linux-kernel - Re: RCU idle CPU detection is broken in linux-next

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Message-ID: <CAFTL4hwqzS8iO2zOOGaizzMtT85MJExTxEgGbponJ4_gfv0nwA@mail.gmail.com>
Date:	Mon, 24 Sep 2012 23:29:07 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Sasha Levin <levinsasha928@...il.com>
Cc:	paulmck@...ux.vnet.ibm.com,
	Michael Wang <wangyun@...ux.vnet.ibm.com>,
	Dave Jones <davej@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: RCU idle CPU detection is broken in linux-next

2012/9/23 Sasha Levin <levinsasha928@...il.com>:
> On 09/23/2012 02:21 AM, Paul E. McKenney wrote:
>> On Sat, Sep 22, 2012 at 02:27:35PM -0700, Paul E. McKenney wrote:
>>> On Sat, Sep 22, 2012 at 07:50:29PM +0200, Sasha Levin wrote:
>>>> On 09/22/2012 05:56 PM, Paul E. McKenney wrote:
>>>>> And now the prime suspect is the new CONFIG_RCU_USER_QS=y.  Do these
>>>>> warnings ever show up with CONFIG_RCU_USER_QS=n?
>>>>
>>>> It seems that disabling that does make the warnings go away.
>>>>
>>>> I'll keep the tests running in case it just reduces the chances or something
>>>> like that.
>>>
>>> Thank you for testing this!
>>>
>>> And of course the reason that I didn't see these problems is that I
>>> failed to update my tests to enable CONFIG_RCU_USER_QS.  :-/
>>
>> Also the fact that I run 32-bit guests on x86.  Sigh!
>>
>> I take it that you are running 64-bit guests?
>
> Yes, that's correct.

Sasha,

Can you please test the following branch:

git://github.com/fweisbec/linux-dynticks.git  rcu/idle-for-v3.7-take3

with CONFIG_RCU_USER_QS and CONFIG_RCU_USER_QS_FORCE enabled.

I hope this fixes the warning.
The changes are:

* add "x86: Unspaghettize do_general_protection()"
* updated "x86: Exception hooks for userspace RCU extended QS" to
handle some missed trap handlers. Especially do_general_protection()
because I can see the problem triggered there in Sasha's warnings. I
fixed more handlers in the way.

Thanks.
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