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

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Message-ID: <5059F458.3000407@gmail.com>
Date:	Wed, 19 Sep 2012 18:35:36 +0200
From:	Sasha Levin <levinsasha928@...il.com>
To:	paulmck@...ux.vnet.ibm.com
CC:	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

On 09/19/2012 05:39 PM, Paul E. McKenney wrote:
> On Wed, Sep 12, 2012 at 07:56:48PM +0200, Sasha Levin wrote:
>> > Hi Paul,
>> > 
>> > While fuzzing using trinity inside a KVM tools guest, I've managed to trigger
>> > "RCU used illegally from idle CPU!" warnings several times.
>> > 
>> > There are a bunch of traces which seem to pop exactly at the same time and from
>> > different places around the kernel. Here are several of them:
> Hello, Sasha,
> 
> OK, interesting.  Could you please try reproducing with the diagnostic
> patch shown below?

Sure - here are the results (btw, it reproduces very easily):

[ 13.525119] ================================================
[ 13.527165] [ BUG: lock held when returning to user space! ]
[ 13.528752] 3.6.0-rc6-next-20120918-sasha-00002-g190c311-dirty #362 Tainted: GW
[ 13.531314] ------------------------------------------------
[ 13.532918] init/1 is leaving the kernel with locks still held!
[ 13.534574] 1 lock held by init/1:
[ 13.535533] #0: (rcu_idle){.+.+..}, at: [<ffffffff811c36d0>]
rcu_eqs_enter_common+0x1a0/0x9a0

I'm basically seeing lots of the above, so I can't even get to the point where I
get the previous lockdep warnings.
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