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

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Date:	Mon, 21 Nov 2011 15:55:11 +0800
From:	Chen Gong <gong.chen@...ux.intel.com>
To:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
CC:	"Rafael J. Wysocki" <rjw@...k.pl>, pavel@....cz, lenb@...nel.org,
	ak@...ux.intel.com, tj@...nel.org, linux-kernel@...r.kernel.org,
	linux-pm@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v3] PM/Memory-hotplug: Avoid task freezing failures

[...]
>
> 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?
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