linux-kernel - Re: [RT] Lockdep warning on boot with 2.6.31-rc5-rt1.1

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Date:	Sat, 8 Aug 2009 11:20:29 +0800
From:	Dave Young <hidave.darkstar@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Clark Williams <williams@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	RT <linux-rt-users@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Alan Stern <stern@...land.harvard.edu>,
	"greg@...ah.com" <greg@...ah.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Kay Sievers <kay.sievers@...y.org>
Subject: Re: [RT] Lockdep warning on boot with 2.6.31-rc5-rt1.1

On Fri, Aug 7, 2009 at 11:09 PM, Peter Zijlstra<peterz@...radead.org> wrote:
> On Fri, 2009-08-07 at 09:46 -0500, Clark Williams wrote:
>> Peter,
>>
>> I'm getting this warning from lockdep when booting on my T60.
>>
>> The two addresses reported (0xffffffff812664a2 and 0xffffffff812664ae)
>> actually bracket one call to mutex_lock() in driver_attach() so I'm not
>> sure what the complaint is.
>>
>> Clark
>>
>> =============================================
>> [ INFO: possible recursive locking detected ]
>> 2.6.31-rc5-rt1.1 #37
>> ---------------------------------------------
>> swapper/1 is trying to acquire lock:
>>  (&dev->mutex){+.+...}, at: [<ffffffff812664ae>]
>> __driver_attach+0x48/0x81
>>
>> but task is already holding lock:
>>  (&dev->mutex){+.+...}, at: [<ffffffff812664a2>]
>> __driver_attach+0x3c/0x81
>>
>> other info that might help us debug this:
>> 1 lock held by swapper/1:
>>  #0:  (&dev->mutex){+.+...}, at: [<ffffffff812664a2>]
>> __driver_attach+0x3c/0x81
>
> Oh, that's tglx who's gone wild with sem->mutex conversions.
>
> It used to be that _all_ dev->sem instances were taken on suspend or
> something like that, I think that got fixed a long while back.
>
> I'd have to look at what the current locking requirements for dev->sem
> are.
>
> I remember talking to Alan on several occasions about this, and I just
> went over some of the old emails, but I must say the precise
> requirements stay hidden from me. Also, I'm not sure these emails are
> still representative of the current state.

I think you means this thread:

http://lkml.org/lkml/2008/4/17/305

>
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-- 
Regards
dave
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