linux-kernel - Re: [PATCH v2 0/3] Freezer, CPU hotplug, x86 Microcode: Fix task freezing failures

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Date:	Mon, 10 Oct 2011 19:53:36 +0200
From:	Borislav Petkov <bp@...64.org>
To:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
Cc:	Borislav Petkov <bp@...64.org>,
	Alan Stern <stern@...land.harvard.edu>,
	"rjw@...k.pl" <rjw@...k.pl>, "pavel@....cz" <pavel@....cz>,
	"len.brown@...el.com" <len.brown@...el.com>,
	"tj@...nel.org" <tj@...nel.org>, "mingo@...e.hu" <mingo@...e.hu>,
	"a.p.zijlstra@...llo.nl" <a.p.zijlstra@...llo.nl>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"suresh.b.siddha@...el.com" <suresh.b.siddha@...el.com>,
	"lucas.demarchi@...fusion.mobi" <lucas.demarchi@...fusion.mobi>,
	"rusty@...tcorp.com.au" <rusty@...tcorp.com.au>,
	"rdunlap@...otime.net" <rdunlap@...otime.net>,
	"vatsa@...ux.vnet.ibm.com" <vatsa@...ux.vnet.ibm.com>,
	"ashok.raj@...el.com" <ashok.raj@...el.com>,
	"tigran@...azian.fsnet.co.uk" <tigran@...azian.fsnet.co.uk>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"hpa@...or.com" <hpa@...or.com>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>
Subject: Re: [PATCH v2 0/3] Freezer, CPU hotplug, x86 Microcode: Fix task
 freezing failures

On Mon, Oct 10, 2011 at 01:30:34PM -0400, Srivatsa S. Bhat wrote:
> But I do agree that offlining and onlining CPUs while suspending might
> not seem all that useful or even wise, but like I said, it was designed to
> bring out such problematic race conditions.
> 
> So, in the interest of making the important components involved in
> suspend/resume call path (namely cpu hotplug) more robust and stable,
> I think it makes sense to fix any issue we hit (atleast when we
> practically hit it and it is proved that such a scenario is no longer
> hypothetical).
> 
> For that, we can either go with the simple one-line fix that I posted
> earlier (which has got another motivation now, thanks to Borislav) or
> with this elaborate solution, whichever seems better/worthwhile.
>
> If it is still strongly felt that this "bug" is not worth fixing with such
> mutual exclusion schemes, it will still get solved anyway by applying that
> one-line patch.

Well, this is easy: the oneliner is needed anyway for removing
unnecessary ucode reloading and since it fixes your test cases _and_ is
_simpler_, the whole deal is a no brainer.

And although Pavel had a valid concern there about suspending when low
on battery/failing UPSs and, AFAIUI, it might happen that the machine
automatically suspends while you offline one of your cores, I can't find
it in me to care about a case like that, sorry.

Thanks.

-- 
Regards/Gruss,
Boris.

Advanced Micro Devices GmbH
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