Re: [PATCH v2 3/6] cgroup: cgroup v2 freezer

Oleg Nesterov
2018-11-13T15:48:29Z

On 11/12, Roman Gushchin wrote:
>
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -83,7 +83,8 @@ struct task_group;
> #define TASK_WAKING 0x0200
> #define TASK_NOLOAD 0x0400
> #define TASK_NEW 0x0800
> -#define TASK_STATE_MAX 0x1000
> +#define TASK_FROZEN 0x1000
> +#define TASK_STATE_MAX 0x2000

Just noticed the new task state... Why? Can't we avoid it?

...

> +void cgroup_freezer_enter(void)
> +{
> + long state = current->state;

Why? it must be TASK_RUNNING?

If not set_current_state() at the end is simply wrong... Yes, __refrigerator()
does this, but at least it has a reason although it is wrong too.

> + struct cgroup *cgrp;
> +
> + if (!current->frozen) {
> + spin_lock_irq(&css_set_lock);
> + current->frozen = true;
> + cgrp = task_dfl_cgroup(current);
> + cgrp->freezer.nr_frozen_tasks++;
> +
> + WARN_ON_ONCE(cgrp->freezer.nr_tasks_to_freeze <
> + cgrp->freezer.nr_frozen_tasks);
> +
> + if (cgrp->freezer.nr_tasks_to_freeze ==
> + cgrp->freezer.nr_frozen_tasks)
> + cgroup_queue_notify_frozen(cgrp);
> + spin_unlock_irq(&css_set_lock);
> + }
> +
> + /* refrigerator */
> + set_current_state(TASK_WAKEKILL | TASK_INTERRUPTIBLE | TASK_FROZEN);

Why not __set_current_state() ?

If ->state include TASK_INTERRUPTIBLE, why do we need TASK_WAKEKILL?

And again, why TASK_FROZEN?

> + clear_thread_flag(TIF_SIGPENDING);
> + schedule();
> + recalc_sigpending();

I simply can't understand these 3 lines above but I bet this is not correct ;)

if nothing else recalc_sigpending() without ->siglock is wrong, it can race
with signal_wakeup/etc.

> + set_current_state(state);

see above...

Oleg.