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SubjectRe: [PATCH -mm 3/5][AIO] - export good_sigevent()
> +/***
> + * 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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