On Wed, Jun 26, 2013 at 8:57 AM, Oleg Nesterov <o...@redhat.com> wrote: > On 06/25, Andy Lutomirski wrote: >> >> On Tue, Jun 25, 2013 at 2:52 PM, Cyrill Gorcunov <gorcu...@gmail.com> wrote: >> > On Tue, Jun 25, 2013 at 02:36:31PM -0700, Andy Lutomirski wrote: >> >> On Tue, Jun 25, 2013 at 1:17 PM, Oleg Nesterov <o...@redhat.com> wrote: >> >> > On 06/26, Cyrill Gorcunov wrote: >> >> >> >> >> >> On Tue, Jun 25, 2013 at 12:51:45PM -0700, Andy Lutomirski wrote: >> >> >> > This is currently only available if CONFIG_CHECKPOINT_RESTORE, which >> >> >> > is hidden under CONFIG_EXPERT. It's generally useful functionality, >> >> >> > though, so expose it unconditionally. >> >> >> > >> >> >> > Cc: Cyrill Gorcunov <gorcu...@openvz.org> >> >> >> > Signed-off-by: Andy Lutomirski <l...@amacapital.net> >> >> >> Acked-by: Cyrill Gorcunov <gorcu...@openvz.org> >> >> > >> >> > I didn't see the patch but I guess it is trivial and I agree with >> >> > intent ;) >> >> >> >> The patch works, but "children" is only listed under task/<tid>, not >> >> under /proc/<pid>. Is that intentional? Fixing it would be a >> >> one-liner. >> > >> > Yeah, it's intentional. Here some explanations from Oleg (check out >> > the whole thread, it's not that big https://lkml.org/lkml/2011/12/9/220) >> > in short this might require some more code, but i'll re-check tomorrow. >> >> This is a little strange. It looks like ppid (in status) shows the >> tgid, > > Yes, > >> but the actual real_parent can refer to a thread (as opposed to >> a thread group leader), > > Yes. > > This is mostly the internal implementation detail. And probably it > would be nice to move ->children from task_struct to signal_struct. > > However. See __WNOTHREAD in man waitpid. I think this is the only > (historical) reason. Otherwise the real_parent's tid doesn't matter, > the parent is always the whole process, not sub-thread. > >> and task/tid/children respects that. > > Well, it should respect if you want to restart and keep __WNOTHREAD > working. > > But there is another reason. It is not trivial to list all children > under /proc/<pid>, and the fix would not be a one-liner ;) You need > to fight with the exiting sub-threads and reparenting. > >> So the >> tree that you get by following task/tid/ children won't be quite the >> same as the tree you get by following ppid. > > Not sure I understand... but in any case, yes you need to read > /proc/pid/task/*/children to construct the tree. > >> I wonder if the ptid should be added to status. Is there anything >> (other than task/tid/children) > > Perhaps, I dunno. > > Better yet, we should kill __WNOTHREAD ;) I am wondering if it is still > used.
Ugh. I'll submit a follow-up patch to Documentation/filesystems/proc.txt to explain the situation. All I really care about is being able to iterate the children of a single-threaded process, and the current semantics are fine for that. --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
