linux-kernel - Re: kernfs/rtc: circular dependency between kernfs and ops

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Message-ID: <53394C5E.2030207@metafoo.de>
Date:	Mon, 31 Mar 2014 13:07:10 +0200
From:	Lars-Peter Clausen <lars@...afoo.de>
To:	Alessandro Zummo <a.zummo@...ertech.it>
CC:	Sasha Levin <sasha.levin@...cle.com>, Tejun Heo <tj@...nel.org>,
	Greg KH <greg@...ah.com>, rtc-linux@...glegroups.com,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: kernfs/rtc: circular dependency between kernfs and ops_lock

On 03/31/2014 12:43 PM, Alessandro Zummo wrote:
> On Mon, 31 Mar 2014 11:52:36 +0200
> Lars-Peter Clausen <lars@...afoo.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
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