Matrix determinant with system calls - c

Question

So, this is my program that calculates matrix determinant using system calls, not good at all, but, the trouble is that when i put in a number bigger than 8 for dimension of matrix, it crashes somehow and i can't figure why it keeps happening. Please, give me some ideas.
The task was to calculate determinant using multithreading. Maybe, the problem is that I exceed max threads? valgrind says that
Use --max-threads=INT to specify a larger number of threads
and rerun valgrind
valgrind: the 'impossible' happened:
Max number of threads is too low
compile it with gcc -g -pthread
#include <stdlib.h>
#include <pthread.h>
#include <math.h>
#include <time.h>
#include <malloc.h>
pthread_mutex_t mutex;
typedef struct {
int **matrix;
int size;
} T_MS;
void* determinant(void *npt) {
T_MS* tmp = (T_MS*) npt;
int i,j;
double det = 0;
pthread_t *array = malloc(sizeof(pthread_t) * tmp->size);
T_MS *mtarr = malloc(sizeof(T_MS) * tmp->size);
if (tmp->size == 1) {
det = tmp->matrix[0][0];
} else if (tmp->size == 2) {
det = tmp->matrix[0][0] * tmp->matrix[1][1] - tmp->matrix[0][1] * tmp->matrix[1][0];
} else {
for (i = 0; i < tmp->size; ++i) {
mtarr[i].matrix = (int **)malloc(sizeof(int *) * tmp->size);
mtarr[i].size = tmp->size - 1;
for (j = 0; j < tmp->size - 1; ++j) {
if (j < i)
mtarr[i].matrix[j] = tmp->matrix[j];
else
mtarr[i].matrix[j] = tmp->matrix[j + 1];
}
pthread_create(&array[i], NULL, determinant, mtarr + i);
}
for (i = 0; i < tmp->size; ++i) {
void *res;
for (j = 0; j < tmp->size - 1; ++j) {
}
pthread_join(array[i], &res);
double x = *(double *)&res;
det += (-1 + 2 * !(i % 2)) * x * tmp->matrix[i][tmp->size - 1];
double answer = *(double*)&det;
free(mtarr[i].matrix);
}
}
free(mtarr);
free(array);
void* ans = *(void **)&det;
return ans;
}
int main(int argc, char const *argv[]) {
srand(time(NULL));
int **matrix;
int n = 0;
int a;
pthread_t tid;
pthread_attr_t attr;
pthread_attr_init(&attr);
printf("Insert the demention of matrix:\n");
scanf("%d", &n);
matrix = (int**)malloc(n * sizeof(int*));
for (int i=0; i<n; ++i)
matrix[i] = (int*)malloc(n * sizeof(int));
printf("Insert matrix:\n");
for (int i = 0; i < n; ++i) {
for (int j = 0; j < n; ++j) {
matrix[i][j]=rand()%15;
//matrix[i][j] = i;
}
}
for (int i = 0; i < n; ++i) {
for (int j = 0; j < n; ++j) {
printf("%d ", matrix[i][j]);
}
printf("\n");
}
T_MS* npt = (T_MS*)malloc(sizeof(T_MS));
npt->matrix = matrix;
npt->size = n;
void *det;
pthread_mutex_init(&mutex, NULL);
pthread_create(&tid, NULL, determinant, npt);
pthread_join(tid, &det);
double answer = *(double*)&det;
printf("Det is: %f\n", answer);
for (int i = 0; i < n; ++i)
free(matrix[i]);
free(matrix);
free(npt);
return 0;
} ```