setns() && PR_SET_CHILD_SUBREAPER

[Oleg Nesterov <oleg@redhat.com>]

And this discussion reminds me again that I do not understand how setns()
and PR_SET_CHILD_SUBREAPER should play together... Add cc's.


Suppose we have a process P in the root namespace and another namespace X.

P does setns() and enters the X namespace.
P forks a child C.

C forks a grandchild G.
C exits.

The question is, where should we reparent the grandchild G? In the normal
case it will be reparented to X->child_reaper and this looks correct.

But lets suppose that P runs with the ->has_child_subreaper bit set. In
this case it will be reparented to P's sub-reaper or a global init, and
given that P can't control its ->has_child_subreaper flag this does not
look right to me.

I can make a simple patch but perhaps I missed something or we actually
want this (imo strange) behaviour?

Oleg.