linux-kernel - Re: frequent lockups in 3.18rc4

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Date:	Tue, 16 Dec 2014 20:28:03 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Andy Lutomirski <luto@...capital.net>,
	Steven Rostedt <rostedt@...dmis.org>,
	Tejun Heo <tj@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Don Zickus <dzickus@...hat.com>, Dave Jones <davej@...hat.com>,
	the arch/x86 maintainers <x86@...nel.org>
Subject: Re: frequent lockups in 3.18rc4

On Fri, Nov 21, 2014 at 02:55:27PM -0800, Linus Torvalds wrote:
> On Fri, Nov 21, 2014 at 1:11 PM, Thomas Gleixner <tglx@...utronix.de> wrote:
> >
> > I'm fine with that. I just think it's not horrid enough, but that can
> > be fixed easily :)
> 
> Oh, I think it's plenty horrid.
> 
> Anyway, here's an actual patch. As usual, it has seen absolutely no
> actual testing, but I did try to make sure it compiles and seems to do
> the right thing on:
>  - x86-32 no-PAE
>  - x86-32 no-PAE with PARAVIRT
>  - x86-32 PAE
>  - x86-64
> 
> also, I just removed the noise that is "vmalloc_sync_all()", since
> it's just all garbage and nothing actually uses it. Yeah, it's used by
> "register_die_notifier()", which makes no sense what-so-ever.
> Whatever. It's gone.
> 
> Can somebody actually *test* this? In particular, in any kind of real
> paravirt environment? Or, any comments even without testing?
> 
> I *really* am not proud of the mess wrt the whole
> 
>   #ifdef CONFIG_PARAVIRT
>   #ifdef CONFIG_X86_32
>     ...
> 
> but I think that from a long-term perspective, we're actually better
> off with this kind of really ugly - but very explcit - hack that very
> clearly shows what is going on.
> 
> The old code that actually "walked" the page tables was more
> "portable", but was somewhat misleading about what was actually going
> on.
> 
> Comments?

While going through this thread I wondered whatever became of this
patch. It seems a shame to forget about it entirely. Maybe just queued
for later while hunting wabbits?
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