[Devel] [PATCH rh7 2/3] ve: Wait till ve's attaching work finished

[Vladimir Davydov]

On Fri, Oct 16, 2015 at 07:25:00PM +0300, Kirill Tkhai wrote:
...
> @@ -1565,6 +1565,10 @@ struct task_struct {
>  #ifdef CONFIG_VE
>  	struct ve_struct *task_ve;
>  	struct callback_head task_ve_work;
> +	union {
> +		struct task_struct *task_ve_mover;
> +		atomic_t task_ve_nr_works;
> +	};

Isn't it possible to allocate it before attaching a task and freeing
them once we are done? Cgroup attach doesn't worth blowing task_struct.

>  #endif
>  #ifdef CONFIG_MEMCG /* memcg uses this to do batch job */
>  	struct memcg_batch_info {
...
> @@ -703,11 +703,25 @@ static void ve_destroy(struct cgroup *cg)
>  
>  static void ve_attach_work(struct callback_head *head)
>  {
> +	atomic_t *nr = &current->task_ve_mover->task_ve_nr_works;
> +
>  	rcu_read_lock();
>  	current->task_ve = cgroup_ve(task_cgroup(current, ve_subsys_id));
>  	rcu_read_unlock();
>  	smp_mb(); /* Pairs with smp_mb() in ve_can_attach() */
>  	init_task_work(&current->task_ve_work, NULL);
> +
> +	atomic_dec(nr);
> +}
> +
> +static void ve_wait_work(struct callback_head *head)
> +{
> +	atomic_t *nr = &current->task_ve_nr_works;
> +
> +	while (atomic_read(nr))
> +		schedule_timeout(1);

Let's not introduce such temporary solutions. They look misleading and
don't ease review. I think it'd be OK to merge patches 2 and 3.

> +
> +	init_task_work(&current->task_ve_work, NULL);
>  }
>  
>  static int ve_can_attach(struct cgroup *cg, struct cgroup_taskset *tset)