signal

Linux v6.6: kernel/signal.c
Linux v6.6: arch/arm64/kernel/signal.c
Linux v6.6: include/linux/signal.h

	if (!WARN_ON_ONCE(sig->group_stop_count == 0))
		sig->group_stop_count--;

	/*
	 * Tell the caller to notify completion iff we are entering into a
	 * fresh group stop.  Read comment in do_signal_stop() for details.
	 */
	if (!sig->group_stop_count && !(sig->flags & SIGNAL_STOP_STOPPED)) {
		signal_set_stop_flags(sig, SIGNAL_STOP_STOPPED);
		return true;
	}
	return false;
}

void task_join_group_stop(struct task_struct *task)
{
	unsigned long mask = current->jobctl & JOBCTL_STOP_SIGMASK;
	struct signal_struct *sig = current->signal;

	if (sig->group_stop_count) {
		sig->group_stop_count++;
		mask |= JOBCTL_STOP_CONSUME;
	} else if (!(sig->flags & SIGNAL_STOP_STOPPED))
		return;

	/* Have the new thread join an on-going signal group stop */
	task_set_jobctl_pending(task, mask | JOBCTL_STOP_PENDING);
}

/*
 * allocate a new signal queue record
 * - this may be called without locks if and only if t == current, otherwise an
 *   appropriate lock must be held to stop the target task from exiting
 */
static struct sigqueue *
__sigqueue_alloc(int sig, struct task_struct *t, gfp_t gfp_flags,
		 int override_rlimit, const unsigned int sigqueue_flags)
{
	struct sigqueue *q = NULL;
	struct ucounts *ucounts = NULL;

		if (why) {
			/*
			 * The first thread which returns from do_signal_stop()
			 * will take ->siglock, notice SIGNAL_CLD_MASK, and
			 * notify its parent. See get_signal().
			 */
			signal_set_stop_flags(signal, why | SIGNAL_STOP_CONTINUED);
			signal->group_stop_count = 0;
			signal->group_exit_code = 0;
		}
	}

	return !sig_ignored(p, sig, force);
}

/*
 * Test if P wants to take SIG.  After we've checked all threads with this,
 * it's equivalent to finding no threads not blocking SIG.  Any threads not
 * blocking SIG were ruled out because they are not running and already
 * have pending signals.  Such threads will dequeue from the shared queue
 * as soon as they're available, so putting the signal on the shared queue
 * will be equivalent to sending it to one such thread.
 */
static inline bool wants_signal(int sig, struct task_struct *p)
{
	if (sigismember(&p->blocked, sig))
		return false;

	if (p->flags & PF_EXITING)
		return false;

	if (sig == SIGKILL)
		return true;

	if (task_is_stopped_or_traced(p))
		return false;

	return task_curr(p) || !task_sigpending(p);
}