Re: Odroid U3 mutex deadlock.

[Marek Szyprowski]

Hi Anand,

On 2016-01-02 06:14, Anand Moon wrote:
> Hi Krzysztof
>
> On 14 December 2015 at 05:15, Krzysztof Kozlowski
> <k.kozlowski@xxxxxxxxxxx> 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@xxxxxxxxxxx>
> 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@xxxxxxxxxxx>
>      Signed-off-by: Kukjin Kim <kgene@xxxxxxxxxx>
> -------------------------------------------------------------------------------------
> 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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