Re: [PATCH v3] PM/Memory-hotplug: Avoid task freezing failures

[Chen Gong <gong.chen@linux.intel.com>]

[...]
>
> Actually, I think I have a better idea based on a key observation:
> We are trying to acquire pm_mutex here. And if we block due to this,
> we are *100% sure* that we are not going to run as long as hibernation
> sequence is running, since hibernation releases pm_mutex only at the
> very end, when everything is done.
> And this means, this task is going to be blocked for much more longer
> than what the freezer intends to achieve. Which means, freezing and
> thawing doesn't really make a difference to this task!
>
> So, let's just ask the freezer to skip freezing us!! And everything
> will be just fine!
>
> Something like:
>
> void lock_system_sleep(void)
> {
> 	/* simplified freezer_do_not_count() */
> 	current->flags |= PF_FREEZER_SKIP;
>
> 	mutex_lock(&pm_mutex);
>
> }
>
> void unlock_system_sleep(void)
> {
> 	mutex_unlock(&pm_mutex);
>
> 	/* simplified freezer_count() */
> 	current->flags&= ~PF_FREEZER_SKIP;
>
> }
>
> We probably don't want the restriction that freezer_do_not_count() and
> freezer_count() work only for userspace tasks. So I have open coded
> the relevant parts of those functions here.
>

This new design looks clean and better than old one. I just curious how do
you design your test environment? e.g. when hibernating is in progress,
try to online some memories and wait for hibernation fails or succeeds?