linux-kernel - Re: Bisected KVM hang on x86-32 between v3.12 and v3.13

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Message-ID: <5342EB78.3060002@gmx.de>
Date:	Mon, 07 Apr 2014 20:16:24 +0200
From:	Toralf Förster <toralf.foerster@....de>
To:	Peter Zijlstra <peterz@...radead.org>,
	Michele Ballabio <barra_cuda@...amail.com>
CC:	linux-kernel@...r.kernel.org, fweisbec@...il.com, mingo@...nel.org,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: Bisected KVM hang on x86-32 between v3.12 and v3.13

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On 04/07/2014 05:07 PM, Peter Zijlstra wrote:
> On Mon, Apr 07, 2014 at 05:03:37PM +0200, Peter Zijlstra wrote:
>> So what I suspect at this point is that because i386 and x86_64
>> have a difference in current_thread_info() (i386 is stack based),
>> we end up setting the TIF_NEED_RESCHED bit on the wrong stack.
>> 
>> Now I have some vague memories of propagating the TIF flags on
>> stack switch, but I cannot remember what arch we did that for.
>> Let me stare at this a little more.
>> 
>> Also, IFF this is the case, then the fingered patch above (and
>> your suggested 'fix') aren't the real curlpit/cure but simply
>> make it more/less likely to happen.
>> 
>> Now, Steve had a patch somewhere that would make i386 use
>> per-cpu variables for current_thread_info() just like x86_64
>> already does I think. Let me go find them too.
> 
> Ohh, goodie, they're already in Linus' tree. Could you see if
> current git still suffers this problem?
> 
v3.14-10353-g2b3a8fd works fine AFAICS
(BTW the fix is stable material, right ?)

- -- 
MfG/Sincerely
Toralf Förster
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