Re: [PATCH -mm 3/5][AIO] - export good_sigevent()

[Christoph Hellwig <hch@infradead.org>]

> +/***
> + * good_sigevent - check and get target task from a sigevent.
> + * @event: the sigevent to be checked
> + *
> + * This function must be called with tasklist_lock held for reading.
> + */
> +struct task_struct * good_sigevent(sigevent_t * event)
> +{
> +	struct task_struct *rtn = current->group_leader;
> +
> +	if ((event->sigev_notify & SIGEV_THREAD_ID ) &&
> +		(!(rtn = find_task_by_pid(event->sigev_notify_thread_id)) ||
> +		 rtn->tgid != current->tgid ||
> +		 (event->sigev_notify & ~SIGEV_THREAD_ID) != SIGEV_SIGNAL))
> +		return NULL;
> +
> +	if (((event->sigev_notify & ~SIGEV_THREAD_ID) != SIGEV_NONE) &&
> +	    ((event->sigev_signo <= 0) || (event->sigev_signo > SIGRTMAX)))
> +		return NULL;
> +
> +	return rtn;
> +}

And while we're at it we should badly beat up the person that wrote this
mess in the first time.  To be somewhat readable it should look like:

static struct task_struct *good_sigevent(sigevent_t *event)
{
	struct task_struct *task = current->group_leader;

	if ((event->sigev_notify & ~SIGEV_THREAD_ID) != SIGEV_NONE) {
		if (event->sigev_signo <= 0 || event->sigev_signo > SIGRTMAX)
			return NULL;
	}

	if (event->sigev_notify & SIGEV_THREAD_ID) {
		if ((event->sigev_notify & ~SIGEV_THREAD_ID) != SIGEV_SIGNAL)
			return NULL;
		task = find_task_by_pid(event->sigev_notify_thread_id);
		if (!task || task->tgid != current->tgid)
			return NULL;
	}

	return task;
}

And btw, looking at its currentl caller I see why we need the PF_EXITING
flag I recommended to remove easiler on, it even has a big comment that
we should copy & paste to aio.c aswell.  Still no idea why it's doing
the selectiv reference grabbing, though.
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