[PATCHSET cgroup] extend threadgroup locking

[Tejun Heo <htejun@gmail.com>]

Hello,

cgroup currently only blocks new threads from joining the target
threadgroup during migration, and on-going migration could race
against exec and exit leading to interesting problems - the symmetry
between various attach methods, task exiting during method execution,
->exit() racing against attach methods, migrating task switching basic
properties during exec and so on.

This patchset extends threadgroup locking such that it covers all
operations which can alter the threadgroup - fork, exit and exec, and
update cgroup to take advantage of it.  rwsem read ops are added to
exit path but exec is excluded by grabbing the existing
cred_guard_mutex from threadgroup locking helper.

This makes threadgroup locking complete and resolves cgroup issues
stemming from the target taskset being unstable.

This patchset is on top of the current pm-freezer + "freezer: fixes &
simplifications" patchset and contains the following four patches.
Patch list and diffstat follow.

Thanks.

 [PATCH 1/4] cgroup: change locking order in attach_task_by_pid()
 [PATCH 2/4] threadgroup: rename signal->threadgroup_fork_lock to
 [PATCH 3/4] threadgroup: extend threadgroup_lock() to cover exit and
 [PATCH 4/4] cgroup: always lock threadgroup during migration

 include/linux/init_task.h |    9 ++----
 include/linux/sched.h     |   58 ++++++++++++++++++++++++++++---------------
 kernel/cgroup.c           |   62 +++++++++++++++++++++-------------------------
 kernel/exit.c             |   16 ++++++++---
 kernel/fork.c             |    8 ++---
 5 files changed, 88 insertions(+), 65 deletions(-)

--
tejun

[1] http://thread.gmane.org/gmane.linux.kernel/1187553