linux-kernel - Re: Odroid U3 mutex deadlock.

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Date:	Mon, 04 Jan 2016 11:38:29 +0100
From:	Marek Szyprowski <m.szyprowski@...sung.com>
To:	Anand Moon <linux.amoon@...il.com>,
	Krzysztof Kozlowski <k.kozlowski@...sung.com>
Cc:	"linux-samsung-soc@...r.kernel.org" 
	<linux-samsung-soc@...r.kernel.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Javier Martinez Canillas <javier@....samsung.com>,
	Kukjin Kim <kgene@...nel.org>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: Odroid U3 mutex deadlock.

Hi Anand,

On 2016-01-02 06:14, Anand Moon wrote:
> Hi Krzysztof
>
> On 14 December 2015 at 05:15, Krzysztof Kozlowski
> <k.kozlowski@...sung.com> wrote:
>> On 12.12.2015 13:32, Anand Moon wrote:
>>> Hi Krzysztof,
>>>
>>> I am just observing this deadlock om my Odroid U3.
>> This is not a deadlock yet, just a report from lockdep. Could be a real
>> issue, could be false positive, maybe some locks miss nesting annotations.
>>
>> Typical information for bug report would be useful, like the exact
>> version (it is mentioned in lockdep report but is it really correct?)
>> and reproducibility. And of course git-bisect would be nice to have, see:
>> Documentation/BUG-HUNTING
>>
>> Best regards,
>> Krzysztof
>>
>>
> Thanks for your inputs. I narrowed down to this commit.
> ----------------------------------------------------------------------------------
> commit ec459c0c77faca53cf161830cb264e51bb1abba6
> Author: Marek Szyprowski <m.szyprowski@...sung.com>
> Date:   Wed Feb 4 23:44:15 2015 +0900
>
>      ARM: dts: add dependency between TV and LCD0 power domains for exynos4
>
>      TV Mixer needs both TV and LCD0 domains enabled to be fully operational.
>      This dependency is modelled by making TV power domains a sub-domain of
>      LCD0 power domain.
>
>      Signed-off-by: Marek Szyprowski <m.szyprowski@...sung.com>
>      Signed-off-by: Kukjin Kim <kgene@...nel.org>
> -------------------------------------------------------------------------------------
> After reverting this I am not observing below lockdep warning report.
> But after reverting this patch I observer another bug.

The mentioned lockdep warning is a false positive. Such warning is 
reported for
every subdomain present in a system. As you noticed that removing dependency
between power domains also removes this warning, but it will introduce real
problems with power on/off sequences of graphics devices.

I will send a patch for genpd core fixing the deplock warning. Thanks for
reporting the issue and pointing a good place to start digging in the 
source :)

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland

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