Re: [PATCH v2 5/7] clone4: Add a CLONE_AUTOREAP flag to automatically reap the child process

[Josh Triplett]

On Sun, Mar 15, 2015 at 08:55:06PM +0100, Oleg Nesterov wrote:
> On 03/15, Josh Triplett wrote:
> > On Sun, Mar 15, 2015 at 03:52:23PM +0100, Oleg Nesterov wrote:
> > > On 03/15, Josh Triplett wrote:
> > > > Add a CLONE_AUTOREAP flag to request this behavior unconditionally,
> > >
> > > Yes, CLONE_AUTOREAP is much better. And I agree (mostly) with that
> > > we should rely on do_notify_parent().
> > >
> > > Howver the patch still doesn't look right. First of all, ->autoreap
> > > should be per-process, not per-thread.
> >
> > Ah, you're thinking of the case where the parent process launches a
> > ...
> 
> Not really, although we probably need more sanity checks.
> 
> It should be per-process simply because this "autoreap" affects the whole
> process. And the sub-threads are already "autoreap". And these 2 autoreap's
> semantics differ, we should not confuse them.

Will the approach I suggested, of having clones with CLONE_THREAD
inherit the autoreap value rather than setting it from CLONE_AUTOREAP,
implement the semantics you're looking for?

Also, are you suggesting that CLONE_AUTOREAP with CLONE_THREAD should
produce -EINVAL, or just that it should be ignored?

> > (As an aside, what *is* the use case for CLONE_PARENT without
> > CLONE_THREAD?)
> 
> To me CLONE_PARENT is another historical mistake and the source of misc
> problems ;)

I kinda figured. :)

> > > And there are ptrace/mt issues,
> > > it seems. Just for example, we should avoid EXIT_TRACE if autoreap in
> > > wait_task_zombie() even if we are going to re-notify parent.
> >
> > I don't see how EXIT_TRACE can happen in wait_task_zombie if autoreap is
> > set.  wait_task_zombie does a cmpxchg with exit_state and doesn't
> > proceed unless exit_state was EXIT_ZOMBIE, and I don't see how we can
> > ever reach the EXIT_ZOMBIE state if autoreap.
> 
> Because you again forgot about ptrace ;)
> 
> Josh. Let me try to summarise this later when I have time. Again, I am
> not sure, perhaps this is even simpler than I currently think. And let
> me apologize in advance, most probably I will be busy tomorrow.

I look forward to your later review and feedback.

- Josh Triplett
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/