errno 14 when trying to implement buffered MPI_Get

Question

I tried to implement a buffered version of MPI_Get, so no global fence is necessary when one process gets something from only one other process. However, I get this error:

Read -1, expected 40, errno = 14

I used openmpi version 4.1.2, and ran the program below with mpirun -n 2.

#include <mpi.h>
#include <stdlib.h>
#include <stdint.h>
#include <sys/mman.h>

void *ptr;
static MPI_Win win;

void setup(size_t maxmem)
{
    if ((ptr = mmap (NULL, maxmem, PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0))
        == (void *)(intptr_t)-1) {
        MPI_Abort(MPI_COMM_WORLD, 1);
    }

   MPI_Win_create (ptr, maxmem, 1, MPI_INFO_NULL, MPI_COMM_WORLD, &win);
}

void bufferedGet(void *origin, size_t count,
    size_t owner_rank, size_t offset)
{
    MPI_Win_lock (MPI_LOCK_SHARED, owner_rank, 0, win);
    MPI_Get (origin, count, MPI_BYTE, owner_rank,
                       offset, count,
                       MPI_BYTE, win);
    MPI_Win_unlock (owner_rank, win);
}

int main(int argc, char **argv)
{
    MPI_Init(&argc, &argv);

    size_t size = 409600;
    setup(size);

    void *result = malloc(10);

    bufferedGet(result, 10, 0, 1);

    free(result);
    MPI_Win_free(&win);
    munmap(ptr, size);

    MPI_Finalize();
}

Answer 1

I think you are just missing | PROT_READ to your mmap call.