2012/10/20 Frederic Weisbecker <fweis...@gmail.com>:
> 2012/10/19 Tejun Heo <t...@kernel.org>:
>> Hello, Frederic.
>>
>> On Fri, Oct 19, 2012 at 03:44:20PM -0400, Frederic Weisbecker wrote:
>>> > For -stable, I think it's better to revert. If you want to remove
>>> > task_lock, let's do it for 3.8.
>>>
>>> I don't think that a wrong comment justifies a patch to stable.
>>
>> I'm not really sure whether it's safe or not. It seems all usages are
>> protected by write locking css_set_lock but maybe I'm missing
>> something and as the commit is born out of confusion, I'm very
>> inclined to revert it by default. Are you sure this one is safe?
>
> Thinking about it further, one scenario is worrying me but it
> eventually looks safe but by accident.
>
> CPU 0
> CPU 1
>
> cgroup_task_migrate {
> task_lock(p)
> rcu_assign_pointer(tsk->cgroups, newcg);
> task_unlock(tsk);
>
> write_lock(&css_set_lock);
> if (!list_empty(&tsk->cg_list))
> list_move(&tsk->cg_list, &newcg->tasks);
> write_unlock(&css_set_lock);
>
> write_lock(&css_set_lock);
> put_css_set(oldcg);
> list_add(&child->cg_list, &child->cgroups->tasks); (1)
gmail mangled everything :(
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