Re: [PATCH v1 3/5] cgroup: Protect access to task_cls_classid() when built as module

On 08/20/2012 09:03 PM, Neil Horman wrote:

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2) Keep a separate internal counter to track the number of cgroup instances

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so that you only inc the static key on the first create and dec it on the last
delete.

If I got you right, than this would not be different then direclty using
static_key_slow_[inc|dec].

As long as a cgroup subsystems ->destroy method is only called when the
subsystem is being removed, then I think thats correct.  I'm not 100% sure thats
the case though.

THAT is correct, but not the call itself. ->destroy() is called with the
cgroup_lock held, and there is a lockdep dependency created by cpuset
that prevents the cpu_hotplug lock, taken by static branch updates, to
be taken inside cgroup_lock.

So unless cpuset is fixed - which is a major work, we can't do
static_branch updates while holding the cgroup_lock.