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

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Message-Id: <201111212105.52210.rjw@sisk.pl>
Date:	Mon, 21 Nov 2011 21:05:51 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
Cc:	Tejun Heo <tj@...nel.org>, 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 Monday, November 21, 2011, Srivatsa S. Bhat wrote:
> 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?

Yes, it would.

Thanks,
Rafael
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