Re: [RFC][PATCH 04/20] pspace: Allow multiple instaces of the process id namespace

["Serge E. Hallyn" <serue@us.ibm.com>]

Quoting Kirill Korotaev (dev@sw.ru):
> >>1.
> >>flags are neither atomic nor protected with any lock.
> >
> >
> >flags are atomic as they are a machine word.  So they do not
> >require a read/modify write so they will either be written
> >or not written.  Plus this allows write-sharing of the appropriate
> >cache line which is very polite (assuming the line is not shared with
> >something else)
> Eric I'm familiar with SMP, thanks :)
> Why do you write all this if you agreed below that have problems with it?
> 
> >>2. due to 1) you code is buggy. in this respect do_exit() is not 
> >>serialized with
> >>copy_process().
> >Yes. I may need a memory barrier in there.  I need to think
> >about that a little more.
> memory barrier doesn't help. you really need to think about.
> 
> >>3. due to the same 1) reason
> >>> +		kill_pspace_info(SIGKILL, (void *)1, tsk->pspace);
> >>can miss a task being forked. Bang!!!
> >
> >Well the only bad thing that can happen is that I get a process that
> >can run and observe pid == 1 has exited.  So Bang!! is not too
> >painful.
> And what about references to pspace->child_reaper which was freed already?

This seems a very valid point.  And even if you implement code to detect
when a process exits whether it is a child_reaper for some pspace, you
can't just make pspace->child_reaper = pspace->child_reaper->child_reaper,
as the wid may not be valid in the grandparent's namespace, right?

-serge
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