WARNING: CPU: 2 PID: 42 at drivers/gpu/drm/drm_modeset_lock.c:276

[Maxime Ripard]

On Wed, Dec 28, 2022 at 11:16:11PM +0100, Stefan Wahren wrote:
> Hi Maíra,
> 
> Am 28.12.22 um 20:49 schrieb Maíra Canal:
> > Hi Stefan,
> > 
> > I was able to reproduce this error on drm-misc-next. I bisected,
> > and I got into commit 6bed2ea3cb38. I noticed that the crtc->mutex is
> > being locked twice, and this might be causing the problem. I wrote a
> > patch to try to fix this issue, and after applying the patch, I wasn't
> > able to reproduce the error anymore.
> > 
> > Let me know if you were able to reproduce the warning after applying
> > this patch.
> 
> the patch works as expected and avoid the warning. I tested it on top of
> v6.1 with RPi 3 B+ and RPi 4 B.
> 
> In case you send the patch please add the Fixes tag so the patch get
> backported to stable.

This isn't a proper fix, we do need to take the crtc mutex: it protects
the crtc->state pointer we dereference next, and vc4_hdmi_reset_link can
be called outside of a modeset through the interrupt handler.

Maxime
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