Function fork_exit

freebsd/kern/kern_fork.c:1036–1085

* Handle the return of a child process from fork1(). This function * is called from the MD fork_trampoline() entry point. */

 * is called from the MD fork_trampoline() entry point.
 */
void
fork_exit(void (*callout)(void *, struct trapframe *), void *arg,
    struct trapframe *frame)
{
	struct proc *p;
	struct thread *td;
	struct thread *dtd;

	td = curthread;
	p = td->td_proc;
	KASSERT(p->p_state == PRS_NORMAL, ("executing process is still new"));

	CTR4(KTR_PROC, "fork_exit: new thread %p (td_sched %p, pid %d, %s)",
	    td, td_get_sched(td), p->p_pid, td->td_name);

	sched_fork_exit(td);
	/*
	* Processes normally resume in mi_switch() after being
	* cpu_switch()'ed to, but when children start up they arrive here
	* instead, so we must do much the same things as mi_switch() would.
	*/
	if ((dtd = PCPU_GET(deadthread))) {
		PCPU_SET(deadthread, NULL);
		thread_stash(dtd);
	}
	thread_unlock(td);

	/*
	 * cpu_fork_kthread_handler intercepts this function call to
	 * have this call a non-return function to stay in kernel mode.
	 * initproc has its own fork handler, but it does return.
	 */
	KASSERT(callout != NULL, ("NULL callout in fork_exit"));
	callout(arg, frame);

	/*
	 * Check if a kernel thread misbehaved and returned from its main
	 * function.
	 */
	if (p->p_flag & P_KPROC) {
		printf("Kernel thread \"%s\" (pid %d) exited prematurely.\n",
		    td->td_name, p->p_pid);
		kthread_exit();
	}
	mtx_assert(&Giant, MA_NOTOWNED);

	if (p->p_sysent->sv_schedtail != NULL)
		(p->p_sysent->sv_schedtail)(td);
	td->td_pflags &= ~TDP_FORKING;
}

/*
 * Simplified back end of syscall(), used when returning from fork()