Re: [PATCH v2 5/7] clone4: Add a CLONE_AUTOREAP flag to automatically reap the child process
From: Josh Triplett
Date: Sun Mar 15 2015 - 19:35:00 EST
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
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