Segmentation fault (core dumped) on C loop with pthreads - c

Question

I keep getting a segmentation fault on the following code and cannot figure out why.
Please help me fix it.
#include <string.h>
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include "tempo.h"
int num_thread = 12;
//int ini[20];
//time_t start, end;
int threadShare;
int end = 127;
int start = 32;
void *loop(void *arg);
pthread_t *m;
void
main(int argc, char *argv[])
{
double qt = (((double) end - (double) start) / (double) num_thread);
threadShare = round(qt);
m = malloc(sizeof(pthread_t) * num_thread);
int ptStart[num_thread + 1];
// creates the pthreads and divides the work
for (int i = 0; i < num_thread; i++) {
pthread_create(&m[i], NULL, loop, (void *) &ptStart[i]);
ptStart[i + 1] = ptStart[i] + threadShare;
// i, ptStart[i]);
}
// closes the pthreads
for (int i = 0; i < num_thread; i++) {
pthread_join(ptStart[i], NULL);
}
}
void *
loop(void *arg)
{
//password to be broken
char senha[40] = "!!!#(,4#";
char linha[40];
// 8 loops parsing through the ascii characters
for (char v1 = 32; v1 < 127; v1++) {
linha[0] = v1;
for (char v2 = 32; v2 < 127; v2++) {
linha[1] = v2;
for (char v3 = 32; v3 < 127; v3++) {
linha[2] = v3;
for (char v4 = 32; v4 < 127; v4++) {
linha[3] = v4;
for (char v5 = 32; v5 < 126; v5++) {
linha[4] = v5;
for (char v6 = 32; v6 < 127; v6++) {
linha[5] = v6;
for (char v7 = 32; v7 < 127; v7++) {
linha[6] = v7;
for (char v8 = 32; v8 < 127; v8++) {
linha[7] = v8;
printf("%s\n", linha);
// compares the password with the
// characters parsed in the loop
int ok = strcmp(senha, linha);
if (ok == 0) {
exit(0);
}
}
}
}
}
}
}
}
}
}
This code should divide the task of brute forcing a password among a variable number of pthreads. I am a newbie at c and cannot figure out the issue.
I am pretty sure the issue occurs inside the loop, as v1 will iterate through the ascii characters before the segmentation fault occurs.
Edit: Tried to clean up the code a little, alas i am a total beginner with c