Re: Possible regression with cgroups in 3.11

[Markus Blank-Burian <burian-iYtK5bfT9M8b1SvskN2V4Q@public.gmane.org>]

Thanks for the patch Johannes!

I tried tried it immediately, but it still hangs. But this time the
worker threads have a slightly different call stack. Most of them are
now waiting in css_killed_work_fn:

  [ffff880c31a33e18] mutex_lock at ffffffff813c1bb4
  [ffff880c31a33e30] css_killed_work_fn at ffffffff81080eba
  [ffff880c31a33e50] process_one_work at ffffffff8103f7db
  [ffff880c31a33e90] worker_thread at ffffffff8103fc7d
  [ffff880c31a33eb0] worker_thread at ffffffff8103fb39
  [ffff880c31a33ec8] kthread at ffffffff8104479c
  [ffff880c31a33f28] kthread at ffffffff81044714
  [ffff880c31a33f50] ret_from_fork at ffffffff813c503c
  [ffff880c31a33f80] kthread at ffffffff81044714

The other few workers hang at the beginning of proc_cgroupstats_show
and one in cgroup_rmdir:

  [ffff8800b7825e40] mutex_lock at ffffffff813c1bb4
  [ffff8800b7825e58] proc_cgroupstats_show at ffffffff8107f5f0
  [ffff8800b7825e78] seq_read at ffffffff81107953
  [ffff8800b7825ee0] proc_reg_read at ffffffff81135f73
  [ffff8800b7825f18] vfs_read at ffffffff810ed3ea
  [ffff8800b7825f48] sys_read at ffffffff810edad6
  [ffff8800b7825f80] tracesys at ffffffff813c52db

  [ffff880c308e1e40] mutex_lock at ffffffff813c1bb4
  [ffff880c308e1e58] cgroup_rmdir at ffffffff81081d25
  [ffff880c308e1e78] vfs_rmdir at ffffffff810f8bed
  [ffff880c308e1ea0] do_rmdir at ffffffff810f8d02
  [ffff880c308e1f18] user_exit at ffffffff8100aed1
  [ffff880c308e1f28] syscall_trace_enter at ffffffff8100c356
  [ffff880c308e1f70] sys_rmdir at ffffffff810f9a95
  [ffff880c308e1f80] tracesys at ffffffff813c52db

The looping thread is still this one:

  [ffff880c30049d50] mem_cgroup_reparent_charges at ffffffff810e637b
  [ffff880c30049de0] mem_cgroup_css_offline at ffffffff810e679d
  [ffff880c30049e10] offline_css at ffffffff8107f02f
  [ffff880c30049e30] css_killed_work_fn at ffffffff81080ec2
  [ffff880c30049e50] process_one_work at ffffffff8103f7db
  [ffff880c30049e90] worker_thread at ffffffff8103fc7d
  [ffff880c30049eb0] worker_thread at ffffffff8103fb39
  [ffff880c30049ec8] kthread at ffffffff8104479c
  [ffff880c30049f28] kthread at ffffffff81044714
  [ffff880c30049f50] ret_from_fork at ffffffff813c503c
  [ffff880c30049f80] kthread at ffffffff81044714