[RFC] [PATCH v3 0/2] cgroups: implement moving a threadgroup'sthreads atomically with cgroup.procs

[Ben Blum]

This patch series is a revision of http://lkml.org/lkml/2010/5/29/126 .

These patches use an rwlock in signal_struct which access is dependent
on Oleg's recent changes to signal_struct's lifetime rules.

It is okay to write the tid of any task in the threadgroup. This is
implemented by taking task->group_leader right after find_task_by_vpid
while still rcu_read-side. This makes it necessary to check if
thread_group_leader(leader) every time we want to iterate over
->thread_group; each of these checks can fail with -EAGAIN.
Unfortunately this also means I needed to put these checks in can_attach
for each subsystem that needs to check each thread in the group.

I handle EAGAIN in the file's write handler, since hey, it's a super
expensive operation, might as well make it unbounded-time to boot - this
is optional and would work just as well with -EAGAIN sent to userspace.

-- bblum

---
 Documentation/cgroups/cgroups.txt |   13 -
 include/linux/cgroup.h            |   15 -
 include/linux/init_task.h         |    9
 include/linux/sched.h             |   10
 kernel/cgroup.c                   |  449 +++++++++++++++++++++++++++++++++-----
 kernel/cgroup_freezer.c           |    4
 kernel/cpuset.c                   |    4
 kernel/fork.c                     |   10
 kernel/ns_cgroup.c                |    4
 kernel/sched.c                    |    4
 10 files changed, 462 insertions(+), 60 deletions(-)
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