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Date: Mon, 31 Mar 2014 13:07:10 +0200
From: Lars-Peter Clausen <lars@metafoo.de>
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To: Alessandro Zummo <a.zummo@towertech.it>
CC: Sasha Levin <sasha.levin@oracle.com>, Tejun Heo <tj@kernel.org>,
        Greg KH <greg@kroah.com>, rtc-linux@googlegroups.com,
        LKML <linux-kernel@vger.kernel.org>
Subject: Re: kernfs/rtc: circular dependency between kernfs and ops_lock
References: <5308E3AE.3040405@oracle.com> <20140222205217.GC16272@mtj.dyndns.org> <20140224120427.6394d5dd@linux.lan.towertech.it> <5331FA9E.20506@oracle.com> <20140325233936.655a798e@linux.lan.towertech.it> <53321D04.2040102@oracle.com> <5337653D.6020002@oracle.com> <53384080.9020502@oracle.com> <20140331114627.5e1a4609@linux.lan.towertech.it> <53393AE4.505@metafoo.de> <20140331124351.43033c93@linux.lan.towertech.it>
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On 03/31/2014 12:43 PM, Alessandro Zummo wrote:
> On Mon, 31 Mar 2014 11:52:36 +0200
> Lars-Peter Clausen <lars@metafoo.de> wrote:
>
>> It's the same bug, device_unregister(&rtc->dev) will try to unregister all
>> sysfs files attached to the device and that function is still called with
>> the rtc mutex held.
>
>   rtc-cmos tries to unregister the rtc device in the probe function,
>   which should not be done.
>
>   the last patches fixes it. I'll keep trying to trigger the bug on my systems.
>

It doesn't really matter where it is unregistered. device_unregister() will 
(somewhere down it's callchain) take the kernfs lock, hence it must be 
callled with the rtc mutex being held.

- Lars