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

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Message-ID: <4ECA9217.7020205@linux.vnet.ibm.com>
Date:	Mon, 21 Nov 2011 23:31:59 +0530
From:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
To:	Tejun Heo <tj@...nel.org>
CC:	"Rafael J. Wysocki" <rjw@...k.pl>, pavel@....cz, lenb@...nel.org,
	ak@...ux.intel.com, 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

On 11/21/2011 11:22 PM, Tejun Heo wrote:
> Hello,
> 
> On Mon, Nov 21, 2011 at 10:34:40PM +0530, Srivatsa S. Bhat wrote:
>>>> I haven't tested this solution yet. Let me know if this solution looks
>>>> good and I'll send it out as a patch after testing and analyzing some
>>>> corner cases, if any.
>>
>> I tested this, and it works great! I'll send the patch in some time.
> 
> Awesome.
> 
>>> * I think it would be better to remove direct access to pm_mutex and
>>>   use [un]lock_system_sleep() universally.  I don't think hinging it
>>>   on CONFIG_HIBERNATE_CALLBACKS buys us anything.
>>>
>>
>> Which direct access to pm_mutex are you referring to?
>> Other than suspend/hibernation call paths, I think mem-hotplug is the only
>> subsystem trying to access pm_mutex. I haven't checked thoroughly though. 
>>
>> But yes, using lock_system_sleep() for mutually excluding some code path
>> from suspend/hibernation is good, and that is one reason why I wanted
>> to fix this API ASAP. But as long as memory hotplug is the only direct user
>> of pm_mutex, is it justified to remove the CONFIG_HIBERNATE_CALLBACKS
>> restriction and make it generic? I don't know...
>>
>> Or, are you saying that we should use these APIs even in suspend/hibernate
>> call paths? That's not such a bad idea either...
> 
> Yeap, all.  It's just confusing to have two different types of access
> to a single lock and I don't believe CONFIG_HIBERNATE_CALLBACKS is a
> meaningful optimization in this case.
> 

Ok that sounds good, I'll send a separate patch for that.
Rafael, do you also agree that this would be better?

Thanks,
Srivatsa S. Bhat

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