Re: [RFC][PATCH] cgroup_threadgroup_rwsem - affects scalability and OOM

[Balbir Singh <bsingharora-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

On Wed, Aug 10, 2016 at 12:26 AM, Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org> wrote:
> Hello, Balbir.
>
> On Tue, Aug 09, 2016 at 05:02:47PM +1000, Balbir Singh wrote:
>> > Hmm? Where does mem_cgroup_iter grab cgroup_mutex?  cgroup_mutex nests
>> > outside cgroup_threadgroup_rwsem or most other mutexes for that matter
>> > and isn't exposed from cgroup core.
>> >
>>
>> I based my theory on the code
>>
>> mem_cgroup_iter -> css_next_descendant_pre which asserts
>>
>> cgroup_assert_mutex_or_rcu_locked(),
>>
>> although you are right, we hold RCU lock while calling css_* routines.
>
> That's "or".  The iterator can be called either with RCU lock or
> cgroup_mutex.  cgroup core may use it under cgroup_mutex.  Everyone
> else uses it with rcu.
>
> Thanks.
>

Hi, Tejun

Thanks agreed! Could you please consider queuing the fix after review.

Balbir Singh.