linux-kernel - Re: Another preempt folding issue?

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Date:	Thu, 20 Feb 2014 16:50:41 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Stefan Bader <stefan.bader@...onical.com>
Cc:	Borislav Petkov <bp@...en8.de>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	kvm@...r.kernel.org, Marcelo Tosatti <mtosatti@...hat.com>,
	MASAO TAKAHASHI <masao-takahashi@...no.co.jp>,
	Joerg Roedel <joro@...tes.org>
Subject: Re: Another preempt folding issue?

On Thu, Feb 20, 2014 at 04:38:13PM +0100, Stefan Bader wrote:
> On 14.02.2014 18:21, Peter Zijlstra wrote:
> > On Fri, Feb 14, 2014 at 06:02:32PM +0100, Stefan Bader wrote:
> >> One thing I likely should do is to reinstall the exact same laptop with 64bit
> >> kernel and userspace... maybe only 64bit kernel first... and make sure on my
> >> side that this does not show up on 64bit, too. I took the word of reporters for
> >> that (and the impression that otherwise many more people would have complained).
> > 
> > Yeha, I'm going to try and install some 32bit userspace on a usb
> > harddisk I've got and see if I can boot my Core2 laptop from that to try
> > and reproduce.
> > 
> > But all that is probably going to be Monday :/
> > 
> *sigh* Already Thursday...
> 
> Peter, did you get to reproduce this locally? Unfortunately I had some
> interruption and have not more Information than on last Friday (which is that
> the same hw but 64bit kernel does not show it).

I got side-tracked as well, someone reported crashes, which come above
weird behaviour :/

> Meanwhile I wonder whether it would make sense to push the following (or more?)
> to stable for 3.13.y:
> 
> 1) 16824255394f55adf31b9a96a9965d8c15bdac4c
>    x86, acpi, idle: Restructure the mwait idle routines
> 2) 7e98b71920464b8d15fa95c74366416cd3c88861
>    x86, idle: Use static_cpu_has() for CLFLUSH workaround, add barriers
> 3) 8cb75e0c4ec9786b81439761eac1d18d4a931af3
>    sched/preempt: Fix up missed PREEMPT_NEED_RESCHED folding
> 4) 215393bc1fab3d61a5a296838bdffce22f27ffda
>    sched/preempt/x86: Fix voluntary preempt for x86
> 
> 1+2 would be to avoid touching 3 too much and looked to be improvements on their
> own. 3+4 would be cherry-picks if not for some fuzz 2.

I'll not object; but if someone wants a smaller set you could do with
just the idle.c hunk from 3.

> I saw a few more things labelled preempt between 3.13 and current HEAD but am
> not sure whether or which of those are strictly required. Namely some fixing to
> preempt_enable_no_resched() mis-usage and maybe one fixing an issue of ftrace
> locking up.

Yeah, that's all fresh breakage and doesn't go back to 3.13 I think.
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