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Date: Thu, 19 Jan 2012 01:16:06 +0530
From: "Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>
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To: Tejun Heo <tj@kernel.org>
CC: "Rafael J. Wysocki" <rjw@sisk.pl>,
        Linux PM list <linux-pm@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>, horms@verge.net.au,
        "pavel@ucw.cz" <pavel@ucw.cz>, Len Brown <lenb@kernel.org>
Subject: Re: [Update][PATCH] PM / Hibernate: Fix s2disk regression related
 to unlock_system_sleep()
References: <201201172345.15010.rjw@sisk.pl> <201201180015.56510.rjw@sisk.pl> <4F16C24A.4050007@linux.vnet.ibm.com> <CAOS58YMBWrD2cMyPJG0Xf16i1vnkB8xerdeqWJ=fk7HVNpoPAw@mail.gmail.com> <4F16F94C.4020000@linux.vnet.ibm.com> <CAOS58YPW3hB3ibaYPLBqhu=2jZTAjjF7DZaXO=hK5tookAX7YA@mail.gmail.com> <4F16FF0D.1030606@linux.vnet.ibm.com> <20120118173037.GE30664@google.com> <4F171BF8.50803@linux.vnet.ibm.com> <20120118193040.GA28538@google.com>
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On 01/19/2012 01:00 AM, Tejun Heo wrote:

> Hello,
> 
> On Thu, Jan 19, 2012 at 12:52:32AM +0530, Srivatsa S. Bhat wrote:
>> Somehow I don't think its a hack, based on my perception as described
>> above. But feel free to prove me wrong :-)
> 
> Thanks for the explanation.  Yeah, I agree and it's much simpler this
> way, which is nice.  So, in short, because freezing state can't change
> across lock_system_sleep(), there's no reason to check for freezing
> state on unlock and this nicely resolves the freezer problem together.
> 


Absolutely!

> The only thing to be careful is, then, we need to set and clear SKIP
> inside pm_mutex.
> 


Not exactly. We need to set SKIP before grabbing pm_mutex and clear it
inside pm_mutex. The reason is that we decided to set SKIP in the first
place just to avoid the freezer from declaring failure when we are
blocked on pm_mutex. If we move it to *after* mutex_lock(&pm_mutex), that
original intention itself is not satisfied, and we will hit freezing
failures - IOW making the set and clear exercise useless!

So, something like this should work perfectly:

lock_system_sleep()
{
	freezer_do_not_count();
	mutex_lock(&pm_mutex);
	current->flags &= ~PF_FREEZER_SKIP;
}

But in the interest of making the code look a bit symmetric, we can do:

lock_system_sleep()
{
	freezer_do_not_count();
	mutex_lock(&pm_mutex);
}

unlock_system_sleep()
{
	current->flags &= ~PF_FREEZER_SKIP;
	mutex_unlock(&pm_mutex);
}
 
Regards,
Srivatsa S. Bhat
IBM Linux Technology Center