Re: [BUG] cgroup/workques/fork: deadlock when moving cgroups

From	Tejun Heo <tj@kernel.org>
Newsgroups	linux.kernel
Subject	Re: [BUG] cgroup/workques/fork: deadlock when moving cgroups
Date	2016-04-15 16:40 +0200
Message-ID	<rod4B-4sD-11@gated-at.bofh.it> (permalink)
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Hello, Michal.

On Fri, Apr 15, 2016 at 09:06:01AM +0200, Michal Hocko wrote:
> Tejun was proposing to do the migration async (move the whole
> mem_cgroup_move_charge into the work item). This would solve the problem
> of course. I haven't checked whether this would be safe but it at least
> sounds doable (albeit far from trivial). It would also be a user visible
> change because the new memcg will not contain the moved charges after we
> return to user space. I think this would be acceptable but if somebody

Not necessarily.  The only thing necessary is flushing the work item
after releasing locks but before returning to user.
cpuset_post_attach_flush() does exactly the same thing.

> really relies on the previous behavior I guess we can solve it with a
> post_move cgroup callback which would be called from a lockless context.
> 
> Anyway, before we go that way, can we at least consider the possibility
> of removing the kworker creation dependency on the global rwsem? AFAIU
> this locking was added because of the pid controller. Do we even care
> about something as volatile as kworkers in the pid controller?

It's not just pid controller and the global percpu locking has lower
hotpath overhead.  We can try to exclude kworkers out of the locking
but that can get really nasty and there are already attempts to add
cgroup support to workqueue.  Will think more about it.  For now tho,
do you think making charge moving async would be difficult?

Thanks.

-- 
tejun

Thread

[BUG] cgroup/workques/fork: deadlock when moving cgroups Petr Mladek <pmladek@suse.com> - 2016-04-13 11:50 +0200
  Re: [BUG] cgroup/workques/fork: deadlock when moving cgroups Tejun Heo <tj@kernel.org> - 2016-04-13 20:40 +0200
    Re: [BUG] cgroup/workques/fork: deadlock when moving cgroups Tejun Heo <tj@kernel.org> - 2016-04-13 21:00 +0200
    Re: [BUG] cgroup/workques/fork: deadlock when moving cgroups Michal Hocko <mhocko@kernel.org> - 2016-04-13 21:30 +0200
    Re: [BUG] cgroup/workques/fork: deadlock when moving cgroups Michal Hocko <mhocko@kernel.org> - 2016-04-13 21:30 +0200
      Re: [BUG] cgroup/workques/fork: deadlock when moving cgroups Michal Hocko <mhocko@kernel.org> - 2016-04-13 21:50 +0200
        Re: [BUG] cgroup/workques/fork: deadlock when moving cgroups Michal Hocko <mhocko@kernel.org> - 2016-04-14 09:10 +0200
          Re: [BUG] cgroup/workques/fork: deadlock when moving cgroups Tejun Heo <tj@kernel.org> - 2016-04-14 17:40 +0200
      Re: [BUG] cgroup/workques/fork: deadlock when moving cgroups Tejun Heo <tj@kernel.org> - 2016-04-13 21:50 +0200
      Re: [BUG] cgroup/workques/fork: deadlock when moving cgroups Johannes Weiner <hannes@cmpxchg.org> - 2016-04-14 20:00 +0200
        Re: [BUG] cgroup/workques/fork: deadlock when moving cgroups Michal Hocko <mhocko@kernel.org> - 2016-04-15 09:10 +0200
          Re: [BUG] cgroup/workques/fork: deadlock when moving cgroups Tejun Heo <tj@kernel.org> - 2016-04-15 16:40 +0200
            Re: [BUG] cgroup/workques/fork: deadlock when moving cgroups Michal Hocko <mhocko@kernel.org> - 2016-04-15 17:10 +0200
              Re: [BUG] cgroup/workques/fork: deadlock when moving cgroups Tejun Heo <tj@kernel.org> - 2016-04-15 17:30 +0200
                Re: [BUG] cgroup/workques/fork: deadlock when moving cgroups Michal Hocko <mhocko@kernel.org> - 2016-04-17 14:10 +0200
            Re: [BUG] cgroup/workques/fork: deadlock when moving cgroups Petr Mladek <pmladek@suse.com> - 2016-04-18 16:50 +0200
              Re: [BUG] cgroup/workques/fork: deadlock when moving cgroups Michal Hocko <mhocko@kernel.org> - 2016-04-19 16:10 +0200
                Re: [BUG] cgroup/workques/fork: deadlock when moving cgroups Petr Mladek <pmladek@suse.com> - 2016-04-19 17:40 +0200
        [PATCH for-4.6-fixes] memcg: remove lru_add_drain_all() invocation  from mem_cgroup_move_charge() Tejun Heo <tj@kernel.org> - 2016-04-15 21:30 +0200
          Re: [PATCH for-4.6-fixes] memcg: remove lru_add_drain_all()  invocation from mem_cgroup_move_charge() Michal Hocko <mhocko@kernel.org> - 2016-04-17 14:10 +0200
            Re: [PATCH for-4.6-fixes] memcg: remove lru_add_drain_all()  invocation from mem_cgroup_move_charge() Tejun Heo <tj@kernel.org> - 2016-04-20 23:30 +0200
              Re: [PATCH for-4.6-fixes] memcg: remove lru_add_drain_all()  invocation from mem_cgroup_move_charge() Michal Hocko <mhocko@kernel.org> - 2016-04-21 05:30 +0200
                Re: [PATCH for-4.6-fixes] memcg: remove lru_add_drain_all()  invocation from mem_cgroup_move_charge() Petr Mladek <pmladek@suse.com> - 2016-04-21 17:10 +0200
                Re: [PATCH for-4.6-fixes] memcg: remove lru_add_drain_all()  invocation from mem_cgroup_move_charge() Tejun Heo <tj@kernel.org> - 2016-04-21 18:00 +0200
            [PATCH 2/2] memcg: relocate charge moving from ->attach to  ->post_attach Tejun Heo <tj@kernel.org> - 2016-04-22 01:10 +0200
              Re: [PATCH 2/2] memcg: relocate charge moving from ->attach to  ->post_attach Petr Mladek <pmladek@suse.com> - 2016-04-22 16:00 +0200
              Re: [PATCH 2/2] memcg: relocate charge moving from ->attach to  ->post_attach Michal Hocko <mhocko@kernel.org> - 2016-04-25 10:30 +0200
                Re: [PATCH 2/2] memcg: relocate charge moving from ->attach to  ->post_attach Tejun Heo <tj@kernel.org> - 2016-04-25 21:50 +0200
              Re: [PATCH 2/2] memcg: relocate charge moving from ->attach to  ->post_attach Tejun Heo <tj@kernel.org> - 2016-04-25 21:50 +0200
            [PATCH 1/2] cgroup, cpuset: replace cpuset_post_attach_flush() with  cgroup_subsys->post_attach callback Tejun Heo <tj@kernel.org> - 2016-04-22 01:10 +0200
              Re: [PATCH 1/2] cgroup, cpuset: replace cpuset_post_attach_flush()  with cgroup_subsys->post_attach callback Tejun Heo <tj@kernel.org> - 2016-04-22 01:20 +0200
          [PATCH for-4.6-fixes] memcg: remove lru_add_drain_all() invocation  from mem_cgroup_move_charge() Tejun Heo <tj@kernel.org> - 2016-04-21 18:00 +0200

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