[PATCH 0/3] clone3 & cgroups: allow spawning processes into cgroups

[Christian Brauner <christian.brauner@ubuntu.com>]

Hey Tejun,

This is the promised series to enable spawning processes into a target
cgroup different from the parent's cgroup. With this cgroup migration
will be a lot easier, and accounting will be more exact. It also allows
for nice features such as creating a frozen process by spawning it into
a frozen cgroup.
The code simplifies container creation and exec logic quite a bit as
well.

I've tried to contain all core changes for this features in
kernel/cgroup/* to avoid exposing cgroup internals. This has mostly
worked.
When a new process is supposed to be spawned in a cgroup different from
the parent's then we briefly acquire the cgroup mutex right before
fork()'s point of no return and drop it once the child process has been
attached to the tasklist and to its css_set. This is done to ensure that
the cgroup isn't removed behind our back. The cgroup mutex is _only_
held in this case; the usual case, where the child is created in the
same cgroup as the parent does not acquire it since the cgroup can't be
removed.

The series already comes with proper testing. Once we've decided that
this approach is good I'll expand the test-suite even more.

(This is a pre-holiday patchset and I'm moving so I might be a little
 slower responding to reviews but I wanted to send this out before the
 new year.)

The branch can be found in the following locations:
[1]: kernel.org: https://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux.git/log/?h=clone_into_cgroup
[2]: github.com: https://github.com/brauner/linux/tree/clone_into_cgroup
[3]: gitlab.com: https://gitlab.com/brauner/linux/commits/clone_into_cgroup

Thanks!
Christian

Christian Brauner (3):
  cgroup: unify attach permission checking
  clone3: allow spawning processes into cgroups
  selftests/cgroup: add tests for cloning into cgroups

 include/linux/cgroup-defs.h                   |   7 +-
 include/linux/cgroup.h                        |  25 +-
 include/linux/sched/task.h                    |   4 +
 include/uapi/linux/sched.h                    |   5 +
 kernel/cgroup/cgroup.c                        | 300 +++++++++++++++---
 kernel/cgroup/pids.c                          |  25 +-
 kernel/fork.c                                 |  18 +-
 tools/testing/selftests/cgroup/Makefile       |   6 +-
 tools/testing/selftests/cgroup/cgroup_util.c  | 126 ++++++++
 tools/testing/selftests/cgroup/cgroup_util.h  |   4 +
 tools/testing/selftests/cgroup/test_core.c    |  67 ++++
 .../selftests/clone3/clone3_selftests.h       |  19 +-
 12 files changed, 536 insertions(+), 70 deletions(-)


base-commit: d1eef1c619749b2a57e514a3fa67d9a516ffa919
-- 
2.24.0