On 2013/4/20 4:58, Tejun Heo wrote:
> Hello,
>
> On Fri, Apr 19, 2013 at 08:29:24PM +0800, Li Zefan wrote:
>> +static void update_tasks_cpumask_hier(struct cpuset *root_cs,
>> + bool update_root, struct ptr_heap *heap)
>> +{
>> + struct cpuset *cp;
>> + struct cgroup *pos_cgrp;
>> +
>> + if (update_root)
>> + update_tasks_cpumask(root_cs, heap);
>> +
>> + rcu_read_lock();
>> + cpuset_for_each_descendant_pre(cp, pos_cgrp, root_cs) {
>> + /* skip the whole subtree if @cp have some CPU */
>> + if (!cpumask_empty(cp->cpus_allowed)) {
>> + pos_cgrp = cgroup_rightmost_descendant(pos_cgrp);
>> + continue;
>> + }
>> +
>> + update_tasks_cpumask(cp, heap);
>> + }
>> + rcu_read_unlock();
>
> I don't think we can call update_tasks_cpumask() under
> rcu_read_lock(). It calls into set_cpus_allowed_ptr() which may
> block, so you'll probably have to punt it to a work item like how
Oh, will fix.
> migration is being done. Another approach would be converting cgroup
> to use SRCU instead, which would lessen pain on other places too. The
> only problem there would be that srcu_read_lock() is a bit more
> expensive than rcu_read_lock(). I'm not sure whether that'd show up
> in some hot path or not. Ideas?
>
I guess we can live with rcu_read_lock() for now, and see if we can
change it to srcu when other significant changes are done in all
cgroup controllers. (hierarchy support in blkcg, etc..)
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