Re: [PATCH v3 4/7] cgroup: cgroup v2 freezer

[Roman Gushchin]

On Tue, Nov 20, 2018 at 08:25:29AM -0800, Tejun Heo wrote:
> On Fri, Nov 16, 2018 at 04:38:27PM -0800, Roman Gushchin wrote:
> > +void cgroup_freezer_migrate_task(struct task_struct *task,
> > +                            struct cgroup *src, struct cgroup *dst)
> > +{
> > +   lockdep_assert_held(&css_set_lock);
> > +
> > +   /*
> > +    * Kernel threads are not supposed to be frozen at all.
> > +    */
> > +   if (task->flags & PF_KTHREAD)
> > +           return;
> > +
> > +   /*
> > +    * Adjust counters of freezing and frozen tasks.
> > +    */
> > +   if (test_bit(CGRP_FREEZE, &src->flags)) {
> > +           src->freezer.nr_tasks_to_freeze--;
> > +           WARN_ON_ONCE(src->freezer.nr_tasks_to_freeze < 0);
> > +   }
> > +
> > +   /*
> > +    * If the task is frozen, let's bump nr_tasks_to_freeze even
> > +    * if the target cgroup isn't frozen: the counter will be decreased
> > +    * in cgroup_leave_frozen().
> > +    */
> > +   if (test_bit(CGRP_FREEZE, &dst->flags) || task->frozen)
> > +           dst->freezer.nr_tasks_to_freeze++;
> > +
> > +   if (task->frozen) {
> > +           src->freezer.nr_frozen_tasks--;
> > +           dst->freezer.nr_frozen_tasks++;
> > +           WARN_ON_ONCE(src->freezer.nr_frozen_tasks < 0);
> > +           WARN_ON_ONCE(dst->freezer.nr_frozen_tasks >
> > +                        dst->freezer.nr_tasks_to_freeze);
> > +   }
> 
> If a non-frozen task is being moved into a frozen cgroup, shouldn't
> that also trigger frozen state update?

It does! Just below these lines:

        /*
         * If the task isn't in the desired state, force it to it.
         */
        if (task->frozen != test_bit(CGRP_FREEZE, &dst->flags))
                cgroup_freeze_task(task, test_bit(CGRP_FREEZE, &dst->flags));


It's also covered by the 5th kselftest.

Thanks!