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Subject[PATCH v2 0/2] Expose task pid_ns_for_children to userspace
pid_ns_for_children set by a task is known only to the task itself,
and it's impossible to identify it from outside.

It's a big problem for checkpoint/restore software like CRIU,
because it can't correctly handle tasks, that do setns(CLONE_NEWPID)
in proccess of their work. If they have a custom pid_ns_for_children
before dump, they must have the same ns after restore. Otherwise,
restored task bumped into enviroment it does not expect.

This patchset solves the problem. It exposes pid_ns_for_children
to ns directory in standard way with the name "pid_for_children":

~# ls /proc/5531/ns -l | grep pid
lrwxrwxrwx 1 root root 0 Jan 14 16:38 pid -> pid:[4026531836]
lrwxrwxrwx 1 root root 0 Jan 14 16:38 pid_for_children -> pid:[4026532286]

v2: Do not allow to take a pid namespace, if there is no child reaper
created. This prevents race between creation of the child reaper and
other tasks.

Kirill Tkhai (2):
ns: Allow ns_entries to have custom symlink content
pidns: Expose task pid_ns_for_children to userspace

fs/nsfs.c | 4 +++-
fs/proc/namespaces.c | 1 +
include/linux/proc_ns.h | 2 ++
kernel/pid_namespace.c | 34 ++++++++++++++++++++++++++++++++++
4 files changed, 40 insertions(+), 1 deletion(-)

Signed-off-by: Kirill Tkhai <>

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