[PATCHSET cgroup/for-3.12] cgroup: decouple cgroup_subsys_state lifetime from that of cgroup

[Tejun Heo]

Hello,

Currently a css's (cgroup_subsys_state) lifetime is tied to that of
the cgroup it's attached to.  css's are created when the cgroup is
created and destroyed together.  The access rules depend on it too -
e.g. css's can be dereferenced while holding RCU read lock because
cgroup is protected with RCU.

With the planned unified hierarchy, we'll be dynamically creating and
destroying css's through the lifetime of a cgroup, so we can no longer
hitch css lifetime management onto cgroup's.  This patchset separates
out css lifetime management from that of cgroup.  After the patchset,
each css is individually RCU protected.

This patchset contains the following 14 patches.

 0001-cgroup-always-use-cgroup_css.patch
 0002-cgroup-rename-cgroup_subsys_state-dput_work-and-its-.patch
 0003-cgroup-add-cgroup_subsys_state-parent.patch
 0004-cgroup-cgroup_css_from_dir-now-should-be-called-with.patch
 0005-cgroup-make-cgroup_file_open-rcu_read_lock-around-cg.patch
 0006-cgroup-add-__rcu-modifier-to-cgroup-subsys.patch
 0007-cgroup-reorganize-css-init-exit-paths.patch
 0008-cgroup-move-cgroup-subsys-assignment-to-online_css.patch
 0009-cgroup-bounce-cgroup_subsys_state-ref-kill-confirmat.patch
 0010-cgroup-replace-cgroup-css_kill_cnt-with-nr_css.patch
 0011-cgroup-decouple-cgroup_subsys_state-destruction-from.patch
 0012-cgroup-factor-out-kill_css.patch
 0013-cgroup-move-subsys-file-removal-to-kill_css.patch
 0014-cgroup-RCU-protect-each-cgroup_subsys_state-release.patch

The patchset is on top of

  cgroup/for-3.12 61584e3f4 ("cgroup: Merge branch 'for-3.11-fixes' into for-3.12")
+ [1] cgroup: use cgroup_subsys_state as the primary subsystem interface handle
+ [2] cgroup: cgroup: make css_for_each_descendant() and friends include the origin css in the iteration

and available in the following branch.

 git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup.git review-rcufy-css

diffstat follows.

 include/linux/cgroup.h |   24 +-
 kernel/cgroup.c        |  423 +++++++++++++++++++++++++++++--------------------
 kernel/events/core.c   |    3
 3 files changed, 268 insertions(+), 182 deletions(-)

Thanks.

--
tejun

[1] https://lkml.org/lkml/2013/8/1/722
[2] https://lkml.org/lkml/2013/8/4/130
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