int __tty_check_change(struct tty_struct *tty, int sig)
{
	unsigned long flags;
	struct pid *pgrp, *tty_pgrp;
	int ret = 0;

	if (current->signal->tty != tty)
		return 0;

	rcu_read_lock();
	pgrp = task_pgrp(current);

	spin_lock_irqsave(&tty->ctrl_lock, flags);
	tty_pgrp = tty->pgrp;
	spin_unlock_irqrestore(&tty->ctrl_lock, flags);

	if (tty_pgrp && pgrp != tty->pgrp) {
		if (is_ignored(sig)) {
			if (sig == SIGTTIN)
				ret = -EIO;
		} else if (is_current_pgrp_orphaned())
			ret = -EIO;
		else {
			kill_pgrp(pgrp, sig, 1);
			set_thread_flag(TIF_SIGPENDING);
			ret = -ERESTARTSYS;
		}
	}
	rcu_read_unlock();

	if (!tty_pgrp)
		tty_warn(tty, "sig=%d, tty->pgrp == NULL!\n", sig);

	return ret;
}

The product contains a concurrent code sequence that requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence operating concurrently.