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Date: Mon, 23 Jan 2017 17:44:20 +0100
From: Oleg Nesterov <oleg@redhat.com>
To: Pavel Tikhomirov <ptikhomirov@virtuozzo.com>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        Lennart Poettering <lennart@poettering.net>,
        Kay Sievers <kay.sievers@vrfy.org>
Cc: Ingo Molnar <mingo@redhat.com>, Peter Zijlstra <peterz@infradead.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Cyrill Gorcunov <gorcunov@openvz.org>,
        John Stultz <john.stultz@linaro.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Nicolas Pitre <nicolas.pitre@linaro.org>,
        Michal Hocko <mhocko@suse.com>,
        Stanislav Kinsburskiy <skinsbursky@virtuozzo.com>,
        Mateusz Guzik <mguzik@redhat.com>, linux-kernel@vger.kernel.org,
        Pavel Emelyanov <xemul@virtuozzo.com>,
        Konstantin Khorenko <khorenko@virtuozzo.com>
Subject: setns() && PR_SET_CHILD_SUBREAPER
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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.