[mpich-discuss] Shared Memory Segfaults

[Junchao Zhang]

I can reproduce the segfault with the latest mpich. In Clean_List(), I
think there is a data race, since all shmem members update the head node
            head->next_win = temp_win;
            head->next = temp_next;
I tried to simplify Clean_List() further as follows,

void Clean_List()
{
    Node *cur_node = head;
    MPI_Win cur_win = head_win;
    Node *next_node;
    MPI_Win next_win;

    while (cur_node) {
        next_node = cur_node->next;
        next_win = cur_node->next_win;
        MPI_Win_free(&cur_win);
        cur_node = next_node;
        cur_win = next_win;
    }

    head = tail = NULL;
}

But I still met segfault. With gdb, the segfault disappears. If I comment
out the call to Clean_List in main(), the error also disappear.
I Cc'ed our local RMA expert Xin to see if she has new findings.

--Junchao Zhang

On Sat, May 2, 2015 at 10:26 AM, Brian Cornille <bcornille at wisc.edu> wrote:

>  Hello,
>
>
>  In working on a project that is attempting to use MPI shared memory
> (from MPI_Win_allocate_shared) I began getting inconsistent segfaults in
> portions of the code that appeared to have no memory errors when
> investigated with gdb.  I believe I have somewhat reproduced this error in
> a small code (attached) that creates a linked list of MPI shared memory
> allocated elements.
>
>
>  The attached program segfaults for me when run with more than one
> process.  However, will not segfault if run in gdb (e.g. mpirun -n 2 xterm
> -e gdb ./mpi_shmem_ll).  I have done what I can to eliminate any apparent
> race conditions.  Any help in this matter would be much appreciated.
>
>
>  Thanks and best,
>
> Brian Cornille
>
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