linux-kernel - Re: [PATCH] drm/i2c: tda998x: Fix lockdep warning about possible circular dependency

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Message-ID: <20170720142413.GB31807@n2100.armlinux.org.uk>
Date:   Thu, 20 Jul 2017 15:24:13 +0100
From:   Russell King - ARM Linux <linux@...linux.org.uk>
To:     Liviu Dudau <Liviu.Dudau@....com>
Cc:     David Airlie <airlied@...ux.ie>,
        DRI devel <dri-devel@...ts.freedesktop.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drm/i2c: tda998x: Fix lockdep warning about possible
 circular dependency

On Thu, Jul 20, 2017 at 03:19:10PM +0100, Liviu Dudau wrote:
> On Thu, Jul 20, 2017 at 02:08:29PM +0100, Russell King - ARM Linux wrote:
> > On Thu, Jul 20, 2017 at 01:54:04PM +0100, Liviu Dudau wrote:
> > > On Thu, Jul 20, 2017 at 12:44:49PM +0100, Russell King - ARM Linux wrote:
> > > > Actually, scrub that idea - drm_helper_probe_single_connector_modes()
> > > > calls drm_edid_to_eld() for these cases anyway, so we must call
> > > > drm_helper_probe_single_connector_modes() with the audio_mutex held.
> > > 
> > > OK, so the lockdep warning is spurious?
> > 
> > I don't think so.  I think there's two ways to solve this:
> > 
> > 1. replace the audio_mutex in tda998x_audio_get_eld() and
> >    tda998x_connector_fill_modes() with a new mutex (eld_mutex) to
> >    protect just the ELD.
> > 
> > 2. remove the mutex from these two functions, and take the connection_mutex
> >    modeset lock in tda998x_audio_get_eld().
> > 
> > However, I don't have a view on which would be best.
> 
> If you don't mind, I took the liberty of picking option 2, just because
> I don't like adding new locks when existing ones might do the job.

I don't mind - but one question for the DRM people in connection with
your patch is whether we need the acquire context for this relatively
simple lock/copy/unlock sequence.  This path for getting the ELD
shouldn't be holding any other DRM locks.

-- 
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