OSC shared memory fence segfault

[PeterGottesman]

When running the onesided/c_strided_getacc_indexed_shared test, an open syscall is failing when initializing shared memory with MPI_Win_allocate_shared. Execution is continuing until the uninitialized shared memory is accessed by a call to MPI_Win_fence, at which point the process segfaults.

The segfault specifically occurs at line 103 of osc_sm_active_target.c (because module->global_state is NULL).
The failing open syscall occurs during at line 495 of shmem_mmap_module.c.

The stdout/stderr can be seen here:
https://mtt.open-mpi.org/index.php?do_redir=2633

@hjelmn I believe this is up your alley

[hjelmn]

That looks like a new failure mode. Will take a look tomorrow.

[jsquyres]

@hjelmn FWIW, the file that fails to open in shmem_mmap_module.c:495 is /dev/shm/vader_segment.savbu-usnic-a.58f00001.1.

[PeterGottesman]

@hjelmn This is still appearing on MTT. Any luck tracking down the issue?

[hjelmn]

Not yet. I haven't been able to recreate the issue. Plan to try again this week.

[jsquyres]

Per 2018-06-26 webex, please re-create with a debug build and run with osc_base_verbose 100 and send output to @hjelmn.

Note: this is happening across the board on master, v3.0, v3.1. 😢

[jsquyres]

Per off-issue discussion, @hjelmn found the issue before we sent him the verbose output. See #5341.