Segmentation fault(signal 11) - c

Question

I'm new to coding and started learning MPI through examples. After executing with mpirun -np 7 ./lab1part2 , I encountered this problem.
I read a few other threads with similar error but non of them seems to be an identical case to me. I'm guessing that I made some simple error syntax wise but i just can't find it. Thanks in advance for any helpful input!
#include <stdio.h>
#include <stdlib.h>
#include <mpi.h>
int Global_sum(int my_int, int my_rank, int comm_sz, MPI_Comm comm);
const int MAX_CONTRIB = 20;
int main(void) {
int i, sum, my_int;
int my_rank, comm_sz;
MPI_Comm comm;
int* all_ints = NULL;
MPI_Init(NULL, NULL);
comm = MPI_COMM_WORLD;
MPI_Comm_size(comm, &comm_sz);
MPI_Comm_rank(comm, &my_rank);
srandom(my_rank + 1);
my_int = random() % MAX_CONTRIB;
sum = Global_sum(my_int, my_rank, comm_sz, comm);
if ( my_rank == 0) {
all_ints = malloc(comm_sz*sizeof(int));
MPI_Reduce(&my_int, &all_ints, 1, MPI_INT, MPI_SUM, 0, comm);
printf("Ints being summed:\n ");
for (i = 0; i < comm_sz; i++)
printf("%d ", all_ints[i]);
printf("\n");
printf("Sum = %d\n",sum);
free(all_ints);
} else {
MPI_Reduce(&my_int, &all_ints, 1, MPI_INT, MPI_SUM, 0, comm);
}
MPI_Finalize();
return 0;
}
int Global_sum(
int my_int,
int my_rank,
int comm_sz,
MPI_Comm comm ) {
int partner, recvtemp;
int my_sum = my_int;
unsigned bitmask = 1;
while (bitmask < comm_sz) {
partner = my_rank ^ bitmask;
if (my_rank < partner) {
if (partner < comm_sz) {
MPI_Recv(&recvtemp, 1, MPI_INT, partner, 0, comm, MPI_STATUS_IGNORE);
my_sum += recvtemp;
}
bitmask <<= 1;
} else {
MPI_Send(&my_sum, 1, MPI_INT, partner, 0, comm);
break;
}
}
return my_sum;
}