[PATCH v4 0/2] cgroups: implement moving a threadgroup's threads atomically with cgroup.procs

[Ben Blum <bblum@andrew.cmu.edu>]

This patch series is a revision of http://lkml.org/lkml/2010/6/25/11 .

This patch series implements a write function for the 'cgroup.procs'
per-cgroup file, which enables atomic movement of multithreaded
applications between cgroups. Writing the thread-ID of any thread in a
threadgroup to a cgroup's procs file causes all threads in the group to
be moved to that cgroup safely with respect to threads forking/exiting.
(Possible usage scenario: If running a multithreaded build system that
sucks up system resources, this lets you restrict it all at once into a
new cgroup to keep it under control.)

Example: Suppose pid 31337 clones new threads 31338 and 31339.

# cat /dev/cgroup/tasks
...
31337
31338
31339
# mkdir /dev/cgroup/foo
# echo 31337 > /dev/cgroup/foo/cgroup.procs
# cat /dev/cgroup/foo/tasks
31337
31338
31339

A new lock, called threadgroup_fork_lock and living in signal_struct, is
introduced to ensure atomicity when moving threads between cgroups. It's
taken for writing during the operation, and taking for reading in fork()
around the calls to cgroup_fork() and cgroup_post_fork(). I put calls to
down_read/up_read directly in copy_process(), since new inline functions
seemed like overkill.

-- Ben

---
 Documentation/cgroups/cgroups.txt |   13 -
 include/linux/init_task.h         |    9
 include/linux/sched.h             |   10
 kernel/cgroup.c                   |  426 +++++++++++++++++++++++++++++++++-----
 kernel/cgroup_freezer.c           |    4
 kernel/cpuset.c                   |    4
 kernel/fork.c                     |   16 +
 kernel/ns_cgroup.c                |    4
 kernel/sched.c                    |    4
 9 files changed, 440 insertions(+), 50 deletions(-)