Messages in this thread | | | Date | Fri, 19 Aug 2011 15:13:39 +0200 | From | Oleg Nesterov <> | Subject | Re: + prctl-add-pr_setget_child_reaper-to-allow-simple-process-supervision .patch added to -mm tree |
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On 08/19, Kay Sievers wrote: > > On Fri, Aug 19, 2011 at 14:25, Oleg Nesterov <oleg@redhat.com> wrote: > > >> + case PR_SET_CHILD_SUBREAPER: > >> + me->signal->is_child_subreaper = !!arg2; > >> + me->signal->has_child_subreaper = true; > > > > Hmm. This looks wrong... why do we set ->has_child_subreaper? > > That's the flag we pass down to our childs, hence we need to set it here.
Aha, I see. I've misread copy_signal(), it copies ->has_child_subreaper, _not_ ->is_child_subreaper (as I wrongly thought) from parent. And I was going to blame this logic in the next email, I already started to write it ;)
But this has other (OK, minor) problems too, afaics. First of all, this ->has_child_subreaper = T is not right when the caller exits. We should not look for ->is_child_subreaper parent, our children should to find us.
Right?
And. afaics this makes the semantics of prctl(REAPER) a bit unclear... Suppose a task P does
C1 = fork();
prctl(REAPER);
C2 = fork();
In this case it "owns" the children of C2, but not C1. This is fine, and perhaps this is even better.
But what if P->parent did prctl(REAPER) too? Then P becomes the sub-reaper for the tasks which were forked before prctl().
In short, in general the caller of prctl(REAPER) doesn't know how this can affect the forks in the past.
Again, again, I am not arguing. Just I think we should discuss everything if we are going to add the new feature.
Finally. I am not sure this is really better, but it seems we can can ->has_child_subreape "more correct" with the same effect.
- prctl(PR_SET_CHILD_SUBREAPER):
me->is_child_subreaper = !!arg2; // ->has_child_subreaper is not set
- copy_signal():
me->has_child_subreaper = parent->has_child_subreaper || parent->is_child_subreaper;
Oleg.
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