Process switch with clone()

Now, I have to write a c program and use clone() to make process do things asynchronous. I've read the manual of clone() ; however, I still don't know how to make it work asynchronous. I use flags CLONE_THREAD, CLONE_VM and CLONE_SIGHAND and there's an infinite loop in parameter fn. I got segmentation fault(core dumped) first, then using gdb to debug. Then, I got Program received signal SIGSEGV, Segmentation fault. [Switching to LWP xxx]. I would like to make the processes switch successfully ? Below is my code: #define _GNU_SOURCE #include #include #include #define FIBER_STACK 1024*1024*8 int counter; void * stack; int do_something(){ int i; while(1) { if (counter == 1000) { free(stack); exit(1); } else { counter++; i++; } printf("Process %d running total runs %d, and this process runs %d \n", getpid(), counter, i); } } int main() { void * stack; counter = 1; stack = malloc(FIBER_STACK); if(!stack) { printf("The stack failed\n"); exit(0); } int i; for (i = 0; i < 26; i++) { clone(&do_something, (char *)stack + FIBER_STACK, CLONE_THREAD|CLONE_SIGHAND|CLONE_VM, 0); // CLONE_VFORK } }