Hi John Sorry to say, but there is no way to really answer your question as the OMPI community doesn't actively test MPIR support. I haven't seen any reports of hangs during MPI_Init from any release series, including 4.x. My guess is that it may have something to do with the debugger interactions as opposed to being a true race condition.
Ralph On Nov 8, 2019, at 11:27 AM, John DelSignore via devel <devel@lists.open-mpi.org <mailto:devel@lists.open-mpi.org> > wrote: Hi, An LLNL TotalView user on a Mac reported that their MPI job was hanging inside MPI_Init() when started under the control of TotalView. They were using Open MPI 4.0.1, and TotalView was using the MPIR Interface (sorry, we don't support the PMIx debugging hooks yet). I was able to reproduce the hang on my own Linux system with my own build of Open MPI 4.0.1, which I built with debug symbols. As far as I can tell, there is some sort of race inside of Open MPI 4.0.1, because if I placed breakpoints at certain points in the Open MPI code, and thus change the timing slightly, that was enough to avoid the hang. When the code hangs, it appeared as if one or more MPI processes are waiting inside ompi_mpi_init() at line ompi_mpi_init.c#904 for a fence to be released. In one of the runs, rank 0 was the only one the was hanging there (though I have seen runs where two ranks were hung there). Here's a backtrace of the first thread in the rank 0 process in the case where one rank was hung: d1.<> f 10.1 w > 0 __nanosleep_nocancel PC=0x7ffff74e2efd, FP=0x7fffffffd1e0 >[/lib64/libc.so.6] 1 usleep PC=0x7ffff7513b2f, FP=0x7fffffffd200 [/lib64/libc.so.6] 2 ompi_mpi_init PC=0x7ffff7a64009, FP=0x7fffffffd350 [/home/jdelsign/src/tools-external/openmpi-4.0.1/ompi/runtime/ompi_mpi_init.c#904] 3 PMPI_Init PC=0x7ffff7ab0be4, FP=0x7fffffffd390 [/home/jdelsign/src/tools-external/openmpi-4.0.1-lid/ompi/mpi/c/profile/pinit.c#67] 4 main PC=0x00400c5e, FP=0x7fffffffd550 [/home/jdelsign/cpi.c#27] 5 __libc_start_main PC=0x7ffff7446b13, FP=0x7fffffffd610 [/lib64/libc.so.6] 6 _start PC=0x00400b04, FP=0x7fffffffd618 [/amd/home/jdelsign/cpi] Here's the block of code where the thread is hung: /* if we executed the above fence in the background, then * we have to wait here for it to complete. However, there * is no reason to do two barriers! */ if (background_fence) { OMPI_LAZY_WAIT_FOR_COMPLETION(active); } else if (!ompi_async_mpi_init) { /* wait for everyone to reach this point - this is a hard * barrier requirement at this time, though we hope to relax * it at a later point */ if (NULL != opal_pmix.fence_nb) { active = true; OPAL_POST_OBJECT(&active); if (OMPI_SUCCESS != (ret = opal_pmix.fence_nb(NULL, false, fence_release, (void*)&active))) { error = "opal_pmix.fence_nb() failed"; goto error; } OMPI_LAZY_WAIT_FOR_COMPLETION(active); <<<<----- STUCK HERE WAITING FOR THE FENCE TO BE RELEASED } else { if (OMPI_SUCCESS != (ret = opal_pmix.fence(NULL, false))) { error = "opal_pmix.fence() failed"; goto error; } } } And here is an aggregated backtrace of all of the processes and threads in the job: d1.<> f g w -g f+l +/ +__clone : 5:12[0-3.2-3, p1.2-5] |+start_thread | +listen_thread@oob_tcp_listener.c <mailto:listen_thread@oob_tcp_listener.c> #705 : 1:1[p1.5] | |+__select_nocancel | +listen_thread@ptl_base_listener.c <mailto:listen_thread@ptl_base_listener.c> #214 : 1:1[p1.3] | |+__select_nocancel | +progress_engine@opal_progress_threads.c <mailto:progress_engine@opal_progress_threads.c> #105 : 5:5[0-3.2, p1.4] | |+opal_libevent2022_event_base_loop@event.c <mailto:opal_libevent2022_event_base_loop@event.c> #1632 | | +poll_dispatch@poll.c <mailto:poll_dispatch@poll.c> #167 | | +__poll_nocancel | +progress_engine@pmix_progress_threads.c <mailto:progress_engine@pmix_progress_threads.c> #108 : 5:5[0-3.3, p1.2] | +opal_libevent2022_event_base_loop@event.c <mailto:opal_libevent2022_event_base_loop@event.c> #1632 | +epoll_dispatch@epoll.c <mailto:epoll_dispatch@epoll.c> #409 | +__epoll_wait_nocancel +_start : 5:5[0-3.1, p1.1] +__libc_start_main +main@cpi.c <mailto:main@cpi.c> #27 : 4:4[0-3.1] |+PMPI_Init@pinit.c <mailto:PMPI_Init@pinit.c> #67 | +ompi_mpi_init@ompi_mpi_init.c#890 : 3:3[1-3.1] <<<<---- THE 3 OTHER MPI PROCS MADE IT PAST FENCE | |+ompi_rte_wait_for_debugger@rte_orte_module.c <mailto:ompi_rte_wait_for_debugger@rte_orte_module.c> #196 | | +opal_progress@opal_progress.c <mailto:opal_progress@opal_progress.c> #251 | | +opal_progress_events@opal_progress.c <mailto:opal_progress_events@opal_progress.c> #191 | | +opal_libevent2022_event_base_loop@event.c <mailto:opal_libevent2022_event_base_loop@event.c> #1632 | | +poll_dispatch@poll.c <mailto:poll_dispatch@poll.c> #167 | | +__poll_nocancel | +ompi_mpi_init@ompi_mpi_init.c#904 : 1:1[0.1] <<<<---- THE THREAD THAT IS STUCK | +usleep | +__nanosleep_nocancel +main@main.c <mailto:main@main.c> #14 : 1:1[p1.1] +orterun@orterun.c <mailto:orterun@orterun.c> #200 +opal_libevent2022_event_base_loop@event.c <mailto:opal_libevent2022_event_base_loop@event.c> #1632 +poll_dispatch@poll.c <mailto:poll_dispatch@poll.c> #167 +__poll_nocancel d1.<> I have tested Open MPI 4.0.2 dozens of times, and the hang does not seem to happen. My concern is that if the problem is indeed a race, then it's possible (but perhaps not likely) that the same race exists in Open MPI 4.0.2, but the timing could be slightly different such that it doesn't hang using my simple test setup. In other words, maybe I've just been "lucky" with my testing of Open MPI 4.0.2 and have failed to provoke the hang yet. My question is: Was this a known problem in Open MPI 4.0.1 that was fixed in Open MPI 4.0.2? Thanks, John D.