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Subject[PATCHSET] cgroup: stable threadgroup during attach & subsys methods consolidation


This patchset is combination of the following two patchsets.

[1] cgroup: extend threadgroup locking
[2] cgroup: introduce cgroup_taskset and consolidate subsys methods, take#2

Changes from the last postings are

* 0001-cgroup-add-cgroup_root_mutex.patch replaces mutex ordering
reversal patch, which Oleg found out to be broken. Instead, a new
sub-mutex cgroup_root_mutex is introduced to break circular

* Rebased on top of the current linus/master.

* Other minor changes to reflect comments from reviews.

* Reviewed/Acked-by's added.

This patchset addresses the following two issues.

1. 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 is resolved by extending 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.

2. cgroup has grown quite some number of subsys methods. Some of them
are overlapping, inconsistent with each other and called under
different conditions depending on whether they're called for a
single task or whole process. Unfortunately, these callbacks are
complicated and incomplete at the same time.

* ->attach_task() is called after migration for task attach but
before for process.

* Ditto for ->pre_attach().

* ->can_attach_task() is called for every task in the thread group
->but attach_task() skips the ones which don't actually change

* Task attach becomes noop if the task isn't actually moving.
Process attach is always performed.

* ->attach_task() doesn't (or at least aren't supposed to) have
access to the old cgroup.

* During cancel, there's no way to access the affected tasks.

This patchset introduces cgroup_taskset along with some accessors
and iterator, updates methods to use it, consolidates usages and
drops superflous methods.


0001-0004 implement stable thread group.

0005-0010 introduce taskset and consolidate subsys callbacks.

This patchset is on top of the current linus/master 839d881074 "Merge
branch 'i2c-for-linus' of ..." and also available in the following git

git:// cgroup-cleanup

If this looks okay, I think it would be best to route this through pm
tree as there are and will be intersecting changes (mostly around

diffstat follows.

Documentation/cgroups/cgroups.txt | 51 ++----
block/blk-cgroup.c | 45 +++--
include/linux/cgroup.h | 31 ++-
include/linux/init_task.h | 9 -
include/linux/sched.h | 62 +++++--
kernel/cgroup.c | 320 +++++++++++++++++++++++---------------
kernel/cgroup_freezer.c | 27 +--
kernel/cpuset.c | 105 +++++-------
kernel/events/core.c | 13 -
kernel/exit.c | 17 +-
kernel/fork.c | 8
kernel/sched.c | 31 ++-
mm/memcontrol.c | 16 -
security/device_cgroup.c | 7
14 files changed, 430 insertions(+), 312 deletions(-)




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