppression file

-- 
Kind regards,
Luca Boccassi

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