[PATCH v4 0/3] cgroup: replace global percpu_rwsem with per threadgroup resem when writing to cgroup.procs

[Yi Tao]

Changes in v4:
- Adjust commit log and comments.
- Rename take_per_threadgroup_rwsem to cgroup_enable_per_threadgroup_rwsem and
add attr __read_mostly.
- Trigger a warning that per_threadgroup opreation can't be
disabled once enabled instead of actually turning it off.
- Split the code for retrying when the threadgroup leader changes into a
separate patch.
- Refactor the cgroup_attach_lock code to make it clearer.

Changes in v3:
- Expend commit log and comments.
- Put argument @tsk at end in cgroup_attach_lock/unlock.
- down_write global cgroup_thread_rwsem when flipping favordynmods to
synchronize with task between cgroup_threadgroup_change_begin and end.
- Rename group_rwsem to cgroup_threadgroup_rwsem.
- Fix bug causing abnormal cgroup migration due to threadgroup leader changes。

Changes in v2:
- Use favordynmods as the enabling switch.
- Determine whether to use the per-thread-group rwsem based on whether
the task is NULL.
- Fix system hang caused by acquiring cgroup_threadgroup_rwsem inside
rcu_read_lock.

Yi Tao (3):
  cgroup: replace global percpu_rwsem with per threadgroup resem when
    writing to cgroup.procs
  cgroup: retry find task if threadgroup leader changed
  cgroup: refactor the cgroup_attach_lock code to make it clearer

 include/linux/cgroup-defs.h     |  25 +++++-
 include/linux/sched/signal.h    |   4 +
 init/init_task.c                |   3 +
 kernel/cgroup/cgroup-internal.h |   8 +-
 kernel/cgroup/cgroup-v1.c       |  14 +--
 kernel/cgroup/cgroup.c          | 149 ++++++++++++++++++++++++--------
 kernel/fork.c                   |   4 +
 7 files changed, 161 insertions(+), 46 deletions(-)

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2.32.0.3.g01195cf9f