Re: [PATCH v3 3/7] cgroup: protect cgroup->nr_(dying_)descendants by css_set_lock

Tejun Heo
2018-11-20T16:18:45Z

On Fri, Nov 16, 2018 at 04:38:26PM -0800, Roman Gushchin wrote:
> Now the number of descendant cgroups and the number of dying
> descendant cgroups are synchronized using the cgroup_mutex.
>
> The number of descendant cgroups will be required by the cgroup v2
> freezer, which will use it to determine if a cgroup is frozen
> (depending on total number of descendants and number of frozen
> descendants). It's not always acceptable to grab the cgroup_mutex,
> especially from quite hot paths (e.g. exit()).
>
> To avoid this, let's additionally synchronize these counters
> using the css_set_lock.

Can you change it so that writes are cgroup_mutex and css_set_lock
protected and reads can be done under either cgroup_mutex or
css_set_lock?

Thanks.

--
tejun