Messages in this thread | | | From | Alexander Mikhalitsyn <> | Date | Mon, 14 Aug 2023 15:34:22 +0200 | Subject | Re: [PATCH] pid: allow pidfds for reaped tasks |
| |
On Mon, Aug 14, 2023 at 3:21 PM Oleg Nesterov <oleg@redhat.com> wrote: > > On 08/14, David Rheinsberg wrote: > > > > Hi Oleg, > > > > On Fri, Aug 11, 2023, at 1:57 PM, Oleg Nesterov wrote: > > >> What code do we need to allow userspace to open a pidfd to a leader pid > > >> even if it has already been exited and reaped (without also accidently > > >> allowing to open non-lead pid pidfds)? > > > > > > I'll try to think more, but can you also explain why do we need this? > > > > > > See my another email. Can't we simply shift the pid_has_task(PIDTYPE_TGID) > > > check from pidfd_prepare() to pidfd_create() ? (and then we can kill > > > pidfd_prepare and rename __pidfd_prepare to pidfd_prepare). > > > > Yes, the easiest solution would be to use `__pidfd_prepare()` and ensure > > that the caller only ever calls this on tg-leaders. This would work just > > fine, imo. And this was my initial approach. > > Great, > > > I think Christian preferred an explicit assertion that ensures we do not > > accidentally hand out pidfds for non-tg-leaders. The question is thus whether > > there is an easy way to assert this even for reaped tasks? > > Or whether there is a simple way to flag a pid that was used as tg-leader? > > I do not see how can we check if a detached pid was a leader pid, and I don't > think it makes sense to add a new member into struct pid... > > > Or, ultimately, whether this has limited use and we should just use > > `__pidfd_prepare()`? > > Well, if you confirm that sk->sk_peer_pid and scm->pid are always initialized with > task_tgid(current), I'd certainly prefer this approach unless Christian objects.
Dear colleagues,
I can confirm that sk->sk_peer_pid and scm->pid are always thread-group leaders.
Kind regards, Alex
> > Oleg. >
| |