[Intel-gfx] [PATCH] drm/i915: Don't oops during modeset shutdown after lpe audio deinit

[Chris Wilson]

Quoting Ville Syrjala (2018-11-05 19:46:04)
> From: Ville Syrjälä <ville.syrjala at linux.intel.com>
> 
> We deinit the lpe audio device before we call
> drm_atomic_helper_shutdown(), which means the platform device
> may already be gone when it comes time to shut down the crtc.

Doesn't this mean that we fail to notify the audio codec of it being
turned off? I'm wondering if we shouldn't do the display/gt idling first
(like a i915_driver_unload_prepare).

> As we don't know when the last reference to the platform
> device gets dropped by the audio driver we can't assume that
> the device and its data are still around when turning off the
> crtc. Mark the platform device as gone as soon as we do the
> audio deinit.
> 
> Cc: stable at vger.kernel.org
> Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
> ---
>  drivers/gpu/drm/i915/intel_lpe_audio.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_lpe_audio.c b/drivers/gpu/drm/i915/intel_lpe_audio.c
> index cdf19553ffac..5d5336fbe7b0 100644
> --- a/drivers/gpu/drm/i915/intel_lpe_audio.c
> +++ b/drivers/gpu/drm/i915/intel_lpe_audio.c
> @@ -297,8 +297,10 @@ void intel_lpe_audio_teardown(struct drm_i915_private *dev_priv)
>         lpe_audio_platdev_destroy(dev_priv);
>  
>         irq_free_desc(dev_priv->lpe_audio.irq);
> -}
>  
> +       dev_priv->lpe_audio.irq = -1;
> +       dev_priv->lpe_audio.platdev = NULL;
> +}

This thanks to HAS_LPE_AUDIO() (confusing macro of the day) will prevent
a use-after-free during crtc shutdown.

Reviewed-by: Chris Wilson <chris at chris-wilson.co.uk>
-Chris