Concurrency error in your implementation of Allgatherv?

[mquinson]

Hello,

I get an 'Invalid write' error in any code that contains a call to MPI_Allgatherv(), such as the following. This code is supposed to be correct.

#include <mpi.h>
#include <stdio.h>
#include <stdlib.h>

#define buff_size 128

int main(int argc, char **argv) {
  int nprocs = -1;
  int rank = -1;

  MPI_Init(&argc, &argv);
  MPI_Comm_size(MPI_COMM_WORLD, &nprocs);
  MPI_Comm_rank(MPI_COMM_WORLD, &rank);
  printf("Hello from rank %d \n", rank);

  if (nprocs < 2)
    printf("MBI ERROR: This test needs at least 2 processes to produce a bug.\n");

  int dbs = sizeof(int)*nprocs; /* Size of the dynamic buffers for alltoall and friends */
  int *rbuf1 = malloc(dbs), *rcounts1=malloc(dbs),  *displs1=malloc(dbs);
  for (int i = 0; i < nprocs; i++) {
    rcounts1[i] = 1;
    displs1[i] = 2 * (nprocs - (i + 1));
  }

  if (rank % 2) {
    MPI_Allgatherv(&rank, 1, MPI_INT, rbuf1, rcounts1, displs1, MPI_INT, MPI_COMM_WORLD);  
  } else {
    MPI_Allgatherv(&rank, 1, MPI_INT, rbuf1, rcounts1, displs1, MPI_INT, MPI_COMM_WORLD);
    
  }

  free(rbuf1);free(rcounts1);free(displs1);
  
  
  MPI_Finalize();
  printf("Rank %d finished normally\n", rank);
  return 0;
}

The produced stack trace (in the HTML) reads as follows:

0x10CF47: aislinn_call (aislinn.c:61)
0x10B9EE: MPI_Allgatherv (mpi_generated.c:643)
0x108CD9: main (CollCorrect_Allgatherv.c:59)