on 2010-2-23 6:06, David Rientjes wrote:
>>>> Right, but the callback_mutex was being removed by this patch.
>>>>
>>>
>>> I was making the case for it to be readded :)
>>
>> But cgroup_mutex is held when someone changes cs->cpus_allowed or doing hotplug,
>> so I think callback_mutex is not necessary in this case.
>>
>
> Then why is it taken in update_cpumask()?
when we read cs->cpus_allowed, we need just hold one of callback_mutex and cgroup_mutex.
If we want to change cs->cpus_allowed, we must hold callback_mutex and cgroup_mutex.
>> /*
>> @@ -1391,11 +1393,10 @@ static void cpuset_attach(struct cgroup_subsys *ss, struct cgroup *cont,
>>
>> if (cs == &top_cpuset) {
>> cpumask_copy(cpus_attach, cpu_possible_mask);
>> - to = node_possible_map;
>> } else {
>> guarantee_online_cpus(cs, cpus_attach);
>> - guarantee_online_mems(cs, &to);
>> }
>> + guarantee_online_mems(cs, &to);
>>
>> /* do per-task migration stuff possibly for each in the threadgroup */
>> cpuset_attach_task(tsk, &to, cs);
>
> Do we need to set cpus_attach to cpu_possible_mask? Why won't
> cpu_active_mask suffice?
If we set cpus_attach to cpu_possible_mask, we needn't do anything for tasks in the top_cpuset when
doing cpu hotplug. If not, we will update cpus_allowed of all tasks in the top_cpuset.
>
>> @@ -2090,15 +2091,19 @@ static int cpuset_track_online_cpus(struct notifier_block *unused_nb,
>> static int cpuset_track_online_nodes(struct notifier_block *self,
>> unsigned long action, void *arg)
>> {
>> + nodemask_t oldmems;
>
> Is it possible to use NODEMASK_ALLOC() instead?
Yes. I will write another patch to fix it.(These are the same problems in the other functions)
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