[Devel] [PATCH 0/3 v2 RHEL7] cgroup: do not use cgroup_mutex in cgroup_show_options

[Valeriy Vdovin]

The patchset fixes lock order inversion problem https://jira.sw.ru/browse/PSBM-121438:

Thread A:
  m_start() --> down_read(&namespace_sem);
    cgroup_show_options() --> mutex_lock(&cgroup_mutex);

Thread B:
attach_task_by_pid()
  cgroup_lock_live_group -->  mutex_lock(&cgroup_mutex);
  threadgroup_lock() -->  down_write(&tsk->signal->group_rwsem);

Thread C:
 copy_process
  threadgroup_change_begin() --> down_read(&tsk->signal->group_rwsem);
  copy_namespaces
   create_new_namespaces
     copy_mnt_ns
      namespace_lock() --> down_write(&namespace_sem)

It's split logically so that the first patch fixes pre-existing incorrect resource release order
in ve_drop_contex, that was behaving not as expected in cgroup_show_options.
In the next patch cgroup_show_options itself get's slightly rewritten to not use cgroup_mutex
which fixes the bug.
One more patch is added to clean up the coding style of the function ve_get_release_agent_path,
which is relevant to current problem.

v1: original patch
v2: Added logic that depends on validness of ve->root_css_set instead of cgroup_mutex. Added coding-style fixes.


Valeriy Vdovin (3):
  ve/cgroup: change resource release order in ve_drop_context
  cgroup: do not use cgroup_mutex in cgroup_show_options
  ve: cleanup in function ve_get_release_agent_path

 kernel/cgroup.c | 9 ++-------
 kernel/ve/ve.c  | 7 ++++---
 2 files changed, 6 insertions(+), 10 deletions(-)

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1.8.3.1