Re: [PATCH v3 2/4] pid: check init is created first after idr alloc

[Oleg Nesterov <oleg@redhat.com>]

On 02/26, Oleg Nesterov wrote:
>
> On 02/26, Oleg Nesterov wrote:
> >
> > Now that I look at this code again... Why do we bother to check
> > "pid_allocated & PIDNS_ADDING" at all? copy_process() does
> >
> > 	/* Don't start children in a dying pid namespace */
> > 	if (unlikely(!(ns_of_pid(pid)->pid_allocated & PIDNS_ADDING))) {
> > 		retval = -ENOMEM;
> > 		goto bad_fork_core_free;
> > 	}
> >
> > I am going to send the patch which removes this check from alloc_pid...
> > Need to recheck.
>
> No, we can't remove either of these 2 checks...
>
> This probably deserves another comment in alloc_pid().

something like

	We need this even if copy_process() does the same check. If two
	or more tasks from parent namespace try to inject a child into a
	dead namespace, one of free_pid() calls from the copy_process()
	error path may try to wakeup the possibly freed ns->child_reaper.

perhaps? does it look clear enough?

Oleg.