linux-kernel - Re: [BUG][tip/master] kernel panic while locking selftest at qspinlock

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Message-ID: <55A1DA85.3090803@hp.com>
Date:	Sat, 11 Jul 2015 23:09:57 -0400
From:	Waiman Long <waiman.long@...com>
To:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
CC:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>, Ingo Molnar <mingo@...e.hu>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [BUG][tip/master] kernel panic while locking selftest at qspinlock_paravirt.h:137!

On 07/11/2015 01:05 AM, Masami Hiramatsu wrote:
> On 2015/07/11 10:27, Waiman Long wrote:
>> On 07/10/2015 08:32 PM, Masami Hiramatsu wrote:
>>> On 2015/07/10 23:28, Peter Zijlstra wrote:
>>>> On Fri, Jul 10, 2015 at 03:57:46PM +0200, Ingo Molnar wrote:
>>>>> * Peter Zijlstra<peterz@...radead.org>   wrote:
>>>>>> Do we want to make double unlock non-fatal unconditionally?
>>>>> No, just don't BUG() out, don't crash the system - generate a warning?
>>>> So that would be a yes..
>>>>
>>>> Something like so then? Won't this generate a splat on that locking self
>>>> test then? And upset people?
>>> Hmm, yes, this still noisy...
>>> Can't we avoid double-unlock completely? it seems that this warning can
>>> happen randomly, which means pv-spinlock randomly broken, doesn't it?
>> It shouldn't randomly happen. The message should be printed at the first
>> instance of double-unlock. If that is not case, there may be some
>> problem in the code.
> Ah, OK. That comes from locking selftest. In that case, do we really
> need the warning while selftest, since we know it always fails ?
>
>> Anyway, I have an alternative fix that should better capture the problem:
> Do we need both Peter's BUG() removing patch and this?
>

No, you can choose either one. They are just different ways to solve the 
same BUG() problem.

Cheers,
Longman
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